Plumbing Roof-Mounted Solar Collector Arrays

You are here

When you're plumbing flat-plate collectors , you need to attach the incoming colder supply part of the solar loop to one end of the array, at the bottom. The outgoing hot part of the loop must exit at the other end of the array, at the top. Do not connect the incoming and outgoing pipes to the same end of the array or you will get a very uneven flow through the combined collectors.

The same goes for a multi-collector array – the cold supply comes in at the bottom of the collector at one end of the string of collectors and the hot exit is at the other end, at the top of the last collector in the set. Make sure you never string together more than eight collectors in a set, as this risks damage from expansion and contraction as their internal manifolds cope with significant temperature differences across the array.

Never plumb the collectors in series. The only time anyone does this is in commercial applications which need to generate an extremely hot water supply.

In most cases, you will plumb the flat-plate collectors together using their internal manifolds in parallel, connecting top to top and bottom to bottom. This gives the most even flow and, therefore, the best efficiency. There are some situations when you may need to construct an external manifold, rather than using only the internal ones. This is true of "sawtooth" layouts. The sawtooth structure is necessary for homes without a nice, flat installation area facing the right direction.

Three ways to plumb flat-plate collectors togetherImagine a house with a roof that runs from east to west: the tilted face of the roof faces south, so solar collectors can be installed without any trouble. But what if the roof runs north-south, with sloped sides facing east and west, or if it's completely flat?

Sawtooth installations

In this case, the collectors need to be arranged like a saw's teeth (hence a "sawtooth" configuration), but great care must be taken to space the collectors far enough apart. If they are too close, they will shade each other when the sun is low in the sky, especially at the winter solstice – which is, of course, the time when you need to optimize solar collection!

The table on this page shows how far apart you should space the collectors in a sawtooth array, for a variety of latitudes. Find your location's latitude along the top and the tilt angle of your collectors just below it. Then cross-reference that with the roof pitch on the left. The result is a multiplier figure.

Calculating the distance between the teeth in a sawtooth collector array installationNow take that multiplier number and multiply it by the length of your collectors. The result is the distance between the top of one collector and the top of the next. You can use the same multiplier whether you calculate in feet or meters.

Distance from top to top = (Length of collector) x (Multiplier from table)

For example, at latitude 35° with collectors tilted at 35° and a roof pitch of 6:12 (27°), the multiplier is 1.104. If we were installing a sawtooth