Domestic Hot Water

Free Hot Water Through Solar CHP (Cooling, Heating, Power)  Solar CHP ™ is Pollution-Free-Power and Energy Through the Simultaneous Generation of Cooling, Heating and Power With our Solar CHP ™ Solar Cogeneration ™ or Solar Trigeneration ™ Power and Energy Systems  "Cut the Cord" to Your Electric Company and  Dis-connect from Expensive, Dirty-Power! GO GREEN WITH OUR COMBINATION 

SOLAR ELECTRIC POWER & SOLAR HEATING AND COOLING SYSTEM! THERE IS NO CLEANER, GREENER, CHEAPER POWER AND ENERGY SYSTEM THAN OURS!  REBATES, INCENTIVES, GREEN TAGS  AND TAX CREDITS AVAILABLE

Our Solar Electric Power Systems Combined with our Solar Heating and Cooling system will eliminate your electric bills  "Green" Cooling, Heating and Power is Here! Homes, Schools, Office Buildings, Hospitals, and  most any other building or facility can now have Clean, Green, Power and Energy for *free! 

Our Solar Heating and Cooling System – Uses the "free" Power of the Sun to Heat and Cool your Commercial Business or Home for Free!

Solar Energy Systems is a subsidiary of Cogeneration Technologies located in Houston, Texas. We provide the following power and energy project development services: 

• Project Engineering Feasibility & Economic Analysis Studies
• Engineering, Procurement and Construction
• Environmental Engineering & Permitting 
• Project Funding & Financing Options; including Equity Investment, Debt Financing, Lease and Municipal Lease
• Shared/Guaranteed Savings Program with No Capital Investment from Qualified Clients 
• Project Commissioning 
• 3rd Party Ownership and Project Development
• Long-term Service Agreements
• Operations & Maintenance 
• Green Tag (Renewable Energy Credit, Carbon Dioxide Credits, Emission Reduction Credits) Brokerage Services; Application and Permitting

We provide Net Energy Metering project development services as well as "turnkey" products and services in the areas of "Renewable Energy Technologies" and in developing clean power/energy projects that will generate a "Renewable Energy Credit," Carbon Dioxide Credits and Emission Reduction Credits. Through our strategic partners, we offer "turnkey" power/energy project development products and services that may include; Absorption Chillers, Adsorption Chillers, Automated Demand Response, Biodiesel Refineries, Biofuel Refineries, Biomass Gasification, BioMethane, Canola Biodiesel, Coconut Biodiesel, Cogeneration, Concentrating Solar Power, Demand Response Programs, Demand Side Management, Energy Conservation Measures, Energy Master Planning, Engine Driven Chillers, Solar CHP, Solar Cogeneration, Rapeseed Biodiesel, Solar Electric Heat Pumps, Solar Electric Power Systems, Solar Heating and Cooling, Solar Trigeneration, Soy Biodiesel, and Trigeneration.

Unlike most companies, we are equipment supplier/vendor neutral. This means we help our clients select the best equipment for their specific application. This approach provides our customers with superior performance, decreased operating expenses and increased return on investment. 

Concentrating Solar Thermal Heating Systems

Solar thermal systems convert sunlight into heat. "Flat-plate" solar thermal collectors produce heat at relatively low temperatures (80 to 140°F [27 to 60°C]), and are generally used to heat air or a liquid for space and water heating or drying agricultural products. Concentrating solar collectors produce higher temperatures. They are most often used where higher temperature heat is desirable, there are large thermal loads, and/or where there are limitations in the area available for installing solar collectors, since they provide more energy per unit of collector surface area. They can also be applied in the production or refining of chemicals and fuels or to produce mechanical or electrical energy. The following is a discussion of concentrating systems for space or water heating. Such collectors can also be used to produce heat for absorption cooling.

There are a variety of types of concentrating solar thermal collectors. They achieve higher temperatures by using a concentrating reflector to direct sunlight from a large area to a smaller receiver and absorber area. A liquid is pumped through the absorber, where it is heated and then sent to a storage system or used directly for heating. Concentrating collectors work best in climates that have a high amount of direct solar radiation. They do not function as well on cloudy days, when available solar radiation is mostly diffuse. The amount of useful heat they produce is mainly a function of the intensity of solar radiation available, the size of the reflector, how well they concentrate solar energy onto the receiver, the characteristics of the absorber, and the control of the flow rate of the heat transfer fluid.

A concentrating collector system can have a fixed or stationary collector, or it can track the sun. In stationary systems the reflector and absorber are in a fixed position, usually oriented directly true south. Tracking devices shift the position of the reflector and the receiver to maximize the amount of sunlight concentrated on the receiver.

Tracking collectors are either single-axis or double-axis. Single-axis tracking devices move the collector on one axis: east to west or north to south. Dual-axis tracking devices track the sun on all axes. The entire collector, containing the reflector and receiver, generally moves as a unit in both types. Systems with dual-axis tracking concentrate solar energy the most and therefore produce the highest temperatures, but are the most complex and expensive.

The most common types of concentrating solar thermal heating collectors are based on the parabolic trough. Parabolic troughs are U-shaped, concentrators that focus sunlight onto a linear receiver tube located along the focal line of the trough. The receiver may be enclosed in a transparent glass tube to reduce heat loss from the absorber and maximize absorption of solar energy. They generally have single-axis tracking.

Another type of concentrating system that is possible to use in a heating application is the parabolic dish. This has a bowl shaped reflector that focuses the sun onto a relatively small receiver. For optimum performance they require dual axis tracking and the receiver moves with the reflector. This complicates their practical application for water and space heating. Most parabolic dish systems are very sophisticated systems used for electricity generation or very simple systems for cooking food on a small-scale. Other types of concentrating systems have an array of reflectors that individually track the sun and focus sunlight onto a central receiver located on a tower. Development of these systems has focused on electric power generation.

There are two basic types of parabolic trough solar heating collectors that have been commercially developed: cylindrical parabolic troughs and compound parabolic collectors.

A standard cylindrical parabolic trough has a fixed receiver/absorber positioned in the middle of the trough at or slightly above the radius across the edges of the reflector. The shape of the trough (rim angle) determines the focal point, and thus the position of the receiver. The reflector surface is usually polished aluminum, aluminized plastic, silvered glass, or stainless steal. The receiver usually has an absorber tube coated with a selective material that has a high absorption for the solar spectrum and low emittance for infrared radiation. The absorber tube may be enclosed in glass with a vacuum to reduce heat loss due to convection and radiation. Receiver temperatures can reach 750°F (400°C).

The trough can be oriented east to west or north to south. They are typically single-axis tracking. When the trough is oriented east to west, the collector moves north to south or south to north as the sun's altitude (height above the horizon) changes throughout the day. When the trough is oriented north to south, the collector moves east to west following the sun's movement across the sky, and returns at sunset to face the sunrise in the morning.

Systems with north-south orientation can be installed so that the collector is at an angle that optimizes performance for different seasons of the year, much like flat-plate solar collectors. For example, if maximum winter performance is preferred, the angle of the collector would be set at 15 degrees plus the site latitude; if summer performance is to be maximized, the angle would be set at 15 degrees less than the site's latitude. An angle equal to the site latitude is a compromise for year round performance.

Most applications of tracking parabolic troughs are relatively large systems to supply heat for domestic water and space heating in commercial and institutional buildings. Examples include the headquarters of the U.S. Department of Agriculture in Washington, DC and at correctional facilities in Phoenix, AZ, Adams County, CO, and Tehachapi, CA. Parabolic solar concentrators are also used for electric power generation at the Solar Electric Generating Systems (SEGS), located in the Mojave Desert at Harper Lake and Kramer Junction, California. The SEGS consist of nine hybrid solar thermal parabolic trough/natural gas turbine power plants. These power plants have a combined generation capacity of 354 MW (peak), and are the largest in the world.

Compound parabolic- or Winston-collectors, have two half-parabolic reflectors with a metal absorber pipe located at the bottom of the trough. The compound parabolic collector funnels solar radiation to the absorber pipe. If oriented from east to west, troughs with low concentration ratios can be stationary. They are able to collect some diffuse, as well as direct, solar radiation. These stationary collectors are efficient for medium temperature uses. These systems are much less common than the cylindrical trough type.

• Solar Water Heating Systems

Solar water heating systems use the energy from the sun to heat either water or a heat-transfer fluid in collectors. There are passive systems and active systems. A typical solar water heating system will reduce the need for conventional water heating by at least two-thirds, depending on several factors. 

Sometimes the plumbing from a solar water heating system can connect to a house's existing water heater, which stays inactive as long as the water coming in is hot or hotter than the temperature setting on the indoor water heater. When it falls below this temperature, the home's water heater can kick in to make up the difference. High-temperature solar water heaters can provide energy-efficient hot water and hot water heat for large commercial and industrial facilities. 

• Solar Water Heating Systems
• Direct Systems

This system uses a pump to circulate potable water from the water storage tank through one or more collectors and back into the tank. The pump is regulated by an electronic controller, an appliance timer, or a photovoltaic panel. 

• Indirect Systems

In this system, a heat exchanger heats a fluid that circulates in tubes through the water storage tank, transferring the heat from the fluid to the potable water. 

• Thermosiphons

A thermosiphon solar water heating system has a tank mounted above the collector. As the collector heats the water, it rises to the storage tank, while heavier cold water sinks down to the collector. 

• Draindown Systems

In cold climates, this system prevents water from freezing in the collector by using electric valves that automatically drain the water from the collector when the temperature drops to freezing. "Drainback systems," a variation of this approach, automatically drain the collector whenever the circulating pump stops. 

• Swimming Pool Systems

In solar heated swimming pools, the pool's filter pump pumps water through a solar collector, and the pool itself stores the hot water.  Cooling and heating your building (home, office, school, hospital, etc.) costs you up to 60%, or more, every month you receive your electric bill. You can eliminate the heating and cooling portion of your electric bill forever, and cool and heat your home with the sun's power with our Solar Heating and Cooling system! 

Our Solar Heating and Cooling system is the cleanest, greenest, and lowest cost method to cool and warm your home or commercial office or other buildings. Our Solar Heating and Cooling system will eliminate your energy costs for heating and cooling your home, office, school, or any other commercial facility for *free: Requires the purchase of our Solar Heating and Cooling system. Minimum size is 10 tons. You must be located in a qualified geographic location, which means our system must be located to receive direct sunlight. For qualified customers, we will install the system with little to no money down and you pay for the system with the savings our system provides! 

Solar Absorption Cooling. Solar heat can be used to displace electricity used for cooling. Absorption chillers use a heat source, such as natural gas or hot water from solar collectors, to evaporate the already-pressurized refrigerant from an absorbent/refrigerant mixture. Condensation of vapors provides the same cooling effect as that provided by mechanical cooling systems. Although absorption chillers require electricity for pumping the refrigerant, the amount is very small compared to that consumed by a compressor in a conventional electric air conditioner or refrigerator. Solar Absorption Cooling systems are typically sized to carry the full air conditioning load during sunny periods.

Solar Electric Power Systems (PV)

Solar electric power systems transform sunlight into electricity. Sunlight is an abundant resource. Every minute the sun bathes the Earth in as much energy as the world consumes in an entire year. Solar cells employ special materials called semiconductors that create electricity when exposed to light. Solar electric systems are quiet and easy to use, and they require no fuel other than sunlight. Because they contain no moving parts, they are durable, reliable, and easy to maintain.

How It Works

Solar cells, also known as photovoltaic (PV) cells, do the work of making electricity. Several types of solar electric technology are under development, but four—crystalline silicon (a form of refined beach sand), thin films, concentrators, and thermophotovoltaics—are illustrative of the range of technologies. Solar cells are connected to a variety of other components to make a solar electric power system.

Crystalline Silicon

Crystalline silicon solar cells are used in more than half of all solar electric devices. Like most semiconductor devices, they include a positive layer (on the bottom) and a negative layer (on the top) that create an electrical field inside the cell. When a photon of light strikes a semiconductor, it releases electrons (see animation). The free electrons flow through the solar cell's bottom layer to a connecting wire as direct current (DC) electricity. Some solar cells are made from polycrystalline silicon, which consists of several small silicon crystals. Polycrystalline silicon solar cells are cheaper to produce but somewhat less efficient than single-crystal silicon.

A simple silicon solar cell can power a watch or calculator. However, it produces only a tiny amount of electricity. Connected together, solar cells form modules that can generate substantial amounts of power. Modules are the building blocks of solar electric systems, which can produce enough power for a house, a rural medical clinic, or an entire village. Large arrays of solar electric modules can power satellites or provide electricity for utilities.

Solar Electric Power System Components

In addition to modules, several components are needed to complete a solar electric power system. Many systems include batteries, battery chargers, a backup generator, and a controller so that people in solar-powered homes and buildings can turn on the lights at night or run televisions or appliances on cloudy days. Grid-connected systems don't require batteries or backup generators because they use the grid for backup power. Some remote system applications, such as those used to pump water, do not require a backup power source.

Components of a typical standalone PV system using crystalline silicon technology. (Source: Solar Electric Power Association)
Solar electric power systems can incorporate inverters or power control units to transform the DC electricity produced by the solar cells into alternating current (AC) to run AC appliances or sell to a utility grid. Complete systems usually include safety disconnects, fuses, and a grounding circuit as well.

Thin Films

Solar electric thin films are lighter, more resilient, and easier to manufacture than crystalline silicon modules. The best-developed thin-film technology uses amorphous silicon, in which the atoms are not arranged in any particular order as they would be in a crystal. An amorphous silicon film only one micron thick can absorb 90% of the usable solar energy falling on it. Other thin-film materials include cadmium telluride and copper indium diselenide. Substantial cost savings are possible with this technology because thin films require relatively little semiconductor materials. Thin films are produced as large, complete modules, not as individual cells that must be mounted in frames and wired together. They are manufactured by applying extremely thin layers of semiconductor material to a low-cost backing such as glass or plastic. Electrical contacts, antireflective coatings, and protective layers are also applied directly to the backing material. Thin films conform to the shape of the backing, a feature that allows them to be used in such innovative products as flexible solar electric roofing shingles.

Concentrators

Concentrators use optical lenses (similar to plastic magnifying glasses) or mirrors to concentrate the sunlight that falls on a solar cell. With a concentrator to magnify the light intensity, the solar cell produces more electricity. Today, most solar cells in concentrators are made from crystalline silicon. However, materials such as gallium arsenide and gallium indium phosphide are more efficient than silicon in solar electric concentrators and will likely see more use in the future. These materials are now used in communications satellites and other space applications. Concentrators produce more electricity using less of the expensive semiconductor material than other solar electric systems. A basic concentrator unit consists of a lens to focus the light, a solar cell assembly, a housing element, a secondary concentrator to reflect off-center light rays onto the cell, a mechanism to dissipate excess heat, and various contacts and adhesives. The basic unit can be combined into modules of varying sizes and shapes. Concentrators only work with direct sunlight and operate most effectively in sunny, dry climates. They must be used with tracking systems to keep them pointed toward the sun.

Thermophotovoltaics

Thermophotovoltaic (TPV) devices convert heat into electricity in much the same way that other PV devices convert light into electricity. The difference is that TPV technology uses semiconductors "tuned" to the longer-wavelength, invisible infrared radiation emitted by warm objects. This technology is cleaner, quieter, and simpler than conventional power generation using steam turbines and generators.

TPV converters are relatively maintenance-free because they contain no moving parts. In addition to using solar energy, they can convert heat from any high-temperature heat source, including combustion of a fuel such as natural gas or propane, into electricity. TPV converters produce virtually no carbon monoxide and few emissions. They may be used in the future in gas furnaces that generate their own electricity for self-ignition (during power outages) and in portable generators and battery chargers.

Advantages

Solar electric systems offer many advantages. Standalone systems can eliminate the need to build expensive new power lines to remote locations. For rural and remote applications, solar electricity can cost less than any other means of producing electricity. Solar electric systems can also connect to existing power lines to boost electricity output during times of high demand such as on hot, sunny days when air conditioners are on. Solar electric systems are flexible. Solar electric modules can stand on the ground or be mounted on rooftops. They can also be built into glass skylights and walls. They can be made to look like roof shingles and can even come equipped with devices to turn their DC output into the same AC utilities deliver to wall sockets. These advances mean individual homeowners and businesses can relieve pressure on local utilities struggling to meet the increasing demand for electricity.

More than 30 states offer grid-connected solar electric system owners the chance to save money on their energy bills by feeding any excess power their solar electric system produces into the utility grid—an arrangement called net metering. Solar power systems require minimal maintenance. They run quietly and efficiently without polluting. They are easy to combine with other types of electric generators such as wind, hydro, or natural gas turbines. They can charge batteries to make solar electricity continuously available. For utilities, large-scale solar electric power plants can help meet demand for new power generation, especially in distributed applications. A solar electric power plant is created from multiple arrays that are interconnected electronically. Solar electric plants are easier to site and are quicker to build than conventional power plants. They are also easy to expand incrementally—by adding more modules—as power demand increases.

Solar electric power systems are good for the environment. When solar electric technologies displace fossil fuels for pumping water, lighting homes, or running appliances, they reduce the greenhouse gases and pollutants emitted into the atmosphere. The use of solar electric systems is particularly important in developing nations because it can help avert the expected increases in emissions of greenhouse gases caused by the growing demand for electricity in those countries. Solar electric technologies also benefit the U.S. economy by creating jobs in U.S. companies. Exporting solar electric technologies to developing nations expands U.S. markets while protecting the global environment.

Disadvantages

Although solar electric systems make financial sense in remote areas that lack access to power lines, they are usually more expensive than fossil fuels for grid-connected applications. This disadvantage is significant for utilities considering large-scale solar electric power plants. Although solar electricity costs considerably more than electricity generated by conventional plants, regulatory agencies often require utilities to supply electricity for the lowest cash cost.

Utilities view solar electric power plants differently than they view conventional power plants. Solar electric modules produce electricity intermittently—only when the sun shines. Their output varies with the weather and disappears altogether at night. Integrating solar electricity into a utility system requires creative planning.

A combination of solar electric arrays and pool-heating solar collectors were used to provide power and heat to the Georgia Tech University Aquatic Center, site of the 1996 Olympic swimming competition. (Credit: Heliocol)

Applications

A combination of solar electric arrays and pool-heating solar collectors were used to provide power and heat to the Georgia Tech University Aquatic Center, site of the 1996 Olympic swimming competition. (Credit: Heliocol) Solar electricity has powered satellites since the dawn of the space program. It has run remote communications outposts high in the mountains and turned on the lights, kept medicines cold, and pumped water in rural areas for more than 30 years. Small solar cells are used to power wristwatches, calculators, and other electronic gadgets. More recently, solar electric systems have been used to provide supplemental power to homes and commercial buildings in cities.

Solar electric technology has important roles to play in both the developing and developed worlds. From the farmer irrigating his crops in rural Mexico to an innovative lighting system for an Olympic sports arena, solar electric solutions abound. Electric utilities harness solar electricity for distributed applications—near substations or at the end of overloaded power lines, for example, to avoid or defer costly line upgrades. They use solar electricity during hot, sunny periods when the demand for air conditioning stretches conventional power generation to its limit. The Sacramento Municipal Utility District, for example, uses large solar electric arrays as part of its power generation mix. Utilities also rely on solar electricity to power remote, standalone monitoring systems. Consumers and builders are integrating solar electric modules into their homes and offices. Innovative solar electric technologies can replace conventional roofing and facade materials in new buildings. Solar electric roofing shingles, for example, are being used in some new residences. In grid-connected applications, solar electricity supplies some of a consumer's energy needs; the local utility provides the rest.

Standalone solar electric systems power a variety of applications far from the reaches of the power grid. These applications include remote communications systems such as television and radio transmitters and receivers, telephone systems, and microwave repeaters. Standalone solar electric power is also used to prevent corrosion of metal pipes, tanks, bridges, and buildings. Many remote residences worldwide use solar electricity as their source of power. For instance, more than 100,000 vacation homes in Scandinavia rely solely on solar electric technology to run lights and appliances.

Villages around the world are building solar electric systems to bring electricity to their homes and local industries, often for the first time. To make the maximum use of available resources, village power is typically produced by a hybrid power system that combines solar electricity with diesel backup generators and sometimes another renewable energy technology such wind power. Villages also use standalone solar electric systems for pumping water—an application shared by rural farmers and ranchers in the United States.

Solar Hot Water Heating

These solar collectors provide 80% of the hot water for the residence

An estimated one million residential and 200,000 commercial solar water-heating systems have been installed in the United States. Although there are a large number of different types of solar water-heating systems, the basic technology is very simple. Sunlight strikes and heats an "absorber" surface within a "solar collector" or an actual storage tank. Either a heat-transfer fluid or the actual potable water to be used flows through tubes attached to the absorber and picks up the heat from it. (Systems with a separate heat-transfer-fluid loop include a heat exchanger that then heats the potable water.) The heated water is stored in a separate preheat tank or a conventional water heater tank until needed. If additional heat is needed, it is provided by electricity or fossil-fuel energy by the conventional water-heating system. By reducing the amount of heat that must be provided by conventional water-heating, solar water-heating systems directly substitute renewable energy for conventional energy, reducing the use of electricity or fossil fuels by as much as 80%.

Today's solar water-heating systems are well proven and reliable when correctly matched to climate and load. The current market consists of a relatively small number of manufacturers and installers that provide reliable equipment and quality system design. A quality assurance and performance-rating program for solar water-heating systems, instituted by a voluntary association of the solar industry and various consumer groups, makes it easier to select reliable equipment with confidence. Building owners hould investigate installing solar hot water-heating systems to reduce energy use. Before sizing a solar system, water-use reduction strategies should be put into practice.

There are five types of solar hot water systems:

• Thermosiphon Systems
• Direct-Circulation Systems
• Drain-Down Systems
• Indirect Water-Heating Systems
• Air Systems

Thermosiphon water heaters are shown on employee housing at Yosemite National Park. 

Thermosiphon Systems. These systems heat water or an antifreeze fluid, such as glycol. The fluid rises by natural convection from collectors to the storage tank, which is placed at a higher level. No pumps are required. In thermosiphon systems fluid movement, and therefore heat transfer, increases with temperature, so these systems are most efficient in areas with high levels of solar radiation.

Direct-Circulation Systems. These systems pump water from storage to collectors during sunny hours. Freeze protection is obtained by recirculating hot water from the storage tank, or by flushing the collectors (drain-down). Since the recirculation system increases energy use while flushing reduces the hours of operation, direct-circulation systems are used only in areas where freezing temperatures are infrequent.

Drain-Down Systems. These systems are generally indirect water-heating systems. Treated or untreated water is circulated through a closed loop, and heat is transferred to potable water through a heat exchanger. When no solar heat is available, the collector fluid is drained by gravity to avoid freezing and convection loops in which cool collector water reduces the temperature of the stored water.

Indirect Water-Heating Systems. In these systems, freeze-protected fluid is circulated through a closed loop and its heat is transferred to potable water through a heat exchanger with 80% to 90% efficiency. The most commonly used fluids for freeze protection are water-ethylene glycol solutions and water-propylene glycol solutions.

Air Systems. In this indirect system the collectors heat the air, which is moved by a fan through an air-to-water heat exchanger. The water is then used for domestic or service needs. The efficiency of the heat exchanger is in the 50% range. Direct-circulation, thermosiphon, or pump-activated systems, require higher maintenance in freezing climates. For most of the United States, indirect air and water systems are the most appropriate. Air solar systems, while not as efficient as water systems, should be considered if maintenance is a primary concern since they do not leak or burst.

A close-up view of flat-plate collectors.

Types of Collectors

There are basically three types of collectors: flat-plate, evacuated-tube collectors, and concentrating collectors.

A close-up view of flat-plate collectors. 

A flat-plate collector, the most common type, is an insulated, weatherproofed box containing a dark absorber plate under one or more transparent or translucent covers. Evacuated-tube collectors are made up of rows of parallel, transparent glass tubes. Each tube consists of a glass outer tube and an inner tube, or absorber, covered with a selective coating that absorbs solar energy well but inhibits radiative heat loss. The air is withdrawn (evacuated) from the space between the tubes to form a vacuum, which eliminates conductive and convective heat loss. The vacuum also helps them achieve extremely high temperatures (170°-350° F); so they are appropriate for commercial and industrial uses.

Concentrating collectors are usually parabolic troughs that use mirrored surfaces to concentrate the sun's energy on an absorber tube (called a receiver) containing a heat-transfer fluid. They provide hot water and steam, usually for industrial and commercial applications.

Parabolic-trough collectors use curved mirrors to focus the sunlight on a receiver tube (sometimes encased in an evacuated tube) running through the focal point of the mirrors and can heat their transfer fluid to as much as 570°F (299°C). Because they use only direct-beam sunlight, parabolic-trough systems require tracking systems to keep them focused toward the sun and are best suited to areas with high direct solar radiation. Because they are particularly susceptible to transmitting structural stress from wind loading and require large areas for installation, parabolic-trough collectors are usually ground mounted. For electrical generation or industrial uses that require very high temperatures (greater than 392°F [200°C]), a heat-transfer fluid such as oil is used, but depending on the degree of danger of freezing, antifreeze or water is used in the heat-transfer loop for domestic water-heating systems. Parabolic-trough collectors generally require greater maintenance and supervision and particularly benefit from economies of scale, so are generally used for larger systems.

Parabolic-trough solar hot water heating system at a prison. 

Low-, Mid-, and High-Temperature Collectors

The collectors can be low-temperature, mid-temperature, or high-temperature. The glazed, flat-plate collectors most commonly used for commercial or residential domestic hot water are classified as "mid-temperature" collectors, generally increasing water temperature to as much as 160І (71°C). Flat-plate collectors consist of an insulated, weather-tight housing or box, a clear glass or plastic cover glazing, a black absorber plate, and a system of passages for the heat-transfer fluid to pass through the collector. Special coatings on the absorber maximize absorption of sunlight and minimize re-radiation of heat. Gaskets and seals at the connections between the piping and the collector and around the glazing ensure a watertight system.

Low-temperature collectors, which generally increase water temperature to as much as 90°F (32°C), are less expensive because they consist simply of an absorber with flow passages and have no covering glass (glazing), insulation, or expensive materials such as aluminum or copper. These collectors are less efficient in retaining solar energy when outdoor temperatures are low, but are quite efficient when outside air temperatures are close to the temperature to which the water is being heated. They are highly suitable for swimming pool heating and other uses that require only a moderate increase in temperature and are most commonly used in warmer areas. For the last several years, they have been the most frequently installed collectors. In warm climates, low-temperature collectors are sometimes used in hybrid systems that heat a pool in the winter and supplement domestic water heating in the summer, when pool heating is not needed.

Solar Hot Water Pool Heating

Solar pool heating was used at the 1996 Summer Olympics in Atlanta. Such heating systems are one of the most cost-effective applications of solar energy. It is relatively simple to integrate a solar water heater since most pools require a pump, filter, and plumbing. With a solar energy system, the pool's water is pumped through the filter and then through a solar energy collector(s) instead of directly back to the pool. The sun heats the water in the collector(s) before it returns to the pool. Solar pool heating can be used for residential, commercial, or community swimming pools.

Swimming pool water heating is a popular use for solar collectors.

Large facilities or ones with quasi-industrial operations such as laundries may be able to efficiently use more sophisticated high-temperature collectors. Although they are also used in mid-temperature systems, evacuated-tube collectors can be designed to increase water/steam temperatures to as much as 350°F (177°C). They may use a variety of configurations, but generally encase both the absorber surface and the tubes of working fluid in a tubular glass vacuum for highly efficient insulation. Evacuated-tube collectors are the most efficient collector type for cold climates with low-level diffuse sunlight. They can be mounted either on a roof or on the ground, but they need to be protected from vandalism and can be damaged by hail or hurricanes.

Solar Equipment Certification

The Solar Rating and Certification Corporation (SRCC) is an independent, nonprofit trade organization that creates and implements solar equipment certification programs and rating standards. SRCC certifies solar thermal equipment that meets minimum standards jointly set by private and public sectors. The compiled information is published in the Directory of SRCC Certified Solar Collector and Systems Ratings, priced at $26.00. The guidebook rates the performance, durability, and safety of solar thermal collectors and systems. It also lists certified products and consumer tips for suitable solar product selection. This and other publications are available for downloading from SRCC Web site.