Fig. 1 The sun is an inexhaustible source of energy.
Wereceive a huge amount of energy from the sun every day. Have you imagined how much sunlight falls on Hong Kong every day? The total amount of solar energy Hong Kong receives is more than 40 times the electrical energy generated by the two electric companies in Hong Kong every day! Could we use part of this energy, for example, to power our home appliances or our transportation system?
We could benefit greatly by changing a very small percentage of sunlight into electricity. The conversion of sunlight into electricity is called solar electricity. Energy exists in many different forms and can be converted from one form to another. A photovoltaic cell (solar cell) is an energy converter used to convert light energy into electrical energy. Photovoltaic cells are commonly found in wrist watches, electronic calculators and battery chargers etc. You can also find many interesting toys, e.g. toy cars, that use solar cells in the souvenir corner of the Hong Kong Space Museum.
Fig. 2 This battery charger converts light energy into electrical energy to charge up rechargeable batteries.
Most solar cells can convert around 10-20% of the light energy they receive into electrical energy. See the video below for some applications of solar cells.
Videos: Small applications of solar cells
1. Solar toy car
2. Solar battery charger
Many solar cells are grouped to form large, flat solar panels. However, building large solar panels is very expensive. Moreover, in cloudy conditions or winter seasons, the amount of sunlight is reduced, and there is no sunlight at night. So a way to store solar electricity is required in order to maintain a continuous electricity supply. In comparison, using conventional methods to generate electricity is much cheaper and the supply is not affected by the weather, seasonal changes or the time of day.
Fig. 3 A solar cell can collect solar energy and convert it to electrical energy.
Fig. 4 Building a large array of solar panels is very expensive. (Image courtesy of DOE/ NREL)