Energy tip #16: solar thermal energy for your home

solarhotwater.gifThere has been much in the news lately (and on this blog) about the potential of solar power. From Google’s solar panels to Gov. Schwarzenegger’s speech at the 2006 Solar conference, it seems solar has arrived onto the scene in a big way. While much of the focus has been on the photovoltaic variety, there is a low tech solar option that is still a relatively hidden gem: solar thermal.

This relatively basic technology can be employed to capture the energy of the sun both actively and passively. The passive technology is perhaps the simplest and most cost effective of any solar home improvement projects. The 4-5 year payback period and low maintenance costs (there are no moving parts) make it very attractive. Unfortunately, installing a system can run between $5,000-6,000, a hefty expenditure for most homeowners. Nevertheless, for those who can afford it, solar thermal can be a great investment.

The principle employed is to take advantage of the great furnace in the sky to heat water in a closed loop system (preferably on a south-facing roof). The system can provide warm showers and hot water with little need for gas or electricity. With a lifespan of roughly 35 years, these systems pay dividends long after they’re installed.

Solar thermal systems are also exempt from property taxes and add value to most residences in the U.S. Though, as we’ve seen with other tips (see air drying your clothes), cultural barriers do exist in certain locales and may marginally drop the value of the home.

Looking at the numbers (courtesy of the Solar Living Institute and heliodyne.com)…

Cost of solar thermal system: $5,000-6,000
Annual energy bill savings: $500-1,000
CO2 reductions (annual): 10,500-21,000 lbs
CO2 reductions (35 year lifetime estimate): 367,500 – 735,000 lbs





Last week, 18 people pledged to look into insulation. At 1,900-9,500 lbs saved per insulation project, the represents a potential savings of 171,000 lbs of CO2. Reality would suggest that this number be closer to 30-50,000 lbs, still a significant savings. Let’s keep it going! For a list of all previous conservation tips, click here.

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  1. disdaniel - October 24, 2006

    Thank you, thank you for highlighting this often overlooked yet affordable and highly efficient solar technology.

    Every company that uses hot water can SAVE money by investing in solar thermal systems (especially if they live in “good sun” states). Oh and of course you get all the same feel good vibes of using solar for 1/4 the price of PV.

  2. Hal Newnan - October 24, 2006

    My house just got a solar thermal hot water heater – it preheats water going to the natural gas heater, thus saving an estimated 3/4 of my energy bill. I live in Michigan, and even so the payback period is estimated at only 6 years. I am planning to deduct $2,000 from my taxes using the Federal Tax credit that extends from 2006 through 2007.
    My choice for the installer: Mechanical Energy Systems, please ask for Hal!

  3. Rachel - October 25, 2006

    Do these panels work in areas that receive below freezing weather in the winter? Won’t the water in the pipes freeze?

  4. Flashdaddy - October 25, 2006

    The system is closed loop and uses an antifreeze solution in the solar collectors which then travels to a heat exchanger and heats the water. In cold climates, using the right solution and insulating the exposed pipes is critical, but easily done. Other systems exist that drain the panels when the temperature in the collectors drops below an appropriate level (when the sun goes down).

  5. L Yates - October 25, 2006

    We have a solar water heating system. It is not entirely passive, uses a small electric pump to get the water up to the roof. When it gets cooler, all the water comes back into the house, so no freezing issues. (We are in the mountains of northwestern Virginia.) During sunny periods, winter or summer, it provides all of our water heating, but we still have an electric heater in line to pick up the slack for cloudy periods. I got this installed by an experienced Virginia outfit, and have had no maintenance issues. Which is good, because I have no related skills or expertise.

  6. Phil - October 25, 2006

    I’ve read that heating water accounts for almost 30% of a home’s energy usage. Integrating a solar thermal system is not only less costly than PV, but it is also a much more efficient way of reducing your energy footprint.

  7. bw - October 25, 2006

    I live on the Central Coast of California. How effective are the panels during long periods of fog?

  8. Pam Guthrie - October 25, 2006

    I’d love to implement some of this at my place, but I rent. Does anyone have suggestions for a renter?

  9. 1985 Gripen - October 25, 2006

    I have some questions:
    does the water get hot enough for a nice hot shower or is it just warmish water?
    What happens on days when the sun isn’t out, do you have to have a supplemental water heater?
    How do you get the water up to the panels on the roof? Do you have to have an electric water pump?
    If the water itself doesn’t run through the pipes but rather anti-freeze which then thermally-transfers to the water, do you have to have an electric pump to circulate the antifreeze through the closed-loop system? How much electricity does that use?

  10. Donna - October 25, 2006

    Solar Thermal Water Heating systems are a great way to reduce the 2nd. highest energy cost in your home. If you think about it, we heat hot water every day of the year. Even in state with lower sun levels, such as Michigan, we can produce up to 70% of your hot water needs. The Solar Boiler System by Thermo-
    Dynamics even utilizes a PV panel to power a small circulating pump to circulate the anti-freeze glycol in the system. Contact me if you are interested in more info.

  11. Daniel Barker - October 25, 2006

    It is interesting to consider photovoltaics as a potential source of energy.
    Let’s look at a simple comparision. PVs cost about $5.00 a watt. A kilowatt installation would cost $5,000. This does not included the cost of the power inverter to go from D.C. to A.C.
    The sun produces about one kilowatt/meter squared for about four hours a day, so you would produce about four kilowatt hours a day. Assuming a national average of $0.10 per kwatt hour, this is $0.40 per day. Dividing $5,000 by $0.40 yields 12,500 days, or about 34 years.
    There are cloudy days, and the typical cloud cover is 40%. This means the kwatt unit would produce 4 kwatt hours less 40%, or about 2.4kwatt hours, or $0.24. This results in a cost-breakdown of $5,000/.24, or 20833 days or 57 years.
    Photoelectricity is cost-effective: off the grid. A good example is a simple battery charger for your car. It produces a modest amount of power, about 1.8 watts. This is enough to produce a trickle-charge on a car battery so it will start in the winter time. If the battery charger makes the difference that the car starts, it saves the cost of a tow truck, which is more than the cost of the battery charger so it pays for itself in one use! (It also means the battery lasts longer, which reduces pollution.)
    Obviously, we need a cheaper form of electricity. There are steps we can take. For example, we can cheat nature by bouncing more light on the solar panel. A French scientist achieved a record amount of 1,000 times the rated output of a solar panel by bouncing tremendous amounts of light on it.
    In a domestic setting, we could easily bounce ten times the amount of light on our solar panel, which would greatly reduce the payback time.

  12. disdaniel - October 25, 2006

    In response to bw’s question about fog: there are many great things about solar energy but providing lots of energy with low/no sunlight is not among them.
    To 1985 Gripen: our solar heater can heat water up to ~170 F in summer (although we have a “governor” to mix that temperature down to 130 F max because we have small children around). When the sun isn’t out the solar heater doesn’t heat water. Although our water tank(s) hold/store 80 gallons each, we still have as a back-up our original water heater so we will never be without hot water. We use a small electric pump to pump the heater fluid up to roof. We have a anti-freezing compound in the system (and the same pump circulates this fluid through the water tank) that drains back into the house at night/when it is too cold outside for system to work.
    I just have to know, where does D. Barker live? I agree that solar PV is expensive but not nearly as expensive as Mr. Barker thinks. The topic was solar thermal not solar PV, that said:
    On average (across the year) most places (in the US) get more than 4 hours a day. Since that is an average across the year, you don’t need to subtract out cloudy days, they are already taken into account. Below is a link to one such average sun map..fyi
    http://www.nrel.gov/gis/images/us_pv_annual_may2004.jpg
    Another thing is that many states (and recently even the feds) have created incentives like tax credits, or rebates specifically to reduce the time to simple payback such that it can frequently (either b/c of incentives or better than average solar resource, or both) take less than 20 years to get to a simple payback on solar panels.
    Of course when you buy and install PV you will have paid for your next 30+ years of energy from a clean energy source. So you decrease the US reliance on foreign or polluting energy sources.

  13. gail - November 1, 2006

    I live in a ground floor condominium unit. Any ideas would be greatly appreciated.

  14. Question Consumption - December 28, 2006

    Here’s an idea for Pam Guthrie- talk with the person you rent from about your interest. Maybe you can work out a deal where you purchase the system upfront and they reduce your monthly rent by a specified amount over a specified time period. Be sure to point out that adding this system could help raise the property value as well. Or work out a “you pay half, I’ll pay half” if you’re a long term renter. Be sure to have your information all together when you go to discuss this with them. Good Luck!

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