Thursday, 7 July 2011
Cost of solar thermal power as a baseload supplier
Giles Parkinson reported in Climate Spectator that "last week, Gemasolar,
a 19MW solar tower plant located near Seville in southern Spain, delivered electricity
continuously over a 24-hour period to the grid." The consortium operating
the plant, Torresol
Energy, was founded in 2008 as a joint venture between SENER Grupo de Ingeniería
of Spain (owner of 60% of the company), and MASDAR, an alternative power company
based in Abu Dhabi (owner of 40%).
Torresol Energy is has three plants in Spain : the subject of this blog entry,
Gemasolar, a 19.9-MW plant with central tower receiver technology located in
Fuentes de Andalucía (Seville); and two 50-MWe plants, Valle 1 and Valle 2,
located in Cadiz, using cylindrical-parabolic collectors.
The Gemasol plant uses an array of 2650 heliostats concentrating solar radiation
on a receiver placed at the top of a 140-m high central tower. The high level
of concentration (a ratio of 1000:1 is quoted at the company web site) generates
temperatures over 500oC at the receiver and makes it possible to
use molten salt directly as the heat transfer fluid. The power is generated
by the molten salt by providing heat to a steam Rankine cycle. The steam Rankine
cycle converts only part of the solar heat to power and the remainder of the
heat is stored as the latent and sensible heat in molten salt in a large storage
tank. The storage tank is large enough to let the plant keep producing electricity
for 15 hours without sun.
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Gemasol solar field - 2650 panels spread across 185
hectares (about 460 acres or 1.85 km2)
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Molten storage tank during construction (September 2010)
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Diego Ramírez, Director of Production at Torresol Energy, explained how it
was possible to achieve 24-hour production in record time, after barely a month
of commercial operation at the plant: "Gemasolar achieved optimal performance
in its systems in the last week of June. The high performance of the installations
coincided with several days of excellent solar radiation which made it possible
for the hot-salt storage tank to reach full capacity. We're hoping that in the
next few days our supply to the network will reach an average of 20 hours a
day." The Torresol expectation is for the plant to provide 110 GWh/year in a
typical year. This corresponds to a capacity factor of 63%.
The capacity factor is respectable and justifies calling this a baseload power
generator technology. What would be the cost of this electricity?
There are slightly different figures quoted for the cost of the plant. Giles
Parkinson in his article mentions a figure of $18/W without supplying a reference.
The UK
Daily Mail reported on 3 June 2011 that the project took two years to construct
and cost £260million (A$390m) or $20/W.
If we use the average of these two numbers and assume a plant life of 30 years
and running costs as 1% of the capital investment, and using a discount rate
of 10%, the cost of Gemasol electricity comes to about 40 cents/kWh. This is
about one-third higher than the present cost of EGS-sourced electricity (27
cents/kWh -- see my blog entry on 28 June 2011 to see where this comes from).
The 40 cents/kWh Gemasol cost of electricity applies to an area of Spain where
the sun shines most of the year. Most places in Australia would have similar
conditions so this is a representative cost for future Australian solar thermal
plants using the same technology.
I copy the short MATLAB script that I used to calculate the levelised cost.
i=0.10;
n=30;
CRF=(i*(1+i)^n)/(((1+i)^n)-1);
OCC=19000;
OM=OCC*0.01;
CF=0.63;
LCOE=(OCC*CRF+OM)/(8760*CF)*100;
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% Interest Rate
% Plant life, years
% Capital Recovery Factor
% Overnight Capital Cost, $/kWe
% O&M Costs, $/kW
% Capacity Factor
% Levelised Cost of Electricity, cents/kWh
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