February 6, 2009

Is wind/solar intermittency a fatal problem?


There are many solutions to wind & solar intermittency, each of which is very expensive if taken to an extreme, including pumped storage, CAES, or a planet girdling HVDC system. If you combine the best of each, you're likely to get a much lower cost system.

More importantly, Demand Side Management is very, very cheap, and extremely effective. It's overlooked because it's not "incented" by utility rate regulation.

220M plug-in's and EV's could provide all of the demand buffering that wind could every want. Add V2G (see here for a UK-oriented discussion), which is a bit more expensive but very practical, and you get all of the capacity you need for handling system variance on an hourly or daily basis.

All you'd need is to retain large fossil fuel plants for the 5-10% of the time when wind was calm for a week or more.

The obstacles to a renewable grid aren't technical, they're social: up to 20% of the workforce would be made obsolete. They have an enormous incentive to fight change.

Do you have references for this?

Here's a discussion by Amory Lovins's RMI: http://www.rmi.org/images/PDFs/Transportation/RMIPHEV_decouple_AESP.pdf.

On the other hand, it's very easy to analyze - no experts or peer-reviewed papers are needed.

Take 220M vehicles, with 25KWH effective capacity battery (3x that of the Volt), for a total of 5.5 Terawatt hours. Charging them using 220 volt, 30 amp connections will take about 4 hours, but create peak demand of more than the grid's current capacity, so vehicle charging would be spread out over several days, giving lots of leeway for dynamic scheduling.

If you want, say, 50% of KWH from wind then you need an average of 225 gigawatts from wind. At 30% capacity factor, that's about 750GW of nameplate capacity. An individual wind turbine can hit 100% of capacity, but a windfarm rarely goes above 85%, and a nationwide network would very rarely go above 50%, just based on the laws of large numbers (variance rises more slowly than the mean), and the fact that many windfarms would be negatively correlated to each other (one part of the country is windy, and another is calm).

That means peak wind generation might be 375GW. Night time demand might be 200GW, so we need to soak up 175GW. Our 5.5Twhr plug-in/EV fleet could draw that for 10 hours, using less than 1/3 of it's capacity.

Similar calculations apply for V2G.

Solar appears to have more short-term intermittency, which suggests that PHEV/EV buffering, with it's very fast response time, would be especially valuable for solar.

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