Tuesday, 31 March 2015

100 GW of renewable energy is how much?

Renewable energy capacity is growing so fast that last year 100 GW was installed worldwide [1]. That sounds really good but what does it really mean? Well, that depends on the sort of renewables and where they are. The article also says this is equivalent to the entire fleet of nuclear power stations in the US but that is certainly not true in terms of generated power. The US nuclear fleet is indeed about 100 GW capacity [2] but it generates at least twice as much as the 100 GW of renewables the UN was talking about. The chart below shows the load factors of different types of power stations and renewables in the UK in 2013.

Data from Digest UK Energy Statistics[3]

The load factor tells you how much the plant actually generated compared to its theoretical maximum. So if a plant runs at three quarters capacity half the time its overall load factor is 3/4 x 1/2 = 37.5%. A plant may not be running at full capacity for a whole variety of reasons. It could be down for maintenance, it could have run out of fuel, or it may be the power isn't wanted right then - there are other cheaper sources that are enough for the moment. For the main renewable power generators such as wind, hydro-electric power and solar PV the weather is an important factor - you can regard wind, rainfall and sunshine as fuel if you like. Generally, when that fuel is available renewables are cheap so the load factor for renewables depends mostly on the weather. The load factor for CCGT (gas turbines) and coal power stations depends a lot on the relative cost of those fuels and hence which is cheaper to run. In the years 2009 to 2013 the load factor for CCGT dropped from 64% to 28% while coal went up from 38% to 58%. Nuclear however is always cheap so its load factor depends more on maintenance issues. It has been as low as 60% and as high as 74%. In the US in 2013 the load factor for nuclear was 91%.

So, the 100GW of nuclear in the US might be equivalent to about 300 GW of wind or 900 GW of solar PV in the UK, in terms of actual power generated.

However the UN was talking about global renewables, not just in the UK. Some places are a lot sunnier and windier than others. Generally speaking, people build renewables where they are most economic to run, if they can get permission. It also depends on subsidies and the availability of finance, since renewables are very capital intensive. Worldwide, load factors for wind vary from about 40% (New Zealand) to about 16% (China) [4] and for PV vary from about 18% (SW USA) to 8% (Norway).

I do wish people would stop quoting renewables in GW and start quoting them in GWh/year. It may be a bit less pithy but it would be a lot more meaningful.


[1] UN: New renewables broke through 100GW barrier in 2014 (BBC) 31/3/23015
[2] US Nuclear Power Plants (Nuclear Energy Institute)
[3] Digest UK Energy Statistics (www.gov.uk)
[4] The Efficiency of Wind Power (Energy Matters)
[5] Estimating Global PV load factors (Energy Matters)


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