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Solar energy is energy from the sun. This energy is in the form of light and heat. Light energy is used to produce electricity via photovoltaics. The sun’s heat energy is used to produce heat and is often referred to as solar thermal.
Photovoltaic panels (solar modules) use the sun’s light energy to generate electricity. A solar module is made up of multiple cells of semiconductors. When the cells are exposed to light they absorb photons. The individual solar cell is designed with a positive and a negative layer to create an electric field, just like a battery. As photons are absorbed in the cell their energy causes electrons to become free. The electrons move toward the bottom of the cell and exit through the connecting wire. The flow of electrons is what we call electricity.
Solar panels can be very practical in the alpine because they are simple, have no moving parts, and need no maintenance. Photovoltaic cells operate more efficiently in colder temperatures, however the overall efficiency of the system is lower in winter due to decreased availability of energy from the sun. Ongoing research in photovoltaics promises to increase efficiency and reduce production costs.
Here are the main considerations for effective use of solar power in alpine climates:
- Photovoltaic panels will produce less energy during winter in northern latitudes. It is important to size the system for the appropriate energy demand during the peak season because there are fewer hours of daylight in winter.
- While the conversion efficiency of photovoltaic systems compares favourably to that of small generators, it involves high capital costs and is generally not practical for powering electric resistance heaters.
- Photovoltaic panels should be placed in a location where they won’t be shaded by overhanging trees or mountains during certain months of the year. Even partial shading of a solar panel can significantly reduce its power output.
- In order to provide continous power throughout the day and night, electrical energy produced by solar modules must be stored in batteries. Deep cycle sealed batteries are recommended. The efficiency of a battery reduces significantly with declining temperature. Batteries can be damaged if subjected to freezing. This can be prevented by supplying good insulation, a small heat source, or by simply maintaining a high charge rate so that the battery does not regularly deep cycle.
TRENDS FOR PHOTOVOLTAICS
Ongoing research in photovoltaics promises to increase efficiency and reduce production costs. Optical engineering, nanotechnology, solid-state lighting and low cost organic materials have the greatest potential to make it happen.
Light concentration, by focusing sunlight onto small solar cell areas, can reduce the cost. Micromechanical mirrors and lens systems are the key components for light guidance and concentration on photovoltaic modules. Micro-machined mirror arrays can be used as an alternative to an external rotation mechanism to track the sun position. Nanotechnology research is moving forward to improve photovoltaic conversion of sunlight to power. Photo catalysis and chemical conversions of solar energy will contribute to cost reduction of solar power. SUNRGI declares their PV technology using an X2000 magnification converts 37% of the sunlight directly into electricity by concentrating sunlight onto PV solar cells. This system sends the heat away from the concentration area to keep PV cells cool. The low cost mass production and field installation could result in inexpensive energy production. A production of a commercial product is expected to begin by mid-2009.
Developing cheaper solar cells is at the centre of attempts to make solar electricity cost effective. Designs using inexpensive materials and low cost fabrication methodologies are being investigated at the University of Manchester. Hybrid solar cells have the potential for mass production. The cells are made up of both carbon-based polymeric organic materials and small particles of inorganic materials. Nanotechnology will play a significant role in this investigation.
The development of new thin-film solar cells has reduced the cost of manufacturing. Thin-film PV technologies use considerably less silicon and other materials, so are less expensive to produce. The cells are thin and therefore flexible in nature. The production cost is down to about $1.25 per watt, whereas wafer-based silicon PV modules cost $2.50 per watt. First Solar, a producer of thin-film PV modules, have advertised a goal to achieve 23% of the world market by 2010. New electroplating methods that involve submerging the panels in liquid are less expensive and more environmentally friendly than other methods.
Solar energy can be used to preheat outside air before it is introduced into a building by installing an unglazed air collector or transpired solar collector (solar wall). The warmed air can be distributed as is or further heated in a building’s primary heating system. A minimum of about 100 ft2 (10 feet by 10 feet) of surface area is required for this technology to make an impact. There is no maintenance required with air collection heating systems (the fan is the only moving part) and the expected lifespan is over 30 years. They are small investments with potentially big return on lowered heating and ventilation costs.
Unglazed air collectors can be combined with photovoltaic panels to create a hybrid solar system. The heat from the back of the PV modules (which is often 4 times more than the electrical energy produced by the PV module) is removed by the solar air system (which doubles as the PV racking system) and is used for building heating purposes.
Glazed solar collector or solar thermal collectors capture radiation from the sun and transfer the thermal energy to air via conduction heat transfer. This heated air is then ducted to the building.
Solar energy can be used to heat water. Active solar water heaters use pumps to circulate water or a glycol (antifreeze) solution through heat-absorbing solar thermal collectors. In a direct system, the water used by building occupants to bathe or wash their clothes is the same water that is pumped through the solar collector. In an indirect system, an antifreeze solution is pumped through the solar heat collector, which is then used to heat the water used by building occupants.