For the past few years there has been huge interest in Solar Electricity (photovoltaic’s, PV, or solar panels), there are lots of incentives at both a state and federal level, there are often photo opportunities for politicians, gazing towards the future over a vast array or solar panels. But there are problems with this vision: solar electricity is expensive to purchase and install; it has a long pay back period; it converts sunlight to usable energy fairly inefficiently, and because of that, you need quite a lot of roof space or land to put up enough panels to power your home.
The ugly one that I prefer is solar thermal, specifically solar hot water, a much older technology. It is also much cheaper to install, much more efficient and has a much faster payback. It can even be a do-it-yourself project if you are reasonably handy. As for the payback, that’s easy: you don’t have to pay for 70-100% of your hot water heating costs, and with a clever tweak, you can save 10-15,000 gallons of water annually, and reduce your water and electricity costs.
Let’s start with a few details, then I will tell you how I added solar hot water (SHW) with a twist, to my house. I live in Los Angeles on a hillside in the Santa Monica Mountains, about 2 miles inland from the beaches in Malibu. We heat water with propane which comes from a storage tank filled every month or so by a delivery truck, and until recently we used about 30% of our total home energy to heat water. We are an ordinary family, with 2 kids at home, and have the usual uses for hot water, washing clothes, running the dishwasher, bathing and so on.
My wife and I have become more eco-conscious over the past few years, and have taken some steps to being green. For instance we have switched all of our light bulbs to compact fluorescent bulbs (CFL’s), and we’re using tote’s rather than plastic or paper shopping bags. So I was looking for a project that would make a real difference, and would give me something to keep me busy for a while. We could afford to invest maybe $2-3,000, preferably spread over a few months. I had known about solar hot water from our travels in Greece, where pretty much every house has it installed. I got hold of a book, and spent some time reading up on Solar Water Heating by Bob Ramlow and Benjamin Nusz.
The concept seemed pretty simple, and could be added to our existing hot water set-up, effectively using the sun to pre-heat water before it went into the propane hot water tank. I used Microsoft Excel to draw up some plans, and a system schematic (see image below), and marched off to the local permit office. Here is a schematic of the eventual system, which has evolved a bit from my first permit office visit. Largely as a result of their help, and the help of a yahoo group called Solar Heat, the design evolved into something that works.
There are actually only 6 new components, plus pipe work, (which seemed daunting at first, but with patience and practice, was actually pretty simple). The main components were: (1) Solar Collector, (2) small Solar Panel to power the (3) Pump, a (4) Solar Storage Tank, a (5) Tempering Valve, and finally the twist, the (6) Hot Water Recirculation box.
Starting from the top, the solar collector is a 10ft by 4ft by 4in panel, (a Sunearth EP-40 from Solartrope) with a copper plate to absorb solar energy, and pipes inside to transfer the heat into the water. It weighs about 150lbs, so the permit office was concerned about the strength of the roof being able to hold the weight. They wanted a structural engineer to assess the strength of the roof, but someone on the Yahoo group suggested that if it was safe, I should just take a picture of me on the roof. I weigh (lots) more than 150lbs so it would prove the roof was strong enough, and took a picture of a 400lb stress test, which the permit office accepted.
Next (2) is the small Solar Panel which supplies the 12 volt, 10 watts needed to operate the circulation pump. I bought this on e-bay for about $80. While seeming really simple, this is in fact a pretty sophisticated control system. The pump only runs when there is enough solar energy to allow the panel to create electricity, and if there is enough sun to do that, there is enough sun to heat the water. Also it is the true eco-option because you don’t even have to plug the pump in to an electric power source.
The pump (3) is very small, but quite expensive. What you are paying for is for it to last 20-25 years and operate reliably for the whole of that time. Again, some web research produced the option of an El Sid pump, which I got from Solar Developments. The pump is really quiet, and the only way to tell that it is on is that the LEDs in the cover light up.
The Solar Storage Tank (4) is a completely standard electric hot water tank, except that it is not plugged in. I chose a Whirlpool Energy Star 50 gallon tank which I got from Lowes. The key is to get a tank with as much insulation around it as possible, efficiency is measured by Energy Factor (EF), and this is a good choice with an EF of 0.95 (out of 1.0) and 3 inches of insulation. This high EF will keep the water heated during the day and hot throughout the night.
We now have the basic components of the Solar Hot Water system that is capable of heating water to over 140 degrees. The system can also store the water until it is needed, water pressure will move that water into the propane water storage tank (which of course won’t light because the thermostat tells it that the water is already hot enough). There is a small problem though: water this hot represents a bit of danger. If we allow it to go through to the faucets it can burn or scold, so we need to control the heat on its way out of the propane tank.
Yes that’s right, our solar hot water system can make water that is too hot for use so we have to cool it down a bit! To do that we added a Tempering Valve (5) to the outlet pipe, this mixes cold water in with the hot until it is at the temperature you set. In our house that is 125 degrees, because my wife likes really hot baths, but would normally be 110 to 120 degrees.
That is the system in full, except for the twist, which I will talk about now.
Have you noticed that when you turn the hot faucet on in a hotel it gives you hot water straight away, and compare that with your house where you might have to wait 2 minutes and gallons of water before the hot water “comes through”, well the hotels have what is called a Hot Water Recirculation system (6), and when applied to a house it can save 10-15,000 gallons of water a year, which otherwise just runs out of the faucet while you are waiting for the hot water.
What this system does is measure the temperature in the hot pipe and when it gets cooled, it pushes that water into the cold pipe and draws more hot water from the tank. When you are paying for the water to be heated this can be expensive, but when water heating is free (or solar) then it costs nothing and saves lots of water. There is one other energy-efficient factor to this system, when the dishwasher is switched on, without re-circulation, cool water from the hot pipes is drawn into the dishwasher, and then re-heated to wash the pots and pans, so incredibly, you just paid for that water to be heated twice! With recirculation, hot water is pulled from the hot pipe into the dishwasher, where it does not have to be re-heated, and it can get used straight away. Re-circulators vary in price, with the expensive ones having better control systems and timers, I picked a RedyTemp system which seems great, but is at the top end of the cost range.
That’s it really. The system took about 3 months from initial drawings to a working system, using weekends and the odd hour here and there, if you want a professional to install a system it can be done in just a few days. I still have all of the receipts but have not added them up yet, I think they will add up to about $3,000, and I get a federal tax break for 30% of that, a professional installation would probably have cost me $6-8,000 including all of the parts.
There were times when I got things wrong and had to undo and redo them again. The scariest moments were drilling holes in the roof for the pipes to go through, but as long as I followed the old adage “measure 20 times, cut once” it would work out. I have added 3 temperature gauges to the system since it was initially finished to measure the temperature being generated by the solar panel, the temperature being transferred to the Propane water tank, and finally the temperature being delivered to the house. The hottest water to date is 180 degrees from the panel, the outside temperature was over 100 degrees that day, and the system seems to be saving about $80-100 per month so our payback should only take 3-4 years.
