Upgrading both Geothermal and Solar Energy

Geothermal energy has many advantages over solar and other renewables. These advantages include: 1) weather-proof; 2) base-load power; 3) high stability and reliability with a capacity factor over 90% in many cases; 4) less land usage and less ecological effect; 5) high thermal efficiency. The total installed capacity of geothermal electricity, however, is much smaller than those of solar energy. On the other hand, solar energy, including photovoltaic (PV) and concentrated solar power (CSP), has a lot of disadvantages and problems even it has a greater installed power and other benefits. Almost all of the five advantages geothermal has are the disadvantages of solar. Furthermore, solar PV has a high pollution issue during manufacturing. There have been many reports and papers on the combination of geothermal and solar energies in recent decades. This article is mainly a review of these literatures and publications. Worldwide, there are many areas where have both high heat flow flux and surface radiation, which makes it possible to integrate geothermal and solar energies. High temperature geothermal resource is the main target of the geothermal industry. The fact is that there are many geothermal resources with a low or moderate temperature of about 150C. It is known that the efficiency of power generation from thermal energy is directly proportional to the resource temperature in general. Alternatively, solar could be used to increase the temperature of geothermal fluids significantly and then improve the efficiency of geothermal power generation significantly. Geothermal fluids could be served as the storage systems of solar energy, which may solve the problems of solar such as weather dependence and stability. It is concluded that the integration of geothermal and solar systems could upgrade the quality of both geothermal and solar energies in terms of either efficiency or power generation cost in many cases.