Concentrated Solar Power Systems: Feasibility for Buildings in Rio
Concentrated solar power (CSP) systems involve solar energy being focused to a point and used to heat water or generate electricity. Sunlight is usually focused by mirrors in the form of parabolic troughs, parabolic dishes or a system of mirrors. For the context of building-installed renewable technology in Rio, parabolic dish Stirling systems and parabolic solar thermal technologies should be considered.
Concentrated Solar Energy to Electrical Energy: Dish Stirling Systems
Dish Stirling systems convert the thermal energy in solar radiation to mechanical energy and then to electrical energy. A mirrored parabolic dish concentrates solar radiation to a focal point on the heat exchanger of a Stirling engine. Heat is then converted into mechanical energy by the engine, which uses a crankshaft to drive an electrical generator. The parabolic dish tracks the sun’s path in two axes, which maximises power output throughout the day.
Dish Stirling systems operate autonomously and have a hybrid capability – the heat source could easily be a burner of some sort (possibly using a suitable biofuel). The location of the generator is typically near the focal point of the dish, so heat losses are minimal. The generating capacity of individual dishes is small – typically ranging from 5 to 50 kW. Of all solar technologies, dish/engine systems have demonstrated the highest solar-to-electric conversion efficiency (29.4%), and therefore have the potential to become one of the least expensive sources of renewable energy . Dish Stirling systems are suitable for installation on buildings, either in a standalone or array format. They require little space and can be erected and commissioned relatively quickly. As such, dish Stirling systems are technically feasible for deployment on buildings in Rio.
Parabolic Solar Trough Systems
These systems use a mirrored parabolic trough to focus solar energy onto a linear collector, usually in the form of a tube. Solar thermal energy is collected in by water passing along the tube. The hot water produced can be used for process heat, to generate electricity, to provide hot water or to drive chillers. The trough is usually aligned on a north-south axis, and rotated to track the sun as it moves across the sky. When used to generate electricity, the overall efficiency from collector to grid is about 15 % .
Both parabolic solar troughs and Stirling dish systems are relatively new to the market, there is evidence that they are beginning to compete with solar PV in terms of cost per kWh. In terms of solar irradiance, Rio de Janeiro is marginally suitable for CSP plants. It is thought that for CSP to be economically viable, direct normal irradiance (DNI) levels of greater than 2,000 kWh/m2/year are required, although there are no technical reasons why CSP plants cannot run at lower levels of irradiance . Rio has a DNI of approximately 1,900 kWh/m2/year .
While these systems might be technically possible, their deployment on buildings in Rio de Janeiro is probably not feasible. They are specialist systems that require non-standard installation & maintenance procedures. For this reason, they are probably best suited to medium/large scale power generating plants.
- IRENA, “Concentrating Solar Power,” IRENA, 2012. [Online]. Available: http://www.irena.org/DocumentDownloads/Publications/RE_Technologies_Cost_Analysis-CSP.pdf [Accessed: 16-Oct-2012].
- P. O’Shea, “Photovoltaics vs Concentrated Solar Power – Energy Harvesting,” Digi-Key. [Online]. Available: http://www.digikey.com/us/en/techzone/energy-harvesting/resources/articles/Photovoltaics-vs-Concentrated-Solar-Power.html [Accessed: 16-Oct-2012].
- “SWERA | maps.nrel.gov.” [Online]. Available: http://maps.nrel.gov/swera?visible=swera_dni_nasa_lo_res&opacity=50&extent=-179.14,18.92,-65.57,71.41 [Accessed: 28-Sep-2012].