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  • Solar panel central heating

    I am looking for information regarding the use of solar panels for central heating. Can you use the water from a solar panel system to be stored in an emersion tank that can be heated electrical if the temperature is not high enough before it is pumped to the radiators.

  • #2
    Just to clarify things, I assume you are asking about solar hot water (SHW) panels (compared to solar panel that generate electricity)? Although some have tried, it really does not work that well. I have owned a SHW system for close to 20 years and even have a radiator on the loop in cold climate and can assure you its not a great option.The fundamental problem is that when you need to heat, the sun is normally not out and the outside temps are cold. Yes you can store the heat during the day and try to reuse it at night but you need a lot of volume of water. Think hundreds of gallons of water in an insulated tank. Solar electric panels work better in the cold but SHW panels work worst. Using standard SHW panels, the typical maximum temperature difference between the fluid in the panels and the outdoor temperature is 80 degrees F. Evacuated tube SHW systems can supply higher fluid temps but they are far more expensive, a combination of the actual equipment cost and how much collector area is required. Evacuated tubes are also infamous for failing a few years after installation. If you do want to heat a house with a standard panel you will need to use special radiant panel heaters as conventional baseboard needs far higher temps. The other big issue is when you dont want or need the heat the system still wants to collect heat and you need to cover it over and get rid of that heat of the panels will be damaged.

    Heating with solar electric panels with a grid connected system is done routinely by using heat pump technology. I have access to net metering in my state so I take all the extra sunlight in the summer when I do not want heat and turn it into kilowatts that get credited to my account and then use a MiniSplit heat pump to heat my house in colder weather. Heat Pumps do not generate heat they just move it around so it can be more than 100% efficient. Depending on the equipment you can get 2 to 3 1/2 times more heat out than what you put in with electricity. There is a variant using heat pump that take heat from outdoor air and converts it to warm water which can be stored in tank for heating when needed but the equipment is not yet sold in the US and has the same limitations with only being able to heat the water to 140 F at best. In order for it to work the house needs to be switched over to low temperature radiant heat and a another source of low cost heat (like wood) is needed to supplement the system.

    BTW this is not just theory, I have 20 year old SHW system that works great for supplying hot water for my house from about April to October. It even has a short length of baseboard radiator on it. The radiator was just in case I needed to dump heat from the system but I changed the tilt angle of the panels and the system mostly self regulates.With the exception of sunny days in the spring and fall that radiator doesnt do much so its valved out. I also have 500 gallons of hot water storage that I use for heating my home. I heat my tank with wood from a wood boiler. I have standard baseboard heat so I need at a minimum 140 F to heat my house, I can heat the water at most to 185 degrees so my 500 gallon tank of water can store 180,000 Btus. This sounds like a lot but with my fairly efficient home in winter that stores about 18 hours of heat demand. I am far better using my minisplit using my surplus solar then using electrical resistance heater to keep my tank warm.

    If you want to try out solar heating, the lowest cost option is doing solar air heating with no storage. Lots of home brew systems on Builditsolar.com.


    • #3
      While mostly agreeing with what Peakbagger writes, I'd add a couple of comments as someone who's a big solar and alternate energy advocate and been at it for ~ 45 years:

      Using active solar thermal energy systems to supplement (note, not totally supply - solar HVAC is hardly ever a 100% deal) heating to a conventionally constructed residence as a retrofit, while possible, is well beyond what the average homeowner is able to supply with respect to time, energy, and financial assets. When it is, it's usually in combination with super insulated home designs (retrofit's harder than a start from scratch design for this, but still possible) that can reduce the heating loads to levels low enough to make a 100 % solar fraction possible. However, at that point, depending on winter sun availability, passive solar features are incorporate into the design that also usually incorporate high thermal mass construction techniques that are much harder to use as a retrofit measure.

      A bit like the average Jane/Joe thinking (s)he can pull the plug and thumb her/his/ nose at the POCO by going back to nature with a few PV panels and a couple of car batteries, most solar thermal systems the average (and that includes being averagely naive) homeowners could (and it seems usually) conjure up to retrofit to a dwelling that they think would meet their energy heating needs are little more that toys.

      Toys and hobbies are fine, but if a significant (and here that may also mean measurable) portion of residential space heat over a winter is to be supplied by solar thermal energy in a safe, practical, serviceable, fit for purpose and cost effective way, it'll take more than toys and hobbies.

      Most solar thermal space heating system retrofits in places that are cold and cloudy in the winter that do supply significant fractions of a winter space heating load usually turn out being cost inefficient eyesores that don't meet much in the way of space heat load, require a lot of maintenance, fail a lot, and are usually abandoned after a few years. One big reason for those shortcomings seems to be that most of them are done by DIYers who are simply ignorant of what's required. One reason so much DIY stuff is seen (and a lot of it derelict) is that professionals with ethics avoid such scams.

      If you live in a sunny climate - think places where there's direct sunlight (that is, no clouds) about 70 % or more of the daylight hours in winter - the best way, and probably the only real practical way to achieve a cost effective and significant alternate energy supplement (note, not total replacement) to conventional methods of space heating is by using passive solar designs, methods and techniques. Even then (and similar to those who think going off grid is a cake walk), it's been my experience to find most folks are unwilling to take the time to find out what all that entails much less make the lifestyle changes that will enable those designs, methods and techniques to work effectively.

      As a suggestion, educate yourself before you spend dime one - and avoid thinking about possibilities in ways that only confirm what you want to believe. If nothing else, you'll learn more, be disappointed less, pleasantly surprised more often, and keep a few more bucks in your pocket until you know what you want to do and what real possibilities exist to meet your goals. Another bennie is that you'll get screwed less by the peddlers and con men when they quickly spot your solar ignorance and use it to separate you from some of your financial assets. It'll also be easier for you to spot their B.S. and their ignorance of what they're peddling.

      If one of the motivating factors for your quest about solar thermal space heating is financial: As another respectful suggestion, before getting into solar energy methods, I'd start by studying how heat is gained and lost in a dwelling as well as some of the consequences of reducing that flow (think of mold and smelly air), and then learning SAFE, practical and cost effective ways and methods of reducing that loss and mitigating the usually not talked about consequences of too tight a dwelling for example. If, like most folks, reducing your winter heating bills with a minimum disruption in your lifestyle is one of the driving forces behind your quest for using solar energy, you may well find that a few simple lifestyle changes and SAFE, cost effective conservation methods are much more cost effective and less disruptive. They also help make any alternate energy retrofits you subsequently add will be easier to pull off, probably simpler, more cost effective and easier to maintain.

      Take what you want of the above. Scrap the rest.

      Welcome to the neighborhood and the forum of few(er) illusions.


      • #4
        You need to do a lot more number crunching for something that works.

        Heating and cooling with solar panels is a significant project, and its success will depend a lot on the
        site conditions. The financial aspects here are debatable, but 5000 sq ft in 2 buildings have been
        maintained at the most comfortable indoor temp year around (outdoor -20F to 100F), by a PV solar
        panel system. The system requires very little attention or maintenance. In 8 winters it has blown an
        MC4, a loose 6 gauge connection, and a 40A circuit breaker, all simple and cheap things to deal with
        the same day for a DIY owner.

        Insulation here is mediocre 1970s construction, for now I have compensated with more solar panels.
        It runs on a 25,000 KWH annual budget, made possible by several things.
        1. A ground mount system 300' long, optimized for clouds and snow removal here,
        2. A net metering contract that allows directly trading summer day KHWs for night and winter needs.
        3. A wide temp range, high efficiency heat pump technology, which allows multiplying collected solar
        energy several times over the entire outdoor temp range here at 42 lat.

        And of course all electrical needs are also supplied by the sun, a minor part of the project. The use of
        electrical panels eliminates a lot of maintenance, distances, and problems with outdoor temp range.
        The heat pump multiplyer largely compensates for the poorer panel efficiency. Bruce Roe