Coyote Blog

Professor Rizzo was keen that I check out the $12,000 solar picnic table at University of Rochester

Most kids use this to hook up their laptops.   Here are a few assumptions

• 3 hours of use per day (heroic, I am pretty sure it is less than this)
• 65 watt draw from one laptop
• 160 days with sun (Rochester is apparently in the top 10 US cities for number of heavy cloud days)
• 10 cents per kw-hour

This means the table would produce 31,200 W-hr per year or 31.2 KW-hr per year.  This yields an annual electricity savings of $3.12, giving the table a payback time on its investment of 3,846 years.  If one assumes a cost of capital anywhere north of 0.026% per year, then the sun will go dark before this table pays itself off.

Bloom Energy is introducing what looks like a 200kW fuel cell that runs on natural gas for about $700,000.  That compares pretty favorably with the current cost of at least $2,000 per KW to build a coal plant, especially when one factors in reduced distribution and pollution costs.  We have gobs of natural gas and are finding more all the time, and (unlike something like hydrogen) the distribution and storage infrastructure is already in place.  Hope it works.

I often critique new energy technologies here, and that critique is often confused with a hostility to new technologies.  This is far from the case.  Living here in Phoenix, I would love to have cheap solar cells to spread over my roof like carpet.  What I am opposed to is government subsidies for technologies that are not even close to economic compared to current alternatives.   I don't know the Bloom business model  (I am suspicious they have a large rent-seeking component if KP is funding them) but if they can make these work subsidy free, that's great.

Why can't our newspaper here in Arizona apply any skepticism to alternate energy technologies?  Sure, I think this technology is cool, where large solar dishes concentrate heat on what appears to be Stirling cycle engines  (the article, true to form, does not explain the technology, but a few hints plus the name of the company "Stirling Energy Systems" seems to point to that answer).  Other concentrator technologies focus on boiling water, so this a new approach to me.

However, why can't the article actually address real issues, like "how does this technology stack up, based on cost and efficiency, vs. other solar technologies."  It says it uses less water than other concentrator technologies, but is it more or less efficient?  No answer.

We can figure a few things out.  First, as with many "renewable" energy technologies, the company selling it engages in nameplate capacity abuse.  A 1MW coal plant produces 1MW all day long.  A 1MW wind plant produces 1MW when the wind is blowing hard, and less at other times.  And a solar plant produces 1MW when the sun is at its peak.   We can address this latter because folks have calculated sun equivalent hours, the number equivalent max sun-hours per day a site gets through the year.  For the best desert sites in the US, this number is around 6.  This means that the actual capacity of this plant is not 1.5MW, as stated in the article, but about a fourth of that, or  0.375MW.

This matters for a couple of reasons.  They state their build cost as $2.8 million per MW, which seems competitive to coal plants which cost $1.0-2.0 per MW, but in fact the reference number for this solar based on an apples to apples capacity comparison is actually  $11.2 million per MW.   The solar plant gets some credit for having no fuel costs, so it might be possible still for its power to be competitive, but it appears form the limited information in the article that it is not:

Singleton would not disclose what SRP will pay for the electricity, but said the utility will pay a premium for the environmental benefits of the power, and that the price is competitive with other sustainable-energy sources such as wind and geothermal power.

In other words, it is not competitive, so much so that they will not even reveal the price, and only subsidies and government mandates make it possible for a power company to buy the power.

Let's do a reality check.  At best, they get 8 dishes per acre, and 25Kw per dish at max sun.  So this is 8 x 25 x 6/24 = 50Kw per acre.   Lets say we want to get rid of coal.  The US generating capacity of coal plants is about 336,000 MW, or 336,000,000 KW.  To replace it with this solar technology would require 6,720,000 acres (10,500 sq miles or 10% of the state of Arizona) and cost $3.76 trillion dollars if located in the best possible solar areas.   This is not cheap but is not awful.

If I am doing the math right, I get something like $70,000 per dish   (1 dish = 25Kw, $2.8 million per MW).  I would think there are a lot of rich folks with some acreage that would pay $70,000 for one of these bad boys.  It would look much cooler than solar panels on the roof.