The industry standard for solar fluid is a mix of propylene glycol and water. It's non-toxic, biodegradable and relatively stable. However, you should always mix as much water as possible with your choice of glycol product, as simple water is the ideal solar fluid.

As solar power becomes more familiar, innovations appear and new ideas are applied to existing technology to either improve output or come up with entirely new ways of harnessing the sun's renewable energy for everyday use. Solar chimneys are one of those innovations that could one day produce power on a grand scale.

Since evacuated tube collectors are, by necessity, a closed system inside their collector box, many of them use a neat technological idea called a heat pipe. Instead of simply passing the gathered heat out along a piece of metal to the manifold (and thence to the storage tank to heat your water), they use a two-stage approach.

These systems have three main advantages:

• They are simple, cheap and easy to install compared to most active systems.
• They can use a PV-powered pump for automation and further savings.
• They offer more collector placement options than an ICS setup.

It's also important to consider the disadvantages: