Two large solar plants were approved Tuesday for construction on federal lands.  Department of Interior (DOI) post.  See analysis of the proposed plants below the position statements.

Position Statements:
1. Solar thermal is more cost effective than PV solar.
2. Construction per kW is extremely high while operating expenses are low for solar installation relative to other sources of energy generation.
3. Capacity factor for solar is 18-25% and therefore is useful for peak power only.  Given the high cost of construction it is not a generation source which can offset current baseline power generation methods (Coal, Hydro, Nuclear).  It can offset peaking power provided by gas turbine and diesel generation. If it is to be used for sustainable power than it must be supplemented with other generation sources to cover the low capacity factor.
4. Do projects like these make business or financial sense?  If the goal is to have renewable generation at any expense than yes.  If the goal is to reduce dependence on CO2 emitting baseline power generation (Coal, gas turbine, diesel, natural gas) than I submit there are more efficient and cost effective ways.
5. The large footprint of solar and wind generation requires remote siting and challenges with energy transmission.
6. A carbon tax and solar efficiency gains coupled with a transmission network will be required to make solar cost competitive.

Proposed Projects
The projects approved will employ two different types of solar energy technology. The Imperial Valley Solar Project, proposed by Tessera Solar of Texas, will use Stirling Energy System's SunCatcher technology on 6,360 acres of public lands in Imperial County, California. The plant is expected to produce up to 709 megawatts from 28,360 solar dishes, enough to power 212,700 – 531,750 homes (my note: 20% of the time). Estimated cost $2.1 Billion. The initial installation will include 300MW. The rest would require a new line, like San Diego Gas & Electric’s 123-mile proposed Sunrise Powerlink, which has been approved but faces challenges in federal and state courts.

The Chevron Lucerne Valley Solar Project, proposed by Chevron Energy Solutions of California, will employ photo-voltaic solar technology on 422 acres of public lands in San Bernardino County, California, and will produce up to 45 megawatts from 40,500 solar panels, enough to power 13,500 – 33,750 homes (my note: 20% of the time).

Let's break down the various technologies that will be used:

Tessera Solar and the Stirling Energy System SunCatcher
The SunCatcher is a 25 kWe solar dish that automatically tracks the sun.  It collects and focuses solar energy on a power conversion unit which is a closed loop high efficiency four cylinder reciprocating solar Stirling engine.  Closed loop in that it uses an internal working fluid that is recycled through the engine.  The solar energy heats and pressurizes the fluid and turns the Stirling engine. 

A generator is connected to the Solar Stirling Engine; this generator produces the grid-quality electrical output of the SunCatcher. Waste heat from the engine is transferred to the ambient air via a radiator system similar to those used in automobiles. The gas is cooled by a radiator system and is continually recycled within the engine during the power cycle. The conversion process does not consume water, as is required by most thermal-powered generating systems. Data and picture Source.



Cost:
7.09x10^5kw at $2.1B is $2961 per kW which is equivalent to the 2008 estimated cost of building a nuclear power plant (Mid 2008 vendor figures for overnight costs (excluding owner's costs)) .  Factor in the low capacity factor and you have an expensive generation source!!  Not to mention the lack of transmission lines for 409 of the 709MW.


Other Cost Comparisons (source):

-Nuclear overnight capital costs in OECD ranged from US$ 1556/kW for APR-1400 in South Korea through $3009 for ABWR in Japan, $3382/kW for Gen III+ in USA, $3860 for EPR at Flamanville in France to $5863/kW for EPR in Switzerland, with world median $4100/kW.  In China overnight costs were $1748/kW for CPR-1000 and $2302/kW for AP1000, and in Russia $2933/kW for VVER-1150. EPRI (USA) gave $2970/kW for APWR or ABWR, Eurelectric gave $4724/kW for EPR.

-OECD black coal plants were costed at $807-2719/kW, those with carbon capture and compression (tabulated as CCS, but the cost not including storage) at $3223-5811/kW, brown coal $1802-3485,

-Gas plants $635-1747/kW and onshore wind capacity $1821-3716/kW. (Overnight costs were defined here as EPC, owner's costs and contingency, but excluding interest during construction.)

Photo-voltaic Solar Technology
Systems larger than 750 kilowatts averaged $6.80 per watt in 2007 according to this source.
Giving us an estimated project cost of  $306M or $6800/ kW for the proposed 45MW plant. No cost estimate was found for this specific project.  Other sources show $4/Wp which does not include all of the infrastructure costs.  That would lower the estimate to $4000/kW.  Now this may not truly reflect economy of scale for major PV installation.  Still the number is high relative to other forms of energy.

Analysis of Efficiency  Factors
Capacity Factor    (2008 data source)
Coal 72%
Nuclear 91%
Nat Gas 41%
Wind 33-40%
Solar 18-20%  Tessera Solar claims 25%

-In 2008 solar generated 864 GWhrs with a total capacity of .539 GW 1 yr = 8,765.81277hrs for a total of 4725 GWhrs giving a total CF of 18% (source).  Seems low but 18% is substantiated here.
-Quote from Carnegie Mellon paper "While wind’s capacity factor varies from 32% at the sites examined to 40% at excellent sites, the capacity factor for a 4.6 MW PV array in Arizona is determined to be 19% over two years."


Operating Expenses
Nuclear 21.16
Fossil Steam 35.67
Hydro 9.67
Gas turbine and small scale 69.93 (seems high-this data includes fuel burners such as gas turbine, internal combustion, PV and wind)
Values in mills per kW (1 mill = 1/10 of one cent)