Using solar energy

Solar energy is transformed into other energy forms for our use on Earth – energy for food (chemical energy), electrical energy and heat energy.

Food

Solar energy (sunlight) is crucial for our survival on Earth. Sunlight (visible light) falls on the leaves of plants where a process called photosynthesis takes place. The energy (red and blue light) that plants absorb from the Sun is the energy supply for the building of simple sugars that are then converted into starch for storage. The plant can then use this energy store to grow. When we eat plants, the stored chemical energy from the plant is transferred to us. This provides us with an energy store for all our life processes such as growing, moving, making sounds and breathing. All life is dependent on the Sun’s energy.

Electricity

Just as solar energy is transformed to a useful form of energy in plants and animals (through the food chain), scientists have discovered that we can also convert solar energy into electrical energy (electricity) for our needs.

There are at least 2 ways currently used for converting solar energy into electricity:

• Solar (photovoltaic) cells are used to convert solar light energy into electricity.
• Concentrating solar power (CSP) allows a large area of sunlight to hit a trough where solar collectors (lenses, mirrors and tracking systems) concentrate it into a beam that boils liquid in order to make steam, which moves turbines to make electricity.

Using solar energy for electricity is environmentally friendly. It does not produce greenhouse gases or other atmospheric emissions. The major component for this power generation is just sunlight. Using this power source means we can reduce our use of fossil fuels, which are a limited resource.

With new technology, bright sunlight is not needed to generate electricity from solar energy. Solar cells can work on gloomy days if the temperature is moderate.

Solar energy can be used to supply electricity in underdeveloped countries where there is no access to electricity but there is an abundance of sunlight (such as some African countries). Solar power generation facilities can be set up to provide electricity for a whole village.

Heating

Scientists have found that dark coloured objects become warmer than light coloured objects in the Sun. This is because dark colours absorb more light energy. The light energy from the sun causes the particles of the object to vibrate, transforming the light energy into heat energy. The heat energy is then radiated out as infrared light. The article Heat energy explains these processes in greater detail.

Dark objects heat up and cool down faster than light coloured objects because they are better at absorbing and radiating infrared light. Materials that are not good at absorbing visible light will reflect it away again. This is why these objects appear as light colours. Light coloured objects then reflect most of the light energy and therefore are cooler than darker objects.

Passive heating is when the Sun warms objects with no extra help. The Sun warms buildings through the roof, walls and windows in this way. Buildings in cooler countries are often designed to face the Sun to trap a lot of solar heat energy. Painting the walls dark colours or black make the surfaces very good at absorbing light to produce heat energy. In hot parts of the world, people paint their houses white or other lighter colours to reflect solar energy to help keep their houses cool.

Water can be heated using solar energy. This is done through solar collectors. Solar collectors trap and absorb the Sun’s energy. Generally, the solar collector has three layers. The first layer is a see-through layer that lets in the Sun’s rays. The bottom layer is painted black to absorb as much solar energy as possible (which is then radiated as heat energy). In between these layers are pipes filled with water that are warmed by the radiated heat energy. The pipes then conduct the heat energy to the water. The heated water might be used for household needs, to heat the interior of the house (through insulated piping) or for swimming pools.

Heat energy can also be collected using large arrays of mirrors as solar collectors. Some industries in the world (refining metals and firing ceramics, for example) use mirrors to focus sunlight on an oven or furnace. Temperatures from these ovens have yielded more than 3,300°C.