“Think global, act local”.
The global reason is climate change. If the world carries on burning fossil fuels (coal, oil and gas) the way it is now, the effects this century will be catastrophic – so bad that most people don't even want to think about it. There will be radical changes, that we cannot escape. Either we choose to make them, or worse ones will be forced on us. There is more on the climate change page.
Our local response is to use a local resource, the River Thames, to generate power right here. When we looked at this project more closely, we saw other advantages. It was an opportunity for community ownership. It has a good location, by a public footpath, with easy access. Although the amount of electricity is not large, it is a very visible advertisement for renewable energy. It will be fascinating to watch, an educational resource and a visitor attraction.
The feed in tariff
The feed in tariff is what makes it feasible, so when hydro FiTs were announced in 2010, that was a prompt to get going. At the time we were concerned that a commercial developer might get in before us. The FiTs are part of the government's response to climate change, by encouraging investment in renewable energy. Fossil fuel energy has low capital cost and high running cost; renewables have high capital cost and low running cost, so, like all new technologies, they need investment before they can compete. The FiT lasts for 20 years, to give investors confidence to make the investment. They were in effect a tax on fossil fuel energy, that is used to subsidise renewable energy. However following a campaign by the energy companies against "green taxes", government is moving to payment out of general taxation.