Hybrid solar and geothermal heating and cooling

In energy applications, a design engineer generally selects a hybrid system to obtain a process that has some benefits over a conventional uncombined system. The benefits of combined systems in fulfilling heating and cooling purposes are generally found in the form of energy efficiency. As shown in previous chapters, energy efficiency is a key factor in (environmental) sustainability and economy, the latter of which can be used as a measurement of how well individual technical solutions can compete with other alternatives. Thus, thermal solar energy systems, characterized by the capability to provide energy at a high density though with intermittent availability, and geothermal systems, having constant availability but mostly present at low temperature levels, are emerging as replacements for fossil-fuel based systems. Without a doubt, harvesting solar energy has been integrated into human activities since prehistoric times and geothermal energy usage was first reported at least a few centuries ago; however, both lost prominence in covering human energy needs with the onset of the industrial revolution. The exception has been during the last few decades as renewable energies have gained market share, a trend mostly driven by the scarcity of fossil fuels.