If you're planning a solar thermal installation for a large building or a communal property such as apartments, you may need to consider a very large water storage tank. This is also true if your project is solar space heating – both of these installations require outsized tanks. Think big: we're talking between 300 and 500 gallons, here.

Most large tanks are made of steel, stainless steel or fiberglass. Occasionally, a solar space heating installation will use a concrete tank, though it's not common.

With such huge containers, it's obviously tempting to construct them on-site and line them with plastic or rubber. This has been tried many times over the years but, unfortunately, it just doesn't work: the linings can't withstand the constant high temperatures and become brittle. This leads to cracking and leaks.

Consequently, you're going to have to choose between shipping one very large tank or buying several smaller ones that you plumb together. A single, large tank is always preferable: it's more efficient and, ignoring installation problems such as getting it through doorways and so on, easier to work with.

If you're building from scratch, it's definitely worth getting a pre-built tank and setting it up before there are doorways to worry about but, if you're retrofitting, you'll need to figure out how to get a large, bulky piece of equipment into place. Thankfully, some manufacturers offer a solution: they produce large tanks that come as a kit and are either cold-welded (using epoxy) or bolted together on-site.

These kits are usually fiberglass models and work very well, though you need to check that the fiberglass is heat resistant to constant operating temperatures of at least 180°F (82°C).