Just after we finished planting in the vegetable garden (May 2007), Kim and I decided to install a Solar Hot water system to lower our natural gas usage. This was because we had learned that heating water made up 16% of the Greenhouse Gas Emissions of the average Australian home. We knew that because of our weekly monitoring that our daily average gas usage was 55 MegaJoules (Mj). This was the non-winter average (we have gas heating), and it still seamed quite high to me. My existing hot water system (HWS) was a 6 star rated AquaMax 340 litre natural gas system, which I purchased about 18 months before hand. At the time it was more efficient than the previous HWS which used double the amount of gas. Not efficient enough, as far as I was concerned!
I was browsing through the Origin Energy website and found out that Origin advertised that they could “solarize” your existing HWS for approximately A$2100, and be fully installed by a licensed plumber. Not a bad price as I had seen other systems for over $4000.
After discussion with Kim about the pro’s and con’s, we decided to sell some shares that I had saved up and buy the system from Origin Energy. I would get a far better return on investment from a solar HWS than I would the shares. The proposed system had one large collector, a 300 litre pre-heat tank, a low wattage pump and a temperature sensor (located in the collector).
On the installation day, two plumbers arrived at 0830 in a Land Cruiser with a huge box on the roof and another in the back of the truck. After a quick inspection, they recommended that the collector be placed on a west facing roof. This was because the copper pipe run was about 8 metres shorter than where I wanted it, which was a north facing roof. The reasoning behind this was that during Winter the heat loss from the pipes would be greater than the heating value of the collector. Therefore there would be no heating effect. Also in summer the water would get so hot (99 degrees) that the safety valve on the tank would activate and then dump half the water until enough cold water entered and cooled it down. So being a wise man, I took his expert advice and let him install the collector on the west facing roof.
The plumber was three quarters complete when the electrician arrived to install the general purpose outlet. It was a simple job as there was already a 15 amp cable run that was the remains of a previous electric HWS. The cable run terminated in our fuse box and therefore only took them 20 minutes to complete. The electrician left as soon as his job was finished. Then something crazy happened. About 15 minutes later another electrician arrived to install a GPO! He was so surprised when I showed him the newly completed GPO from the previous electrician. He had just driven 80 Km from Frankston. Now that is what I call service!
Soon after the second electrician departed, the plumber announced that he was finished the job. He now showed me how it worked. The mains cold water entered the pre-heat tank. When the sensor on the collector determined that the collector was hot enough, it started the pump. The water was drawn from the bottom of the tank to the collector and returned to the middle of the tank. The pre-heated water was then fed on-demand whenever the existing gas HWS required a top up. Fairly simple really!. As the water is already heated when it enters the gas HWS it does not required to be reheated by that system.
My experience so far has been that the solar HWS is reliable. For five months of the year I have turned the thermostat of the gas HWS to zero, effectively only leaving the pilot light on. I did this so that if we had more than four cloudy days in a row, I could turn up the temperature of the water quickly to one and a half on the dial which equals about 40 degrees C.
Since the installation in July 2007, we now average 17 Mj of gas per day in the non-winter months, which is all taken up by our cooking needs. During the 3 or 4 colder months of the year we now average about 26 Mj, which is still greater than a 50% reduction in natural gas use. This we considered a great result, and the cost avoidance of gas purchase will pay for the solar HWS in approx three years. After that we technically have free hot water for 75% of the year.
You have just got to love the Sun!