Renewable Energy Focus Group,
By Tad Finkler, Kathleen Hannon
"Renewable Energy: Status and Struggles"
by Tad Finkler
The finite reserves of fossil fuels are dwindling, and global energy consumption is on the rise, possibly by as much as 75% in the next thirty years. The impact of emissions from the combustion of fossil fuels and the hazards of extracting, transporting, and refining these fuels are also taking a toll on the atmosphere and the environment. Carbon dioxide is a major contributor to the growing envelope of the so-called "greenhouse" gases in the earth's atmosphere, which scientists now see as the probable explanation for the rising trend of global temperatures. The current net carbon dioxide production is largely a result of carbon being released from sources (i.e., fossil fuels) that cannot reabsorb on time-scales relevant to human activity.
The sum of these factors, along with a desire to produce cheaper energy and to decrease national dependence on foreign petroleum reserves, has led to the large investment in energy research in recent years with the goal of developing energy generation methods that will serve well for the long-term support of human activity. Besides economic feasibility, two major considerations that guide this research are renewability-whether the technology depends consumption of a fuel that ultimately is in finite supply-and cleanliness. The ideal solution to the energy problem would be both extremely clean and rapidly renewable.
The purpose of this paper is two-fold: to familiarize the reader with the most popular and probable technologies; and to summarize the policy issues that will be critical to the future development and proliferation of these technologies. The first section describes the various technologies that are likely to play a major role in supplying future society with energy, and gives indications of the extent to which those technologies are now contributing to energy production in the United States and in the world. The second section addresses some of the important obstacles which must be overcome in order for these technologies to successfully replace fossil fuels.
Probable Options for Energy Generation from Renewable Sources
For ages, mankind has been contriving schemes to manipulate energy. The use of fire for warmth and cooking is probably the most primitive example. Through the millennia, this has evolved to steam engines and generators, uses of solar radiation, fossil fuel combustion processes, and even nuclear generators.
The wide variety of energy strategies used in the past gives some indication that the range of possibilities for energy production in the future is indeed vast. However, as today's scientists and researchers strive to develop means for cleaner and more renewable means of energy generation, a handful of technologies has emerged as the most promising renewable energy sources for the near future. In this section of the report, these technologies-nuclear, wind, hydro, geothermal, solar, and biomass-are briefly summarized, including their current contributions to energy generation. A graphical depiction of current cost comparisons between these technologies is included at the end of the section.
Nuclear energy has always been an extreme technology: extremely powerful, extremely capital-intensive, and extremely mystifying to the general populace. The ominous mushroom cloud that accompanies nuclear explosions and the unfortunate accidents at Three-Mile Island and Chernobyl are prevalent in the public consciousness, contributing to a widespread sentiment-at least in the United States-that nuclear energy is still an untamed beast that doesn't belong anywhere near a neighborhood.
Nuclear energy technology has made strides since the late 1970s when the aforementioned accidents occurred. New designs for light-water reactors, the Process Inherent Ultimate Safety reactor and the modular gas-cooled reactor incorporate automatic shutdown and cooling methods that require little operator and/or mechanical involvement to avoid runaway reactions. Despite these design improvements there has been little growth in the nuclear power industry in the United States since the early 1970s, when the last new plant was constructed. Nevertheless, in 1990, nuclear generation accounted for 20% of the electricity produced in the United States.
Nuclear power is a thorny issue among energy researchers. Historically, it has been hailed as the panacea for society's energy needs because of the vast amounts of energy produced from very small volumes of fuel. More recently, however, it has come under attack for several valid reasons. The first reason for hesitancy in developing further dependence on nuclear technology is that it is neither truly clean nor truly renewable, while many of the other emerging technologies are. The world's supply of uranium is finite, and moving to plutonium-based reactors entails a host of new dangers. The toxic waste from either of these cannot yet be dealt with. The second reason that nuclear power is being shunned is that its capital-intensive, centralized power generation nature is at odds with the current desires for deregulation of public utilities and decentralization of energy production to alleviate distribution losses.
Wind energy is one of the cleanest energy generation techniques imaginable. It creates no harmful emissions, consumes no fuel, and presents no great environmental hazards in the event of equipment malfunction. Additionally, it consumes very little actual land area, since the land on which wind turbines are installed can simultaneously serve other uses such as farming or grazing. The land could even be used for biomass crops, thereby optimizing the energy production of that land.
Wind turbine applications can be separated into three categories. Large, grid-connected wind turbine generators (WTG) tend to be congregated in windfarms, where 500 to 800 kW machines are combined for total capacities in the hundreds of MW. Intermediate sized (10 to 100 kW) turbines are usually used in small quantities in hybrid energy systems, producing off-the-grid power in conjunction with other generation technologies (often solar or diesel) and a small-scale storage medium, such as batteries. Small wind turbines (<10 kW) are usually used in remote settlements for water pumping or battery charging.
There are a limited number of locations worldwide in which the wind is consistently powerful enough for profitable large-scale WTG installations, at least with current technology and energy markets. The appropriate sites tend to be near coastal regions, since ocean-influenced wind patterns are highly dependable. In the United States, the most promising sites for WTGs are along the two coasts and in a broad band across the northern portion of the Great Plains. California currently has the most installed capacity. In Europe, the Scandinavian nations and the UK have several regions with high potential for development as wind farms.
In 1992, wind energy accounted for 1% of California's electricity, equivalent to the demands of about 600,000 residential customers.3 Researchers expect that as the mechanical technology continues to be refined, allowing currently unprofitable sites to be developed as profitable wind farms, wind energy could supply 20% of the United States' electricity. Globally, the United States and Europe are the major users of grid-connected WTGS. The global installed capacity of grid-connected WTGs in 1996 was about 3700 MW, of which the United States contributed 1700 MW and Europe 1650 MW.4 Wind power does account for a significant portion of third-world energy generation, but most of these are non-grid applications.
Although the basic strategy of hydrodynamic energy generation, much like wind energy generation, is not at all modern, current research aims at expanding the possible configurations and locations of hydrodynamic generation. It still boils down to using gravity or wind induced (in the case of ocean waves) fluid motion to turn an electrical generator. However, the trend in new applications is away from the monstrous dam projects of this past century, with their high capital investments and environmental impacts. Instead, researchers are working toward low-head turbines that can be used in rivers without disturbing their flow (often termed 'run-of-river" installations), in concentrated ocean currents, or in conjunction with tidal fluctuations.
Hydrodynamic energy generation is similar to wind energy generation in several important ways. Both are inherently renewable in that they don't consume fuel in order to produce power, but instead convert a natural form of mechanical energy into electrical energy. An important consequence of having no fuel consumption is that it means there are no exhaust emissions. Also, once a facility has been installed, the costs of power generation are mostly from facility operation and maintenance. Another similarity to wind generation is that geography is the major determinant of locations in which small hydro generators are feasible. All the scenarios being pursued work with natural bodies of water, and only select locations of these bodies provide conditions suitable for development. Usually the deciding factors are flow velocity and volume.
Recent estimates attribute about 20% of global energy production to hydropower. In North America, small hydropower installations (<10 MW) account for slightly over 3% of total hydrodynamic electricity generation, which as a whole is responsible for about 3% of total electricity productions in Western Europe, the ratio is slightly higher, with small hydro contributing over 7% of the total hydro production, which in turn represents about 17% of the regional electricity demand. Most experts expect these numbers to grow significantly in the next 20 years, especially in developing nations. Optimistic scenarios indicate total hydropower contributions near 37% during that time.
Geothermal technologies for generating electricity use naturally occurring heat from beneath the surface of the earth, either directly for district heating or as the energy to drive a thermodynamic electricity generating cycle. The most mature geothermal technologies tap into steam vents or hot-springs, which limits the possibilities for development to available locations along the edges of tectonic plates. Most of these sites are along the Pacific Rim or in East Africa. Iceland also makes extensive use of geothermal technologies.
Another source of geothermal energy is hot dry rock (HDR), present everywhere on the globe at some varying depth beneath the earth's surface. Scenarios for making use of this huge thermal resource involve drilling two adjacent wells deep into the rock, using pressure to fracture the rock between the wells, and then pumping water down one well and out of the other. In essence, this is a huge artificial heat exchanger. The heated water produced by this cycle can be used either directly for heating or for electricity generation. HDR technologies have not yet been commercialized, but have been successful in small demonstration projects.
Iceland is by far the world's leader in exploiting geothermal resources, with 80% of its population using geothermal heat for space heating.8 Hungary and Japan also have high installed capacities for geothermal heating. In the United States, the installed capacity for heating is only about 463 MW(th), while the installed capacity for electricity generation is about 2800 MW(e). Many sources indicate that most of the sites in the United States available to current technology have been developed, but geothermal sources could drastically reshape energy production with the commercialization of HDR technology. According to a study in 1990, the total accessible HDR resource in the United States alone is about 11.7 million EJ, or 100,000 times the yearly national energy use.
Solar energy has always had a unique place in the vision of clean and renewable energy, since at first look it seems to involve almost no environmental impact and be available in quantities far beyond the needs of humans. Actually, with the exception of nuclear, geothermal, and tidal energy production, all energy production techniques can trace their source back to solar irradiation of the earth. Fossil fuels are derived from chemical energy stored in decayed organic materials, which at some point in ancient history thrived on solar energy transformed through photosynthesis. Wind is a result of temperature gradients within the atmosphere, and waves are a result of wind shear on the surface of the ocean. Even the water cycle that provides precipitation to feed rivers and hydropower facilities is a result of the sun.
Solar energy generation, however, usually refers to the handful of technologies which directly utilize the radiation of the sun. These can be divided into two groups: photovoltaics and solar thermal power plants. Additionally, passive solar architecture and solar thermal collectors for buildings are often treated as energy generation technologies because of their enormous potential for reducing the energy required for space heating, lighting, and hot water. In this section of the paper, however, we will focus the discussion of the first two categories.
Photovoltaic (PV) cells use semiconductor technology to generate electrical current directly from the impact of photons from the sun. The output from a single solar cell is quite small, so these cells are typically installed in large arrays to generate sufficient current and voltage. A 10 cm square cell in full sunlight might be expected to generate about 4A and 0.5 VDC. Typical state-of-the-art cells are able to attain about 35% conversion efficiency, so despite the 1000 W/m2 typical irradiation at the earth's surface, large areas are needed to generate quantities of electricity large enough to support a home or contribute to the grid. Slightly better performance can be obtained from systems that optically concentrate the radiation onto a condensed array of PV cells, but these require more equipment and active tracking of the sun. PV systems, whether flat arrays or optical concentrators, are well suited for remote installations with low power requirements. They are typically not connected to large distribution grids.
Solar thermal power plants collect energy from the suns rays to heat a working fluid, which then is used to drive a thermodynamic cycle for generating electricity. These plants typically use either long troughs of parabolic reflectors focusing solar radiation on a duct through which the working fluid passes, or large arrays of small independent paraboloid mirrors that focus radiation on a central tower collector. These systems differ from PV setups in that they require direct radiation, so they must include some means of tracking the motion of the sun across the sky. PV cells, although they work best with direct radiation, are able to make some use of diffuse or reflected radiation.
It is difficult to estimate the total generation of energy from direct solar technologies, since most PV applications are remote and not monitored in any official way. However, the sales of PV modules worldwide is steadily rising, with new shipments near 80 MW(peak capacity) in 1995. Of that, about 30 MWp were shipped in the United States. As a whole, solar technologies are estimated to contribute only 4 MW annually in North America, and about 16 MW annually worldwide.
The group of renewable energy strategies that many researchers expect to supply the majority of the global energy demand once fossil fuels are phased out is known collectively as biomass technology. Biomass strategies use the chemical energy stored in organic materials such as municipal waste, process byproducts, or specialized crops such as short-rotation forestry or select grasses. Some of the biomass technologies directly combust these feedstocks to generate heat and/or electricity, while other techniques extract fuels from the organic materials to be burned elsewhere.
Wood-fired power plants and stoker boilers are examples of direct combustion biomass technology, where the biomass is basically packed into a huge furnace and burned at high temperatures. The heat generated is usually used to drive a thermodynamic cycle. Fluidized-bed combustors are another example of direct combustion, where the biomass is suspended in a fluidized state in order to achieve more complete combustion. The general challenge faced by all biomass direct combustion methods is overcoming the low energy density of the feedstock. A typical feedstock such as wood has only 60% of the energy density of coal, making its transport in raw form uneconomical and requiring high levels of conversion efficiency for its use to be economical.
A second subset of biomass technologies that has a special place in the gallery of renewable energy options includes processes such as gasification, liquefaction, and biochemical conversion or biogas digestion. These approaches all process the biomass feedstock to extract liquid or gaseous fuels whose chemical structure is usually similar to methanol or ethanol, and which can be used in many of the same applications that natural gas, gasoline, and diesel fuel are currently used. Gas fired furnaces, gas turbines, and internal combustion engines can all be made to run on these fuels, sometimes with very little modification. These represent the only major renewable technologies whose end product is not immediately restricted to heat or electricity and which can cater to the demands of the transportation industry.
Biomass combustion currently accounts for 2400 TJ of energy production in the United States, of which some 66% is from direct combustion technologies, including residential heating from wood burning stoves.16 In the industrial arena, the paper and pulp industries lead the trend toward biomass conversion by consuming their own byproducts in cogeneration facilities, supplying about half of their own heat and electricity needs.17 The state of Hawaii also has an impressive biomass program, and recently could claim 229 MW installed capacity, largely using byproducts of the local sugar industry.18 On a worldwide scale, biomass strategies accounted some 0.04 EJ in 1990, more than 65% of renewable energy use and 12% of total energy use.
+ Except where noted by (*), data for the charts on the following pages were adapted from EUREC Agency's The Future for Renewable Energy (London: James & James (Science Publishers) Ltd. 1996), using an exchange rate of US$1.09 = I ECU (www.oanda.com/converter/classic). * Fossil fuel prices from www.eia.doe.gov/eneuf/electricity ** Nuclear prices from www.nci.org/basics/ga.html
Obstacles for Renewable Energy Proliferation
The technological developments in the past two decades of energy research have brought the goal of clean and renewable energy much closer to realization. We are already beginning to see the benefits of implementing some of the technologies described above, in California's wind farms and solar collectors, in the biomass industry of Hawaii, and in the successes of experimental hot dry rock facilities. However, goals that scientists-and some policy makers-have set for the integration of renewable technologies into the energy infrastructure are far from being realized. There are many significant non-technical obstacles that currently stand in the way of progress in this area. This section of the paper will look at a few key policy domains where renewable energy technologies currently suffer unfairly in their struggle to compete with established fossil fuel technologies.
The biggest difference between fossil fuel technologies and most renewable technologies is that almost the entire cost of the latter is wrapped up in the initial facilities investment. Since there is no fuel consumed in wind, hydro, geothermal, or solar generation, the production costs are simply operation and maintenance of the facilities once they are installed. Because of current tax laws and economic policies, this difference puts renewable technologies at a great initial disadvantage as they try to capture a share of the energy market.
Current tax laws tend to penalize corporations for capital investments and allow recurrent operating expenses to be deducted from their tax liability. This means that if a company spends a dollar investing in new facilities-perhaps wind turbines-they will have to pay additional fees for that investment when tax time rolls around. On the other hand, if the company instead deepens its dependence on fossil fuel technologies that are likely to have a lower equipment cost-perhaps a diesel generator-the subsequent costs of purchasing fuel for the generator could be deducted from the year's taxes. This is a classic case of antiquated policies holding the "good old boys" out of reach of newer and better technologies. Changing tax laws so that large corporations can economically invest in cleaner energy sources is a necessary first step if renewables are to capture a significant share of the market.
Homeowners run into a similar barrier if they try to invest in energy efficient upgrades to their homes. Because typical interest rates for credit purchases are so high, a homeowner who wanted to invest in a solar water heating system would experience a significantly longer payback time than what is required to simply recover the initial cost of the system. if, on the other hand, homeowners were permitted to add such investments to their home mortgages with lower interest rates, the interest paid on the system could be cut in half, significantly improving the appeal of such systems to the penny-wise homeowners. Interestingly, there was a very strong market for solar water heating systems up until the mid 1980s, when a surplus of petroleum made fossil fuel heating incredibly cheap and a change in tax laws ended residential renewable energy tax credits.21
Changing taxation policies will improve the plight of competing renewable energy technologies, but without direct government intervention in some form, renewable technologies will remain in the development stage longer than necessary. The problem has often been illustrated as the chicken-and-the-egg dilemma: without investor confidence, renewable technologies cannot leave the laboratory and prove themselves in direct application. But without demonstration of their viability, investors will not put their confidence in renewables.
The current dependence on fossil fuels will, of course, come to an end. But hopefully this will occur before it is brutally forced upon society by an abrupt slurping sound from the oil pipelines, indicating that the world's reserves have been sucked dry. Avoiding this situation requires foresight on the part of policy makers and industry. The change to clean and renewable resources needs to be fostered immediately in order to implement a smooth transition. Unfortunately, several cases in which legislatures tried to encourage such changes by levying mandates on electric vehicle sales have backfired, probably diluting the impact of future legislative actions on the subject. Also, the recent deregulation of utilities in many states has decreased the impact that lawmakers have on energy producers, instead turning them over to the forces of the free market. (More on deregulation in a subsequent section of this document.)
Hidden Cost Inclusion
Besides changing tax laws and creating avenues for development, another step necessary for setting renewable energy technologies on equal footing with current fossil fuel technologies is a re-evaluation of the total costs associated with each. Currently, many of the environmental and social costs of fossil fuel use are not reflected in the cash price paid by users, nor in the economic analyses conducted by businesses. Placing dollar amounts on the environmental and social consequences of fossil fuel use is not an easy task. Fresh air and clean water are priceless. In some cases, however, looking at the costs of associated activities can be a helpful guide. For instance, it is estimated that the United States' military expense incurred defending foreign oil interests in the Persian Gulf adds some $2.50 to the actual price of a barrel of oil. This cost, though ultimately borne by the end user, is not reflected in typical energy cost analyses, and essentially represents a government subsidy of fossil fuel use. If factors such as this are included in economic analyses, the financial benefits of immediate implementation of renewable energy technologies becomes evident.
The Rocky Mountain Institute in Snowmass, Colorado has done extensive work showing that renewable energy technologies, and even the simple pseudo-technology of energy conservation (which they have dubbed "negawatt" generation), can benefit utilities when given the power of equal footing and the forces of the free market economy. Once again, however, the challenge is to establish renewable energy facilities in large enough volumes to prove to the market that they are dependable and to provide the economies of scale that will make them competitive. Investors are generally slow to fund what they view as experimental technology.
Opportunities in Developing Nations
In view of the need for renewable energy proving grounds, and with the realization that much of the opposition to renewable energy proliferation in the United States is at some level a result of the entrenched fossil fuel infrastructure, one can see that developing countries present a unique opportunity. Because these nations have little or no existing energy infrastructure, the cost of dismantling a fossil fuel framework will be eliminated from the picture. Thus, developing nations, operating largely on international capital anyhow, provide a chance to make the step from the laboratory to the field, proving to investors in industrialized nations that these technologies are dependable. Additionally, the predominantly rural populations of most developing countries are ideal for small or medium-scale power generation, since there are no existing distribution grids. Many such projects have been undertaken through myriad investment channels, and with mixed results. The results of several key projects and a discussion of important guidelines taken from case studies can be found in Rethinking Development Assistance for Renewable Electricity, a publication of the World Resources Institute.
Renewable energy technologies are indeed making headway in research, development, and even actual contribution to the world's energy needs. In 1990, renewable sources (including large hydro and traditional biomass combustion) accounted for nearly 18% of the world's energy uses. Some experts expect this contribution to grow to near 50% by the middle of the next century.24 Solar generation equipment prices fell 60-90% in the 80s, and predictions are that wind power will soon under-price fossil fuels.25 Biomass technologies, especially those that yield biogases, need work but promise to eventually be a very significant contributor to the world's energy demands. These positive returns from research investments are encouraging, because the switch to renewables will eventually be forced upon us regardless of the cost.
To make the switch from fossil fuel use to renewable energy source use more easily, policy and tax changes are needed. As they currently stand, unequitable tax policies keep potential developers and even some end users from investing in the capital-intensive forms of renewable energy. Without changing this structure, it will be very difficult for renewable energy to capture its share of the market through natural market forces. Additionally, the hidden costs of fossil fuel dependency need to be reflected in its market price. If these reforms are introduced, renewable energy technologies may well be able to entice investors with significantly shorter payback periods.
As renewable energy technologies seek large-scale demonstration opportunities, the global benefits of implementing the results of renewable research in developing nations should not be ignored. If carried out correctly, with the involvement and enthusiasm of the receiving nation, renewable energy installations can help to bridge the gap between research projects and commercial utility development while providing for the local needs in a healthy way. In any case, proving grounds for renewable technologies need to be established. It is the necessary first step in their proliferation, and the sooner it is taken, the sooner the benefits of clean and renewable energy will be felt in the environment and the economy.
Brower, Michael. Cool Energy: Renewable Solutions to Environmental Problems, Revised Edition.
Cambridge, MA: The MIT Press. 1992
Douglas, Bruce L. "Nuclear Power is Not the Answer," ASME News, vol 18, January 1999. The American Society of Mechanical Engineers.
EUREC Agency. The Future For Renewable Energy: Prosi2ects and Directions. London: James & James (Science Publishers) Ltd. 1996
Green, Joanta H. Renewable Energy Systems in Southeast Asia. Tulsa, OK: PennWell Publishing Company.
Kozloff, Keith and Shobowale, Olatokumbo. Rethinking Develo]2ment Assistance for Renewable Electricity. Washington, D.C.: World Resources Institute. 1994
Rosenburg, Paul. The Alternative Energy Handbook. Lilburn, GA: The Fairmont Press, Inc. 1993
24 EUREC, 1.
25 Brower, 173.
World Energy Council. New Renewable Energy Resources. London: Kogan Page Limited. 1994
"Residential Applications of Renewable Energy"
by Kathleen Hannon
Indirectly, the sun has provided all of man's energy since the beginning of his existence. The most basic uses have been heating a dwelling and cooking food. Later uses included the burning of fossil fuels, which now meet 88% of the world's energy needs. Fossil fuels will be significantly depleted in the next hundred years or so. The sun's energy will as well, though that will be much later. Through scientific advancement, solar power has become a viable alternative- though not cost-effective yet to replace all fossil fuel consumption. This paper will focus on how individuals can limit their consumption of fossil fuels through solar energy use, and on other opportunities for the use of renewable energy.
First of all, it is important to set the stage-where does a California resident's energy come from? Electricity is supplied through the electric utility grid, whose lines are owned and operated by Pacific Gas and Electric, Sacramento Municipal Utility District, or locally (city) owned utility providers, such as in Palo Alto. The fairly recent move to deregulate the California utilities has given California residents more of a say in what sources of power provide them with electricity. The Natural Resources Defense Council calculates the following numbers, on a link from their web page. For California, the distribution of sources is:
NATURAL GAS 35%
LARGE HYDROELECTRIC 24%
These numbers of course vary slightly as individuals now can choose to change this mix at any point by choosing to pay for a provider other the those chosen by PG&E. According to the calculations, a California resident with a $300/ month electric bill will consume 31,774 kWh of electricity/year, create 10,050 lbs of carbon dioxide/year, create 26lbs of nitrogen oxides/year, and 1lb of sulfur dioxides/year27.
Solar Water Heaters
To date, the most common use of solar power by individuals has been in residential solar water heaters. As early as the 1920, they were in use in Arizona, California and Florida. According to the US Department of Energy, about I million homes in the United States use solar energy to heat water. This is just 1% of the US population, though. Scientists expect this percentage to increase dramatically as the cost of solar equipment continues to fall quickly. Also, there are currently more models-78- with Solar Rating & Certification Corporation approval.
Solar water heaters have the same elements as an electric heater, but the heat is supplied to the water through a solar collector, rather than through an electrically heated coil. The collector is usually a flat-plate collector, with glass covers. The collector absorbs energy on a black flat paint surface, or on wavelength specific coating that maximizes absorption. A working liquid (usually water) is then routed under the collector to be heated.
In their article, "Solar Hot Water for the Home", Davidson and Wood conclude that a solar system is not economically feasible as the sole provider of hot water to a home. For individuals looking to have the most cost-effective source of hot water, this is true for most climates. Nevertheless there is data demonstrating the immense opportunity for solar power in reducing demand for electricity from the local utility.
The most extensive study of the latest solar water heaters was done by the Florida Solar Energy Center, under contract with the New York State Energy Research and Development Authority. In this study, 12 solar domestic hot water (SDHW) systems were installed in single family residences in New York State. Each of these homes had at least four residents. During the summer months, these heaters were able to reduce demand from the local utility by 90 percent, compared to electric resistance heaters. Another significant criteria in monitoring the worth of solar -powered systems is their capabilities on the summer peak day, which is the one day of the year in which the utility experiences the highest demand for electricity. In the case of solar power, it also usually corresponds to the day that the solar collector absorbs the most heat. A system's performance on that day is often referred to in studies. For the New York experiment, the SDHW systems were able to reduce their summer peak demand by between 88 and 92 percent.
Also, in addition to these decreased demands, the overall efficiency of the SDHW systems was higher than an electric resistance heater by 63 percent annually. This increased efficiency led to a system savings of between 900 and 3100 kWh/year3l. This large variability can be explained by the fact that each residence's consumption varied significantly, depending on how much hot water they demanded. In the end, the study showed that these water heaters were able to reduce demand in summer and winter, weekdays and weekends. The most exciting result is that on summer weekdays, the demand was just 37 percent of that for an electric resistance heater.
Despite the high efficiency of these solar water heaters, and their ability to provide clean power, they are unlikely to be used universally until the cost is no longer prohibitive. The heaters used in the study cost $3850 installed, and the annual savings (in deferred utility payments) were estimated to be $325. With the estimated $19.74 per year for servicing included, the return rate was 8 percent.
Solar water heating becomes more plausible when one considers the revenue-generating possibilities for utility-owned solar water heaters. If the utility owned the SDHW systems, they could take advantage of federal 10 percent investment credit for solar energy, in addition to environmental credits from the Environmental Protection Agency's Conservation and Renewable Energy Reserve. In addition, a market research survey in the area of the experiment indicate that 28 percent of the utility customers would be "very likely" to pay $5 more per month to participate in a solar water heating program. With all these considerations, the rate of return to the utility become greater than their present rate of return.
Another study by the Florida Solar Energy Center involved smaller SDHW systems. As part of the Florida Solar Weatherization Assistance Program, low-income homeowners were given SDHW systems to use, with the expectation tat their utility bills would be lower. After two years, researchers concluded that these smaller solar systems were capable of yielding significant savings, and that the systems were economically viable in Florida and other warm climates. On average, over the two-year study the smaller SDWH systems reduced summer peak demand by 27 percent.
Another example of solar water heating was quite visible in the recent Atlanta Olympics-the pool there has the largest solar-based pool heating system in the United States. The system was expected to reduce the facilities utility bills by $12,000. This system is much larger in comparison to a residential solar heating system-the Olympic pool required 274 solar collectors, while a home would require about 8. Still, it is important to understand the capabilities of solar water heaters for even very large-scale use.
In light of the New York and Florida studies, it seems that the use of solar water heaters by individual homeowners is economically viable in warmer climates. So in these climates it is worthwhile to consider the option.
Passive Solar Design
Passive solar design options are easiest to incorporate when first designing a home. There are many small changes that add little or no cost to the cost of a conventional design. There are also some quite dramatic changes that can add significant cost, so it is up to the buyer to find the proper mix of energy efficient features. The following two examples of experimental homes are presented to illustrate the best available technology in passive solar design.
The first example is a home designed by the Florida Solar Energy Center, along with Sandia National Laboratories. This study involved two homes of identical layout, built in the same town to ensure common weather. One used a solar array to generate electricity, solar collectors to heat water, and incorporated several passive solar features in the design. This one will be referred to as the PVRES home. The control home had a design similar to most new homes in central Florida. The most expensive difference in the two homes was that the PVRES home had a reflective white tile roof, costing $10,000. The control home had a gray-brown asphalt shingle roof, which obviously absorbed much more of the sun's heat. In homes that have white roofs, there has been a measured 19 percent reduction in cooling energy demand. The differences are most evident in looking at the attic temperatures in the summer. In the control home, the attic temperature reached 131.5 degrees Fahrenheit, while the PVRES home's attic reached just 91.4 degrees Fahrenheit, a 40 degree difference (Figure 1) . It is interesting to note that after World War 11, before the air conditioner was widely used, white tile roofs were universal in South Florida. So, fifty years ago homebuilders understood how this design feature could help to cool the interior, but it has now a white tile roof is a very rare sight in new homes.
Another design difference was that the PVRES home had an overhanging roof by 3 feet, compared to an overhang on the control home of 1.5 feet. Again, this feature is one that people in Florida knew of many years ago. At the turn of the century, almost all homes there had large porches with deep overhangs. Again, with no air conditioning, residents noted that this feature made their home cooler. The shadow cast by the PVRES's overhang was 72 inches, enough to cover 75 percent of the south and west windows in the morning. The smaller overhang in the control home barely covered the tops of the windows. The advantages of shaded windows are obvious--if the window receives less direct solar heat, less heat is absorbed into the home to heat the air38.
Insulation was also slightly altered-better insulation means less heat is absorbed on a hot day, and less is lost to the outside air on a winter day. In choosing insulation, a higher R-value means better insulating ability. A choice of insulation will have less effect in northern climates, but in Florida the decrease in energy used for space cooling can be 5-10 percent.
Another easy passive solar design option is to choose solar control windows. The PVRES home in the study had double-paned windows with a low conductance (U) and a low solar heat gain coefficient (SHGC). The windows they used were made with spectrally selective glazing-they allowed light in the visible spectrum in, but kept infrared and ultraviolet light out. This choice meant that the inhabitants did not lose valuable daylighting, without which they may have resorted to turning on lights. Instead, selective glazing reduces the admitted solar heat, but also protects the inhabitants from unnecessary or even damaging (UV) rays. The control's windows were single-paned, and had a SHGC of .88, compared to .33 for the PVRES home. This is an important number to look at in choosing windows in a hot climate. In many new homes now, double-paned windows are the standard, and builders advertise that double-paned windows have a significant effect in lowering space-conditioning demands, at a low cost. Also in the windows the PVRES home has thermally broken vinyl frames, as opposed to aluminum frames in the control home.
One area that passive solar design is rarely considered is in air ducts The PVRES home had low friction air ducts, and they were located in the conditioned part of the home. Low friction means that they were larger than normal, so less energy was required to push the air through, and it also means there is less noise. The low-friction ducts alone have been shown to increase system efficiency by 12 percent, at almost no added cost. The normal location for air ducts is in the attic-where temperatures are incredibly high, as shown earlier. This means that as the cooled air passes through the attic, it unavoidably gains heat by conduction through the duct walls. This poor design has been shown to increase space-cooling energy demand by 30 percent.
A similar project ran for 3 years in Freiburg, Germany. The home was entirely self-sufficient for that time, by using hydrogen and solar panels. The climate in Germany is dramatically different than Florida's, providing a good contrast in goals of the solar design. In Freiburg, it is the heating of the home, rather than the cooling, that is so energy intensive. There, low-energy homes attempt to reduce space-heating demands, which account for 80 percent of the total energy demand of a residential building in the Central European climate. Therefore, major goals of this project were to optimize ventilation heat recovery, and passive solar energy used for space heating by transparent wall insulation (TI).
According to the project scientists, TI minimizes heat transmission losses, but also makes the building a source of heat, by absorbing much of the solar energy on the walls. Along, with the TI, the home also had an well-insulated building envelope and thermally improved windows. With these design improvements, the space-heating demand was almost zero. Supplementary heat was only needed in the most extreme winter conditions. After the three-year project, scientists were able to conclude that even in the cold Central European climate, design improvements alone could result in homes with almost no heat demand.
Solar-Powered Homes with Grid Connection
For those wishing to have their own source of clean electricity, a solar system is often installed. A solar system takes the energy from the sun, which hits the earth in the form of photons, and uses those photons to produce an electric current, which is used for any electrical applications. The sun emits an enormous amount of energy in the form of photons, most of which never reaches the earth. By the time these photons reach the earth's surface, the energy will range from between 0 and 1050 W/m2. But, if all the energy hitting the earth's surface were to be harnessed for one minute, it would be enough to meet the world's energy demands for an entire year. This shocking potential is what leads scientists to believe that photovoltaics will play an important part in providing for our future energy needs.
It is useful to note the growth and development of the photovoltaic industry to understand its potential. In 1839, Edmond Becquerel first discovered the capability of certain materials to produce a current when exposed to light. Operating efficiency was at about 1-2 percent then. In 1958 solar cells had their first major application on a satellite. In the 1970's, research boomed with the energy crisis, and increased efficiency using elemental and doped silicon. Since the mid-1980's, the progress has been amazing-efficiencies are now in the range of 28-31 percent, using silicon and gallium arsenide. The trend of the early 80's has remained constant since then (Figure 2). More important to its future widespread use, however, is that the PV industry has grown dramatically, and is still growing. With further growth, PV cells will continue to become more cost-effective, especially as fossil fuel prices increase, and higher pollution taxes are enacted.
A photovoltaic cell (PVC) is typically of area 25-100 cm2. These are put together into modules, and modules into arrays. A photovoltaic cell works as follows: a light photon hits the photovoltaic device, which excites electrons in the device to jump to a higher energy level. With a continues supply of photons bumping the material's electrons out, a current is set up across the device. This current can be used to provide direct current (DC) to a battery or another storage device, and used in any electrical application. Most domestic electrical applications require an alternating current (AC). To change the DC current from the PV array to the required AC current, and inverter is used, which produces a sinusoidally varying current.
In homes that are still connected to the utility grid, when the system is converting more solar energy to electricity than is needed; the homes can sell back the excess electricity to the grid. Early on, every homeowner who did this lost money-they would sell the electricity to the utility at the lower, wholesale rate, and then when they needed to buy electricity (on a dark day, or at night), they would have to buy it back at the retail rate. So, even if the homeowner broke even in the course of the month, they would lose money. This policy still exists in some states, but about 19 states in the United States have net metering policies in order. These were either enacted by state legislature, or by utilities, in response to customer demands. There is some paperwork to make this work, as it is unusual. But after a utility representative approves the safety of the system, the homeowner is free to begin. Net metering means that a home's electricity meter runs backward when the solar system is producing more electricity than needed, and therefore feeding electricity back into the grid. At the end of the month, the homeowner will either pay for the difference, if they used m ore than they produced, or they will be paid by the utility if they ended up producing less than they used from the grid. If they owe the utility, they are required to pay the retail rate, but if they have sold more, then they only receive the wholesale rate. Still, most homeowners come close to breaking even, and this policy if far better than losing money with every transaction with the utility grid. Also, there is usually a cap to how much excess electricity the electric utility will buy back. So if a homeowner is producing far more than he is using, it may be more economically advantageous to store that excess electricity in a battery.
Independent Solar Systems
The other option for those wishing to set up a solar system is to be completely disconnected from the utility grid, and to never have to worry about power outages or approval of the system by a utility representative. Just in the past six months, there has been a sharper increase in the number of grid-independent solar systems going onto roofs. Many attribute this trend to worries about Y2K. People are eager to be independent of the utilities on the day, or days, when "the lights go out".
The more common reason for grid-independent systems is that the location of the desired system is very rural. If electricity is needed more than .5 miles from an existing power-line, the individual must pay most of the cost for bringing the line out to the desired location. In these cases, solar systems are then more economical than grid connection. Most commonly the grid-independent systems are used for scientific purposes, such as monitoring the weather or ocean currents. But owners of rural homes also often recognize the advantage of solar generated electricity. Especially in dry desert areas, where homes are often not served by the nearest utility, individuals can save money by setting up their own system.
Still, in applications where utilities provide electricity, the initial investment in a solar system will take at least 5-10 years to get a return through deferred utility bills. In large homes that have higher electricity demands, and therefore require larger arrays, it will take even longer to get a return on the investment.
The main problem with grid-independence is the storage issue. Homes that must supply all of their electricity through solar power need to store excess electricity collected. On sunny days, when there is excess, electricity must be stored in some form. The choice is almost always a battery, which takes up a significant amount of space. These batteries add another element that contributes to system inefficiency. As the batteries age, through charging and recharging, they become less efficient. The batteries also add another cost, as the recommended lithium-cadmium batteries are quite expensive.
Fuel Cell Technology
A possible solution to the storage problem may be the fuel cell. Many scientists and engineers have suggested the fuel cell as a method for converting chemical energy to electricity. A fuel cell is a device that converts the chemical energy of hydrogen to electrical energy. This device has been in use for many years in space, but is only now being looked for domestic uses. Hydrogen has been used in several experimental projects as a means for storing electrical energy. If a home has a solar system that is disconnected from the grid, in cold winter months, the supply of electricity from the sun will probably come up short. But, through electrolysis, water can be converted into hydrogen, and stored. So, in the summer months, where there is an excess of solar energy, hydrogen can be produced, and stored for later use in a fuel cell. In the self-sufficient home in Freiburg, Germany mentioned earlier, hydrogen was used to store energy for the winter months. Researchers have even thought that cars running on fuel cells might someday be plugged into buildings for space heating, and then recharged with electricity from a solar array.
For now, the near future fuel cell technologies that will be seen on the market burn fossil fuels. They will probably be seen in automobiles in the next few years. Automakers will probably convert gasoline or methanol into hydrogen onboard. These fuel cells are still more efficient than the internal combustion engine, and moving to hydrogen based economy seems to be a step in the right direction, since hydrogen can be produced from numerous sources.
Perhaps the easiest choice for an individual to change his energy source is to go directly to his utility. A significant change came about in California with the decision by the legislature to deregulate the California utilities. Several other states have similar laws, but each varies slightly in its implementation. The purpose of each is to give customer choice to residents. Before deregulation, Californians had no choice as to which provided their power- the lines underground belonged to one common utility, who chose which generators to buy electricity from. If an area's provider chose to buy all of the electricity (and then resell it to its customers) from a coal burning plant, the area residents had no other options for electricity service if they were unhappy with that choice. Now a resident can sign up, through the local utility, with a company that produces electricity through renewable energy sources. The customer still pays to the local utility, at the price set by their distributor of choice, but the local utility is then required to buy that amount of electricity from the designated generator. Essentially, competition has been introduced into the market, and it has allowed for the start-up of many "green" power generators. The following table shows those sources that generate at least 75 percent of their electricity from renewable resources (Table 1). There are several other choices from these same companies, with lower percentages of electricity generated with renewable resources. Those choices are cheaper, but still cost more than the standard service.
The choices vary significantly, and the companies index their product according to what percentage of their electricity comes from renewable sources. There are six choices to PG&E customers that produce a significant amount (between 50 and 100 percent) of their electricity from renewable resources. The cost increase varies from 10-30 percent. There is no cost for signing up for one of these sources, but some do charge a cancellation fee within the first few months. PG & E provides power to most areas, though there are some smaller, local utilities, such as the city-owned utility of Palo Alto. For Sacramento Municipal Energy District, there is a Greenergy option-which costs just 10 percent more, and produces all electricity form geothermal energy. Interestingly, the PG & E standard rate went up by ten percent on January 1, 1999. With this increase, some of the renewables come very close to matching the standard rate.
Deregulation has given Californians, and many others, an easy way to make clear their commitment to renewable. As of now, PG&E and other large utilities buy from the cheapest sources, or sometimes sources that they have a vested interest in. These sources are the cheapest for many reasons, one being that they have a consistent buyer with PG&E, another is that the technology for producing electricity from fossil fuels is well developed. If customers continue to force PG&E to buy from green energy sources, those cleaner companies will have more capital to invest with. Newer, more efficient systems and a higher demand from these sources will allow them to lower their prices. Eventually, if renewable technology continues to grow, and pollution taxes increase, renewable energy will become economically advantageous. At that point, no longer will customers have to ask that their money is spent on cleaner electricity, the local utilities will do it because it is the best option for their company?
The United States government made a commitment to domestic solar power with the announcement of the Million Solar Roofs initiative. Their goal was to have I million solar energy systems on US rooftops by 2010. They claimed that if that goal were reached, emissions of carbon dioxide would be down by an amount equal to that produced by 850,000 cars. It also equates to 3-5 coal fired plants. Since then, several utilities have added solar power to their list of sources. In 1997, 5 new photovoltaic plants were added in the United States, and six in 1998.
Also, 68 local utilities, serving 40 percent of the US population, formed a consortium to buy $500 million in photovoltaic panels by 2003. Also, several companies in the oil industry have demonstrated a strong business interest in the photovoltaic industry. In 1996, British Petroleum earned $80 million in the sale of photovoltaic cells. They also hold a contract to supply solar arrays to the athletes' village in the 2000 Sydney Olympics-a very large-scale project, and a very visible one as well. Shell also has also invested heavily, with a projected expenditure of $400 million before 2004.
Clearly, these companies would not be investing in photovoltaic industries if they did not see the end of the fossil fuel era approaching. Several automakers are investing heavily in fuel cell technology as well. These companies have many economists as their advisors-and these marketing experts make the decisions. For some reason, these companies see that the market for energy will soon demand that renewable technology be implemented. This could be because soon a solar powered system will be cheaper than buying electricity from the grid. Or, it could be that analysts expect people to place increasing value in electricity generated by renewable resources, simply because they are cleaner. Even if it turns out to be a simple comparison between the direct costs of electricity from sources, some expect that current environmental crises will lead to high taxing of "dirty" energy. Also, more tax credits for those who invest in distributed generation by renewable resources are expected in the near future. So even if an individual places no value in contributing to the growth of clean resources, the cost of electricity generated from renewables may soon be the cheapest. Until then, photovoltaic arrays on homes will not be commonplace, except in rural areas and with individuals who find distributed generation advantageous, either for its cleanliness, or its contribution to one's self-sufficiency.
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