Shine, baby, shine!


Solar Thermal Electricity (STE) is a proven technology where solar heat is converted to electricity through steam and turbines. Ausra Inc. has published a white paper claiming that this technology could supply over 93 % of the electrical power for the USA (800 GW) within a square of 150 x 150 km filled with solar collectors.
Let’s see if there is any substance to this claim.

The authors assume a “Solar Multiple” (SM) of 3, and heat storage for 1-2 days. Meaning that the actual size of the collectorfarm is 3 times the minimum what is needed to run a turbine at full capacity at solar noon in mid-summer, and excess heat is stored in melted salt or another medium to level out the output over a day’s cycle. According to their modeling only during winterdays additional capacity should be needed to meet demand, the rest of the year the power plant would generate enough (ah, the lovely californian sunshine).
For an SM3 plant with storage, generating 177 MW, an area of 3.9 square km would be needed according to Ausra.

Let’s see. 

The power of the sun which reaches the surface of the earth is approx. 90 PetaW.
The surface of a sphere with a circumference of 40.000 km = approx.522 million x million m2. Half of that is in the dark, so 90 PetaW shines on 261 million x million m2 =345 W/m2 average.
3.9 square km receives therefore in solar energy 1344 MW (peak). 
Divided by 3 (SM3 design requires triplesize arrays to level the output) = 450 MW solar energy on average to be converted in 177 MW.  A 40 % efficiency ratio is required to make this calculation tick.
A bit optimistic but not far out. Interesting.
In 2007 the total electrical power generating capacity in the Netherlands was approx. 24 GW.
Using STE in the above configuration one would need give or take 25 x 25 km in a sunny location, like Spain. An investment of 80.000 million euro for power generation, storage and transmission capacity would be needed for this size of STE power plant. Payback time? The time it takes to reduce the cumulative import of oil by 1 billion barrels.
The current import of oil in NL is 0,9 billion barrels per year. Unfortunately most of it is used for other purposes than generating electricity. However, if we all would switch to electric cars (or Plug-in Hybrids), the demand for electricity would grow fast at the expense of oil imports.
An interesting concept. More to follow.

About Herman

Herman Wagter writes on Dadamotive about facts and figures behind issues that interest him. His work as interim manager and consultant has involved him directly in the impact of hyperconnectivity and sustainability on society. As an independent agent and "mobile warrior" he has experienced the pro's and con's of how organizations and projects can be structured, and what the effects on the final result can be. In his opinion we are entering an era of profound change, driven by these fundamental forces. Following the trends, discovering the fun and debunking the half-truths is a passion he likes to share with others.
Posted in: Life after cheap oil.