Solar energy conversion with thermal cycles - Solar Energy Sciences and Engineering Applications - page 472

its highly flammable nature. Two of the examples presented in Section 14.3 employ
helium as a working fluid, namely Eurodish and Infinia engines, while Stirling Energy
Systems “Sun catcher'' uses hydrogen.

14.6 ECONOMICS AND FUTURE PERSPECTIVES

This last chapter tries to give an indication of the economics of solar thermal plants and
compares it with commercial technologies for power production. The selected compet-
itive technologies are natural gas combined cycles (NGCC) and advanced supercritical
pulverized (ASC) coal plants: the adoption of fossil fuel-based plants occurs because
of the more certain costs and, besides renewables, they are the only kind installed.
In addition to the above-mentioned reference cases, two technologies with CO 2
capture will also be considered. Fossil fuel-based plants with CO 2 capture are the
competitive technologies of renewable for power production. This is because CO 2
is seen as one of the main issues of fossil-fuelled power plants: CO 2 concentration
in the atmosphere amplifies global warming (some believe that it is also the main
reason behind global warming) and power production accounts for 35% of world
CO 2 emissions.
The comparison will be performed using as reference parameters the cost of
electricity (COE) and the cost of CO 2 avoided.
The COE is calculated using International Energy Agency (IEA) models by setting
the net present value (NPV) of the power plant to zero (PH3/14; PH4/33). This can be
achieved by varying the plant COE until the revenues balance the cost over the whole
life time of the power plant. This methodology can be applied both to fossil fuel-based
plants and renewable ones.
The second parameter, the cost of CO 2 avoided, is defined as:

−

( COE ) inn ( COE ) ref

Cost of CO 2 avoided = (14.6.1)

( CO 2 kWh − 1 ) ref − ( CO 2 kWh − 1 ) inn

where ref is the reference technology for power production and inn is the innovative
plant which can be either renewable-based or fossil fuel-based with CO 2 capture. The
cost of CO 2 avoided represents the additional cost of electricity consumed to avoid
the emission of 1 kg of CO 2 into the atmosphere. Another interpretation of the cost
of CO 2 avoided is the value of carbon tax that makes the COE for innovative plants
equal to the reference plant.
The COE and cost of CO 2 avoided assumed for the reference cases are summarized
in Table 14.6.1 (Franco et al., 2010; Gazzani et al., 2012a, 2012b; Manzolini et al.,
2012). The calculated cost of electricity was determined assuming 7500 hrs/y, which
is typical of base load plants such as NGCC and ASC. Considering recent renewable
energy diffusion (in Europe at least), it is difficult to predict what the operating hours
of a power plant are going to be, and whether power plants with CO 2 capture will be
assimilated into green-energy sources or not.
Results show that the COE for conventional NGCC and ASC plants is similar;
moreover, the cost of CO 2 avoided for the two reference cases is also pretty close and
in the range of 50

/t CO2 . To give an idea about the current price of CO 2 emissions

a