Friday, December 17, 2010




Solar Electric (Photovoltaic)

Photovoltaic (PV) devices generate electricity directly from sunlight via an electronic process that occurs naturally in certain types of material, called semiconductors. Electrons in these materials are freed by solar energy and can be induced to travel through an electrical circuit, powering electrical devices or sending electricity to the grid.

PV devices can be used to power anything from small electronics such as calculators and road signs up to homes and large commercial businesses.

The PV effect was observed as early as 1890 by Henri Becquerel, and was the subject of scientific inquiry through the early twentieth century. In 1954, Bell Labs in the U.S. introduced the first solar PV device that produced a useable amount of electricity, and by 1958, solar cells were being used in a variety of small-scale scientific and commercial applications.

The energy crisis of the 1970s saw the beginning of major interest in using solar cells to produce electricity in homes and businesses, but prohibitive prices (nearly 30 times higher than the current price) made large-scale applications impractical.

Industry developments and research in the following years made PV devices more feasible and a cycle of increasing production and decreasing costs began which continues even today.

Present Status
The cost of PV has dropped dramatically as the industry has scaled up manufacturing and incrementally improved the technology with new materials. Installation costs have come down too with more expereinced and trained installers. However, the U.S. still remains behind other nations that have stronger national policies to shift energy use from fossil fuels to solar. Globally, the U.S. is the fourth largest market for PV installations behind world leaders Germany, Japan and Spain.

Most modern solar cells are made from either crystalline silicon or thin-film semiconductor material. Silicon cells are more efficient at converting sunlight to electricity, but generally have higher manufacturing costs. Thin-film materials typically have lower efficiencies, but are simpler and less costly to manufacture. A specialized category of solar cells - called multi-junction or tandem cells - are used in applications requiring very low weight and very high efficiencies, such as satellites and military applications.More info at

Solar Thermal (Heating and Cooling)

Solar heating harnesses the power of the sun to provide solar thermal energy for solar hot water, solar space heating and cooling and solar pool heaters.

Solar Water Heating

Most solar water heating systems have two parts, a solar collector and a storage tank. The solar collector gathers the sun’s energy, transforms it into heat then transfers the heat to water. The heated water is then stored in the storage tank for later use, with a conventional system providing additional heating as necessary. Solar water heating systems can be either active (relying on electric pumps to circulate water) or passive (relying on gravity and the tendency for water to naturally circulate when heated), but the most common type for use in commercial and residential buildings is active.

Solar Space Heating and Cooling

Active solar space heating systems collect and absorb solar energy and use electric fans or pumps to transfer and distribute the heat. These systems also contain an energy-storage system to provide heat at night or when the sun is not shining.

Passive solar space heating capitalizes on warmth through the sun through design features as well as materials in the walls or floors that absorb heat during the day and release that heat at night.

Perhaps the most interesting new solar thermal technology is the absorption chiller – a closed-loop system that converts solar-heated water into air conditioning. Water heated by the sun through flat-panel collectors or evacuated tubes is subjected to a low-pressure loop with lithium bromide, a phase-change catalysts, which causes the water to reach a cool 44 degrees F. This cooled water runs through copper piping; forced air passing over the coils produces air conditioning.

Solar Pool Heating

Solar pool heating systems use the existing pool filtration system to pump the water through a solar collector and the collected heat is transferred directly to the pool water. Solar pool heating collectors typically operate at a slightly warmer temperature than the surrounding air and normally use unglazed, low-temperature collectors made from polymers.More info at

Concentrating Solar Power (CSP)

Concentrating solar power (CSP) plants are utility-scale generators that produce electricity by using mirrors or lenses to efficiently concentrate the sun's energy. CSP technologies include parabolic trough systems, power towers, compact linear Fresnel and dish systems which concentrate the thermal energy of the sun to drive a conventional steam turbine.

Parabolic trough systems use parabolic curved, trough shaped reflectors to focus the sun's energy onto a receiver pipe running at the focus of the reflector. Because of their parabolic shape, troughs can focus the sun at 30 to 60 times its normal intensity on the receiver pipe. The concentrated energy heats a heat transfer fluid in the pipe which is then used to generate steam to power a turbine which drives an electric generator.

Power tower systems use a field of computer-controlled flat mirrors (called Heliostats) to focus solar heat on a central collector tower. The high energy at this point can then be used to heat water to produce steam (and run a central generator) or it can be transferred to a heat transfer material (typically liquid sodium) which can then store the heat for later use.

The Compact Linear Fresnel Reflectors use flat reflectors moving on a single axis while using a Fresnel lens to concentrate the solar thermal energy into collectors. The flat mirrors used in this system allow for a greater density of reflectors in the array, increasing the efficiency of land use.

Dish systems use a large concave dish to track the sun and focus the energy onto a high-efficiency power conversion unit, which generates electricity directly. Dish systems typically produce upwards of 25KW.More info at

Passive Solar

Architects and builders use special siting, design and materials to absorb and distribute the sun's heat and take advantage of sunlight to brighten interior spaces. Passive solar also refers to positioning shading devices to protect buildings from excessive heat. Passive solar does not have mechanical or special equipment like active solar. Instead, design is adapted to the local climate.

There are several ways to use passive solar to achieve direct gain, indirect gain, and insolated gain. Elements used are: absorber material (dark tile); thermal mass that retains heat during the day, then releases it during cooler evening and nights (trombe wall); aperture (south-facing glazed windows); distribution (allows air flow); and control (overhanging roof or deciduous trees to protect from heavy sun in summer, allowing more light in winter when sun is lower and leaves have fallen).

Passive lighting is another important way to reduce the need for electricity and cut costs. North-facing clerestory windows or a sawtooth roof along with south-facing windows add natural light. Flexible light tubes or skylights allow one to brighten interior spaces with limited or no windows.More info at

Solar Ovens

Solar ovens are a low-tech, low-cost option to heating and cooking food. Similar to a crock pot, a solar oven is essentially a well-insulated portable box that captures and holds the sun's heat. There are a number of commercially available models and many do-it-yourself designs.

Solar ovens, once a quaint idea for an elementary science project, are making a comeback as a staple for emergency preparedness supplies and as an affordable convenience for low-income people in developing countries.More info at

Emerging Technology

Research and development by companies and research labs are continually discovering new techniques and materials that improve efficiencies and cut the cost of capturing solar energy. The industry seeks to commercialize the most promising technology to improve delivery of solar power generation for homes, business and government. Examples include applying different materials for thin-film PV applications, solar cooling systems, incorporating PV into building materials for roofing, windows and even painted surfaces.

Other areas being aggressively pursued are storage systems (thermal and electrical); solar hybrid lighting; improved manufacturing techniques; nanotechnology; low-cost semiconductor alternatives to polysilicon; and improving concentrating solar power systems.More info at


Željko Serdar
Head of business association

1 comment:

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