Renewable Energy Resources

Renewable resource — one that is replenished as fast as it is used, so it will not run out.

Wind — moving air turns turbine blades, which turn a generator. For: no fuel cost, no polluting gases, quick to build. Against: output depends on the wind, so it is unreliable and cannot be scheduled; many turbines are needed; some object to their appearance and noise.

Solar cells — transfer energy from sunlight directly to electricity, with no turbine. For: no fuel cost, no pollution in use, ideal for remote locations; useful on individual roofs. Against: no output at night and less on cloudy days; high initial cost; large area needed for significant output.

Hydroelectric — water held behind a dam is released, turning turbines as it falls. For: reliable, and output can be increased very quickly to meet demand; no polluting gases; long-lived. Against: flooding a valley destroys habitats and can displace people; very high construction cost; needs specific geography.

Tidal — a barrage across an estuary traps water at high tide and releases it through turbines. For: tides are entirely predictable, unlike wind or sun; large potential output; no fuel or polluting gases. Against: few suitable estuaries; high cost; damages estuary habitats and affects shipping.

Wave — the up-and-down motion of surface waves drives a generator. For: no fuel cost or polluting gases; useful for small island communities. Against: unreliable, since it depends on the weather; difficult to build equipment that survives storms; currently small outputs.

Geothermal — water is pumped down to hot rocks and returns as steam to drive a turbine. For: reliable and available day and night; very little pollution. Against: only viable where hot rocks are near the surface, such as Iceland and New Zealand.

Biofuel — plant material or waste is burned, or fermented into fuel. For: renewable if crops are replanted; roughly carbon-neutral, because growing the crop absorbs about as much carbon dioxide as burning it releases. Against: large land areas needed, competing with food production; still releases carbon dioxide at the point of burning.

The distinction that runs through every comparison question is reliability. Fossil, nuclear, hydroelectric, tidal, geothermal and biofuel can be relied on or scheduled. Wind, solar and wave cannot — which is why a real grid mixes them rather than choosing one.

Example: a windless winter evening is the hardest case for a grid. Demand peaks, solar is producing nothing and wind may be near zero, so gas or hydroelectric has to cover it. This is why storage and a varied mix matter as much as generating capacity.