Clean Energy Sources

Wind, Solar, Biomass and water are not the only sources of clean, environmentally friendly energy. Other energy sources can also provide heat, light and electricity without polluting the air or disturbing large areas of land or water. This backgrounder covers a few of these new technologies some of which are likely to become mainstream sources of energy in the approaching decades.

Geothermal Heat

People have known since ancient times that the Earth’s interior is very hot. The temperature of the Earth’s core is estimated to be between 3000 and 5000℃ (scientists are still not sure what the exact temperature is). This heat is generated by the slow breakdown of radioactive elements, and by the immense gravitational pressures acting on the rocks and minerals of the Earth’s interior. Temperatures in excess of 500℃ can be found in the Earth’s crust just a few thousand meters below the surface but geothermal heat right at the surface of the land is barely detectable.

Geothermal heat has been used to heat homes and businesses on a commercial scale since 1920’s. In most cases, communities take advantage of naturally occurring geyser, hot springs and steam vents to gather hot water and steam for heating. In some cases, the water is superheated (heated under pressure to temperatures greater than 100℃). Superheated water quickly turns to high pressure steam which can turn high speed turbines that drives electrical generators.

Ground Source Heat Pumps

The temperature of the soil below about 2 meters remains constant regardless of the weather or season. The difference between air and deep soil temperature can be used for heating and cooling in a very efficient manner, with a ground source heat pump, also called a geothermal heat pump.

A ground source heat pump works the same way your refrigerator does. Like your fridge, a heat pump uses a compressor, lengths of sealed tubing for gathering and dispersing heat (heat exchangers) and a gas called refrigerant. Heat from the surrounding soil warms the liquid refrigerant in the buried tubes, changing it to a gas. The refrigerant gas enters the compressor which squeezes it, raising its pressure and temperature. The hot refrigerant circulates through radiators inside the house, releasing the heat collected from soil to inside of the house.

This process changes the refrigerant back into liquid and the process starts again. By reversing the flow of the refrigerant, the heat pump system can cool the house in summer time.

Hydrogen Fuel Cells

One of the main problems with fossil fuels is that they release large quantities of carbon dioxide when they are burned. But what if there was a fuel you could burn that produced no carbon dioxide at all? In fact, there is such a fuel, namely hydrogen. Hydrogen is a flammable gas, which, when burned with oxygen produces harmless water vapour. Combining oxygen with hydrogen is a clean, efficient way to make huge amounts of both heat and electricity.

Instead of burning the hydrogen in the presence of oxygen, fuel cells allow the two gases to pass near each other on opposite sides of a thin membrane. The chemical interaction of oxygen and hydrogen across this membrane produces electric charges, similar to that produced by a regular alkaline battery. But unlike the battery, which goes dead after the chemicals inside it are used up, the fuel cell continues to produce electricity as long as it receives fresh supplies of air and hydrogen. The only by-product of the process is water which the fuel cell releases as steam.