| When thinking about renewable electricity for your | | | | wind turbines get smaller their performance gets |
| home, two options spring to mind; photovoltaic panels | | | | disproportionately worse. This is for two mains |
| and small wind turbines. But which one should you | | | | reasons: |
| choose? The government has introduced a | | | | The first reason is that as the turbine blade length gets |
| feed-in-tariff that pays a subsidized amount for the | | | | shorter, the 'swept-area' decreases quadratically. This |
| electricity they produce and the amount paid for small | | | | means that if you decrease the length of a blade from |
| wind turbines is similar to that paid for small PV | | | | 80 meters to 40 meters, the area covered by the |
| systems (34p/kWh compared to 41p/kWh). | | | | blade decreases from 20 thousand square meters to |
| The key criteria to deciding which technology will be | | | | just 5 thousand. The 'swept-area' determines how |
| the most profitable is the cost of producing a unit of | | | | much wind energy the turbine can use. So when you |
| energy from each one. For this you need to factor in | | | | decrease the blade length you still need all the |
| the up front costs such as equipment and installation, | | | | expensive moving parts like the generator, but you get |
| and then look at how much energy they will produce | | | | disproportionally less energy - for one big wind turbine |
| once out there over an average year. Without going | | | | you would need thousands of smaller ones to cover |
| too heavily into numbers my argument is that in some | | | | the same area. The second reason is that where you |
| instances, micro-wind turbines will have a lower cost of | | | | use micro-wind turbines the wind speed is generally |
| energy than solar panels, but for the majority of cases | | | | slower. This is because most of us live in built up areas |
| solar panels will be better and this can be explained by | | | | where there are other buildings nearby. These buildings |
| some basic science. | | | | disrupt the wind, making it irregular and slow. Wind |
| Without a doubt, on a large scale, wind energy is | | | | speed is crucial to the effectiveness of a wind turbine, |
| cheaper than solar. The cost of energy from | | | | again because the energy contained in the wind is |
| large-scale wind farms is somewhere around 10p/kWh | | | | disproportional to its speed. If the wind speed drops by |
| whereas the cost of energy from large-scale solar is | | | | a factor of 2, the energy produced by a wind turbine |
| three to four times greater at present. Big wind | | | | decreases by a factor of 4. Comparing most built up |
| turbines are now very well designed products and | | | | areas, the average wind speed is much lower than |
| many years of industry development means that the | | | | half the wind speed found high-up in open spaces |
| costs have fallen dramatically and continue to do so. | | | | where you find most wind farms. |
| Big solar farms are also rapidly reducing in cost and | | | | These two factors combine to mean that for most |
| make a lot of sense in some locations, particularly in | | | | homeowners solar panels are the most sensible and |
| the many regions where wind farms are not suitable, | | | | safest option. Of course, if you live near an open |
| but for now they do not compete. | | | | space and get a lot of wind then a micro-wind turbine |
| On the small scale however, the economics are | | | | could be a great investment. However, if you do live |
| drastically different. As the size of a solar installation | | | | near a windy open space, I would suggest trying to |
| decreases, the performance falls linearly with the | | | | build as big a wind turbine as possible, as their cost |
| amount of area used, and therefore the cost of | | | | effectiveness increases dramatically with size. |
| energy does not change so dramatically. In contrast, as | | | | |