Solar thermal heating, solar furnaces and solar ovens

Solar thermal heating and cooking

10 KS2 KS3 Science and Technology
Solar thermal heating
The basic principle of solar thermal heating is to utilize the sun’s energy and convert it into heat which is then transferred into a home or business heating system in the form of hot water and space heating. The solar collector uses the sun's rays to heat a transfer fluid which is usually a mixture of water and glycol (antifreeze) which prevents the water from freezing. The heated water from the collectors is pumped to a heat exchanger which is inside a water tank. The heat from the exchanger will then heat the water inside the tank, which can then be used to supply your home or business' hot water needs for showers, baths, washing up etc. After the transfer fluid releases its heat, it will flow back to the collectors for reheating. 

In the UK solar thermal systems are not able to produce all of a domestic property’s hot water demand. An average UK household requires between 3000kWh-5000kWh worth of water heating annually. A solar thermal system may provide between 40% and 60% of this. During the summer, when solar radiation is high and hot water demand is lower, a system may provide all of a domestic property’s hot water, meaning that you may not have to run your boiler at all. During the winter months, however, when the hot water demand is higher and solar radiation lower, a solar thermal system will only provide around 20% of your water heating needs, meaning that you will need to use a backup heat source (such as gas or electricity).

Solar furnaces
A solar furnace captures the suns power and focuses it into a high temperature stream. The furnace is actually a collection of curved mirrors or mirrored surfaces that capture the rays and reflect them to a single point where the energy is focused. With some solar furnaces, this focused energy can reach a temperature of 4000 ºC. 

The energy or heat collected and focused by a solar furnace can be used in many different ways. It can be harnessed to create electricity, melt metals, or create fuel by turning water into steam. It can also be used to cook food. At the moment there is ongoing development work to harness energy through solar furnace technology on a large scale to serve as a renewable energy source to heat homes and provide power to homes.

A solar furnace is very reliant upon good, sunny weather. Without direct sunlight shining of the reflective surface, the furnace has no power. This is why when using a solar furnace for continuous energy it is important to have other elements, like storage that captures and contains the energy to be used later.

The Odeillo solar furnace is the world's largest solar furnace. It is situated in the south of France. It is 54 metres high and 48 metres wide, and includes 63 heliostats (moveable mirrors). It was built between 1962 and 1968, and started operating in 1970, and has a power of one megawatt (that is 1 million watts!). It serves as a science research site studying materials at very high temperatures.

Solar ovens
A solar cooker is a device which uses the energy of direct sunlight to heat, cook or pasteurise drink. Many solar cookers currently in use are relatively inexpensive, low-tech devices, although some are as powerful as traditional stoves. Because they use no fuel and cost nothing to operate, many organisations working to support developing countries are promoting their use worldwide in order to help reduce fuel costs and air pollution, and to slow down the deforestation and desertification caused by gathering firewood for cooking.

Build your own solar oven
See the following links for some solar oven design and cooking ideas! (more of a class activity, and take care with the proposed glass sheet)