What is a Solar Dish-Engine System?
A Solar Dish-Engine System is an electric generator that “burns”
sunlight instead of gas or coal to produce electricity. The major parts
of a system are the solar concentrator and the power conversion unit.
Descriptions of these subsystems and how they operate are presented below.
THE DISH, which is more specifically referred to as a concentrator, is
the primary solar component of the system. It collects the solar energy
coming directly from the sun (the solar energy that causes you to cast
a shadow) and concentrates or focuses it on a small area. The resultant
solar beam has all of the power of the sunlight hitting the dish but is
concentrated in a small area so that it can be more efficiently used.
Glass mirrors reflect ~92% of the sunlight that hits them, are relatively
inexpensive, can be cleaned, and last a long time in the outdoor environment,
making them an excellent choice for the reflective surface of a solar
concentrator. The dish structure must track the sun continuously to reflect
the beam into the thermal receiver.
THE POWER CONVERSION UNIT includes the thermal receiver and the engine/generator.
The thermal receiver is the interface between the dish and the engine/generator.
It absorbs the concentrated beam of solar energy, converts it to heat,
and transfers the heat to the engine/generator. A thermal receiver can
be a bank of tubes with a cooling fluid, usually hydrogen or helium, which
is the heat transfer medium and also the working fluid for an engine.
Alternate thermal receivers are heat pipes wherein the boiling and condensing
of an intermediate fluid is used to transfer the heat to the engine.
The engine/generator system is the subsystem that takes the heat from
the thermal receiver and uses it to produce electricity. The most common
type of heat engine used in dish-engine systems is the Stirling engine.
A Stirling engine uses heat provided from an external source (like the
sun) to move pistons and make mechanical power, similar to the internal
combustion engine in your car. The mechanical work, in the form of the
rotation of the engine’s crankshaft, is used to drive a generator
and produce electrical power.
In addition to the Stirling engine, microturbines and concentrating photovoltaics
are also being evaluated as possible future power conversion unit technologies.
Microturbines are currently being manufactured for distributed generation
systems and could potentially be used in dish-engine systems. These engines,
which are similar to (but much smaller than) jet engines, would also be
used to drive an electrical generator. A photovoltaic conversion system
is not actually an engine, but a semi-conductor array, in which the sunlight
is directly converted into electricity.