Tom’s Blue-Green World

As I pointed out in my last post, wind power grew at a rate 50 times that of solar power in 2007.  Though solar is much more in the news, it’s still in it’s infancy compared with coal, oil, and gas power generation, only contributing 110MW of power last year.

There are three approaches to scaling solar power that I think are worth attention, and will likely increase solar power generation by an order of magnitude or more in the next 10 years.

1) Solar-thermal Plants in the Desert Southwest

Solar thermal is the best way to generate hundreds of megawatts of power.  As a rule of thumb, a normal sized (ie, huge) coal fired power plant generates 300-500 MW of power.  Using solar-electric power panels on this scale is just stupid: there’s no reason to generate electricity directly with every square foot.  More economical at this scale is to generate heat, and use the heat the generate power.

BrightSource is one of many companies aiming to create huge solar thermal fields, covering tens if not hundreds of square miles of desert with solar thermal arrays.  Their approach is to have hundreds to thousands of computer-controlled panels, all pointing at a central tower, and huge amounts of steam for power generation.

BrightSource solar tower

More here:

http://www.treehugger.com/files/2008/04/brightsource-mojave-desert-solar-thermal-power-500mw.php

Stirling Energy Systems is also working in the desert southwest, but using a Stirling engine at the focal point.  Steam power, while well understood, means lots of industrial piping and heat losses, whereas with a Stirling engine electricity can be produced right next to the power source, theoretically reducing cost and increasing output.

Stirling Energy System mirrors and Stirling engine (click for high-res version)

The promise of Stirling engines has been around for years, but the huge engineering challenge has been getting them to work reliably, year after year.  With a stirling engine, the seal that wipes down the cylinder has to have a very low friction for good power output, and also can’t leak even with severe thermal expansion.  Great progress has been made in materials science the past few years, and seal technology is getting better, but problems remain.

On a down-note, this project was announced 3 years ago, but is still not in construction.  Not much is known except that there are permitting issues, but they may just be dragging their feet on permitting to cover for underlying technical problems they’re experiencing.  Who knows?

2) Municipal Power Systems

I’ve been following bay-area based Nanosolar since their first press release, which promised mile-long rolls of solar electric panels at a cost of under $1 per watt, about 1/3 of traditional silicon-based solar electric panels.  They are well past the press release stage and are in full production at this time.

What’s so compelling about Nanosolar is that they use continuous fabrication technique rather than making each solar panel one at a time like everyone else.  They have this big machine set up where blank rolls of substrate (like a roll of aluminum foil) go in one side, and then they print solar panel material onto it and vapor deposit needed materials onto the substrate, and on the other side they roll up the result.

With this one machine pictured above, they say they can make 1GW of panels per year.  In 2006, a grand total of 110 MW of solar panels were installed in the US.  I think you can see what a game changer this technology can be.

Here’s the machine in action:

Even more interestingly, they recently posted on their blog their vision for how they think their panels will be installed on a mass scale.  They’re advocating having 2-10 MW solar arrays in every city, installed using “specialized tractors”.  I’m imagining a tractor that carries hundreds of posts at a time, and installs them on a 4 feet grid as the operator just drives along.

With a low installation cost, fast installation (months rather than years), and no shortage of solar panel material, they can single-handedly increasing US solar power production and installation by an order of magnitude.

3) Leased solar arrays on warehouse rooftops

If you have at least 30,000 square feet of roof space, and need a moderate amount of power, SunEdison would like to talk to you.  SunEdison started an industry that will install and, more importantly, maintain a rooftop solar array for you.  The only catch is that you have to agree to buy the power generated at or below market rate.  Not much of a catch, is it?  SunEdison has installed at about 100 sites in California, mostly on the roofs of Kohl’s, Walmart, and Staples.  They have a map of all their installations here.

SunEdison-installed array on a Kohl's

Though I’m more fond of solar thermal over solar electric because it scales better, generating power at the point of use, at the time it is needed (the afternoon, when AC systems kick on), gives rooftop solar-electric arrays about a 60-80% boost in efficiency over solar-thermal power plants located hundreds of miles away.  This makes up for the fact that typical solar panels are fairly expensive, use rare-earth materials in their manufacture, and are more difficult to install on a rooftop-by-rooftop basis.  Also, less long-haul electric transmission capacity is a bonus, too.

As an engineer, what I also like about this approach is that since SunEdison makes more money when more power is generated, and have access to the facility after installation, it’s in their best interest to keep tweaking and improving their system to get maximum performance.  This also addresses one of the main problems with residential solar, where a contractor will install a system for a customer, but the system fails to live up to the expected performance.  By putting the installer at risk, the system is more likely to function as expected.

The longer oil stays above $100 a barrel, the more sense these leased rooftop arrays make for the accountants.  Eventually, I think zoning regulations will require rooftop arrays on warehouses, but until then, I think we’ll see more and more of these rooftop leasing agreements over the next couple of decades.