Home > Renewable Energy Systems as Emergency Power Sources
Nature's Power on Demand:
Renewable Energy Systems as Emergency Power Sources
U.S. Department of Energy
Office of Energy Efficiency and Renewable Energy
October 1995
Prepared By: Roberta F. Stauffer TechWrite Services
Prepared For: The National Center for Appropriate Technology
Funding provided by the U.S. Department of Energy's
Office of Energy Efficiency and Renewable Energy
Acknowledgments
This report is an account of the information and opinions shared by the many contacts listed in Appendix One. The author is most grateful for their contributions, especially for the assistance provided by Bill Young, research engineer at the Florida Solar Energy Center, and Ann Deering, president of Environmental Technology & Telecommunications, Ltd.
Review comments provided by William S. Becker of the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy helped to shape and improve the text considerably. Suggestions from reviewers Bill Browning of Rocky Mountain Institute, Roger Hill of Sandia National Laboratories, Andy Walker of the National Renewable Energy Laboratory, and DOE's James Rannels and Karl Rabago were also helpful and appreciated.
Disclaimer
Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement of recommendation.
Only when our electricity is gone do we realize our dependence on it. Without electric power, businesses are forced to close, incurring huge losses for themselves and their utility, communications and insurance companies. Government agencies and institutions become paralyzed; household activity stops; traffic lights fail; health and safety are jeopardized.
This paper is an introduction to the concept of using on-site renewable energy systems to mitigate the crippling impact of power outages. Solar, wind, and hydroelectric systems can provide enough power to meet the basic needs of homes, businesses, and government agencies. Biomass can also be used to generate electricity or as an emergency fuel source for heating and cooking.
Because natural disasters such as hurricanes, earthquakes, and floods commonly cause utility grid failures, particular attention is paid in this booklet to energy issues associated with these disaster types. It's important to acknowledge, however, that natural disasters are by no means the only causes of power outages. Because it is so highly centralized and complex, the utility grid is inherently vulnerable to disruptions. Reliance on sophisticated mega plants and high-capacity transmission lines means that when outages occur, they often affect a correspondingly large geographical area. Back-up renewable power systems can serve as insurance against collapse of electrical systems. When installed in businesses, they can prevent -- or at least reduce -- business interruption losses caused by grid failure.
Two types of renewable energy systems are discussed in this document: fixed and portable. Fixed systems tap the renewable resource most appropriate for specific locations, be it solar, wind, hydro, or biomass. These systems function all the time --supplementing utility power during normal times and providing back-up power during outages.
Portable systems, on the other hand, are deployed following disasters to assist response crews and victims. Solar electricity or photovoltaics (PV) is the most appropriate renewable energy source for these applications because the systems are relatively easy to transport and solar energy is plentiful in many regions.
Now, at the close of the most active hurricane season in 60 years, both PV and solar water heating companies are experiencing a dramatic increase in business, according to Scott Sklar, executive director of the Solar Energy Industries Association. Solar system dealers in Florida are particularly busy with shipments to the U.S. Virgin Islands and the surrounding Caribbean region. Sklar said that natural disasters regularly boost demand for solar products. PV systems have provided emergency power in the aftermath of many past disasters:
Northridge Earthquake, 1994: PV kept some communications links operating and supplied power to Southern California residents that had installed systems in their homes.
Hurricane Andrew, 1992: PV systems were used at shelters and medical clinics and to power street lights and communications systems.
Hurricane Hugo, 1989: A portable solar electric generator powered a community center for six weeks following the storm.
A key benefit of solar systems for emergency use is their self-sufficiency. They require no fuel and very little maintenance; yet they provide reliable power for as long as needed. The availability of fuel supplies is a constant worry to those who rely on fossil-fuel-powered generators during an emergency. Not only do renewable energy systems eliminate that worry, but they also work without producing the overbearing noise and noxious fumes that accompany gasoline and diesel generators.
Fossil-fuel-powered generators are, however, indispensable pieces of equipment for meeting large-scale emergency power needs in such places as sewer and water facilities, hospitals, and emergency operations centers. These locations often require several hundred kilowatts (kW) of emergency power. Portable PV systems are most well-suited for meeting smaller-scale needs requiring a few kW or less.
What's to Come
This paper first discusses how renewable energy systems can prevent power outages by continuing to operate even when the utility grid fails. It then touches on how the overall resilience of the nation's electricity system can be improved by increased numbers of distributed power generating facilities --including renewable energy systems. The third section explores one consequence of power failures -- costly business interruption losses. It's followed by a section discussing new opportunities for fixed renewable systems -- choices that have become available just recently.
By looking at three specific disasters, the fifth section of this booklet explores energy-related issues pertaining to various disaster types. The final part focuses on the emergency response arena and discusses specific energy needs that can effectively be met with solar systems. Many of the potential uses for PV listed here could be applied to meet day-to-day energy needs as well.
Because they can be designed to continue working even when the utility grid fails, renewable energy systems can actually prevent power outages -- keeping homes and businesses functioning during black-outs, or amid the chaos following natural disasters.
A recent example of this benefit involves the Harmony resort facility at Maho Bay Campground on St. John, one of the U.S. Virgin Islands. In mid-September, Hurricane Marilyn swept 115 mile-per-hour winds across the island, tearing roofs off buildings and knocking out electricity and phone service. The recycled building materials used to construct the Harmony facility survived the winds, as did its PV systems. According to Stanley Selengut, president of Maho Bay Camps, Inc., the systems' battery banks never faltered and were once again replenished by the solar panels when the storm passed and sun reappeared. Campground staff remained at Harmony during the hurricane period and were among the few Virgin Islanders who had light, refrigeration, hot showers, flush toilets, and the ability to communicate with the outside world.
The above example demonstrates that the use of quality construction techniques and materials, coupled with the installation of resilient, renewable power systems, can help to ensure the continued health and safety of disaster victims. Upfront investment in these technologies can also significantly shorten the disaster recovery process, cutting costly business interruption losses. The entire Maho Bay Campground complex is slated to reopen in early November -- less than two months after the hurricane.
Other disaster-prone regions can benefit from the Harmony example by striving to replicate its disaster-resistant design techniques at every opportunity. Resilient building technologies and self-sufficient power systems should be employed whenever possible in all new development in disaster-prone areas -- both in construction projects underway during disaster recovery and also in new development undertaken during the normal course of growth. Many of the best building technologies on the market today are most economical in new construction; thus, rebuilding presents an opportunity to greatly improve the health, safety, and economy of individual buildings and even entire communities.
And although it may be initially more expensive to invest in disaster-resistant technologies, taking such precautions will ultimately prove to be much more cost-effective than repeatedly rebuilding following hurricanes, for example. It's important that cost-benefit analyses incorporate not only first costs, but encompass the long-term big picture. In the case of self-sufficient renewable energy systems, business-owners and community leaders must go beyond the simple comparison between the cost of conventional electricity and that of a solar, wind, or hydro system. Life cycle costs must also be taken into account -- including the probability of personal and business disruption losses caused by interruption of energy services during and after disasters. The renewable energy system's ability to prevent those losses must become part of the "benefit" calculation for resilient power systems.
Besides bringing energy self-sufficiency to individual buildings, distributed, renewable energy systems can also improve the overall resilience of the nation's utility grid. The grid is one of the most reliable systems in the world, but it is prone to failures and glitches.
In their book, Brittle Power, Amory B. and L. Hunter Lovins discuss at length just how vulnerable the entire U.S. energy system is to serious disruption and what impact this vulnerability has on national security. Some of their ideas are discussed below, and the book is cited in Appendix Two for further information on this subject.
The Lovinses contend that the highly centralized nature of the system makes it inherently "brittle," or easily broken by unpredictable disruptions. In contrast, an energy system made up of small, distributed energy stations is more resilient by nature, able to absorb minor errors and problems.
Centralized systems demand precision and leave little room for error or disruption. The entire electricity grid, for example, is maintained at constant synchronicity, with alternating current continually flowing back and forth at a rate of 60 cycles per second. Even slight deviations from this pattern can damage equipment and sometimes lead to outages.
Maintaining this precision over vast distances, with huge amounts of energy concentrated at relatively few locations, is challenging, at best. Malicious attacks on or accidental malfunctions at key power plants, substations, transmission lines, or computer control centers could black out entire regions in one fell swoop and leave them without power for extended periods of time. Even weather extremes such as this past summer's heat wave in Chicago can disrupt electrical service as it did there, when transformer problems and a substation fire caused 41,000 Commonwealth Edison customers to lose power when they needed it most.
If the nation's electricity system was more decentralized, the impacts of weather, natural disaster, sabotage, equipment failure or human error wouldn't be nearly as catastrophic. If smaller systems fail, fewer people are affected.
The electric utility industry is moving toward decentralization and distributed generation. As the basic structure of the industry changes due to impending deregulation, smaller electricity generating sites located closer to customers may become more common. The grid will continue to function as an electricity "freeway," though energy is likely to come from many more producers and may not be traveling such vast distances.
In addition to decreasing the overall vulnerability of the electricity system, greater reliance on distributed power will save millions of dollars in transmission and distribution costs. A 1994 conference paper by the engineering firm Black & Veatch stated that new transmission lines can cost over one million dollars per mile. The paper also reported that U.S. utilities spent close to $16 billion on transmission and distribution improvements in 1993. Locating power generating stations closer to the loads they'll be serving will reduce future transmission and distribution expenditures.
Southern California Edison's Solar Neighborhood Program is one current example of utility-scale distributed generation. The utility has installed PV generating stations on rooftops in residential neighborhoods where older, underground power lines are nearing overload capacity and threatening to fail. Over the years, telephone and other utility liens have been installed on top of the power lines, making it very expensive for the utility to replace or repair its old cable. Using local solar power to "shave" the load on those lines allows Southern Cal to indefinitely defer costly, disruptive line replacement projects. In this situation, the greatest stress on the lines occurs on summer afternoons when demand for air conditioning is at its peak. Tapping into the sun's power when it's at its peak makes PV a perfect match. On cloudy days when the PV panels don't produce as much energy, it isn't needed anyway.
The program started with the pilot installation of 15 kW on the roof of an elementary school in South Pasadena. Its success has led to plans to install up to 115 kW at that location, with additional arrays to be placed on the rooftops of individual homes in the neighborhood. About 500 kW of supplementary solar electricity is the program's goal. Another school in La Canada and a library in San Marino are two more potential PV sites.
The Sacramento Municipal Utility District is encouraging its customers to supplement grid power with locally produced solar electricity. Its "Give Us Your Roofs" program has resulted in the installation of more than 100 small PV units on private buildings in its service area.
The majority of these grid-connected PV applications aren't designed to provide emergency back-up power. They go down when the grid goes down. They do increase the resilience of the grid system, however, and it will be possible to add the controls and battery back-up that will enable the systems to function independently of the grid during emergencies in the future.
One major impetus for preventing power outages and bolstering the resilience of the nation's electrical system can be described in three words: business interruption losses. These are the additional costs incurred when natural disasters or utility black-outs force companies to cease operation and close stores, restaurants, offices, and factories.
A recent University of Southern California (USC) study estimated business interruption losses from the Northridge Earthquake to be $5.945 billion. The Great Flood of 1993 in the Midwest caused business interruption losses of $200-$500 million in Des Moines, Iowa, alone.
The interruption of one business can launch a chain reaction by also disrupting those companies that supply it with materials or equipment and those that in turn depend on it for their materials or supplies. For example, some U.S. facilities of The Boeing Company and Apple Computer, Inc. suffered production losses of up to six weeks following the January 1995 earthquake in Kobe, Japan. They could not operate without needed supplies from Kobe.
Some companies insulate themselves from damage occurring anywhere along their particular "chain" by procuring contingent business interruption insurance. These insured business interruption losses can sometimes be up to four times greater than property damage claims following a severe disaster.
Only about one-third of the Northridge losses stemmed from direct business interruption within the geographical areas physically impacted by earthquake; the rest were contingent losses, felt throughout the region, the nation, and the world, since Southern California is an active participant in the global economy.
USC's survey of the Northridge business community turned up the following three main causes of direct business interruption: 1) employees unable to get to work; 2) employees attending to personal matters; and 3) damaged workplace. More than 70 percent of the 389 firms surveyed mentioned these reasons. Reason #4, given by more than 60 percent of the companies, was interrupted utility services.
Staff at the University of Delaware's Disaster Research Center have also documented the business community's reliance on electricity, as part of a larger effort to understand the indirect impacts of natural disasters on businesses. More than 1,800 large and small businesses representing five major business sectors participated in two surveys to determine which lifeline services are most important to business functioning: electricity, telephone, natural gas, or water. Results from both surveys -- one in the Memphis, Tenn., area and the other in Des Moines, Iowa -- indicate that electricity is the most critical lifeline for businesses, and telephone service is second. (Memphis businesses were surveyed because the area could experience an earthquake of magnitude 6 within the next 20 years. Des Moines was chosen because of the widespread business disruption caused by flooding in 1993. Interestingly enough, actual flooding turned out to be a relatively minor cause of business closures in Des Moines. Losing lifeline services disrupted many more businesses.)
Most small businesses aren't insured against utility outages. Those that do purchase business interruption insurance are often covered only if the disruption was caused by immediate damage to their property. If it stemmed solely from loss of utilities, they need to have purchased a separate endorsement that covers off-premises power interruption. This type of coverage is rare, according to Sean Mooney, senior vice president of the Insurance Information Institute. It is an underutilized option that is ignored by most retailers and offices, according to a 1990 article in Business Insurance, an industry periodical.
As rare as it may be in the business community at large, acquiring off-premises power interruption coverage is standard practice for Fortune 1000 companies, says Mike Tuman, vice president for Rollins Hudig Hall Insurance Brokers. Many of those companies are not only insured against power outages at their own facilities, but also at their suppliers' and customers' facilities through the contingent business interruption insurance mentioned earlier.
No matter who ends up paying the damages, insurance companies or individual businesses, power outages are costly. Even very brief outages caused by minor disturbances in power transmission systems cause an estimated $3 billion to $5 billion in damages each year in the United States. Outages are also costly to the utilities themselves. Restoration expenses combined with lost revenues caused by the Northridge Earthquake cost California utilities well over $100 million.
Many companies have invested in uninterruptible power systems (UPSs) that protect equipment from brief power glitches and provide back-up electricity for about 10 to 15 minutes, on average. Others, especially key facilities such as hospitals, have elaborate back-up generator systems on site. A third option is the procurement of hot sites -- fully equipped, alternate office spaces that companies can utilize if their workplace is inaccessible or without utilities.
On-site renewable energy systems, especially PV but also wind, micro-hydro, or biomass systems, represent yet another option for helping businesses reduce the high costs of business interruption stemming from power outages. One such PV installation keeps a U.S. Post Office in Puerto Rico operating through power outages. A major California bank and a large discount store have also installed PV systems.
While each business must undertake its own analysis to determine how best to insulate itself against costly damage from grid disruptions, an on-site, full-time renewable generator is one to add to the list of disaster prevention and recovery options. Key variables that warrant consideration include the size of the critical electrical load, the capital and operating costs of various back-up options, the reliability of each system type, insurance costs and coverage terms, and vulnerability to power outages.
Recent power technology advancements offer new options to those interested in using on-site renewable energy systems to supplement utility grid power and provide emergency back-up power during outages.
Prior to 1994, most renewable energy systems were either/or --either designed to function with the utility grid, or to be free-standing. Utility-connected systems allowed for the sale of excess power to the utility, but they shut down automatically when the grid failed. Free-standing systems could function as emergency power sources, but couldn't accommodate excess power sales. A different kind of inverter was needed for each system type.
In 1994, Trace Engineering introduced an inverter that can work both ways. Its 4,000-watt, true sine wave inverter is compatible with utility power and can operate independently with a battery bank. As a result, system owners can now have the best of both worlds: They can sell excess power when the grid is working and rely on renewable back-up power when it's not. The renewable energy source, be it solar, wind, or micro-hydro, recharges the battery bank to provide continuous power for as long as the grid is down. Safety disconnects are also part of the system to prevent dangerous backfeeding into the de-energized utility grid.
This dual option is also available for larger systems (5 kW and greater) with the use of a bimode inverter/UPS manufactured by Abacus Controls Inc. The post office in Puerto Rico has such an inverter. And KBET Radio, with assistance from Southern California Edison and the U.S. Department of Energy, plans to install a 10-kW grid-connected PV system at its new station building in Santa Clarita, 35 miles north of downtown Los Angeles. If a power outage occurs, the system will instantaneously become an emergency power source for the station's AM radio transmitter. KBET is a key local Emergency Operations Center communications facility, providing a critical link between police, fire, and other disaster response contacts.
Similar projects may soon become more common as renewable energy system costs decrease and efficiencies rise. Residential utility customers in California also have yet another incentive for considering PV. A law passed just last summer will allow customers to use only one meter for both PV- and utility-supplied power. When solar power is fed back into the grid, the meter will run in reverse. The new arrangement, called net energy metering, gives residents the opportunity to bring their electric bills down to zero if their PV systems contribute as much electricity to the grid as they in turn use from the grid.
Prior to the passage of this law, PV-system-owners were required to purchase a separate meter for measuring the amount of solar power contributed to the grid, and they were paid only the wholesale power rate -- two to three cents per kilowatt-hour (kWh). Under this single meter system, PV power is valued at the full retail rate of 12 to 15 cents per kWh until a zero balance is reached. Solar power generated in excess of this zero balance is purchased at the wholesale rate, however, to discourage customers from oversizing their systems. For more information on this development, contact the California Solar Energy Industries Association contact listed in Appendix One.
It's also still an option to install a completely autonomous back-up system which always functions independently of the grid. The homes with power following the Northridge Earthquake had such systems.
Regardless of the type of system chosen, renewable energy systems should be carefully sized to keep costs down. During a power outage, the system-owners may not want to produce all the power their homes and businesses normally use, but only enough to maintain basic operations, such as to power lights, fans, computers, and perhaps a small refrigerator. And, of course, using energy efficiently all the time will keep overall energy costs down and allow more efficient use of back-up power. For example, compact fluorescent lights use only a fraction of the energy consumed by their incandescent counterparts.
Smaller-scale solar-powered emergency options appropriate for homes and businesses include consumer products such as flashlights, radios, lanterns, and battery chargers. About five years ago, Solec International, Inc. offered a Solar Earthquake Emergency Kit that consisted of a flashlight, AM/FM radio, two-way CB radio, rechargeable batteries for the three devices, a solar panel to recharge the batteries, and an AC adaptor plug. The kit sold for about $200, but it was discontinued after a year. It's difficult for solar-powered consumer products to compete with the prices for standard flashlights and radios that are usually powered by alkaline batteries. However, alkaline batteries do wear down, and replacements are not always readily available when they're needed most. With increased use of laptop computers and cellular phones -- both of which could be kept up and running indefinitely with a solar-powered battery charger --there could well be an increase in consumer demand for this type of off-the-shelf emergency solar power. In fact, SolarLife now offers a cellular flip phone with a built-in PV cell to maintain battery charge.
Natural disasters almost inevitably disrupt utility services, and often the disruptions affect a much larger geographical area than that disturbed by the disaster itself. For example, the Northridge Earthquake caused power outages as far north as Idaho and Washington. In rural Idaho, about 150,000 customers lost power for three hours.
The following snapshot views of Hurricane Andrew, the Northridge Earthquake, and two sites in Iowa during the Great Flood of 1993 provide some insight into the particular energy-related circumstances surrounding these three types of natural disasters.
Hurricane Andrew
Hurricane Andrew tore through the southern peninsula of Florida on August 24, 1992, with average winds of about 145 miles per hour and waves almost 17 feet high. The storm left about 3 million homes and businesses without power, including 1.4 million Florida Power and Light (FP&L) customers. About 5,000 traffic signals were damaged, 21,100 utility poles downed, and 26,158 street lights blown out. Several hundred thousand people lost their homes.
Water and wastewater utilities were also hit hard, as felled trees broke water mains and distribution lines and power outages disabled pumps. FP&L customers in the northern part of Dade County (Miami area) had electricity again within two weeks, but power in the devastated southern end was out for at least a month -- in some cases much longer.
Most homeowners, whose only problem was loss of power, relied on portable gasoline-powered generators to keep their refrigerators running and perhaps to operate a light and a small fan for a few hours each night. A boil water advisory was in effect, but only those with gas grills and enough fuel could comply. Most people relied on outside water supplies.
To enhance security at night in the absence of street lights, curfews were imposed, which lasted up to four months in some areas. Repairing street lights was a very low priority item, though their absence was sorely felt. PV-powered street lights in one subdivision survived the storm and became neighborhood gathering spots for residents eager to escape the darkness. They were manufactured by Solar Outdoor Lighting, Inc.
Renewables and Hurricanes
On-site renewable energy back-up systems are well-suited to meet energy needs following hurricanes because the storms often cause such widespread, long-term, infrastructure damage. Getting fuel supplies for fossil-fuel-powered generators is a challenge, especially during the first few days, because downed power poles, trees and debris make many roads impassable, and driving is hazardous on those few routes that are open.
Solar energy is particularly viable since the storms strike in some of the sunniest parts of the country. And since a hurricane usually provides at least some forewarning, PV systems, unlike the utility grid, can be disassembled before the storm hits and then put back up again once it passes. The panels can also be designed to fold down in place prior to storms. Another renewable energy option that may be highly applicable following hurricanes is a portable unit to convert biomass into electricity. Rather than landfilling the tons of woody debris created by the storms, they could be put to use generating valuable power. Another potential option to consider would be a portable pelletizing unit that could at least convert the debris into a usable form.
The Northridge Earthquake
The Northridge Earthquake struck Southern California on January 17, 1994. It measured 6.8 on the Richter Scale and was epicentered in Northridge in the San Fernando Valley.
The earthquake caused widespread power outages throughout the area and beyond, though most of them were not prolonged. The entire Los Angeles Department of Water and Power system went down, leaving 1.3 million customers without electricity. However, power was restored to half of them within six hours, and within 24 hours, 95 percent of customers were back on line. Southern California Edison lost 1.1 million of its 4.2 million customers, but 800,000 of them had power again within hours. Almost all Edison customers regained electricity within a few days.
Despite the utilities' timely restoration of power, close to 100,000 homes and businesses were without electricity for more than 24 hours. Natural gas leaks kept power from being restored in many of the affected areas. Power was available but could not be turned on for fear that sparks would touch off fires. About 100 gas-related fires did erupt, a number of which involved premature restoration of electric power. Any source of electricity would pose similar risks, so even renewable back-up systems would have to be shut down in areas without power due to gas leaks.
Water supply was also disrupted due to breaks in the supply and distribution lines. About 50,000 Los Angeles Department of Water and Power customers didn't have water on the day of the earthquake, and 10,000 customers still lacked water one week later. Water supply difficulties were a major problem for fire-fighters.
Renewables and Earthquakes
Though the damage to major utilities was great, most of the longer-term problems caused by the Northridge Earthquake were concentrated near the epicenter. "Normal life" with its modern conveniences was just a short distance away, and emergency shelters were located in areas still connected to the utility grid.
If an earthquake of greater magnitude were to strike, the damage would be much more widespread and extensive, especially if it were to occur in a region that's not as well-prepared for earthquakes as California. Under such circumstances, the need for all types of emergency power supplies would greatly increase. Back-up renewable energy systems work well in areas that lose power due to earthquakes but escape physical damage. However, it's questionable how the systems would fare if the buildings they were on or near suffered damage. Portable PV generators used following earthquakes must also be especially sturdy so they can withstand powerful aftershocks.
The Great Flood of 1993
On July 11, 1993, the Raccoon River flooded the Des Moines Water Works, leaving 250,000 people without running water for 12 days. The night before, the Raccoon and Des Moines rivers flooded electrical power substations, affecting 35,000 households and the entire downtown business district. Most customers regained power within 24 hours, though some remained without electricity for twice as long.
Many of those who lost utility service in Des Moines weren't directly affected by the flooding. Their homes and businesses stayed dry, though they lacked critical services. That wasn't the case in Eddyville, Iowa, a small town of about 1,000 people southeast of Des Moines. Residents there lost power because their homes were inundated by the waters of the Des Moines River, and the electricity was turned off for safety reasons.
In Des Moines, the power priority was to get the water plant up and running again and that required the use of extremely large generators. Thirteen generators totaling 800 kW powered water pumps, air dryers, and other equipment used in the restoration process. Once the building was dry enough, two 1,600-kW units were brought in to drive the water pump plant motors. Utility power was available, but it remained unreliable and Water Works officials didn't want to take a chance on it.
Des Moines' downtown area remained closed until the water system went back on line. Electrical power was available 48 hours after the flooding, and many businesses could have functioned without water, but the Mayor had closed the downtown area due to fire danger. Without water, building sprinkler systems were inoperable and fire-fighting abilities were extremely limited.
The only emergency water aid that was supplied was drinking water. At first, big tank trucks were brought in and people filled their own containers; later, full water jugs were distributed. Though there were naturally long lines, there was no limit on how much water people could take. Most people left the area to do laundry and bathe; however, some people took showers under drainspouts in their yards. Others caught rain water in buckets and barrels for flushing toilets and washing.
As was the case with the Northridge Earthquake, most emergency shelters in Iowa were located in areas that had grid power, and residents could drive out of the affected areas to obtain needed services and supplies.
Renewables and Floods
In flood situations, back-up renewable power systems are of benefit mainly to homes, businesses, and institutions that lose electrical service but remain accessible. In rare instances, small solar- or wind-powered sump pumps may be able to spare buildings from water damage. It's common for residents in flood-prone areas to install electric sump pumps in their basements. In low water situations, the pumps effectively keep flood water out, sparing furnaces and water heaters from damage. If electrical power is lost, these pumps cease operation and the water starts in. If the pumps were to be equipped with a safe, 12-volt alternate power source, they could continue operating and possibly beat the water -- if the level stays low.
Up to this point, most of the discussion has pertained to fixed, on-site renewable energy systems -- how they can augment the utility grid and what role they can play following natural disasters. This section enumerates the many ways that portable PV systems can aid in the disaster response arena.
A note about photovoltaics...
Since all of the examples discussed in this section involve PV power, some brief background information about the technology is helpful. Photovoltaic cells convert radiant energy from the sun into direct current (dc) electricity. A standard 12-volt, 3-amp solar module consists of 36 4-inch-diameter cells. The cells are wired together in series to obtain the panel voltage. And though this commonly used module type is referred to as a 12-volt panel, it actually produces about 17 volts of dc electricity at around 3 amps. Peak power production per standard panel, therefore, is about 50 watts.*
The modules can be wired together in series to further increase voltage. Or they can be wired in parallel to increase amperage. For example, two standard 12-volt, 3-amp modules in series produce 3 amps at 24 volts; in parallel, they produce 6 amps at 12 volts. And besides this standard module type, there are many other types of panels designed to meet specific needs.
Since the energy is produced only when the sun is shining, it is usually stored in batteries for later use. If the load to be powered requires alternating current (ac) electricity, an inverter, which converts dc power to ac power, is part of the system set-up. Most standard home and business lights and appliances operate on 110-volt ac electricity.
The majority of PV systems operate at remote sites where the power demand is relatively small (less than 1,000 watts) and utility power is either unavailable, unreliable, or cost-prohibitive. Solar power is the most economical and practical option in these cases. The number of viable applications is continually increasing, as panel efficiencies rise and cost decreases.
*Volts are a measure of the strength or pressure of the electricity and amps are a measure of the current or volume of the electricity. Volts (pressure) multiplied by amps (current) equals the amount of actual power produced, measured in watts.
Portable Repeaters
Perhaps the best application for solar power by response teams is to use PV panels to power portable repeater stations that extend the range of hand-held radio communications. This application makes so much sense, in fact, that the Federal Emergency Management Agency (FEMA) has directed its 25 Urban Search and Rescue task forces to obtain solar panels for this purpose.
When a task force is deployed, FEMA pays for the purchase of equipment needed to carry out the mission. Only equipment listed on the Task Force Equipment Cache List is authorized for purchase. The list represents about $700,000 to $1 million worth of equipment, weighing up to 50,000 pounds. Since the 56-person task forces are often transported by military cargo plane to their response destinations, space and weight considerations loom large. Solar is now approved only for use with the portable repeaters; other power needs are met by batteries (both alkaline and rechargeables) and portable generators.
Nida Companies, a small California-based firm founded by Kevin Nida (a 15-year veteran of the Los Angeles City Fire Department and a FEMA search and rescue task force member), has designed a portable PV-powered repeater station specifically for the urban search and rescue environment. The system employs two 3-amp PV panels (about 50 watts each) wired in parallel to float charge the 12-volt, 100-amp-hour sealed lead acid battery that powers the repeater signal. The repeater pulls 5 amps when transmitting information and 1 amp when receiving. PV is ideally suited to meet this power need because it can be set up in a remote spot and then left alone indefinitely. A generator, on the other hand, would be well oversized for such a small load and would need regular refueling.
Angel DeLaFuente, a FEMA operations support specialist and task force member from Florida's Metro-Dade Fire Department, also sees a need for a portable, PV-powered weather balloon repeater. Propelled upward by a helium balloon, this system's antenna would extend at least 300 feet in the air and allow for the far-reaching communication that is often vital following hurricanes. To his knowledge, such as system has yet to be developed, though he believes it would have far-reaching appeal.
Amateur Radio Links
Ham radio operators used solar power to maintain vital communications links following Hurricane Andrew and the Loma Prieta Earthquake, which struck California's Bay Area in 1989.
And when the Northridge Earthquake knocked out utility power at the Sulphur Mountain Microwave Repeater site, amateur radio operators belonging to the Sulphur Mountain Repeater Association brought PV modules from their personal systems to the site to replenish the batteries so that emergency communications between police, fire, and hospitals could continue. Siemens Solar Industries of Camarillo, Calif., donated 22 solar modules (1.2 kW) for the site, making it a permanent PV installation.
Ham radio stations often come through following disasters when much more sophisticated communications systems fail. They are ideal candidates for solar power.
Transportation Aids and Warning Signals
The Florida Department of Transportation used PV-powered advisory radio systems as communications tools following Hurricane Andrew. Drivers could tune in for information on traffic and emergency assistance. Solar-powered changeable message signs also communicated traffic information and alerted motorists to the advisory radio systems.
These systems, along with PV-powered emergency telephone call boxes, flashing barricade lights and other warning signals, come in extremely handy not only during times of crisis, but also for day-to-day use. The signs and barricades inform motorists about road construction projects, and highway call boxes play an important safety role. In New Mexico, PV-powered travelers' information radios inform tourists about the areas they're driving through.
PV also powers warning signals on Coast Guard buoys and navigational beacons; solar energizes railroad signals, aircraft warning lights, and school crossing lights. When a disaster disables the utility grid, these public safety systems continue to function.
Battery Charging
Another potential use for PV in the disaster response arena is for charging batteries. When rechargeable batteries are used to power such items as hand-held radios and cellular phones, they sometimes lose their power before the workers can return to the base camp to recharge them. Work crews are often bussed to work sites, and there they lack the vehicular chargers they can rely on at home. When their battery packs run down, they're finished communicating until someone brings them a fresh one or they return to camp.
Because rechargeables lose power more quickly than alkaline batteries, the rescue crews in California use only alkalines whenever possible during response missions. A search and rescue task force member said one round of AA alkaline batteries lasts 24 hours, as compared to 8 hours for rechargeables.
However, in situations where crews work long shifts and the use of rechargeables cannot be avoided, workers could use small PV panels to charge depleted battery packs while in the field. The U.S. military uses PV for charging batteries to maintain communications between units and headquarters. Photocomm, Inc. designed the ManPac military solar module battery charger precisely for recharging 12-volt batteries at remote sites. The 15-watt unit weighs only 1.7 pounds and folds for easy transport inside a backpack. Price may preclude the widespread use of this particular product, since it retails for $799. More standard panels are much less expensive and may be able to adequately meet disaster response needs, however.
Another PV-battery charging option would be to equip a mobile unit with PV panels. It could be parked at a remote site to recharge an entire bank of cellular phones or radio battery packs simultaneously. Search cameras and high-tech listening devices used to locate trapped victims also operate on DC batteries which could possibly be recharged using PV panels. However, all of these potential battery charging applications will require field testing to determine their need and feasibility.
Portable Power
Portable PV power systems are especially well-suited for meeting long-term emergency power needs at small-scale, isolated sites. For example, following Hurricane Andrew, four PV power
systems were installed throughout hard-hit South Florida. Each system consisted of a 1-kW-peak array, a 21 kilowatt-hour (kWh) battery bank, an inverter, and a battery charger.
All of the solar panels were loaned by the Florida Solar Energy Center (FSEC), and Sandia National Laboratories contributed the batteries and controls. FSEC actually took a system down that was powering one of its buildings to help with the relief efforts.
Three of the systems were installed at small medical clinics and one provided electricity for a relief operations center. They were used to operate vaccine refrigerators, lights, fans, medical equipment, and small radios and televisions. Solar power was especially ideal at the clinic locations because it kept patients away from prolonged exposure to the noise and fumes of portable generators. It also enhanced the operation of medical instruments (stethoscopes, for example) that require a quiet environment for proper use.
At some locations, the PV systems eliminated the need for portable generators, and at others, solar power cut generator use by at least half. The systems enabled workers to turn the generators off at night without having to handle dry ice for the vaccine refrigerators, and they lessened fuel supply worries. A few of the systems were in use for up to two months.
At St. Anne's Catholic Mission in Naranja, Florida, one system powered a medical clinic and another, a relief operations center. Site Coordinator Bruce Netter admitted he was reluctant to accept the offer of solar power, a then-unfamiliar technology to him. After all, it involved setting up two sizable arrays on church property and wiring them right into the buildings' circuitry. He credits Sherri Porcelain, Terri Meinking, and David Kaplan of the University of Miami's Field Epidemiology Survey Team with talking him into the PV option. They knew PV worked well in these situations from their experience at remote island field stations.
Now Bruce Netter is a self-professed solar advocate and wishes PV back-up systems could be standard equipment in all buildings. He said he was particularly struck by the silence of PV power in contrast to the anxiety caused by generator noise. It made a tremendous difference to the staff and to those served by the clinic and those seeking food, supplies, and FEMA or Red Cross assistance from the operations center. A third system was also installed on the roof of a makeshift "grocery store," built to allow people to select their own emergency supplies. The system powered lights and fans at this unusual "Amigo Mart."
Solar electricity was also used during the aftermath of Hurricane Hugo. A mobile PV/generator system developed by Photocomm, Inc. for the State of Arizona provided power for lights and refrigeration to a YMCA community center for over six weeks following the storm. The system, called the Solar Emergency Response Vehicle, consists of a 2-kW PV array with a 6-kW back-up propane generator, battery bank, and inverter. The entire system is mounted on a trailer for easy transport. The City of Tucson has a similar unit. These systems, preassembled and including the trailer and all controls, cost about $15/watt, or $30,000 apiece.
The Sacramento Municipal Utility District in California also has two portable PV units, though they aren't equipped with back-up generators. The trailer-mounted arrays provide 600 to 800 peak watts of electricity, with battery storage of about 4,000 to 5,000 watt hours. They are mostly used as demonstration models at fairs.
Portable units that arrive on the scene ready to go with little user interaction are essential to the expanded use of PV generators in disaster response. During a crisis, there is no time for careful installation of delicate equipment. Rescue workers must also be educated as to the proper use of PV before the disaster occurs, for they are not in the proper frame of mind to learn new technologies in the response environment.
In the past year, Photocomm, Inc. has introduced a new product line that may work well in the disaster response environment. Called SUN PAK generators, the sturdy systems are fully assembled and tested prior to shipment, so they would be easy to set up during an emergency. They consist of efficient solar modules and deep-cycle lead acid batteries, along with system controls and optional chargers and inverters. The solar panels are mounted to the insulated, vented battery/control box and provide shade for it during the summer.
The smallest available SUN PAK is 50 watts, and they are available in 50-watt increments up to 1,000 watts. Custom units are offered in larger sizes. The 50-watt unit costs $1,000, and the 350-watt model, $5,500. Price quotes were not available for the larger units.
Though costly, systems like these could prove invaluable in emergency situations. They were designed to provide continuous power in remote applications. It's also important to keep in mind that PV system costs in general decrease sharply when they are purchased in bulk. For example, if 100 or more systems are purchased, discounts of 25 percent to 50 percent are not uncommon.
Outdoor Lighting
The clinics and relief shelters that hosted PV power systems following Hurricane Andrew also benefited from PV-powered outdoor security lights. Though they were low-power systems compared to traditional street lights (30 watts versus 250 watts), they made a big dent in the total darkness. A few PV-powered street lights in a Dade County subdivision also survived the storm and became popular gathering spots for neighborhood residents. In addition, Kyocera America donated a few hundred solar-powered lanterns to relief efforts, and they were appreciated by those living in the tent cities.
Some outdoor emergency lighting needs are too large to be met with PV systems. Outdoor staging areas where food and water were distributed to hurricane victims were lit with large banks of 400-watt lights powered by 10 to 15-kW generators. Similar systems are used following earthquakes to accommodate the large numbers of people who congregate in parks, afraid to return to their homes.
In less-populated -- but very dark -- areas, however, PV outdoor lights are ideal. They represent yet another PV application that works well not only during emergencies, but all the time. They can be found illuminating parking lots, highway signs, parks, trails, and bus shelters. In many cases, using solar power is more economical and expedient than extending utility service to these locations.
Water Purification
Water system disruptions seem to be almost as common as utility grid failures following disasters. And although rescue workers are proficient at quickly mobilizing clean emergency water supplies into areas of need, it may be more efficient in some cases to transport not water supplies but water purification equipment. Treating tainted water on site would mean one less continual supply chain to tend.
Dr. Ashok Gadgil of the Lawrence Berkeley National Laboratory has developed a highly efficient water purification system that delivers up to four gallons per minute of potable water. The water flows by gravity through a trough below an ultraviolet light. The ultraviolet radiation emitted kills most viruses and bacteria present in the water. The lamp used resembles the standard fluorescent tube common in offices, but it's made of a special glass that is transparent to ultraviolet light and it's not coated with phosphor.
The system's only power needs are the 40 watts of electricity required to operate the lamp, making it an ideal candidate for PV power. And while it was designed to provide clean water to citizens of developing countries, it would be ideal for emergency use wherever water supply disruptions occur.
Water Pumping
PV could also be used to pump water during emergency situations. Some portable solar pumping systems do not require batteries but work directly off the power supplied by the array. These systems have proven to be cost-effective for pumping water for livestock on remote ranches, and they may also be suitable for accessing water in isolated, disaster-affected areas. Most pumps brought in to combat flood waters or restore flooded utility structures have power needs much greater than what PV could feasibly supply, however.
Pumps for gasoline are another emergency need because loss of electricity disables all the gas stations in an area. Although conventional gas pumps require more electricity than could practically be provided by a portable PV system, PV-powered pumps could possibly be used to extract gas from the underground storage tanks. As with battery-charging, this potential application requires further study and field-testing.
Water Heating
Solar thermal technology was employed to provide hot water for a relief kitchen in Florida City following Hurricane Andrew. Steven K. Gorman of Renewable Energy Group in Jacksonville, Florida, donated a water heating unit capable of providing up to 1,000 gallons of hot water per day. Without hot water to ensure health and safety, emergency kitchens cannot function. The solar unit allowed this particular kitchen to continue operating. The system has since been equipped with PV-powered pressure pumps, allowing it to deliver pressurized hot water. It's been mounted on a flat-bed trailer for portability, and Gorman says it has been used to provide emergency hot water on numerous occasions. One additional water-related solar option that is a sure bet is "solar shower" devices. These low-tech products generally consist of a simple black plastic water-bottle-type bag with a spout attached. The bag is filled with water and then left in the sun, so it can provide a warm shower at the end of the day. About of dozen of these were donated to Hurricane Andrew relief efforts. They were a big hit with relief crews after long, hard shifts.
Remote Monitoring
Solar power is involved in many emergency situations even before disaster strikes. Hundreds of remote PV-powered sensors, dataloggers and information transmitters send continuous data to central offices for use in flood, drought, and forest fire forecasting. Information on weather patterns and seismic data, water quality and highway conditions, is transmitted in this manner. In the Los Angeles area, PV powers a radio link that would inform the Southern California Gas Co. of any leaks affecting its natural gas storage well.
Consolidated Edison Co., the electric utility which serves New York City, uses photovoltaics to power oil-detection buoys in waterways near its generators. The system was jointly developed by ConEd, EXXon Corp., and Spectrogram Corp., and it's now commercially available through Spectrogram, which is based in North Haven, Conn.
The system, called the Oil Spill Remote Alarm System, or OSPRA System, consists of buoys equipped with sensors that continuously monitor the water quality and detect the presence of oil by sensing its fluorescent properties. If a spill is detected, the sensor immediately reports data to the base station computer. Both the sensor and the information transmitting functions are powered by a battery kept float-charged by PV panels located on top of the buoys.
Renewable energy systems can be significant contributors to energy emergency preparedness and can help to bolster the overall resilience of the U.S. electrical energy system.
PV-powered warning and detection devices already help to prevent some disasters and ensure a rapid response to others. Once a disaster has occurred, portable PV systems can meet a number of small-scale emergency power needs.
The emergency response community must now build on its experience with portable PV power. It is certain that the systems must be preassembled and ready to go when they arrive at disaster sites. Further field-testing and design work is needed to identify optimal system sizes and applications. Once completed, agencies such as FEMA, the Red Cross, and the U.S. Army Corps of Engineers may want to consider stockpiling PV systems and providing their energy staffs with advance training on how to install and use them.
Beyond the emergency response realm, power failures in general can be prevented through increased use of on-site renewable energy systems using solar, wind, micro-hydro, or biomass energy. The need for highly reliable back-up power is greater than ever, considering that a major utility grid disruption in one location can not only cause power outages hundreds of miles away, but also result in costly contingent business interruption insurance claims from all over the country.
Given this reality, businesses, utilities, insurance companies, and government and private emergency-response agencies should actively investigate the feasibility of on-site renewable energy systems. While they'll find that the purchase price of conventional fossil-fueled back-up generators is lower, they'll also discover that the costs of renewable energy technologies are becoming increasingly competitive. They also cost less to operate, free system owners of a worrisome dependence on fuel, and offer hard-to-quantify benefits such as silence and clean air.
Institutions and local governments should also regularly monitor renewable energy costs, looking for new opportunities to employ systems. For example, the emergency benefits of PV-powered security lighting are great, especially when factored against the high cost of rampant looting that often accompanies black-outs.
And finally, renewable energy industries may want to begin devoting more attention to the domestic emergency power market. The frequency of natural disasters has risen sharply over the past five years, and when disaster strikes, it almost inevitably disrupts the utility grid. The time may be ripe to demonstrate the preeminent usefulness of renewable systems to provide vital electricity when it's sorely needed.
The renewable energy industry associations -- the Solar Energy Industries Association, the American Wind Energy Association, and the National Wood Energy Association -- can provide further information, including manufacturers' lists, on the renewable energy technologies mentioned in this report.
Additional information is available by contacting the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy:
doe.erec@nciinc.com
1-800-DOE-3732
Below is a list of those who provided information to assist in the preparation of this report. It is provided to allow for direct follow-up on points discussed. Industry listings do not constitute endorsements.
Emergency/Disaster Response Contacts
Sean Foohey
Deputy Director, Operations Division
Federal Emergency Management Agency (FEMA)
(202) 646-3597
Kevin Nida
FEMA Urban Search and Rescue Task Force Member
Los Angeles City Fire Department
President, Nida Companies
(818) 957-1248
Angel DeLaFuente
FEMA Operations Support Specialist and Task Force Member
Metro-Dade Fire Department (Miami)
(305) 596-8037
Joanne Nigg
Disaster Research Center at the University of Delaware
(302) 831-6618
Michael Douglass
Acting Deputy Chief, Fire and Rescue Division
California Office of Emergency Services
(916) 262-1685
Sherri Porcelain
Field Epidemiology Survey Team at the University of Miami
(305) 243-5616
Bruce Netter
Emergency Manager for the Catholic Archdiocese of Miami
(305) 378-6306
Photovoltaics Contacts
Government
Jim Rannels
U.S. Department of Energy's Photovoltaic Technology Division
(202) 586-1720
Bill Young and Jim Dunlop
Florida Solar Energy Center
(407) 638-1000
Roger Hill
Sandia National Laboratories
(505) 844-6111
Ashok Gadgil
Lawrence Berkeley Laboratory
(510) 486-4651
Utilities
Ray Paz and Doug Whyte
Southern California Edison
(818) 815-7255 and 7256, respectively
Pete Eckert
Arizona Public Service Company
(602) 350-3170
Don Osborn
Sacramento Municipal Utility District
(916) 732-6679
Arthur Kressner
Consolidated Edison (New York City)
(212) 460-4170
Industry
Cathy Murnighan
California Solar Energy Industries Association
(916) 649-9858
(800) 225-7799 (in California)
Scott Sklar
Solar Energy Industries Association
(202) 383-2600
Joel Davidson
Solec International
(310) 970-0065
Bill Cirrito and Eric Souders
Photocomm Inc.
(602) 327-8558
Dan Healy
Sunelco, Inc.
(406) 363-6924
Chris Frietas
Trace Engineering
(206) 435-8826
George O'Sullivan
Abacus Controls Inc.
(908) 526-6010
Joan Friborg
Spectrogram Corp.
(203) 281-0121
Steven Gorman
Renewable Energy Group
(904) 384-6503
Insurance Contacts
Ann Deering
Environmental Technology & Telecommunications, Ltd.
(212) 661-5373
Michael Tuman
Rollins Hudig Hall Insurance Brokers
(312) 701-4284
Sean Mooney
Insurance Information Institute
(212) 669-9200
Funding for this project was provided by the U.S. Department of Energy's Office of Energy Efficiency and Renewable Energy.
This paper's author can be reached at the following:
Roberta F. Stauffer
TechWrite Services
1253 West Aluminum
Butte, MT 59701
(406) 782-5333
The project was completed for the National Center for Appropriate Technology, a national nonprofit organization that has worked on sustainability issues since 1976. Its address and phone number are
P.O. Box 3838
Butte, MT 59702
(406) 494-4572
General Emergency Response
Natural Hazards Observer, March and May 1995 issues, Natural Hazards Research and Applications Information Center, University of Colorado at Boulder.
"Planning Ahead for Rental Generator Set Power at Your Facility," Disaster Recovery Journal, April/May/June 1994.
The Federal Response Plan, Federal Emergency Management Agency, April 1992.
"When Natural Disaster Strikes," American Pharmacy, November 1990.
New Perspectives on Energy Emergency Preparedness, Strom Thurmond Institute Working Paper Series, Clemson University, June 1990.
Brittle Power, Amory R. Lovins and L. Hunter Lovins, Brick House Publishing Co., Inc., Andover, Massachusetts, 1982.
Earthquakes
The Business Interruption Effects of the Northridge Earthquake, Lusk Center Research Center, University of Southern California, April 1995.
Business Disruption Due to Earthquake-Induced Lifeline Interruption, Disaster Research Center, University of Delaware, 1995.
1994 Northridge Earthquake: Performance of Structures, Lifelines, and Fire Protection Systems, National Institute of Standards and Technology, May 1994.
Physical Vulnerability of Electric Systems to Natural Disasters and Sabotage, U.S. Office of Technology Assessment, 1990.
PG&E and the Earthquake of '89 and Report on Lessons Learned from the Loma Prieta Earthquake, Pacific Gas and Electric Co., 1990.
Floods
The Impact of the 1993 Midwest Floods: Business Vulnerability and Disruption in Des Moines, Disaster Research Center, University of Delaware, 1995.
"Overcoming the Flood: How Midwestern Utilities Managed Disaster" and "Surviving the Flood: Teamwork Pays Off in Des Moines," American Water Works Association Journal, January 1994.
"Rental Power: The Pulse of Flood-Ravaged Communities" and other flood-related articles, Disaster Recovery Journal, October/November/December 1993.
Hurricanes
"Weathering the Storm: Water Systems versus Hurricanes," American Water Works Association Journal, January 1994.
Governor's Disaster Planning and Response Review Committee's Final Report Recommendations, State of Florida, December 1993.
Hurricane Andrew Assessment -- Review of Hurricane Evacuation Studies Utilization and Information Dissemination, U.S. Army Corps of Engineers, South Atlantic Division, and Federal Emergency Management Agency, Region IV, January 1993.
Hurricane Hugo: A Review of the Research, City of Charleston, November 1991.
Hurricane Coordinating Procedures, State of Florida, May 1991.
Hurricane Hugo: Lessons Learned in Energy Emergency Preparedness, The Strom Thurmond Institute of Government and Public Affairs, Clemson University, 1990.
Photovoltaics
"Southern California Edison's Innovative Solar Neighborhood Program," Solar Today, July/August 1995.
1995 Product Catalogs from Sunelco, Inc. and Photocomm, Inc.
Photovoltaics Now, Sandia National Laboratories, February 1994 (rev.).
Testing and Evaluation of a Mobile Photovoltaic/Genset Hybrid System, paper presented by Arizona Public Service Co. and Arizona State Energy Office, IEEE Photovoltaic Specialists Conference, October 1991.
Photovoltaic Systems for Government Agencies, Sandia National Laboratories, February 1989.
Photovoltaics for Military Applications, Sandia National Laboratories, December 1988.
The New Solar Electric Home, Joel Davidson, aatec publications, Ann Arbor, Michigan, 1987.
Copyright (c) 1995, US Department of Energy
Hypertext Conversion by CREST
|
