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Solar Hot Water Systems

The world’s first commercial solar hot water system was patented by the American: Clarence M Kemp in 1891. He called it “The Climax”. Apparently his wife was his inspiration :-). Thousands were sold and installed.

Since then, solar hot water technology has come on leaps and bounds. About 1.2 million homes in Australia use the sun to heat their water, reducing their water-heating fuel costs by about 75% on average.

Solar hot water systems come in 3  distinct types. All 3 types are available for sale and installation through, but before you start shopping, let’s go through the each type so you can decide which one is for you.

1. The Flat Plate Collector

Flat plate collectors are the most widely used way to heat hot water the world over. These collectors are “solar water  panels” about 1m x 2m large with a depth of about 10cm.

They are made of a sturdy metal frame, a glass front and a well insulated bottom and sides. Just underneath the glass is an ‘absorber plate’ which is typically made of a special material than reflects almost no light.

Connected to the absorber plate are steel or copper tubes which carry the water through the collector. As the water flows through the pipe it gets hot. Simple as that.

Here’s a cutaway picture of a flat plate collector:

<cutaway pic of collector>

And here’s one in action on a roof:

<pic of flat plate collector>

 2. The Evacuated Tube Collector

Evacuated tube collectors are funky looking things made up of a series of glass tubes. The glass is actually Pyrex. Yes – the same stuff that those expensive glass baking trays are made from. So they are not as fragile as they look (although not as tough as a flat plate).


Caption test: Example

The glass tubes are made with a copper pipe inside and a vacuum inside them. I’ll skip the physics lesson, you just need to know that a vacuum has special properties that will let sunlight heat up the copper pipe, but not let the copper pipe lose much of the heat it gains.

So if you pump water through the copper tube, it’s gonna get hot and stay hot. In fact an evacuated tube can get the water hotter than a flat plate. This can be an advantage or a disadvantage depending on your local climate. In Australia, if you live in cooler climes (e.g. Melbourne, Tassie etc.) then an Evacuated tube system can be a more efficient choice, and a distinct advantage.  If you live in hotter parts of Australia, the more expensive, and more delicate tubes are overkill, as the flat plate collectors will do just fine. Oh boy am I gonna get in trouble if any of our evacuated tube vendors read that! But hey, my Mum told be to always tell the truth. And we sell both types, so I just want you to make an informed decision!

3. Solar Heat Pumps

Many people don’t class the humble heat pump as a solar hot water system. They class it as a very efficient electric hot water system. Which it kinda is. But the electricity is used to pull the heat out of the air and into the water. And the heat in the air comes from the sun. So I’m making the call that it’s a solar hot water system. Hope you don’t mind!

A heat pump solar hot water system is simply a reverse cycle air conditioner in heating mode, connected to a water storage tank in such a way that the heat generated goes into the water.

<pic of heat pump>

They are the cheapest type of solar hot water system because they are not installed up on a roof, saving install costs, and they don’t need an instant hot water booster, saving hardware costs.

They are typically 5 times more efficient than a conventional “large kettle” style hot water system. If you don’t have gas to your home, or have no suitable roof space for a solar hot water collector/panel, they are worth considering.

The downsides are that they share the same problems as any air conditioner. That is: they do make a noise, and they need to be regularly serviced if you want them to last.




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