Inside a Solar Water Heating System

How does a solar water heater work step by step?

1. Sunlight strikes the collector, which has a dark absorber behind glass or inside vacuum tubes.
2. The absorber warms a fluid circulating through it.
3. When the collector is warmer than the bottom of the tank by a set margin, the controller switches on a small pump.
4. The fluid carries heat down to a coil or heat exchanger in the tank and gives it up to the potable water.
5. The cooled fluid returns to the roof and the cycle repeats until the temperature difference closes.

That is the whole principle. The rest is detail about protecting it from freezing and overheating.

Passive variants exist, where the tank sits above the collector and hot water rises by natural circulation with no pump. They suit warm climates and are rare in Canada because exposed pipes and tanks risk freezing. Canadian homes mostly use active systems with a pump and a protected loop, which let the tank sit inside the heated house where it loses very little heat.

What are the main parts?

Collector. Flat plates are glazed boxes with an absorber inside. Tubes are rows of vacuum-insulated glass. The collector comparison covers which suits cold weather.

Loop. Insulated pipes, a pump station, an expansion vessel and a way to protect against freezing. In Canada that is either antifreeze or a drainback design, explained in the drainback versus glycol guide.

Tank. A well-insulated storage tank, either a dedicated solar tank with two coils or a standard tank fed by a preheat tank. Stored heat lasts a day or two, not a season.

Controller. Two temperature sensors and a relay. It also stops the pump if the tank gets hot enough to risk scalding or damage.

What happens on cloudy days and in winter?

The backup element or burner finishes the job. A well-designed system is sized to cover a good share of hot water in the sunnier months and less in December, when days are short and the collectors may sit under snow. Cold air itself is not a barrier, since sunlight on the absorber still heats the fluid. Glazed collectors and tubes both keep working at low outdoor temperatures, though output is smaller.

For the arithmetic of what a system costs against what it saves, see the cost guide.

Sizing follows the same logic. A common starting point is a modest collector area per person, with a tank large enough to hold a day of hot water plus a reserve. Too many collectors for the household means summer overheating; too few means the backup does most of the work. The installer should show the modelled solar fraction by month so you can see how winter differs from July, and explain what assumptions about hot-water use sit behind it.

Why does overheating matter?

In summer, a collector with no hot-water demand can reach stagnation temperatures well above boiling. Designers handle that with generous tank sizing, heat dumps or, in drainback layouts, by letting the fluid drain out. A fluid that is repeatedly overheated breaks down, which is one reason the maintenance checks include testing the antifreeze.

How is this related to the Drake Landing system?

The same principle ran at community scale in Okotoks. 800 flat-plate collectors on garage roofs heated a fluid loop, and instead of a tank in every house the heat went to short-term tanks at the Energy Centre and then to a field of 144 boreholes. Houses then drew from a district loop at roughly 40 to 50 C. The how it works page follows that path, and the solar hot water page places household-scale systems in the same picture.

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