What is the purpose of the glass cover on a flat plate collector?

The glass lets short-wave sunlight in but blocks much of the long-wave infrared the hot plate emits. The cover also stops wind carrying heat away from the absorber.

Why are the back and sides of a flat plate collector insulated?

Insulation reduces heat conduction from the absorber and pipes to the roof and outside air. More of the absorbed energy then reaches the fluid.

Why is antifreeze added to the fluid in most UK solar thermal systems?

A water and glycol mixture will not freeze on winter nights, when collector temperatures can fall below 0°C. Frozen water would expand and could burst the pipes.

Explain how heat collected on the roof reaches the hot water cylinder in a pumped system.

A pump circulates the heated fluid from the collector to a coil inside the cylinder. Heat passes through the coil wall into the stored water, and the cooled fluid returns to the roof.

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Energy From the Sun

Flat plate and evacuated tube collectors

3 things to know
AS 1

Overview

The absorber, selective coating, glazing and insulation of a flat plate collector, antifreeze and pumped circuits, the differential controller, evacuated tubes and heat pipes, a comparison of the two, and thermosiphon heaters.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

How does a heat pipe transfer energy in an evacuated tube collector?

Key term

Describe the structure of a flat plate solar thermal collector.

Key term

Why is the absorber plate given a dark selective coating?

Questions from this subtopic

Each one with the model answer underneath.

1
Describe the structure of a flat plate solar thermal collector.
Model answer
A flat plate collector is an insulated box with a glass cover over a dark metal absorber plate. Copper pipes bonded to the plate carry a heat-transfer fluid.
2
Why is the absorber plate given a dark selective coating?
Model answer
A selective coating absorbs most incoming sunlight but emits little infrared radiation. The plate therefore gets hot and loses less heat by radiation.
3
What is the purpose of the glass cover on a flat plate collector?
Model answer
The glass lets short-wave sunlight in but blocks much of the long-wave infrared the hot plate emits. The cover also stops wind carrying heat away from the absorber.
4
Why are the back and sides of a flat plate collector insulated?
Model answer
Insulation reduces heat conduction from the absorber and pipes to the roof and outside air. More of the absorbed energy then reaches the fluid.
5
Why is antifreeze added to the fluid in most UK solar thermal systems?
Model answer
A water and glycol mixture will not freeze on winter nights, when collector temperatures can fall below 0°C. Frozen water would expand and could burst the pipes.
6
Explain how heat collected on the roof reaches the hot water cylinder in a pumped system.
Model answer
A pump circulates the heated fluid from the collector to a coil inside the cylinder. Heat passes through the coil wall into the stored water, and the cooled fluid returns to the roof.

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