Storage for Solar Thermal Systems

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One of the first questions you need to ask yourself when considering solar thermal systems for hot water supply is whether you will need extra storage.

At their simplest, solar thermal systems simply heat water and send it to a standard, insulated hot-water tank, from where your home takes its supply. If the tank contains enough water for your needs, you may be able to opt for what's called a "batch system".

These simple systems use the sun's energy to heat a water tank or a series of tubes (a "progressive tube solar water heater") and replenish your home's tank as you use hot water.

As you might imagine, a batch system is very cheap to buy and easy to install, since it has no moving parts, no pumps, no sensors, no need for electrical supply and is very durable. With low maintenance costs and few parts to break, the return on investment for the equipment is very good.

However, batch systems also have significant disadvantages. They are low-capacity and only work well in direct, southerly sunlight (that's true south, not magnetic). The tanks they use aren't insulated, so they lose heat quite quickly, especially at night – this makes them completely unsuitable for storage heating uses and often means homeowners need to change their water usage patterns or fall back on conventional systems. They're also heavy (so unlikely to be suitable for roof-mounting) and don't like locations that freeze frequently or for more than very brief periods.

If you're lucky enough (or flexible enough) to fit a batch system setup, you don't need to worry about extra water storage. If, like the majority of homeowners, you're not so lucky, you'll need to look at your water usage – the amount and patterns – and the options available to provide for your needs.