How Solar Power Works - the Basics

The sun has been providing heat and light to the earth since the beginning of time. Humans have been using the sun’s energy to heat homes for thousands of years but it wasn’t until the last century that we discovered how solar power works to generate electricity directly from solar radiation. In the next few decades, solar technology will progress to the point where we can cost-effectively transform our society from fossil fuels to one based on the free energy of the sun.

Solar radiation can be harnessed in two ways, to produce electricity and to produce heat.

Solar Power - Photovoltaic

Photovoltaic cells (PV cells or solar cells) convert sunlight directly into electricity. When sunlight strikes the cell, it causes electrons to flow from one side of semiconductor material, through an external circuit and then back to another side of the PV cell. This direct current (DC) can be used to charge batteries or inverted to create alternating current (AC) to run household appliances.

The efficiency of existing solar panels is around 20 ­ 30 %. The remaining solar energy (70 ­ 80%) is turned into heat rather than electricity. Since the amount of generated current is still quite low, solar panels are relatively expensive compared to other generation technology (i.e. hydro, coal, nuclear). As the efficiency of solar cells increase and manufacturing techniques improve, they will become cheaper for the average residential household and become more widely used.

Solar Heating

The warmth of the sun can be used to generate heated air that can be distributed throughout a building. The easiest application is to allow sunlight to stream threw a window where radiant heat warms the indoor air (passive heating). More sophisticated heaters use solar collectors such as walls, roofs and panels to gather the sun’s heat and transfer it to a heat-collecting fluid (i.e. water, ethylene glycol).

In an active solar heater, a machine such as a ceiling fan is used to move the warm air from the collector and to other parts of the building. More elaborate and efficient methods use fluid systems in which a pump and tubes transport the warmed liquid to radiators. For large buildings, storage tanks collect the heated fluid throughout the day for later use.

Advantages of Solar Power

• Sunlight is plentiful, clean and free. No pollution is created.

• When away from the power grid, solar power can provide cost-effective electricity for small applications.

• Although solar equipment has a large initial cost, it requires very little maintenance after installation.

Disadvantages of Solar Power

• Solar power is only generated during daylight hours and when there is no cloud cover.

• The best locations for producing solar power are arid, uninhabited locations which may not be close to where the power is needed. Transmission lines are costly to install.

• The intensity of the sun changes from season to season and the effect is more pronounced the further away from the equator. This energy fluctuation may not satisfy the local energy requirement.

• Solar power generators are expensive to build (large amount of land and expensive equipment). Even passive solar collectors (i.e. more windows) add to the construction cost of new buildings. Retrofits are expensive.

The type of solar generator and how solar power works for your application depends on location, time of year and the amount of energy required. Since the space needed for solar panels is large, energy conservation may help reduce the energy requirement to within the amount of heat and power produced.