In his galvanizing speech a few weeks ago Academy Award and Nobel Prize-winner Al Gore exhorted the United States to “produce all electricity from “carbon-free sources” by 2018.” This is a pretty abstract goal, in those terms – Gore (appropriately) didn’t go into great detail about how this should be done or even what it means in specific practical steps. Depending on your point of view and background knowledge about energy, the goal may seem easy or incredibly difficult, or even impossible, especially without further analysis.
So I thought it would be interesting to run some numbers on the goal. The idea is not to define how it should be done, but to look at some very simple scenarios for how it could be done to get a sense of the scale involved. The calculation is based on the Topaz Solar Farm project, which California’s PG&E utility just contracted for – a 550 megawatt solar generating station.
My initial calculations makes some gigantic simplifying assumptions, so it’s not “correct” – but it should be the right order of magnitude. For details of the calculation, see the analysis below. The conclusion is as follows:
As a very rough estimate, we would need about 800 Topaz-sized plants, total cost about $1 trillion, to meet the U.S. electricity demand. And it would require about 8,000 square miles of sunny land.
The Key Parameter
- 400 gigawatts: This is the total U.S. electrical power use (from Richard Muller’s excellent “Physics For Future Presidents” I blogged about yesterday)
Gore’s goal is equivalent to saying “We need to be able to generate on the order of 400 GW of electricity from carbon free sources.”
A few other useful or interesting numbers:
- 550 megawatts: Generating capacity of the Topaz Solar Farm, one of two new solar electric plants PG&E is building in the California desert, announced a few weeks ago
- 9.5 square miles: Size of the Topaz Solar Farm
- $1 billion: Cost of the Topaz Solar Farm
- 1 gigawatt: Generating capacity for a “large” coal-fired generating plant
- 50 GW: California’s typical peak energy demand
- 24%: portion of PG&E’s currently contracted generating capacity that is renewable
For the purposes of this analysis, I’m making a few simplifying assumptions. These make the analysis “invalid” from a technical sense, but allow us to quickly see the big picture:
- Electricity demand will stay constant: This may or may not happen – in California energy intensity (the energy used per person) is going down, and this summer absolute energy use went down. Amory Lovins of the Rocky Mountain Institute believes we can cut energy intensity by 50% via efficiency, which would definitely cut energy use. On the other hand, most scenarios dealing with energy use assume it will continue to grow.
- Disregard base load issues: The sun don’t shine at night, but people still use electricity then. This is called “base load.” You often hear that “solar can’t provide base load,” which may or may not be true in the future, depending on storage technologies that might be developed. In any case, I’m not considering it in this analysis – I’m assuming “a megawatt is a megawatt.”
- Disregard transmission issues: We’ll assume that if the energy is generated somewhere in the U.S., it can be used anywhere else it’s needed.
- Disregard technology improvements – this calculation is based on the technology planned for the Topaz Solar Farm
We now have enough data to make the most simplistic conceivable analysis. How many Topaz Solar Farm equivalents (TSFs) would we need to supply total U.S. energy demand (given the assumptions above)?
Total demand = 400 GW
TSF = 550 MW
Demand/capacity = 400 GW/550 MW = 800 (number of plants needed)
Cost = 800 * $1 billion = $1 trillion (approximately)
Conclusion: In our simplified energy world, we’d need about 800 Topaz-sized plants, total cost about $1 trillion, to meet the U.S. electricity demand. And it would require about 8,000 square miles of sunny land.
Now, there are many ways that this analysis is “wrong” – since my assumptions simplify the world quite a bit. So it could easy be off by a factor of 50% or more. But, because the assumptions also tend to cancel each other out, it’s not off by a factor of five, say. For example, I’m not considering base load (which solar PV today can’t provide effectively), but on the other hand, solar PV is the most expensive energy source. We will probably need more than 800 plants, but a lot of them will be cheaper, per megawatt, than the Topaz Solar Farm.
In future posts I will expand this model to make it less simplistic and more realistic, and to take into account technology improvements, base load requirements, the ability of energy efficiency to change the demand line, and lots of other details that are just dropped on the floor for this analysis.
I’m very interested to hear your comments on this analysis. In particular, I hope for some constructive guidance on the next steps for making it more realistic. I want a simple model that’s easy for the layperson to understand, but which doesn’t over-simplify too much (as this model does). I’d consider this a “zero-order” approximation – the next one should be a “first-order” approximation.
- The New York Times’ Dot Earth blog posted the text of Gore’s speech and allowed commenters to annotate it – interesting reading if you have a few hours to get through all the comments!