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Drainback Solar Thermal System Heat Exchangers

Like any closed-loop installation, drainback solar hot water systems use a heat exchanger to pass energy from the solar fluid to the domestic water supply. However, drainback setups include a third, specialized tank – the drainback tank – which holds all the solar fluid when the system is idle. This fluid can still be very hot when circulation stops, so it makes sense to have a means of passing that energy to the domestic supply rather than waste it.

Integral Collector Storage Solar Thermal System Layout

Integral collector storage (ICS) solar hot water systems are remarkably simple and cheap when compared to the other types. They don't use pumps, they don't need controllers, they use only one tank and they require very few extra components beyond a big water tank, some pipes and a pile of insulation materials.

Thermosiphon Solar Thermal System Basics

Probably the least popular solar hot water installation, thermosiphon systems come in two types – direct and indirect – and are passive. They use no pumps but instead rely on the fact that hot fluids rise to provide circulation.

Flooded Open-Loop Solar Thermal Systems

The simplest of the active solar hot water installation, flooded open-loop systems have water in the pipes, collector array and tank at all times. They are more complex than a passive system because they use a pump and controller, but compared to other active systems they are cheap and easy to install and maintain.

Recirculation Solar Thermal Systems

A recirculation solar hot water system is almost exactly the same as a flooded open-loop installation. However, it has one significant advantage: in times of very cold weather, it can recirculate warm water from the storage tank through the pipes and collector array to prevent freeze damage.

Recirculation Solar Thermal System Pros and Cons

These systems have the following advantages:

They are simple, cheap and easy to install compared to most active systems.
They offer more collector placement options than an ICS setup.
They provide cold weather protection, provided freezes are mild, infrequent and short.

It's also important to consider the disadvantages:

Draindown Solar Thermal Systems

Draindown solar hot water systems work as a kind of "solar add-on" to a grid-tied hot water setup. They consist of a collector array, a tank and piping which connects to the normal household plumbing, plus optional controllers, valves and gauges.

Refrigerant-Based Solar Water Heaters

It may seem a novel concept to heat your domestic water supply with a refrigerant, but it's not so odd when you really think about it. After all, the area behind the refrigerator in the kitchen is pretty warm, so surely there's a way to turn this to your advantage?

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