Green Design Solar Water Heater

Published on July 9th, 2008 | by Low Impact Living

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Low Impact Living: My Solar Hot Water Experience

Editor’s note: this piece has been contributed by guest blogger Kevin Hughes. Kevin was generous enough to share his own experience with installing a solar hot water system on his home. Thank you, Kevin!

I live in Los Angeles and I prefer the ugly one! Please don’t get me wrong, my wife is very beautiful, but when it comes to solar power, I prefer the ugly one.

Let me explain, 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 pay back. 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.

solar plan chart

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.

In case you’re not as handy as Kevin, you can find a solar installer near you here.

To learn more about tax rebates and other incentives for solar power, click here.




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  • http://www.grumpyoldman.be Eddy De Clercq

    Hi,

    Once a sun boiler installed, I recommend to install a thermostatic water mixing systems like mentioned in this blog which enables you to provide warm water to you washing machine in order to save energy.

    Eddy

  • http://www.grumpyoldman.be Eddy De Clercq

    Hi,

    Once a sun boiler installed, I recommend to install a thermostatic water mixing systems like mentioned in this blog which enables you to provide warm water to you washing machine in order to save energy.

    Eddy

  • Scott

    Why not switch the old water heater out for the other and have the solar heated water go straight into the water heater? Since it doesn’t have to be heated all the time thus letting the water stay hotter longer in the new tank and not having the heat escape from the other older less insulated one.

  • Scott

    Why not switch the old water heater out for the other and have the solar heated water go straight into the water heater? Since it doesn’t have to be heated all the time thus letting the water stay hotter longer in the new tank and not having the heat escape from the other older less insulated one.

  • Aaron

    Thanks for a clear, informative article. You make it sound so easy, I now plan to put a solar hot water system in when I buy a house next year.

  • Aaron

    Thanks for a clear, informative article. You make it sound so easy, I now plan to put a solar hot water system in when I buy a house next year.

  • http://YouthBusiness.us Cynthia

    WONDERFUL article! I’ve printed it off and will be placing it in front of my husband along with his coffee cup this morning. We have solar panels on our travel trailer and love them, but it is time to start thinking seriously about our home.

    It’s not just the initial cost factor that’s important. To me, the cost will be inconsequential when power (electric or gas) is either rationed or not available at all. Think about it.

    By the way, my granddaughter is a Youth Entrepreneur who is doing her part for the environment, as well as helping people prevent spoilage of their increasingly costly groceries. You can check out her website at YouthBusiness.us You’ll be glad you did.

    Thanks again for the very practical and informative article. You have spurred me to action – to get my husband to act!

  • http://YouthBusiness.us Cynthia

    WONDERFUL article! I’ve printed it off and will be placing it in front of my husband along with his coffee cup this morning. We have solar panels on our travel trailer and love them, but it is time to start thinking seriously about our home.

    It’s not just the initial cost factor that’s important. To me, the cost will be inconsequential when power (electric or gas) is either rationed or not available at all. Think about it.

    By the way, my granddaughter is a Youth Entrepreneur who is doing her part for the environment, as well as helping people prevent spoilage of their increasingly costly groceries. You can check out her website at YouthBusiness.us You’ll be glad you did.

    Thanks again for the very practical and informative article. You have spurred me to action – to get my husband to act!

  • http://thaihaus.info/hausbau Martin in Thailand

    It’s not possible for me to see on the pictures if you use heat exchangers or not. Since also your excellent description does not mention it, let me add that important aspect.

    The hot water in the solar panels, and the hot water in the heat storage tank, and the hot water in the hot water recirculation system should be separated by heat exchangers.

    One reason for that is that you avoid corrosion in the solar panels if the water in there is a closed circuit. Same is true for the hot water storage tank. That water should not leave the tank, but receive its heat form the solar panel water circuit through heat exchangers, and pass the heat though another heat exchanger to the hot water recirculation system.

    Another reason is that warm water, especially standing warm water, is a breeding ground for bacteria. Separating the water circuits with heat exchangers minimizes the possibility for these bacteria to breed and to get passed on to the consumer.

  • http://thaihaus.info/hausbau Martin in Thailand

    It’s not possible for me to see on the pictures if you use heat exchangers or not. Since also your excellent description does not mention it, let me add that important aspect.

    The hot water in the solar panels, and the hot water in the heat storage tank, and the hot water in the hot water recirculation system should be separated by heat exchangers.

    One reason for that is that you avoid corrosion in the solar panels if the water in there is a closed circuit. Same is true for the hot water storage tank. That water should not leave the tank, but receive its heat form the solar panel water circuit through heat exchangers, and pass the heat though another heat exchanger to the hot water recirculation system.

    Another reason is that warm water, especially standing warm water, is a breeding ground for bacteria. Separating the water circuits with heat exchangers minimizes the possibility for these bacteria to breed and to get passed on to the consumer.

  • Uncle B

    How much do you save in air-conditioning due to the shade from the solar hot water collector? Also: Do you have much ‘sky’ left for solar-voltaic collection? and: Have you oriented your house for solar heating? Next: Do you still have room for a green house to grow GMO ‘Super-Veggies’in for survival case of a huge depression? Also: do you conserve water? This is a great article – do more like it!

  • Uncle B

    How much do you save in air-conditioning due to the shade from the solar hot water collector? Also: Do you have much ‘sky’ left for solar-voltaic collection? and: Have you oriented your house for solar heating? Next: Do you still have room for a green house to grow GMO ‘Super-Veggies’in for survival case of a huge depression? Also: do you conserve water? This is a great article – do more like it!

  • Kevin Hughes

    Thanks for the positive comments, to answer a few questions raised

    Scott,
    Keeping both tanks means that the propane tank can act as a backup if there is no sun, and when this is the case propane is cheaper than electricity, plus it is already there, I am adding more insulation to the propane tank.

    Cynthia,
    My aplogies to your husband!!

    Martin
    There is no heat exchanger, the flow of water through the system means that none is still for long, no more so than a normal hot water tank, the whole system is copper and there are anode rods in the tank so corrosion is not a problem

    Uncle B
    Unfortunately the panel is over the garage so no savings on cooling, but i am thinking about a solar thermal project to generate electricity which will be over the living area, and I am hoping this will cool the house somewhat.

    Kevin

  • Kevin Hughes

    Thanks for the positive comments, to answer a few questions raised

    Scott,
    Keeping both tanks means that the propane tank can act as a backup if there is no sun, and when this is the case propane is cheaper than electricity, plus it is already there, I am adding more insulation to the propane tank.

    Cynthia,
    My aplogies to your husband!!

    Martin
    There is no heat exchanger, the flow of water through the system means that none is still for long, no more so than a normal hot water tank, the whole system is copper and there are anode rods in the tank so corrosion is not a problem

    Uncle B
    Unfortunately the panel is over the garage so no savings on cooling, but i am thinking about a solar thermal project to generate electricity which will be over the living area, and I am hoping this will cool the house somewhat.

    Kevin

  • Jim Miller

    Kevin:

    Next you will be doing radiant floor heating with solar heated water.

    By the way, as to the hot water reciculator, the PSI of the hot is the same as the cold and could not move from the warm side to the cold side without a pump. So how does the cirulator work. Please give me the law of physics on this solution.

    I owned a two story, 8 unit apartment and had a small cirulation pump installed with a 3/8″ copper line running from the most distant hot water point, drawing hot water from that point back to the water heater.

    Jim Miller

  • Jim Miller

    Kevin:

    Next you will be doing radiant floor heating with solar heated water.

    By the way, as to the hot water reciculator, the PSI of the hot is the same as the cold and could not move from the warm side to the cold side without a pump. So how does the cirulator work. Please give me the law of physics on this solution.

    I owned a two story, 8 unit apartment and had a small cirulation pump installed with a 3/8″ copper line running from the most distant hot water point, drawing hot water from that point back to the water heater.

    Jim Miller

  • wes

    hi there Kevin,
    I am looking to heat up a weddig hall of about 1800-2000 sqfeet,walls 14′ high, with the least expensive method .someone suggested radiant heat from a wood/pallets burning furnace or solar panels.
    This project is in Europe where gas is very expensive and would like to know weather Solar panels could heat water in such a large space,or just use the panels for kitchen and bath.and then would radiant heat have the ability to heat this area or should I opt for hot water radiators.pallets are small capsule produced from saw dust that burn fairly eficient.olso the cost of the panels and life span.
    thanks.

  • wes

    hi there Kevin,
    I am looking to heat up a weddig hall of about 1800-2000 sqfeet,walls 14′ high, with the least expensive method .someone suggested radiant heat from a wood/pallets burning furnace or solar panels.
    This project is in Europe where gas is very expensive and would like to know weather Solar panels could heat water in such a large space,or just use the panels for kitchen and bath.and then would radiant heat have the ability to heat this area or should I opt for hot water radiators.pallets are small capsule produced from saw dust that burn fairly eficient.olso the cost of the panels and life span.
    thanks.

  • http://www.bubblingspringssolar.com solar thermal collectors

    Solar thermal systems are useful in many homes for several different options. There are many ways to get solar thermal systems to work in your home and it is important to look into available options that will help to lower the costs of energy consumption needed to heat water or a space. There are two main types of thermal systems that use solar power and those are the passive and active systems. Passive systems allow the heat to be absorbed and are naturally distributed amongst the system while active system will use different means to power the collected heat through the system by using pumps or other devices (which can also be powered by solar energy).

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