Solar stirling engine is a mechanical device working on the stirling principle. It is one of the devices which produces energy from renewable resources. Robert Stirling was the Scottish inventor of the closed cycle air engine, stirling engine in the year 1816.
How are solar stirling plants different from solar panels?
Solar stirling plant consists of paraboloid(3D shape of parabola) , with a sterling engine at the focal point of the parabolic dish. The parabolic dish consists of curved mirrors. The parabolic mirror concentrates the solar rays striking the surface at the hot-end of the stirling engine. The stirling engine converts the solar energy to electrical energy.
Solar panels consist of solar cells. Solar cells use the energy of the incident photons to eject the electrons from the semiconductor surface in a process called photoelectric effect to produce energy.
The solar energy gets converted to electrical energy in the following path.
Solar Energy–>Heat Energy–>Thermal Energy–>Electrical Energy
The stirling engine consists of a piston with two closed ends filled with air/gas with one end hot and other end cold. When heated to high temperature the air/gas on one side of the engine raise in temperature & expansion of air and hence temperature difference of the gases on the ends of the piston. This temperature difference leads to pressure difference. The piston moves to nullify the pressure difference. On cooling the gas on an colder end the piston returns back to the position it stayed previously. The piston is connected to shaft. This cyclic process of the piston leads to mechanical work, leading to electrical energy production.
Stirling engine is a reversible engine, meaning that the engine reverts back to the original state without loss of energy.
The solar sterling plant has an efficiency of 31%. Infinia, a concentrating solar thermal power company has developed state of the art solar Stirling generators with outputs ranging from tens of watts to multiple kilowatts and parabolic dishes with a efficiency of 32%.
- The solar sterling plant on comparison with the conventional solar panels are more efficient. The efficiency is about 31%, whereas solar panels have efficiency of 20%.
- DIY Stirling plants are cheaper to make (around 100$)than the DIY solar panels.
- The stirling plants occupy low area space for the energy production compared to the photovoltaic panels.
- The plant operates silently.
- Stirling plants requires less maintenance.
- Stirling plants cannot produce electricity on cloudy days. Stirling engines are not capable of harnessing diffused sun rays(reflected from clouds). Only direct rays from sun can be converted efficiently.
- The parabolic dish converge the solar rays leading to high temperature on the stirling engine. The mirrors may not always converge the rays at the focus. Any exposure to the converged rays can lead to skin burns.
- Ready-made stirling kits are very expensive, hence are not popular among household.
- The engine needs a warm-up time.
- These plants need tracking system to keep track of the sun to produce electricity. When out of focus, these plants have very low efficiency.
- While installing DIY stirling plants for home, precautions need to be taken.