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An independent scientist’s observations on society, technology, energy, science and the environment. “Modern science has been a voyage into the unknown, with a lesson in humility waiting at every stop. Many passengers would rather have stayed home.” – Carl Sagan

Archive for the ‘renewables’ Category

Carbon-Free and Nuclear-Free: A Roadmap for US Energy Policy

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The Institute for Energy and Environmental Research and the Nuclear Policy Research Institute have just released the Executive Summary of Carbon-Free and Nuclear-Free: A Roadmap for U.S. Energy Policy. It is a report that will be published in October 2007 detailing recommendations on how the U.S. can meet future energy demand while eliminating carbon-intensive fossil fuels, as well as eliminating nuclear energy.

Figure 2 on page 9 of the summary details how the US electric grid will be configured by 2050 without fossil or nuclear power.
Solar PV and solar thermal are assumed to generate 40-45% of the electricity supply.

How much solar capacity would be needed to provide 40-45% of the electricity supply?

If solar is to provide 1,824,000 GWh to meet this demand – 45% of current generation capacity – the US would need 1095 GW (1,824,000 GWh / (8760 hours in a year * 19% capacity factor) = 1095 GW).

So the US would need to build more solar capacity than the total current capacity of all the generating capacity in the country just to provide less than half the electricity just at current level of demand.
Ignoring the growth in electricity demand, to build 1095 GW of solar by 2050 the U.S. would need to build roughly 26 GW of solar capacity each year… 500 MW per week.

If this is all from photovoltaic cells, and assuming you can get, say, 170 W per square meter of photovoltaics, you have to build… about 3 square kilometres of photovoltaic panels per week .

IEER claims, for comparison, that 2500 GW of nuclear capacity would need to be built worldwide by 2050 to make a difference to CO2 emissions, and they’re quick to point out that that corresponds to about one nuclear reactor per week. Of course, a nation such as the US does in fact have the capacity to build more than one reactor at a time.

If it takes, say, 150 weeks to build a nuclear power reactor, then 150 need to be built at once in order to meet this rate of construction. Sounds like quite a challenge, but no less so than building PV modules a square kilometer at a time.

Yes, we have better photovoltaic technologies in the pipepine today, that are far cheaper to build, a bit more efficient, and so forth. Sliver cells, which reduce the cost of cell materials greatly, Titanium Dioxide photoelectrochemical devices, and so forth. Whilst in some cases they offer significant increases in efficiency, they still have a low capacity factor, and they still don’t work in the dark.

Don’t get me wrong, I think solar energy is great, and I support its use, and I support research and development – and government money for same – into improving it.

But it’s important to understand what the limitations are. The most fundamental limitations to solar energy are not that that clever physics and engineering of the cells can ever get us around.

Proponents of solar cells say that the key is to do away with large, centralized generation – install solar energy on site, on every building and home.

But in reality, what’s the difference? The electricity demand is the same, except for the relatively small losses over long transmission lines. With the same cell technology, the same amount of cells are needed to meet the same electricity demand.

We often hear the ideas for large-scale pumped hydroelectric storage and so forth, but are there practical alternatives for smaller-scale energy storage systems for the homes and buildings? Electricity storage systems are the key to making large-scale solar energy workable – We’re gonna need something better than a basement full of Lead-acid cells. Hydroelectric pumped storage is all well and good, it’s proven on a large scale, but it only works with large, centralized capacity, and it only works if your country has enough spare water to support expanded Hydroelectricity. Here in Australia, for example, expanded hydroelectricity is really not an option.

Vanadium redox flow cells? Perhaps. Molten-salt thermal storage? Perhaps. Hydrogen? Perhaps.

In future, technologies will develop, and some of these technologies will continue to prove themselves on a large scale.

But today, the set of well-proven workable technologies is limited. Nuclear is one of those. Can we afford to gamble the future on the large-scale adoption of unproven technologies today? No, we can’t , but at the same time, we can’t gamble on ignoring research and development into these potentially promising energy technologies, either.

Written by Luke Weston

August 7, 2007 at 7:25 am