Wednesday, July 8, 2015

Cost of solar heating (1)

RenewEconomy has an interesting story today about a planned solar thermal installation in Oman.  The project name is Miraah, which is Arabic for mirror.  Other sources with details of the Miraah project are here (WSJ) and here (the California-based project developers, GlassPoint).

But Miraah is not for power generation, rather for process heat in the form of steam to be used for enhanced oil recovery.  In brief this involves forcing steam into an oil field so that heavy oil is easier to extract.  At present, the operator of the oil field generates necessary steam from natural gas, so the solar project will free up 5.6 trillion BTU (5.9 billion MJ) of natural gas per year for other use.  If those other uses don’t involve combustion of the natural gas or other release of CO2, then CO2 emissions of 300,000 tons per year would be abated.

The cost of the Miraah project is reported as USD 600 million for a power output of 1,021 MW thermal.  The area of the plant is 3.0 km^2 and 6,000 tons of steam will be produced per day.

The Miraah technology involves parabolic trough mirrors with one-axis tracking.  Steam will be generated directly.  The only unusual feature about the installation is that the parabolic troughs will be deployed inside 36 large glasshouses, which will be used to shelter the mirrors from harsh desert conditions.  That way, the mirrors, presumably the most expensive component of the installation, do not have to be as robust as otherwise.

What can we say about the cost of this heat collection system?  Here’s a back-of-the-envelope calculation …

Suppose the efficiency of heat collection is 65% and that peak insolation is 1 kWth/m^2.  Then the area of the mirrors is 1,021,000 kW/(1kW/m^2 * 0.65) = 1,570,769 m^2.  The cost of the project is USD 600 million, which equates to 600,000,000/1,570,769 = USD 382/m^2.

Another useful metric is the cost per GJ.  Using my normal methodology for calculating CAPEX plus OPEX (see any post entitled “cost of solar power” on this blog), I estimate USD 600 × 106 × (0.094+0.02)/ (5.9 × 106 GJ) = USD 11.6/GJ.  More expensive than natural gas, but maybe the Omani investors have a cheaper cost of capital than the 8% on which my estimate is based. 

None of the press reports that I saw mention the collection temperature, but let's say they want an operating steam pressure of 20 bar (2.0 MPa), at which pressure the boiling point is 212°C.

This project is remote (800 km from the nearest town and 160 km from the Yemen border), so construction costs would not be the cheapest on the planet.  Still, at USD 382 per square metre, the cost of the plant does seem rather high.  I’ve heard lots of enthusiastic solar thermal proponents talking about costs of around USD 100 per square metre.

I’m left pondering the question – what is world-best cost (USD per square metre) for large-scale solar heating?

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