As our energy needs rise, as our supplies of fossil fuels run out and as the state of our planet become more precarious, we increasingly need to look at alternative energy sources to meet our requirements and to allow our modern lifestyles. Each of the methods below has been touted both a possible solution and as an environmentally friendly one.
The sun, a huge burning ball of hydrogen, outputs vast amounts of energy every second. Even the minute fraction that falls on the Earth’s surface is more than enough to supply all our energy needs. In total 122 PW is incident on the surface, that is 122,000,000,000MW; a whopping ten thousand times more than our total energy requirements. The energy produced is clean and solar panels are low maintenance. They are ideal for remote locations where grid connection is difficult or expensive and when used locally you can even overcome the energy loss of transportation.
Sounds great, but like with everything there are problems. The highest power output can be achieved at the equator with 1020 watts per square metre. This rapidly falls off to 125W/m2 at the north of mainland USA. Our most efficient panels can covert 15% of this energy into electricity which, if connected to the grid, must be converted from DC to AC resulting in further power loss. If you factor in the cost of panels, the current shortage of refined silicon and the unreliability of the weather solar panels start to look less attractive.
Every day you can see the wind blowing, all that wasted energy just wafting away. An estimated 72TW of energy onshore it thought to be available and all you need to tap it are a few wind turbines! Currently less than 1% of the Earth’s energy needs are supplied by wind, coming in at a mere 59GW, with Denmark being the most wind friendly producing 23% of its own energy needs. The energy produced is totally clean and also one of the cheapest around; expecting to produce, on average 18 times more energy than is consumed in its construction, compared to nuclear which is estimated at around 5. People are often worried about the aesthetics of wind farms but what they often forget is the land can still be used for farming, with only 1% of the space being taken up by the wind turbines. One of the biggest concerns about wind turbines, especially with the larger 5MW models, is their affect on bats and birds. Most birds will be fine according to a study by Britain’s Royal Society for the Protection of Birds (RSPB), with the exception of birds of prey; in Norway nine out of their ten sea eagles were killed by turbines. Bats too are a serious problem, even the manufacturers of wind turbines are deeply concerned by the numbers of bats being killed. Research into this is still ongoing. Learn more about wind turbine power here.
Hydroelectric is an interesting case. As a renewable energy source it is far from in its infancy, with the first hydroelectric dam being constructed in 1870 in England. Since then it has gone from strength to strength and now provides a staggering 20% of our energy needs worldwide. The biggest complex is the La Grand system of dams in Quebec producing16GW of power. It is easy to vary output to match demand just by letting more or less water pass through and it has proved to be a long lasting technology. Some concerns over pollution have arisen, especially in hotter climates, as plant material breaking down leads to the release of methane. The World Commission on Dams stated that at least 100W/m2 of stored water was needed if it was going to produce fewer emissions than a standard plant. In North American and Canada this figure lies around 8%, so although significantly better than traditional fossil fuels it is still not the cleanest option. The flooding of riverbed drastically alters the local ecosystem both up and down stream, which has knock on effects for the local food chain. The choice as to whether to further develop hydroelectric power around the world is a fairly easy one to make; almost all the suitable sites in the world have already been developed.
All over the globe there are hotspots of underground thermal activity. Geothermal power plants tap into this natural heat source to provide power to homes. Iceland, for example, produces 170MW of energy and heats around 85% of their homes using geothermal power. The largest geothermal plant in the world is located 90 miles north of San Francisco and produces an effective 1GW of power! Most of the arguments over geothermal power are concerned with whether or not it is actually a renewable source as eventually areas will cool down, far quicker when being tapped for power. This could even be on the timescale of decades giving it a very short life span. The Icelandic government states that it should not be considered as renewable in the same way that hydroelectric is. Bearing in mind there are not as many sites for this as wind and solar (which can be used all over the world) and the high costs involved it is not the most promising of the technologies listed here.
Tidal power harnesses the energy of large volumes of water moving in and out from the coast. Tides are extremely reliable and predictable which is useful for power management. Tides occur are due to frictional forces with the moon (occurring due to gravity) and the energy dissipated by this 2500GW, enough to supply our current electrical needs, but not by that much with our current usage being estimated at 2000GW. Tidal plants are very expensive and may not see returns for years due to high build costs. The largest plant currently in operation is on the Rance River producing 240MW and was actually built in the 1960s. Scotland is hoping to have a wave power plant constructed by 2010 aiming to replace one large fossil fuel burning station.
Energy from the sun can either be used directly using solar panels, or from resulting winds, or finally from waves. Wave power has a huge potential to generate power, far greater than that of tidal and can be deployed in many more locations. Once constructed they cause no pollution. The trouble is in constructing devices that are both durable and efficient more often that not efficiency has to be sacrificed for a product that will survive long durations at sea. The first wave farm, consisting of three generators at the Pelamis Wave Energy Converter off of the coast of Portugal generates 2.25MW this is actually less than one modern wind turbine that can produce 5MW. Once again Scotland, the world leaders in terms of wave energy science, are planning on the deployment of wave devices in the near future.
All of these technologies have some problems in common. The first is the intermittency and reliability of the sources. It isn’t always windy, the sun isn’t always shining and waves aren’t always splashing. This causes the inherent problem of providing a constant power supply to users at home. On a country scale this can be solved by using spinning supplies, these would be conventional fossil fuel power stations running at low output, quickly being increased to full output to meet sudden demands. A more eco-friendly way of doing this is to use pumped hydroelectric (water is stored behind a dam until peak demand, released and then pumped back again).
A much better solution is to have a distributed system over an entire continent, when one county is producing too much it pumps its electricity over to someone else. When it’s not windy in Texas it might be blowing in New York. The other problem is that everything we do at the moment is small scale. In the same way that fossil fuels were ok when they weren’t used much, renewable sources can cause problems upon mass deployment. Enough wind farms could change air circulation in the atmosphere and therefore weather patterns. Tidal and wind will affect currents and local ecosystems, too many solar panels would prevent a lot of light falling on the earth and from is being warmed, possibly causing cooling (global dimming). Just as, at the time, we didn’t know what effects mass use of fossil fuels would have it is hard to predict exactly how the widespread use of renewable energy sources would affect the world around us; we must learn from our past mistakes and tread carefully into the future.