SUNPOWER: The Earth's largest energy resource
Every day, the sun showers the Earth with abundant energy. Although many people think of solar energy as a new and emerging technology, capturing this energy source for heat was used historically by many ancient civilizations populations, including those in the Southwestern United States. Hundreds of years ago, the Anasazi Indians designed their cliff dwellings to maximize the solar gain in winter by building into the cliffs. They positioned their buildings under the cliff overhang to allow the winter sun to reach their homes. The sheltering overhang also minimized radiant heat loss at night, and protected them from cold winds. They also used small window openings to conserve heat, and built their structures with heavy stone and clay materials that absorbed and held the solar heat, releasing it slowly after the sun had set. In summer, the cliff overhang provided shade from the high summer sun angle and the mass helped their homes remain cool in the hot months of summer.
These same basic principles of solar design are being used today to make homes comfortable with little assistance from outside energy sources, and more recent inventions allow us to obtain electrical energy from the Sun as well. Making use of the sun's free energy makes particular sense because of the many problems associated with fossil fuel use. As the human population continues to grow and energy demands increase, environmental problems like air and water pollution, global warming and depleted fossil fuel reserves make switching from our reliance on nonrenewable energy sources to renewable sources even more essential. Although every location on Earth receives sunlight, the amount received varies greatly depending on geographical location, time of day, season and clouds. The southwestern United States is one of the world's best areas for sunlight. New Mexico receives more than 3200 hours of sunshine per year, twice the sunlight received by other regions in the United States. The state's average daily energy consumption of over 900 billion BTUs is equivalent to the amount of solar energy received on an average day within an 18 square mile area. This energy is equivalent to 161,000 barrels of crude oil. Hence, the potential for solar energy development in our state is great. For a more detailed look at the solar resource, see The Solar Resource.
There are several primary solar energy technologies including
- Photovoltaics (for obtaining electricity),
- Passive solar design (heating, cooling, and hot water)
- Active solar thermal (heating, cooling, and hot water)
- Solar thermal electric (large scale electricity generation from solar)
- Solar cooking
- Solar distillation
- Solar water pumping
A passive solar system is a solar water-heating or space-heating system that captures and moves sun-heated air or water without using pumps or fans. An active solar system, on the other hand, is a system that moves sun-heated air or water using pumps or fans. Many homes incorporate several aspects, such as passive solar design and photovoltaics, and sometimes other renewable energy forms such as wind systems, and are totally energy sufficient and not connected to or dependent upon utility power lines.
To learn more about solar energy, see our Solar Primer: From Oil Wells to Solar Cells.
Solar Sites in New Mexico
Arrange your own New Mexico Solar Tour!
Here are some of the sites that one can see and learn about, organized by area:
- Amy Bunting Home
- Balcomb Home
- Genoveva Chavez Community Center
- Grid Tied (Net-Metered) Photovoltaic Systems
- KTAOS Solar Powered Radio Station (This is one you listen to by simply tuning in to 101.9 FM from Pojoaque and north).
- Visit an "Earthship": Solar Survival: Call Solar Survival and ask about visiting hours/location.
- Solar Bike (pdf)
- White Sands National Monument features a Visitor Display with a visible 1080 watt PV system and 800 watt inverter (At the Center of the Park). More info is supplied at the Park on the System.
FROM OIL WELLS TO SOLAR CELLS:
A RENEWABLE ENERGY PRIMER
This primer provides an introduction to both renewable energy issues and technology.
For further information on specific subtopics, see:
Good periodicals on renewable energy include
Finally New Mexico Solar Businesses can be located on our Solar Professionals Directory.
Table of Contents
The Big Picture:
A Closer Look at Solar Power:
- How much energy comes from the Sun?
- Types of Solar Energy Technology
- Solar Thermal Electricity
- Stirling Dish (Solar Dish)
- Solar Air and Water Heating
- Photovoltaics (Solar Cells - Direct Solar Electricity)
The Big Picture
What is "renewable" energy?
Renewable energy sources are those that are continually renewed by nature, and hence will never run out (at least as long as the nuclear fusion processes in the Sun and fission processes in the Earth continue). For example:
Solar Power - Capturing sunlight for:< >Driving steam turbines to generate electricity ("Concentrating Solar Power",
Heating homes ("passive solar design" or "active solar heating systems"),
Heating hot water ("active or passive solar hot water systems"),
cooking ("solar ovens"),
generating electricity directly with solar electric ("photovoltaic") cells,
other uses.Explore the Solar Resource)
New Mexico is potentially a Solar Saudi Arabia!
Other examples of renewable energy:
- Hydropower - Channeling falling water to drive turbines (generators) to generate electricity. This is renewable because the Earth's hydrological cycle, which is driven by the Sun, continuously replenishes lakes and rivers through rain. Hydropower is an indirect form of solar power.
- Biomass - Using the heat generated by burning plants, trees, and other organic waste. Biomass is renewable because new organic matter is always being created by photosynthesis. Biomass is also an indirect form of solar power.
- Wind Power - Using the wind to turn propellers connected to turbines. Wind power is considered renewable because the Sun and the Earth's rotation are always generating more winds. Wind power, like biomass and hydropower, is really another form of indirect solar power. The wind power resource of the United States, like its solar power resource, is huge. The dark blue areas in the map below show the areas where "class 6" winds exist. It is estimated that developing even a small fraction of these areas would power the US several times over, without creating adverse environmental or social impacts. Wind power is presently the fastest growing energy source in the world!
Fantastic opportunities for large scale wind power exist in New Mexico, and several projects now exist: A 200 MW facility by Public Service Company of New Mexico, and a smaller facility consisting of several 660 kw turbines by Southwestern Public Service Company of New Mexico. For more information on Wind Power and renewable energy policy in New Mexico in general (and links to the wind power world), see the website of the Coalition for Clean Affordable Energy (CCAE), http://www.cfcae.org (NMSEA is a CCAE member organization).
- Geothermal Power - Using the heat created by the decay of radioactive elements within the earth to heat buildings or generate steam to drive turbines (generators) to generate electricity. Geothermal power is considered renewable because there is enough radioactive elements in the Earth to keep it warm for billions of years to come.
- Landfill Gas - Using the methane (CH4) generated by the breakdown of garbage in land fills (really a form of biomass). Although this is not necessarily renewable for the long term, there is enough landfill gas to provide a significant source of energy in the United States. This should tell us something about how much waste our society generates!
Different definitions of the phrase "renewable energy": Some people argue that nuclear power from earth based uranium should also be classified as renewable because the sun is nuclear powered and because they claim that there is lots of earth based uranium (NMSEA does not subscribe to this view). Others like the word "inexhaustible" instead of "renewable" for renewable energy sources, which better conveys the important point that renewable energy sources will never run out for the foreseeable future of humankind. Another useful term might be "non extracted", reflecting the fact that renewable energy sources do not require extraction of minerals from the ground.
What are the costs of renewable energy?
This is often the first question that people ask about renewable energy. A full answer, however, requires a fairly detailed look at the different types and contexts of renewable energy. We will now explore this question in some detail.
One way to express the costs is to compute the time it takes for a system to pay for itself, relative to the prices of natural gas or electricity from the grid. In other words, how much time does it take for the total energy savings achieved by using a renewable energy system take to equal to the cost of the system? Relative to recent prices for gas and grid power, payback time for renewables were (very) roughly:
- Passive Solar Heating: 0-2 years
- Solar Hot Water: 5-15 years
- Solar Electricity (photovoltaics): 15-25 years
- Utility Scale Wind Electricity: 20 years
One should keep in mind that these estimates do not include the addition savings that a renewable energy system might provide, such as avoiding the cost of installing power or gas lines, which can be enormous for remote sites. Nor do they take into account occasional large jumps in gas and electricity prices, such as those that occurred in the year 2000 and more recently. These can substantially decrease payback times.
The ability of (at least some) renewable energy systems to pay for themselves relative to utility costs means that their costs, in principle, could be included in the long term financing of homes and actually decrease total monthly costs, because in some cases the savings on utility bills will more than balance out the extra cost added to payments to buy the systems over the long term.
From another perspective, instead of dwelling on payback times, it might instead be more sensible to focus on the fact that (some) renewable energy systems can in fact pay for themselves at all, period! How many other appliances can do this? This is not a requirement that we place on many other commodities, such as RV's, boats, patios, etc. The payback of these commodities are there specific benefits (travel, etc). The payback of renewable energy systems from this perspective is the satisfaction of using and promoting sustainable technology, and protecting the planet for future generations.
When comparing costs of renewable electricity, one should also be careful to distinguish retail costs from wholesale (or production) costs. The production cost of utility scale (centralized) renewables that is commonly quoted (e.g. 4 cents/kwh for wind) should be compared to wholesale cost that utilities pay to either produce or acquire energy from nonrenewable sources. In contrast, the cost of home solar systems should be compared to the retail cost of grid electricity, because the home solar system does not require transmission and distribution of its power - the Sun takes care of that part! The Sun is Earth's built-in transmission and distribution system!
For example, solar electricity (in the form of photovoltaics) is about 7 times the wholesale cost of utility scale wind power, but only about 2-3 times the cost of retail electricity.
Utility Scale Renewables: Keeping in mind the average wholesale cost of electrical power from the grid, which is about 3.5 cents per kilowatt-hour for coal in New Mexico, wholesale renewable energy sources rank in cost as follows:
- Hydropower: 2 cents/kwh -cheapest of all, cheaper than coal
- Wind (utility scale): 4-6 cents/kwh - just above coal.
- Geothermal: 6-8 cents/kwh - twice the cost of coal.
- Solar Thermal Plants: 10-14 cents/kwh - 3-4 times the cost of coal.
Home Scale Solar: Relative to an average retail cost of electrical grid power, which was around 10 cents per kilowatt-hour in the 1990s:
- Photovoltaics (home solar electricity): 19-25 cents/kwh - twice to three time the cost of grid power.
For more on cost, see our solar curriculum project: Calculate the cost of Photovoltaic Systems (Home Solar Electricity), or the section further on in this primer: System Costs (for PV).
What are nonrenewable sources of energy?
Nonrenewable sources are those based on a finite amount of pre-existing "fuel". By "fuel" we mean any substance which stores energy, for example, gasoline, kerosene, natural gas, uranium, and firewood are all examples of fuel - firewood being the only renewable fuel is this list. The primary nonrenewable fuels are:
Fossil Fuels: Natural Gas, Oil, and Coal - These three fuels are the leftovers from plants and animals that lived millions of years ago - hence the name "fossil fuels". They are all "carbon-based", that is, they consist primary of compounds made of carbon and hydrogen derived from the bodies of ancient plants and animals. Natural gas is the gaseous form (small molecules, consisting of one or two carbon atoms each), oil is the liquid form (several carbon atoms per molecule), and coal is the solid form (many carbon atoms per molecule).
Although they are a form of stored solar energy (because their energy originally came from the sun through photosynthesis), they are considered nonrenewable because there is only a finite amount of them. Unlike renewable sources, they can't be replaced quickly because it took many millions of years for these fuel reserves to form, so that it takes too long for nature to "renew" them for our practical purposes. They are so finite in fact, that it is thought that oil production may peak during the first few decades of this century (the famous "Hubbard Curve"), and that coal and natural gas will last only a few hundred years more (at the current rate of usage). There are also a number of environmental reasons for not using these fuels that we will discuss later.
Nuclear Power - Nuclear power is the generation of heat (say, to drive steam turbines to generate electricity) by the nuclear reactions involving radioactive substances such as uranium 235, an "isotope" of the element uranium. There are two kinds of nuclear power:< >Fission: In this process, radioactive elements split apart to release energy. There are currently about 1100 nuclear "reactors" that use fission. About 430 of these are used to generate electricity in nuclear power plants (the rest are for research or production of special radioactive materials used in medicine, food processing, and scientific research).
Fusion: In this process, radioactive elements (usually hydrogen nuclei) are combined to release energy. This is the source of the Sun's energy. At this point in time, successful fusion reactors have not been achieved, but there is much research on them.
No mining or drilling for the fuel source - the energy is provided from the sky, or via heat in the ground not materials in the ground.
Keep in mind that we must still obtain materials for manufacturing the collection devices for renewable energy, and this may include mining. But these materials are much less than the amount of fossil fuel we extract. For example, photovoltaic solar cells are very thin, so the volume of material relative to the energy they produce is very small. Related to this is the fact that they pay back the energy used to manufacture them in 2 to 3 years in sunny climates. Moreover, they're recyclable and therefore can be used indefinitely!
No paying for the fuel source itself - The energy is free!
One must still pay, however, for the initial manufacturing and maintenance of the collection devices.
No net emissions (such as those from burning fuels) - There are either no emissions associated with fuel at all (solar, wind, hydropower), or the emissions from burning fuel are compensated by photosynthesis initially (biomass, landfill gas), so that the emissions are closed-cycle (at least to a large degree). Thus we avoid many of the environmental problems associated with nonrenewable energy (see below).
Keep in mind that there may be emissions, or other pollution associated with manufacturing the collection devices. Some of these emissions (those associated with energy production at least) could be avoided in the future if new collection devices are manufactured in factories that actually use renewable energy in the first place. Careful attention will always be necessary, however, to minimize the impacts of pollutants associated with manufacturing.
What are the practical and social benefits of renewable energy?
- Economic development! Switching to renewable energy sources is estimated to create at least several times as many jobs as traditional energy sources (some estimates suggest as much as 10 times or more). These jobs would include both manufacturing jobs and the maintenance of collection and energy storage devices. This is possible because one is paying for the manufacturing and maintenance of the collectors, which is labor intensive, and NOT a fuel supply.
- Renewable energy is flexible! Because renewable energy generation can be de-centralized - that is, many small collection devices can be widely distributed instead of having only a few large centralized power plants, the need for transmission lines can be reduced, and the resulting system will likely be more robust with respect to civil disturbances, natural disasters, etc.
- Freedom from Exploitation! Because renewable energy generation can be owned by the end user, switching to renewable energy would put more power, and ultimately money, in the hands of the general public, instead of into the hands of monopolistic energy companies.
What are the environmental dangers of nonrenewable energy sources?
Air pollution - Burning fossil fuel emits a number of noxious chemicals into the atmosphere:< >Carbon Dioxide (CO2): CO2 is emitted when burning any carbon based fuels (as all fossil fuels are), and is widely thought to be the primary greenhouse gas causing global climate change (which includes global warming). For more info, see our primer materials on global climate change.
Carbon Monoxide (CO): CO is emitted when carbon based fuels are burned inefficiently, is poisonous, and contributes to the air pollution in cities associated with automobiles. A malfunctioning furnace can also produce carbon monoxide.
Sulfur dioxide (SO4): SO4 is emitted mostly by the burning of coal, and is the principle cause of acid rain.
Nitrous Oxide (NO2): NO2 , or "nox", is created when fossil fuels are combusted in the presence of air (which is 80% nitrogen). Nox is another greenhouse gas, and also an principle contributor to smog via automobiles.
Particulates: Particles of ash are emitted from the smokestacks of coal fired power plants. These particulates are a serious threat to human respiratory health in many parts of the US.
Mercury: Coal contains significant amounts of mercury, a highly toxic element, that is emitted when coal is burned. Mercury from coal plants is thought to be a major pollutant of land and water in the US. The Environmental Protection Agency is beginning to regulate mercury emissions more stringently.
Radioactive Uranium: Both coal and nuclear power plants can emit uranium (coal deposits often contain significant amounts of uranium).
Water Pollution/Usage:< >Coal-fired power plants use large amounts of water to:
Transport the coal (in some cases)
Wash the coal
Cool the coal (to prevent spontaneous combustion)
To absorb and carry away heat in the form of steam to complete the thermodynamic cycle of power generation.
Nuclear power plants use enormous amounts of water to:
Refine uranium ore into nuclear fuel rods
To absorb and carry away heat in the form of steam to complete the thermodynamic cycle of power generation.
Land/habitat impacts of mining, drilling, and spilling:< >Coal mining and oil and gas drilling disrupt and pollute hundreds of square miles of land per year. Moreover, many of our largest fossil fuel resources are located in environmentally and socially sensitive regions, such as the Four Corners Area, the Cumberland (Appalachian Mountains) region, and the Artic National Wildlife Refuge, to name a few.
Mining underground can lead to poisoning of streams because water seeps into the coal mines and becomes acidic from the sulfur associated with coal seams.
Coal seams are on average only a meter thick, so vast areas must be either tunneled or strip mined to obtain the coal. Coal companies nowadays sometimes demolish entire mountains (called "mountaintop removal") to get at the coal underneath.
Oil spills from grounded tankers regularly contaminate vast areas of the ocean, killing enormous numbers of sea animals and birds.http://www.nmpirg.org/reports/renew_energy/index.html
What are the social dangers of nonrenewable energy sources?
- Dependence on foreign sources - Dependence of foreign sources can greatly corrupt a nation's good intentions towards its neighbors, and also make it more susceptible to foreign exploitation.
- Nuclear Weapons Proliferation - Developing nuclear power can put the technology and know-how for building nuclear weapons into the hands of more and more countries and who knows who else.
- Energy Company Monopolies - Dependence on fuel sources that require large scale extraction and power production facilities tends to encourage the formation of corporate monopolies which can overcharge consumers, flaunt environmental regulations, and corrupt the moral integrity of a society.
What are the obstacles to switching to renewable energy sources?
- Upfront Cost: While some renewable energy sources such as hydropower, wind power, and geothermal are now competitive or almost competitive with fossil fuels, solar electricity is still several times more expensive than coal-fired electricity, and the financial mechanisms needed to avoid this problem (to allow renewable energy systems to pay for themselves naturally) do not commonly exist yet.
- Stranded Cost: US citizens have already paid about a trillion dollars for our fossil fuel infrastructure. Some argue that this investment would be "stranded" if we switched completely to renewables, unless ways to incorporate much of that infrastructure could be found. Thus, this investment would seem to create a considerable economic disincentive to switch to renewables. Others argue that gradually abandoning this infrastructure would actually save money because a more distributed infrastructure would be so much cheaper that it would more than make up for stranding the old infrastructure.
- Politics: People who make money from traditional energy sources simply don't want to lose their profits, and often work hard to avoid doing so. See our pages on political advocacy for more info. NMSEA is an active member organization of the Coalition for Clean Affordable Energy (www.cfcae.org).
- Environmental Impacts: All major sources of energy have significant environmental impacts of some kind, such as land use, material use, etc. Although the impacts of renewable energy generation is small compared to traditional sources in our opinion, some feel it will be too significant. Hydropower is in fact already widely opposed by many environmentalists nowadays, who feel that the impact of large dams on fish and other wildlife is too great a price to pay.
- Lack of Inexpensive Energy Storage: Unlike fossil and nuclear fuels, renewable energy, especially solar and wind, is intermittent by nature and does not come in the form of easily storable fuels. Therefore, the development of practical storage processes is an important long-term research goal. However, in the meantime, it has been estimated that, despite its intermittency, between 15% to 45% of the electricity provided by the electrical grid could come from solar and wind without compromising the reliability of the grid. Therefore there is ample room to begin adding these renewable energy resources now. Some solar and wind plants, however, can also take advantage of existing hydropower storage - that is, they can be used to pump water back into reservoirs, so that water can be used later to generate electricity in a hydropower dam.
The future of renewable energy storage
Presently, off-grid solar electric systems must use batteries (grid-tied pv is growing rapidly - for more on grid interconnection, see our Net-Metering page). There are several principle problems with batteries - short lifetime, added cost and maintenance, and too great a weight per unit energy for mobile (automobile) applications.
In the long term, it is hoped that a fuel such as hydrogen, or a synthetic fuel produced from hydrogen and carbon dioxide, or something similar, will be available for energy storage in conjunction with renewable resources. The process of "electrolysis", for example, can be used to produce hydrogen from water: this is done simply by running an electrical current through water. In principle, the hydrogen can then be stored, and then later converted back into electricity using a fuel cell (to learn more, see our project Explore Fuel Cells). A fuel cell is a device that chemically recombines hydrogen and oxygen to produce water and electricity, without actually burning the hydrogen as a flame. For this reason, many solar advocates talk about the emergence of a solar-hydrogen economy. Our solar curriculum contains an interesting electrolysis project, which includes a discussion of fuel cells, that every kid should try at least once in their life.
Other energy storage techniques such as fly wheels and synthetic fuels also show some promise and are under development.
The use of thermal mass in passive solar buildings will always be an effective means of renewable energy storage. Guidelines for passive solar design are referenced below.
The Even Bigger Picture: Recycling Writ Large
The intrinsic advantage of renewable energy over nonrenewable sources is the fundamental difference that they allow an energy economy with no net emissions of pollutants from the combustion of fuels, i.e, a true closed-cycle economy. This should remain true even if synthetic fuels are eventually introduced to store renewable energy - for example, if production of say, methanol, from atmospheric carbon dioxide and water using renewable electricity as an energy source becomes available. This is because such a fuel, while carbon-based, can be neutral with respect to emissions of greenhouse gasses: the carbon dioxide used to manufacture them could be absorbed from the air (via a collector of via natural biomass growth processes), and then simply released back into the air at the point of use (and similarly with the water used to generate the hydrogen).
Thus, what we are really talking about is recycling writ large: new processes which could eventually lead to closing all of our material cycles.
Moving towards a truly closed-cycle economy will require a fundamental shift in our approach to both energy and manufacturing in general. We therefore urge you to take recycling and renewable energy very seriously: Recycling is not just a nice thing to do for the environment - its really the whole baliwag!
A Closer Look at Solar Power
How much energy comes from the Sun?
The sun provides about 1000 watts per square meter at the Earth's surface in direct sunlight (this reference intensity is often called "one sun" by solar energy scientists). This is enough power to power ten 100 watt light bulbs, or 50 twenty watt compact fluorescent light bulbs! Contrary to what is sometimes repeated by those who oppose solar energy, solar power is really not very diffuse or weak. In fact, the sunlight falling on a very small fraction of a home's roof is typically more than enough to provide all the energy needs of a home. Or put another way, covering less than one percent of the land area of the United States with solar panels could provide all the energy we currently use. For more on this topic, see our solar curriculum project "Exploring the Solar Resource".
Another way to look at this is to consider the enormous energy in the geophysical flows around us as a whole - the sunlight, ocean currents, wind, clouds - the energy in these systems is simply enormous, and dwarfs the scale of human energy usage. Most of this energy ultimately originates from solar power, which drives the hydrological cycle, thermal upwelling of air, and heats the ocean's surface.
As an example that's even more close to home, you, the reader, are solar powered! All the energy you obtain from your food originates with solar power, via the photosynthesis of sugars in plants.
Types of Solar Energy Technology
There are several primary solar energy technologies, most of which are discussed further below, including
Photovoltaics (solar electricity),
Passive Solar Design (solar heating, natural cooling, and can incorporate hot water systems very nicely)
Active solar thermal (Solar Hot Water/Air collectors)
Solar thermal electricity (large and small scale electricity generation from solar heat)
Solar water pumping
A passive solar system is a solar water-heating or space-heating system that captures and moves sun-heated air or water just by the configuration of the building, without using explicit collectors, pumps or fans. An active solar system, on the other hand, is a system that uses collectors of various sorts and moves sun-heated air or water using pumps or fans. Many homes incorporate several aspects, such as passive solar design and photovoltaics, and sometimes other renewable energy forms such as wind systems. Many off-grid homes are totally energy and water sufficient and are not connected to or dependent upon utility power lines, and city water supplies and sewers.
Solar Thermal Electricity
Solar thermal electricity, also called "Concentrating Solar Power" or CSP by many, is the solar power variant on the traditional power plant: Solar energy is focused onto either a central receiver using mirrors (the "power tower" approach) or onto pipes using parabolic troughs (called the "troughs" approach) to heat a working fluid, usually either water or molten salt, which is then used to drive a turbine to generate electricity. This technology is only now beginning to become commercialized (Spain plans to build a large solar thermal electricity plant soon).
Here is a picture of the experimental Solar II plant, near Barstow California:
This 10 megawatt (ten million watt) experimental solar plant, the largest of its kind, used molten salt as a working fluid, which it stored for several hours in order to contour output to demand (including extending power generation well past sunset). This plant could supply power for approximately 10,000 homes from morning until well into evening, at a production cost of 10-14 cents per kilowatt hour (about three to four times the wholesale production cost of coal-fired electricity). Over the period of several decades, this plant uses less land area, and uses it less destructively, than a coal-fired power plant that produces the same power (assuming we including the land area that needs to be mined for the coal).
Sandia National Laboratories, located in Albuquerque New Mexico, built an earlier prototype of Solar II (the Sandia "Power Tower"), and conducted much of the fundamental research embodied by Solar II. See http://www.sandia.gov/Renewable_Energy/ for more information on their solar thermal program.
Stirling Dish (Solar Dish)
Another form of solar thermal electricity generation, or concentrating solar power, is the "stirling dish", or "solar dish" approach. These systems consist of a concave parabolic solar concentrator, which focuses sunlight onto a stirling heat engine. Stirling engines use air as a working fluid, as opposed to water, and therefore may be quite useful in arid climates. These units are also smaller than power tower or trough systems (they usually fall in the 20 to 30 kilowatt range), and may therefore be useful for more distributed applications, such as remote water pumping, or neighborhood systems.
For more info on these see the Solstice pages on solar dishes.
Active Solar Thermal
Although solar air and water heating systems gained a bad reputation in the 1980s, largely due to overly generous tax credits and the immature and sometimes disreputable industry that these credits created, these systems can function beautifully, especially in the sunny southwest, and are still one of the most economical forms of solar energy if properly implemented. They can easily provide between 40% (Seattle) to 80% (Phoniex) of the hot water heating needs of a typical US family. Here is a photo of a solar hot water panel: This type of collector is called a "flat-plate collector":
Active systems such as this involve pumps (for water) or fans (for air) and collect sunlight with flat plate collectors (as pictured in the photo above). The flat plate collector is essentially an insulated box that allows sunlight in on one side through a glass covered window and absorb it with dark colored metallic surfaces. The collected (and trapped) heat is then transferred by conduction into a working fluid (typically water with or without antifreeze, or air), which is continuously pumped through pipes in contact with the collecting surfaces. The working fluid is then routed either to a storage medium, such as a hot water tank, rock bed, or radiant floor, or transferred directly into the air.
Active hot water systems themselves come in several basic types: one type uses antifreeze to keep the water in the collector from freezing on cold winter nights. The other, so-called "drain-back" systems, let the water drain out of the collector at night, so that antifreeze is not needed. The latter can be an "open system", that is the water that flows through the collector can be used directly.
A disadvantage of active solar thermal systems is that they typically need more maintenance than passive systems, and have a higher upfront cost ($3000 to $5000 - passive systems are usually around $2000).
One form of solar water heating that tends to require less maintenance and upfront cost, and which might be characterized as the passive form of active solar thermal is called batch solar water heating. In this approach, the collecting surface is the darkly covered surface of a water tank itself (see picture below). The tank is usually insulated and covered with glass just as is the case with a flat plate collector. Pumps are not generally necessary in this kind of system. Instead, the tank-collector is simply used to pre-heat the water before it goes into a supplemental hot water heater. That way, if the sun has heated the water, the hot water heater need not. Otherwise, the hot water heater kicks in. Another variation on this approach is to have a hot water tank located at the top of, or underneath a flat plate collector. In this approach, cold water naturally flows downwards into the collector, and hot water flows back upwards into the tank, in a convection driven process called thermosiphoning. These systems are called "integral" systems.
Batch systems may be conveniently located underneath skylights or clerestories, with or without insulation on the sides and back sides, giving great flexibility to how they are integrated into a home. For example, here are photos of a batch hot water tank mounted in a clerestory (photos courtesy of Karlis Viceps):
Here is what the tank's insulated mounting box looks like from below:
Finally, some hot water systems are integrated directly into sunspace or clerestories, as hot water pipes running just underneath the glazing and attached to metallic collectors. Here is a picture of one such system, made by Zomeworks, located in a sunspace:
The long white strips across the slanted ceiling are the bottoms of the metallic collectors (manufactured by Zomeworks). The hot water pipes can be seen emanating from the right hand ends of these strips.
Photovoltaics (Solar Cells - Direct Solar Electricity)
Photovoltaics, or "PV" for short, and more commonly known simply as "solar cells", are special semiconductor devices which convert sunlight directly into electricity. The word photovoltaic derives from the words "photo" which means light (Greek for light is "phos"), and "volt", the fundamental unit of electrical energy potential. Therefore, "photovoltaic" literally means "light-electricity".
Many individual solar cells can be packaged together into "pv modules" which can then be placed on a rooftop, carport roof, in stand alone arrays, and many other convenient places. Here is a rooftop system in California, which is part of the Sacramento Utility District's pioneering program (see http://www.smud.org/pv/) where homeowners volunteer to pay a small premium on the electric bill to host a PV system:
PV cells, as we know them now, were first developed in 1954 by Bell Telephone researchers and first applied to power satellites in space.
Our solar curriculum has several projects related to solar electricity, including:
- dc electricity,
- solar cell demonstration project,
- exploring the history, science, and components of PV systems,
- calculating the cost of photovoltaic systems.
Good educational materials on PV can also be found at http://www.eren.doe.gov/pv/.
Photovoltaics System Components
The basic components of a complete home PV system are:
- PV panels: These produce the electricity from sunlight. There are typically 10 to 20 of these.
- Batteries: Used to store the energy. A typical (off-grid) installation uses 10-20 deep-cycle lead acid batteries.
- Charge controller: To regulate the charging of the batteries
- Inverter (pictured below): Converts the low voltage DC (direct current) power from the batteries into 110 volt AC (alternating current) for use by appliances .
The following diagram shows they are connected together:
First, the Sun shines on the pv modules to produce electrical power. That power is routed through a charge controller to the batteries. The charge controller regulates the charging of the batteries: The voltage on the batteries needs to be increased slowly, because charging them too fast or routinely overcharging the batteries quickly degrades them. Charge controllers must also control the voltage that the pv modules output power at to operate at them at their maximum power output (this is called "power point tracking").
Next, the inverter converts the dc (direct current) electrical power from the batteries (or directly from the modules in a grid-tied system) into ac (alternating current) electrical power at 110 volts. This can then be fed to household appliances via a wall socket.
The costs of typical PV system range from anywhere between a few thousand for a vacation cabin size system, to about ten thousand for a small home, and upwards of $35,000 for a large home (for more details on home PV system costs, see our curriculum project "Calculate the cost of Photovoltaic Systems"). Component costs break down roughly as follows:
- About $4-6 per watt for the panels, so for a typical 2 kilowatt system the panels cost about $8,000-12,000.
- Several hundred dollars for the charge controller.
- About $1 per watt for the inverter: a typical 2 kilowatt system typically uses a 2400 watt to 5000 watt inverter: therefore the inverter cost will be $2400 to $5000.
- About $100 per kilowatt-hour (kWh) of energy storage: a typical 2 kilowatt system might require 20 kWh of storage (only 10 kWh in active use to extend battery life) and therefore about $2000 worth of batteries.
Today's crystalline PV panels have a very long lifetime, at least 25 years, and possibly much longer. Today's batteries typically last 3-10 years before they need to be replaced. Fortunately, US law requires that the batteries be recycled, and over 99% are. Many solar enthusiasts are hopeful that energy storage systems using hydrogen fuel cells will become available in coming decades to replace the need for short-lived batteries.
A commonly repeated myth is that PV panels take more energy to manufacture than they produce. In fact, PV panels typically pay back their energy in 2 to 3 years in a sunny climate, as the National Renewable Energy Laboratory (www.nrel.gov) has documented.
New Mexico has many small businesses that specialize in PV installation and maintenance (see our Professional's Directory).
Sandia National Labs in Albuquerque (see http://www.sandia.gov/pv/), and the National Renewable Energy Laboratory in Golden Colorado (http://www.nrel.gov/photovoltaics.html), both have active photovoltaic research and development programs.
There are also several PV cell manufacturers in Albuquerque: Matrix Inc, Emcore Corp., and Advent Solar.
Passive Solar Design (Solar Heating)
(For additional depth after reading this section, see the guidlines listed on our FAQs/Primer page.
Perhaps the most cost-effective and sensible form of solar energy, passive solar design, is the idea of designing buildings to take advantage of the natural sunlight for heating in the wintertime, and to properly block sunlight for cooling in the summer.
The three principles of passive solar design are:
- Gain: Getting enough sunlight in at the right time (and blocking it at the right time as well).
- Thermal Mass: Having enough thick masonry surfaces to store the energy from sunlight to keep the home warm at night, and from overheating during the day.
- Insulation: Having good insulation (and low air leakage) to keep the heat in during the winter, and heat out during the summer.
The key to getting solar gain at the right time (winter), and not at the wrong time (summer) is to take advantage of the fact that the path taken by the winter sun is much lower in the southern sky than the path taken by the summer sun (which passes nearly overhead at high noon:
The way to take advantage of these differing paths is to place most of the windows on the south side of the home, and add overhangs over these south-facing windows for additional summer shade. Here are some pictures of passive solar homes in New Mexico, showing the south-facing side:Both of these homes were designed by NMSEA member and past president Karlis Viceps of Taos, New Mexico. Both have rainwater harvesting, cisterns, trombe walls (a masonry wall with glazing that stores solar energy for night time use), direct gain (many southern windows), and passive "batch" solar hot water.
Passive Solar Design History: Passive solar design has a fascinating history, stretching at least back to the Greeks, who planned entire cities to take advantage of the Sun's energy. A great book on the history of solar energy is "A Golden Thread - 2500 years of solar architecture and technology", by Ken Butti and John Perlin, Cheshire Books, CA, ISBN 0 917352 08 4.
Native American tribes of the southwest, as well, have long applied these techniques. Their cliff dwellings, for example, those at Mesa Verde, faced south, so that they take advantage of the low winter sun during winter, but were shaded by the overhanging rock during summer. Likewise, the thick rock and adobe walls of these dwellings served as thermal mass to store the Sun's energy and keep the buildings warm at night:
The term "passive solar" was coined in New Mexico during the 1970's by passive solar pioneer Benjamin "Buck" Rogers.
Passive solar design techniques were experimented with and widely implemented in New Mexico in the period 1970-1985, by people such as Peter Van Dresser, Bill Yanda, Ed Mazria, Wayne Nichols, Doug Balcomb, Bill Lumpkins, Mark Chalom, Keith Haggard and Michael Reynolds. Several of these people also founded the New Mexico Solar Energy Association, the oldest solar association of its kind in the US. Several books by some of those listed appear in our book list.
Passive solar design was placed on a firm scientific footing at Los Alamos National Laboratory in the 1970s by Doug Balcomb and others. Doug has made his vast experience available to passive solar designers by developing a passive solar design software called Energy-10: See http://www.nrel.gov/buildings/energy10/.
From the enormous experience acquired by passive solar builders and researchers over the years, many good rules of thumb have been developed. Unfortunately, few architects nowadays apply them, or even know them. Moreover, some buildings that are claimed to be passive solar are not designed carefully. To give you a flavor, here are some of the more important ideas (See our Passive Solar Guidelines for a complete presentation).
Right Placement and Sizing of Windows: Windows on the non-south sides should be sharply limited in their surface area to prevent heat loss. Windows on the south side, on the other hand, should have quite large surface area, but not too large:
Recommended Net Glazing (Window) Areas for northern New Mexico:
Orientation Percent of total floor area East 4 North 4 West 2 South 7-12 (depending on whether additional thermal mass is present)
Right Sizing of Overhangs: Overhangs are strongly encouraged for south-facing windows and trombe walls in Northern New Mexico. The following overhang angles were suggested by Doug Balcomb. These angles are not the angles one would get from most books corresponding to the winter and summer solstices. Rather, they have been adjusted by five degrees or so for the climate of New Mexico, such that they provide eight weeks of full solar gain on either side of the winter solstice (as opposed to just on the winter solstice), and a full eight weeks of shade on either side of the summer solstice (as opposed to just on the summer solstice).
Right Surface Area and Thickness of Thermal Mass: The usual sheet-rock, studs, furniture, etc of a house represent a certain baseline amount of thermal mass:
Without additional thermal mass, direct gain (south-facing windows) should not exceed 7% of floor area.
A house that has 7% direct gain is sometimes called a "sun-tempered" house.
Even if adequate additional thermal mass is added to the house, for example, by adding internal masonry walls or floors with masonry thicker than an inch, then direct gain (south-facing windows) can be up to but should not exceed 12% of the total floor area unless you are careful to avoid, or live with, a large degree of glare.
If adequate additional thermal mass is added to the house, an additional indirect gain (e.g. Trombe walls) may also be added to with a glazing area up 8% of the total floor area in addition to the 12% direct gain without overheating the house during the day.
Total solar gain area for a house with added thermal mass can therefore be up to but should never be more than 20% of total floor area.
The simplest rule of thumb is that thermal mass area should have at least 6 times the (uncovered) surface area of the direct gain glass area. More detailed mass sizing info is contained in the guidelines.
Thermal mass effectiveness increases proportionally to thickness up to about 4 inches. After that, effectiveness doesn't increase as significantly. So concentrate on getting the surface area and the first four inches of thickness, and not on excessive thickness and volume.
Contrary to common belief, it is not important to have all the mass in the direct gain path - so don't worry about trying to arrange for this! Rather, strive to have thermal mass in line of sight of sunlit surfaces.
Right Arrangement of Thermal Mass: Once light enters through the windows, reflection and thermal re-radiation can transmit energy from the sunlit surfaces to other thermal mass surfaces which are in line of sight of the sunlit surfaces. Non-sunlit floor area, for example, will not function well as thermal mass with respect to sunlit floor area because it is not in line of sight with sunlit floor areas.
Contrary to common belief, it is not advisable to color all thermal mass surfaces darkly (with the exception of indirect gain surfaces such as Trombe walls and water walls, which need to be very dark). Walls lit by clerestories, for example, are better painted white, such that they reflect the light to other thermal mass surfaces, such as the floor. If the wall becomes too hot, a thermal-siphon airflow can be set up that effectively heats the air and overheating the space.
In general, wall and ceiling thermal mass surfaces should be light-colored, while floors should be dark. Making the floor dark helps keep the floor warm and easier to clean, in addition to providing good adsorption of thermal radiation.
Right Arrangement of Rooms:
Room layout should take advantage of morning sunlight for the kitchen, and possibly a bedroom, winter sunlight for the living room, and make use of buffer spaces and garages as additional northern and western shielding, as the following diagram suggests:
A sunspace might be added with advantage in front of the living room.
These rules of thumb should give you a good feeling for what is required. Nowadays, computer software, such as "Energy-10" exist to assist the architect with perfecting the thermal performance of a building. Every effort should be made to take advantage of these new tools, and of these design principles for energy efficient building.