Most people agree that carbon emissions from power stations are a significant cause of climate change; the debate now is over what to do about it. Many governments are investing in renewable sources of electricity, such as wind turbines, solar farms, hydroelectric and geothermal plants. But countries with large amounts of renewable generation, such as Denmark and Germany, face the highest energy prices in the rich world. In Britain electricity from wind farms costs twice as much as that from traditional sources; solar power is even more expensive. Compared with traditional power stations, renewable generators are cheap to run but costly to build and a further fundamental challenge is that renewable generators also impose costs on the wider electricity grid. The best sites are often far from big cities (on Scottish hillsides, French lakes or American deserts), which make them expensive to connect. Many common types of renewable generators only produce power intermittently—when the sun shines or when the wind blows. Wind turbines, for example, spin only about a third of the time. This means countries which have a lot of renewable generation must still pay to maintain traditional types of power stations ready to utilize when demand peaks. And energy from these stations also becomes more expensive because they may not need to run at full capacity.