Renewable energy

Electricity for light, heating and a phone has to come from somewhere. For a long time coal, oil and gas were mostly burned for it. These supplies will run low one day, however, and burning them produces the greenhouse gas carbon dioxide. Renewable energy is different: it draws from sources that renew themselves again and again and never run empty.

Power from sun and wind

On many roofs there are solar cells. They turn sunlight directly into electricity, entirely without moving parts and without exhaust gases. Wind turbines use the force of the wind: it turns the large blades, and a generator inside makes electricity from it. How hard a system is working right now is given in kilowatts, the amount of electricity produced in kilowatt hours: a device with a power of 1 kilowatt uses exactly 1 kilowatt hour in one hour. Both sources only deliver energy, however, when the sun shines or the wind blows.

Water, biomass and geothermal heat

In a hydropower plant water flows down from a great height and drives a turbine as it does so. Because rivers refill themselves constantly through the water cycle, this energy is renewable too. Biomass is something else again: wood, straw or plant remains are burned or fermented. As long as a new plant grows for every one that is used, that new plant binds about as much carbon dioxide while growing as is released again when it is burned. A fifth source is geothermal heat: deep down the rock is hot, and that heat can be used for heating and for electricity.

Advantages and limits

Renewable energy does not run out and hardly burdens the climate. Its biggest drawback is that it often fluctuates: at night no solar cell delivers electricity, and in calm weather the wind turbine stands still. That is why storage like large batteries is needed, along with a clever grid that brings electricity to where it is needed at the moment. These solutions are being worked on all over the world.