Solar energy conversion with thermal cycles - Solar Energy Sciences and Engineering Applications - page 413

Solar energy conversion with
thermal cycles
Giampaolo Manzolini & Paolo Silva
Dipartimentio di Energia, Politecnico di Milano, Milano, Italy
14.1 INTRODUCTION
The increasing concentrations of gases such as carbon dioxide (CO 2 ) and methane
(CH 4 ) - producing the so-called “greenhouse effect'' - in the atmosphere are regarded
by many members of the scientific community as a consequence of human activities.
The use of energy represents the largest source of emissions, accounting for over
90% of anthropogenic greenhouse gases, while electricity production produces about
35% of the total CO 2 emissions (Key World Energy, 2012).
Renewable energies (i.e. hydropower, biomass, solar, wind) for electricity produc-
tion are seen as one of the best options for reducing the impact of human activities on
the environment. Electricity production from renewable energy is by definition CO 2
neutral 1 , with no resulting impacts on global CO 2 emissions and concentration.
Among renewable energies, solar energy could play a fundamental role in satisfying
energy demand in countries with high solar radiation. In particular, solar thermal
power could easily cover the commercial demand for bulk electricity in the range of
tens to hundreds of MW. Focusing on power production, photovoltaic and thermal
systems are the available technologies. Photovoltaics consist of the direct conversion of
solar radiation into electricity by means of photovoltaic effect. In solar thermal power
plants solar radiation is first converted into thermal energy through a concentrator,
then into electricity through a thermodynamic cycle, as in fossil fuel-based plants.
These kinds of plants are usually called Concentrated Solar Power plants (CSP).
Whilst photovoltaics seems to be a promising and suitable technology for dis-
tributed generation (i.e. small-size plants in the range of 1-100 kW), thermodynamic
plants might be an attractive solution for centralized large-scale electricity production
in the range of tens to hundreds of MW, with predictable low costs and relatively
low land demand. The most significant advantage of solar thermal plants over pho-
tovoltaics is the adoption of thermal energy storage (TES) which can decouple the
electricity production from the energy source. Moreover, TES increases the operating
hours of the plant, with economic benefits.
1 While solar, wind and hydro systems do not emit CO 2 during the power production process,
biomass combustion processes, the emissions from which were previously subtracted from the
atmosphere, do emit CO 2 . The overall balance depends on the non-renewable resources used.