A Stirling dish is a solar power machine that uses mirrors to concentrate sunlight onto a small receiver. The dish has a parabolic shape, so incoming sunlight reflects toward one focal point. At that hot point, thermal energy is delivered to a Stirling engine, which converts heat into mechanical motion and then electricity.
This design matters because it can reach high temperatures and high efficiency using direct sunlight as the energy source.
The receiver heats a sealed working gas inside the Stirling engine, often hydrogen or helium. As the gas is heated and cooled in a cycle, it expands and contracts, pushing pistons that turn a generator. The dish usually tracks the Sun so the reflected rays continue to meet at the receiver throughout the day.
Because it converts concentrated heat directly into engine motion, a Stirling dish is best suited for sunny locations with strong direct solar radiation.
Key Facts
- A parabolic dish reflects parallel sunlight to one focal point.
- Solar power collected by the dish is approximately P = I A, where I is solar irradiance and A is mirror area.
- Useful electric power is Pout = η I A, where η is the overall efficiency.
- The concentration ratio is C = A_dish / A_receiver.
- A Stirling engine works by heating and cooling a sealed gas so pressure changes move a piston.
- Higher receiver temperature can improve possible engine efficiency, but real losses reduce actual output.
Vocabulary
- Parabolic dish
- A curved mirror shaped so that parallel rays of sunlight reflect toward a single focal point.
- Receiver
- The component at the focus of the dish that absorbs concentrated sunlight and becomes very hot.
- Stirling engine
- A heat engine that uses the expansion and contraction of a sealed working gas to produce mechanical motion.
- Working gas
- The gas inside a Stirling engine that is heated and cooled during the engine cycle.
- Solar tracking
- The process of rotating the dish so it stays aimed at the Sun as the Sun appears to move across the sky.
Common Mistakes to Avoid
- Confusing a Stirling dish with a photovoltaic panel is wrong because the dish first makes heat, then engine motion, and then electricity.
- Putting the receiver away from the focal point is wrong because the reflected rays will spread out and much less heat will enter the engine.
- Assuming all collected sunlight becomes electricity is wrong because reflection losses, heat losses, friction, and generator losses reduce output.
- Ignoring the need for direct sunlight is wrong because clouds and diffuse light cannot be concentrated effectively by a parabolic dish.
Practice Questions
- 1 A Stirling dish has a mirror area of 25 m² and receives solar irradiance of 900 W/m². How much solar power reaches the dish before losses?
- 2 If the dish in question 1 has an overall efficiency of 28%, what electric power output does it produce?
- 3 Explain why a Stirling dish must track the Sun more accurately than a flat photovoltaic panel.