 | Hansen to Australian PM: stop coal plants now | TOD: Australia/New Zealand | The Bullroarer - Thursday 3rd April 2008 |  |
197 comments on Concentrating On The Important Things - Solar Thermal Power
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Nice line about raining on my parade - you've brightened up my evening.
However - you seem to be conflating partly cloudy and cloudy with "no sun", which is more than a bit of stretch.
It's still possible to have 12 hours of sunlight on a "partly cloudy" day.
If you look at some of the technical discussions of the solar thermal plants, you'll find they actually have to dump energy in optimal conditions - they aren't expecting to get the absolute best possible solar exposure at all times.
When selecting appropriate locations (using detailed insolation data) they are looking for places which really do get very reliable sun - not somewhere which gets 130 days of sun per year.
16 hours of storage is more than enough except in rare cases (don't forget, plants don't always generate at peak output - and that includes traditional gas and coal fired power too - they get adjusted up and down to match demand - and there is much less demand at night, weekends and days where the weather is mild).
I think the issue of how much solar intensity decreases during winter is probably more important - which points towards locations closer to the equator - and if you do a plot of all the plants being built, you'll see that is where they are heading (as far as is practical - right on the equator is generally too cloudy).
Ausra already used real climatic data (although they arranged them randomly throughout the year) and found >90% correlation with the national load. If the plants are geographically dispersed then the problem of climatic extremes is reduced. But, it makes sense to be prepared for the worst.
Substantially more storage than 12-16 hours to deal with longer climatic irregularities is suboptimal from an economic viewpoint. If CST is to be the main supplier in the national grid, then it will make more sense to install emergence natural gas heaters (relatively cheap). A strategic natural gas reserve, and the existing natural gas networks could be used for this purpose. A month at full load would be more than enough to survive even the longest cloudy periods. In the future, biogas could be used with modest modifications on infrastructure. The quantity required is very low, just for the occasional emergence, not for regular operation, so this should be quite feasible.
Oh, and dealing with the winter load isn't that big a deal. An east-west axis orientation line focus plant, in a good location, has very consistent seasonal output. Most of the parabolic troughs built in the Mojave were north-south oriented to get a high summer bias, which is good for California, but if CST must provide a large chunk of the national generation then most plants would have to be in the east-west orientation.
Thanks for the feedback.
I agree with the natural gas / biogas backup idea - I guess that is why David Mills is only aiming for 90% of the power supply :-)
Thanks. They did say 100% would be possible if required, but that it would increase the cost a bit.
Now, I don't suggest it's a good idea to rely on solar thermal for 100% of electric needs, but in the hypothetical case that it does happen, it's better to use the backup heaters for this last bit as well, as much less energy would have to be dumped from the array and the occasional week or two of bad weather/sandstorms could be dealt with as well. And most of the existing infrastructure could be used, which is great.
With enough biogas in strategic reserve (use existing/depleted natural gas fields), this is one renewable energy scheme that is actually full proof at a plausibly reasonable cost. And that's rare.