In the last few months we have seen both the world’s largest solar bridge and the world’s largest solar farm open. The bridge was opened in London, a city so famous for its fog that they named a fashion label after it. The farm was built in the middle of the Californian desert.

Now, I sit and type this during the supposed beginning of a British Spring so I find it difficult to drum up any enthusiasm for the opening of a solar farm on top of a railway station in our capital city. In these cases political correctness should be abandoned and it should be stated clearly that such things are nothing but public relations ventures.

But a solar farm in the middle of the California desert, this I can be enthusiastic about. At least we have moved on from the strange situation where the world’s largest solar farm was in Bavaria. Progress of a kind.

This power plant however seems to have not been universally popular. And in this case it wasn’t only from subsidy opposing conservatives. Some environmentalists weren’t happy about its potential impact on desert wildlife. Now, I am not going to adjudicate on the environmental merits of the project. However, the people who say no to such things must ask what they are saying yes to.

Is there any evidence that the power plant that would have been built in place of Ivanpah would have been better for the environment? Are tortoises fond of fracking? We often imagine that things are bad, so we oppose them, but often we should be asking instead if something is better or worse than the alternatives. Such attitudes are rare.

Ivanpah then has been built, generating electricity, and people are now free to debate the merits of its carbon emissions reductions and the current state of Californian tortoises. But how big is the thing?

Power density of Ivanpah solar farm

Covering 14.2 square kilomtres the press release tells us that it will have a capacity of 377 megawatts, reduce carbon dioxide emissions by 13.5 million tonnes over 30 years, and power the equivalent of 140,000 homes.

However total capacity only tells us what the output is when the sun is shining at full tilt. The sun goes down in California, so what we really want to know is the average output. This is expected to be 123 MW, that is it will have a capacity factor of 33%. Power density of the power plant is therefore 8.7 watts per square metre.

California consumed 234.8 trillion watt hours (TWh) of electricity in 2012, an average output 26.8 GW. In other words Ivanpah will generate 0.46% of California’s electricity consumption.

So given California’s average electricity demand of 26.8 GW how much land would we need to provide all of California’s electricity with solar thermal if Ivanpah is a reasonable indication of future land requirements?

Total area required is approximately 3,200 square kilometres.

This is a rather approximate estimate. First, until a cheap way to store electricity is found, 100% solar remains off the cards. Second, a very high level of solar energy will require significant losses in electricity production in both storage and as a result of curtailment of excess electricity. This, and our inability to accurately predict future efficiency gains in solar conversions, means that this estimate is somewhat uncertain.

These numbers can be put into context. 3,200 square kilometres is smaller than the Los Angeles metropolitan area, and the equivalent of around 1% of California’s land.

The size of renewable energy power plants will soon start, and already are in some cases, causing problems. However is it possible that a state so famous for its tolerance of suburban sprawl would object to around 1% of its land being used for solar power plants?