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DIY solar space heating. Primary Sidebar

    DIY Solar Water Heater: An Ultimate Guide

    Today consumers have a choice between super-efficient, professionally installed collectors and also the less expensive DIY friendly solar water heater system.

    The bonus is that you don’t need to sacrifice the convenience of a regular hot water system when you install a solar heating system. They are simply designed to tie into conventional electric or gas water heaters.

    Therefore, you can enjoy the convenience, the benefits, and the savings of both options. In the following guide, we’re going to take a look at DIY solar water heater (see also ‘Water Heater Disposal‘) options and why you should be considering them.

    How does a solar water heater work?

    A solar water heater works by absorbing light. Ultimately, the light is absorbed by means of a collector placed on the roof and ultimately converts the sunlight into heat.

    This heat is then transferred to the water tank by means of a circulating pump. Then the exchange is triggered by the regulator but only when the collector is hotter than the water in the tank.

    This prevents the circulating pump from using electricity unnecessarily. It also prevents overheating. At midday, in summer, when skies are cloudless is when the efficiency of the collective is at its highest.

    Alternatively, they also do well when the collectors face south. When there is not enough sunlight, the water is preheated, and a backup system kicks in to bring the water to the required temperature.

    The system ultimately is used to produce hot water at a constant temperature throughout the year without emitting any CO2. You’ll find that solar water heaters are usually described according to the type of connector and the circulating system that they use.

    Do solar water heaters work in winter or fall?

    Many people who haven’t used solar water heater systems before often wonder whether they can be used at night, during the winter and the fall.

    As with all things in life, there are advantages and disadvantages. Let’s take a closer look at how your solar water heating system works during the winter and fall.

    Even with outside temperatures being low in winter, it shouldn’t affect your solar water heater. This is because, with good insulation, the sun will still be able to heat the water even during the winter months.

    This is because the hot water tank is heated up by the radiation energy of the sun which goes through the glass and heats up enclosures even if the outside temperature is well below freezing.

    Therefore providing good insulation can ensure only a small amount of heat loss.

    Diffused sunlight, however, which is often a feature on cloudy days reduces the heating capacity of most solar water heaters. So there is no specific technology to suck out more heat from the sun’s rays to the collector.

    However, you can enhance the amount of light hitting the right area using mirrors such as concave ones so that the few hours of direct sunlight available can be optimized.

    Ultimately though, the quality of the insulation and how much heat can be kept in the system without being lost in the environment are all factors that play a role in how your solar water heater will work during these cold months.

    The reality is that solar water heaters don’t generate as much hot water in winter. However, solar water heating systems that are installed in winter will have anti-freeze protection, and the snow will then melt off your solar water heating collector before it slides off your roof.

    The solar water heating system can be effective because of the sufficient insulation.

    So ultimately, as we mentioned earlier, the radiator fluid technology will kick in during colder days.

    The system makes use of a liquid catalyst radiator which is warmed by the sun’s energy and then pumped into the heat exchange tank. The heat exchange tank exchanges the heat of the fluid with the water in the storage tank.

    The radiator fluid should be checked prior to the winter months. Consequently, the vacuum tubes produced by some small manufacturers may be of poor quality and lead to low-thermal efficiency of hot water production.

    On the other hand, if the anti-freeze installation is weak, then it weakens the insulation effect, making it ineffective. It will consequently struggle to keep your hot water warm. Also, if the pipeline is frozen, the hot water circulation will not be smooth or only partially heated.

    Ultimately, by ensuring that you have good insulation, sunlight will be able to heat the water well in a solar water heater system.

    When it comes to temperatures below freezing, you need to remember that solar water heaters are not developed or designed to replace your water heater altogether. A typical solar water heater will be able to heat 60 to 80% of the water you use over the course of the year.

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    So from April to September, almost all of the hot water will be solar heated. In winter, however, the percentage of your hot water will be more like 10 to 20% due to the shorter days and because of the weaker sun in December.

    Therefore, 99% of solar water heaters installed in the US are connected to a backup conventional water heater, and your water needs continue to be met even in colder months like January.

    Homemade Solar DIY Pool Heater

    Below is the basic schematic showing a solar pool heater at work.

    The concept is quite simple really –

    • The pump pulls the cold water up from the pool.
    • Water goes through a valve to regulate the flow.
    • Water circulates through black hoses and absorbs heat from the sun.
    • Hot water goes back in the pool.

    There are two extremely key components of the solar heater

    The hose – The black hose is where everything happens – absorbs the heat from the sun and heats up the water. We need this to be as long as possible and the best way to do that is to coil it up!

    The valve – Water needs time to heat up in the hose as it flows through. The flow rate makes a huge difference and to be able to control the flow, a valve is placed at the inlet of the hose.

    Materials needed –

    Here is a video showing you how we went about making our solar pool heater. Step by step instructions along with tips and tricks follow below.

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    Step 1 – Build the base

    The purpose of the base is to support the hose and can be built in many ways.

    We tried two ways to do this –

    • Using 2×4 joined in an X with half-lap joints
    • Using 2x4s to make a simple grid.

    We found that the grid built using 2x4s, although used more lumber, was the best because it had more support for the hose.

    Step 2 – Make the hose coil

    Leaving about 2ft of hose free, wrap the hose onto the grid and use strap clamps to clamp it down.

    We found that these with one hole worked best and also saved on the screws.

    This is probably the longest part of the project. The hose gets tangled and is a little hard to wrap so it is best to do it in an open space.

    There was really no pattern on how we added the clamps. We just added as and when we felt like the hose needed support to stay in place.

    You can also use uv-resistant zip-ties if you like but the clamps worked really well for us.

    We decided to make 2 of these coils and will probably make at least one more. The more coils, the faster you can get hot water. We will discuss this in more detail later.

    Step 3 – Paint black

    Paint the hose and the clamps with a matte black spray paint.

    Although this step is optional, I highly recommend it. The key is to minimize all reflections from the surface of the coil – from the clamp or the hose.

    Step 4 – Make reflectors (Optional)

    We also made a few reflectors by stapling aluminum sheets to ¼″ plywood. This can be adjusted to concentrate more sunlight onto the coils.

    Step 5 – Connect

    • If you have multiple coils, connect them in tandem.
    • Connect a valve to the main input of the coil.
    • A hose from the submersible pumpis connected to the other end of the valve.
    • Connect an output hose to the output of the final coil and into the pool.

    Step 6 – Let it run

    Once the pump is on, water will flow through the coils, warm up and go into the pool.

    The valve needs to be adjusted so you can control the amount of water going through the coils so the water gets time to warm up.

    Alternatively – Instead of the pump, you can directly connect the incoming hose to a water outlet if you are trying to fill up a pool.

    So that is the solar pool heater!

    How warm can a solar pool heater get?

    When we started exploring solar pool heaters, I was skeptical about how well it would be able to heat up the pool.

    With ONE coil –

    After we made the first coil, on a 80F day, we let it run for about an hour and we tested it.

    WITH TWO coils –

    Then we added another coil and on a day with similar temperatures, here is what we found –

    • Pool water temperature – 70F
    • Solar heated water temperature – 110F (!!)

    So, you can see that a solar pool heater can get pretty warm! It was able to raise the temperature of the water by 20-40F depending on the length of the hose.


    The flat black paint used inside the collector box plays a critical role in the efficiency of the solar heat collector. Its primary function is to absorb the maximum amount of heat energy from the sun.

    It is essential to choose a flat finish black paint, as opposed to a reflective coating. Reflective paint will reflect the sun back outside of the collector, resulting in a significant loss of potential energy.

    The flat black paint, on the other hand, assists with trapping the heat energy and preventing it from being reflected away from the collector.

    Once the sun’s energy enters the collector box through the glazing, the absorber’s material and flat black paint work together to efficiently absorb the heat and begin to warm the air inside the collector.

    As the air warms up inside the collector and around the absorber, it will naturally expand and rise, creating a convection current. This process of warm air rising will continue as long as the sun is shining, leading to a constant circulation of heated air.

    The warm air’s circulation is aided by the friction generated between the absorber and the air passing over and through it. This process creates an opportunity for the air to absorb more heat from the absorber surface and get heated by the sun.


    After the air is heated by the absorber inside the collector, it needs a way to circulate through the box and into the intended living space.

    To achieve this, we install two vents on the backside of the solar collector facing towards the room or space that requires heating.

    The vent at the top of the collector allows the heated air to flow into the room, while the vent at the bottom allows cooler air to return to the collector for re-heating.

    Installing both a return vent at the bottom and a supply vent at the top of the solar collector allows for the natural convection process to occur.

    As the air inside the collector absorbs heat from the absorber, it begins to warm and expand, causing it to rise up and out of the collector.

    This natural upward movement of the warm air creates a convection current, which draws cooler air from the room or conditioned space into the bottom of the collector box.

    The return vent at the bottom of the collector allows for the cooler air to enter and circulate through the system, while the supply vent at the top allows for the heated air to be distributed into the room or conditioned space.

    The solar collector functions by creating a convection current within the room. The cooler, denser air at the bottom of the room is pulled through the collector, where it is heated by the absorber and transformed into warm air.

    The warm air then exits the collector through the supply duct and is circulated back into the room, effectively raising the ambient temperature.

    By removing cooler air from the bottom of the room and replacing it with warm air, the collector helps to maintain a comfortable living environment.

    The solar collector is constructed using 153 355ml soda cans arranged in 9 rows of 17 cans each. To maximize the absorption of sunlight, each can is coated with flat black paint.

    This coating prevents any reflection of sunlight and ensures that all energy from the sun is absorbed. Additionally, the collector is equipped with a five-inch intake and exhaust manifold at the bottom and top of the unit.

    The manifold design ensures that all air is directed through the interior of the aluminum cans, maximizing the exposure of air to the heat absorbed by the cans.


    To maximize the heat transfer from the sun to air within a given space, we need to build a better heat exchanger. Solar air heating systems use air as the working fluid for absorbing and transferring solar energy.

    Transferring heat from one place to another by definition is a heat exchanger.

    When the sun heats the metal, the hot metal heats the air circulating over the metal of the heat exchanger. The job is to capture radiation from the sun and transfer this thermal energy to air via conduction heat transfer.

    Heat transfer output depends on the rise in temperature and the airflow.

    In order to minimize heat loss through the plexiglass, it is imperative to keep the absorber temperature as low as possible.

    This is because the higher the absorber temperature, the greater the amount of heat lost through the glass.

    One way to achieve this objective is by increasing the airflow while maintaining the same amount of solar energy extraction.

    The increased airflow helps to transfer the absorbed heat away from the absorber quickly, thus preventing the absorber temperature from rising too high.

    By doing so, we can ensure optimal performance of the solar collector while minimizing heat loss through the plexiglass.

    Solar Water Heaters

    Solar water heaters.- sometimes called solar domestic hot water systems.- can be a cost-effective way to generate hot water for your home. They can be used in any climate, and the fuel they use.- sunshine.- is free.

    How They Work

    Solar water heating systems include storage tanks and solar collectors. There are two types of solar water heating systems: active, which have circulating pumps and controls, and passive, which don’t.

    Active Solar Water Heating Systems

    There are two types of active solar water heating systems:

    • Direct circulation systemsPumps circulate household water through the collectors and into the home. They work well in climates where it rarely freezes.
    • Indirect circulation systemsPumps circulate a non-freezing, heat-transfer fluid through the collectors and a heat exchanger. This heats the water that then flows into the home. They are popular in climates prone to freezing temperatures.

    Passive Solar Water Heating Systems

    Passive solar water heating systems are typically less expensive than active systems, but they’re usually not as efficient. However, passive systems can be more reliable and may last longer. There are two basic types of passive systems:

    • Integral collector-storage passive systemsThese consist of a storage tank covered with a transparent material to allow the sun to heat the water. Water from the tank then flows into the plumbing system. These work best in areas where temperatures rarely fall below freezing. They also work well in households with significant daytime and evening hot-water needs.
    • Thermosyphon systemsWater is heated in a collector on the roof and then flows through the plumbing system when a hot water faucet is opened. The majority of these systems have a 40 gallon capacity.

    Storage Tanks and Solar Collectors

    Most solar water heaters require a well-insulated storage tank. Solar storage tanks have an additional outlet and inlet connected to and from the collector. In two-tank systems, the solar water heater preheats water before it enters the conventional water heater. In one-tank systems, the back-up heater is combined with the solar storage in one tank.

    Three types of solar collectors are used for residential applications:

    • Flat-plate collectorGlazed flat-plate collectors are insulated, weatherproofed boxes that contain a dark absorber plate under one or more glass or plastic (polymer) covers. Unglazed flat-plate collectors.- typically used for solar pool heating.- have a dark absorber plate, made of metal or polymer, without a cover or enclosure.
    • Integral collector-storage systemsAlso known as ICS or batch systems, they feature one or more black tanks or tubes in an insulated, glazed box. Cold water first passes through the solar collector, which preheats the water. The water then continues on to the conventional backup water heater, providing a reliable source of hot water. They should be installed only in mild-freeze climates because the outdoor pipes could freeze in severe, cold weather.
    • Evacuated-tube solar collectorsThey feature parallel rows of transparent glass tubes. Each tube contains a glass outer tube and metal absorber tube attached to a fin. The fin’s coating absorbs solar energy but inhibits radiative heat loss. These collectors are used more frequently for U.S. commercial applications.

    Solar water heating systems almost always require a backup system for cloudy days and times of increased demand. Conventional storage water heaters usually provide backup and may already be part of the solar system package. A backup system may also be part of the solar collector, such as rooftop tanks with thermosyphon systems. Since an integral-collector storage system already stores hot water in addition to collecting solar heat, it may be packaged with a tankless or demand-type water heater for backup.

    Installing and Maintaining the System

    The proper installation of solar water heaters depends on many factors. These factors include solar resource, climate, local building code requirements, and safety issues; therefore, it’s best to have a qualified solar thermal systems contractor install your system.

    After installation, properly maintaining your system will keep it running smoothly. Passive systems don’t require much maintenance. For active systems, discuss the maintenance requirements with your system provider, and consult the system’s owner’s manual. Plumbing and other conventional water heating components require the same maintenance as conventional systems. Glazing may need to be cleaned in dry climates where rainwater doesn’t provide a natural rinse.

    Regular maintenance on simple systems can be as infrequent as every 3–5 years, preferably by a solar contractor. Systems with electrical components usually require a replacement part or two after 10 years. Learn more about solar water heating system maintenance and repair.

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    When screening potential contractors for installation and/or maintenance, ask the following questions:

    • Does your company have experience installing and maintaining solar water heating systems?Choose a company that has experience installing the type of system you want and servicing the applications you select.
    • How many years of experience does your company have with solar heating installation and maintenance?The more experience the better. Request a list of past customers who can provide references.
    • Is your company licensed or certified?Having a valid plumber’s and/or solar contractor’s license is required in some states. Contact your city and county for more information. Confirm licensing with your state’s contractor licensing board. The licensing board can also tell you about any complaints against state-licensed contractors.
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