Let's say that you want to heat water with the sun. A traditional system would take some plastic or copper pipes, paint them black and put then in a frame. The frame would be insulated on the bottom and sides and glazed with plastic or glass on the side facing the sun. With a simple system like this, you can easily create hot water for a shower or a swimming pool. Here is an example of the simplest possible system of this type:
This simple system definitely works, but what if you want to heat water to a higher temperature, like boiling, because you would like to use it to run an air conditioning system or a home heating system? (this page shows how a solar-powered air conditioner works). The best alternative currently available is an evacuated tube solar collector, like this:
The advantages of an evacuated tube system as shown in the video include:
Why do evacuated tubes work so well? Because the vacuum works as a near-perfect insulator, like a thermos. You can see the effect that the vacuum has in this simple demonstration:
The bottle on the left is surrounded by a vacuum and can reach significantly higher temperatures.
The system shown above uses heat tubes. What is going on there? In the following video you can see how simple it is to build a heat pipe:
Here you can see how well the heat pipe works:
In the prior video, the bulb of the heat tube directly contacts water in the top header and heats that water. It is also possible to use a manifold instead, like this: