Wednesday, September 12, 2007

Ausra, concentrating solar-thermal startup with new tech approach, raises $40M; Plans biggest plant in CA.... Cost: Solar Thermal vs PV??

Ausra, a new solar thermal startup backed by the illustrious venture firms Khosla Ventures and Kleiner Perkins, just announced the closing of a $40M+ financing round from these backers.

The company, originated in Australia and now in the Bay Area, has a novel technology approach that ideally will make parabolic trough concentrator solar thermal technology obsolete. The technology is essentially the same as traditional parabolic trough technology, with mirrors focusing incoming sunlight onto a linear pipe containing a high heat capacity fluid. The fluid is then pumped to a central boiler where the heat is used to make steam and run a steam turbine to provide electric power.

The novel part is that they have taken the "parabolic trough" part out and replaced it with compact linear fresnel reflector technology. Fresnel basically means that it achieves the same focusing onto a line as a parabolic trough, but using a flat reflector with features on it designed to mimic the focusing effect of a 3D trough reflector in 2D. See this pic for a feel.

The company claims it can deliver 10.4 cents/kWh electric power now and projects that it will be able to do 7.9 cents/kWh in three years. (Are these costs or long term contract sale prices? Somebody help me here.)

Interesting question:

Centralized solar thermal is being sold in many corners as a superior option to distributed photovoltaics, mainly in terms of cost.

However, in any given electric power market, photovoltaics, in that they deliver power on the retail side, should be given a cost "advantage" equal to the delivery (non-generation) costs of power. According to my latest NStar Electric bill, I was charged 10.8 cents/kWh for generation and 7.4 cents/kWh for delivery. So lets give PV an 8 cent/kWh advantage in discussions comparing it to solar thermal, at least in NE, for the sake of argument.

I typically hear PV levelized cost numbers of 20-50 cents/kWh, depending on the resource, interest rate, etc.

If we take Ausra at their word then, PV should be at or below 18 cents/kWh to compete with Ausra now and at or below 15 cents/kWh three years from now.

What are truly reasonable PV cost numbers these days? What are projections (given expected growth rates and learning curve behavior) 3 years, 5 years, 10 years out?

Solar thermal or PV. Weigh in!!


Eerik Hantsoo said...

I'd be interested to hear how well their system responds to diffuse radiation. Traditionally, any concentrating system misses out on all the diffuse light (i.e., cloudy or overcast conditions) that its traditional, flat-panel PV module counterparts can take advantage of. (Martin Green's first book on solar cells touches prominently on this point.) This poor diffuse response usually degrades the kWh/Wp/yr performance of concentrating systems (relative to standard flat PV), making their performance highly geography-dependent. It's unclear how much the game changes with concentrating solar thermal as compared to concentrating PV, but I imagine output still takes a hit under cloudy conditions. Regardless of how much storage you build into a thermal plant (i.e., for smoothing out dips in the plant’s output), you still need to worry about the averaged energy output per year – which is what I wonder about.

Another drawback of any tracking system is that it requires moving parts to perform reliably for years, outdoors, with minimal maintenance and within relatively tight angular tolerances. Not impossible, but definitely expensive.

Costs for their other equipment may also stack up quickly. Think of it this way: in a large installation, Ausra needs mirrors, ground mounts, tracking actuators, piping, storage tanks, pumps, a steam turbine, and a condenser. Now, for comparison, get rid of everything except the ground mounts and tracking actuators. Replace the mirrors with thin-film solar cells (which – like mirrors – are simply sheets of glass with metal layers deposited on them). Now, you’ve got a plant with (conceivably) stronger low-light performance and similar capital costs.

On the plus side, seems like they've gotten a lot of things right in keeping costs down: I like how they use flat reflectors. Also, using steam as their heat transfer fluid presumably simplifies much of the hardware design as compared to earlier solar thermal systems which used molten salts. Molten salts like sodium nitrate and potassium nitrate (see page 4 of the above pdf) are corrosive and consequently require special valves, pumps, piping, fittings, and gaskets (and often, welded-in-place connections) -- which are all expensive. The flip side: Ausra loses out on the superior thermal performance of molten salts, decreasing thermal storage capacity per unit mass of fluid.

Dave, as for your numbers: for flat-plate PV, I agree that you can log a cost advantage because rooftop PV competes with the price of grid-delivered electricity. However, you can’t give utility-scale solar thermal a cost advantage over grid electricity, because it still has to feed into the grid. In other words, you can’t very well put one of these things on your roof, and so you’re competing with costs of other power plants feeding the grid. The numbers you quote are quite compelling nonetheless – it’ll be really interesting to see how large installations perform and how the costs stack up.

christopher.smith said...

I'm organizing a conference on this exact topic. As I am in discussion with the CEO of AUSRA, Brightsource, SolarReserve,I would be happy to bring around any questions you have to them directly at the event.

We are going to have a presentation that gives the levElized cost of the different solar technologies. If anyone is interested in attending at a low rate - or free- drop me a line and I can get you a deep discount..

Find my contact info at: