Solar Energy Pt 3

In part 1, I talked about the basic of solar power.

In part 2, I went into detail about thin-film technologies that stand to dramatically bring the price down.

In this part, I’ll talk about Solar Thermal, focusing in on Concentrated Solar Power, or CSP. This is using the heat energy from the sun to generate power.

Before I begin, some housekeeping. I found an article on west Texas wind power interesting because of the information provided as well as the graph that shows how much power is consumed and how it was generated (coal, natural gas, etc). Just about all the power generated for peak demand (between baseload at 35GW to 61GW at peak demand) as well as an additional 15GW 24/7 is all natural gas. Now regardless of which solar mechanism you use (PV, thermal, etc), that is a lot of natural gas and the resultant pollutants that would be removed if solar gets enough traction to replace a large part of the peak demand.

Likewise, oil tycoon T. Boone Pickens is even supporting west Texas wind power. Wind could help abate the usage of natural gas he says, to be used in vehicles as a replacement for gasoline. While I’m not necessarily in favor of that aspect of his plan, it might be a preferable alternative to high gas prices, and made useful in range-extended electric vehicles (REEV – first x miles on electricity, further range on some other fuel).

Also, Ars Technica tries to calm everyone down about supposed shortages of Indium and Gallium (two key components to the production of CIGS thin film solar cells).

On to the issue of solar thermal energy. I’ll start with a very basic way to use heat to reduce the use of power (either electric or natural gas) – rooftop water heaters. By circulating water with a small 1HP pump up to your home’s roof in a black painted tube or bladder, it will heat up. This is a good way to provide for hot water during the day for either your house or your swimming pool (which is common in Las Vegas).

I’ve even seen alternate implementations of this tactic. Back a few years ago on a camping trip in the Utah high desert, folks on the campsite next to us had black bags full of water they left in the sun while they went on a hike. When they came back the water was hot and ready for them to mix with some colder water to take a shower.

OK, so onto solar thermal power generation. There are several types – parabolic trough and power tower are the two most common. After that, there is dish stirling (using a stirling engine as the focal point for an array of mirrors), Fresnel concentrators and reflectors and a recent invention from MIT that can flash boil water for any number of applications.

Lets go over each type, along with an example.

Parabolic trough is where you have mirrors around a tube containing a heat transfer liquid to focus sunlight on the liquid to heat it. There are several of these types of power stations online, including the 64MW Nevada Solar One. I thought I had heard rumors about troubles, but after some googling, I found this PDF that showed some of their production from June 2007, and it was peaking between 55 and 60MW from 10AM until about 4PM, and from there it trailed off until just before 7:30PM. One of the interesting items also noted in that PDF was the future goal of developing and commercializing thermal storage. Doing this, the plant can siphon off power early in the day when the peak demand hasn’t materialized, and then use that energy at the peak (and sell it for more $) as well as after the sun sets until about midnight the peak finally subsides. The trick is to see if they can figure out

Next is power tower – these designs use an array of mirrors on two-axis trackers on the ground, which reflect the sun’s rays onto a tower holding either water or other heat transfer material to ultimately generate power. There is a lot of momentum behind power tower designs – PG&E in California has agreed to buy power from up to 500MW of power tower plants in CA built by BrightSource Energy. There is an optional expansion of 400MW, with the first 100MW scheduled to go online around 2011.

Next is an interesting technology called Linear Fresnel Reflector, or Fresnel Reflectors. This is where the mirrors, either slightly curved or flat, are mounted just above the ground and then rotate along one axis to heat an elevated conveyance filled with water or some other heat transfer fluid. A company called Ausra has just opened a 700MW/yr Linear Fresnel Reflector manufacturing plant in Las Vegas. The manufacturing plant may only employ 50 people, but the resulting construction jobs, as well as the permanent Operations and Maintenance (O&M) jobs for that 700MW/yr will have a large impact.

Dish/Stirling systems are quite unique. A Stirling engine is an engine that generates energy through concentrated heat. Basically, the heat is focused on an area that contains a gas, and when its heated, it expands. That pushes a piston and generates the movement. After the gas has expanded, its allowed to cool through transfer to another piston, and from there it starts all over again. So the application of this is to use of a dish to focus tremendous amounts of energy into the Stirling engine and generate energy that way. Currently, Stirling Energy Systems should be building an array in Southern California called Solar One (not to be confused with the now-shuttered power tower-based Solar One that is also in Southern California), which is expected to eventually grow to 500MW over 4 years, and possibly 850MW. Power production was supposed to start in 2009, however no announcements have been made as to the progress of a 1MW test array or BLM environmental approval. They also were supposed to build a 300MW as well, but no announcements have been made for that either.

Finally, the MIT project is interesting, they purport that the unit cost per dish is very cheap yet it provides steam for whatever purposes – either steam for a building or turning a turbine for electricity generation. Though for the purposes of electricity generation, you’d have to set the dishes up in parallel, which would require more hardware and that can raise the per unit costs dramatically. The students involved have formed a company and are working to productize the dish.

And thats it for solar thermal.

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