Energy from Sun, Solar energy stirling motor and sunpower

There has been some fuss lately over the first Stirling technology based solar thermal plant in Arizona by the Arizona based producer Stirling Energy Systems and this at the same time as Solar thermal is housed as one of the main technologies for future green electrity production.

There are many other interesting solar thermal technologies out there and the obvious question is then if this technology is any better compared to the others. To answer this we need to find out how it works.

The Sterling engine principle

The Sterling engine has the benefit of using any type of thermal heat source as energy source for generating torque. The engine uses a closed gas container that uses the temperature difference between its hot end and cold end to establish a cycle of a fixed mass of gas, heated and expanded, and cooled and compressed, thus converting thermal energy into mechanical energy. On the hot side the internal gas expands with increased pressure and on the cold side the pressure drops below atmosphere pressure driving the engine piston.

Principle of the Sterling solar thermal dish

The operating principle is made up of a few steps:

1. A two dimensional servo aligns a solar reflector toward the sun.

2. The reflector focuses the sunlight toward a receiver

3. The receiver transfers the heat via a heat exchanger to the sterling engine

4. The Stirling engine drives a generator which produces the electricity

5. An inverter converts direct current from the generator into alternating current that fits the electrical grid of your home.

Sterling technology efficiency

The image above from Stirling energy Systems show that the energy per unit area is quite a lot higher than for example photovoltaics and parabolic trough technologies. I have not found the exact cost of these to calculate cost per kWh compared to CSP solutions but the company seem to focus on the scalability benefits instead of comparing energy costs. Also the benefit of the plant always producing energy even if one unit is broken is being promoted.

Technology potential:
It must be cheaper with a central receiver with large mirrors and the buffering capability for constant electricity production even during night time is lost with this technology however this is a nice complementary technology that will find its place in the green future and it seems like a very good solution for medium size power plants.

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