Solar Panels for Water Heating: What You Need to Know

Selecting and installing tips of solar panels for water heating. See the main differences between flat solar collectors and other types, including advantages and disadvantages.

Solar panel for water heating

Solar panels for water heating: Benefits and considerations

Solar panels: Types

Solar panels are very versatile and are used in various applications. There are ideal for those who live in remote areas and off-the-grid.

When installed in homes, they are mainly used for water and space heating and for generating electricity to power various devices.

Solar water heating panels - Solar thermal

Solar panels for water heating, also known as flat plate collectors or solar thermal systems, are designed to absorb the solar heat energy to heat the water or other fluids.

The heating fluid passes through the device to the storage tank, where it heats the potable water used in bathrooms and kitchens.

They are the most used type of solar collectors in domestic solar water and space heating.

These are about twice as efficient in generating energy than solar PV panels.

Solar PV panels

Solar PV panels convert the sun's energy into electricity using photovoltaic (silicon) cells and other components. The energy can be stored or used to power home appliances, including a water heater.


Solar panels are a good investment. They are considered as the standard and are widely used, inexpensive, effective, and long-lasting. They collect both direct and diffuse solar energy radiation, so they don't have to track the sun during the day.

Efficient. According to some studies and reviews, solar collectors are more efficient than evacuated tubes since the larger collector area is exposed to absorb the solar heat. That means that fewer solar panels are used for the same performance.

Saves money. Solar thermal panels can provide up to 70% of hot water just by using free solar energy, and with government incentives, they can provide some great savings.

Low carbon emissions. Solar thermal systems do not produce carbon emissions as gas and oil burning systems. Electricity is also not clean energy since most of it is generated in nuclear plants or plants that use fossil fuels.


Since solar panels use small riser tubes, it is essential to know that they are prone to clogging if the water is hard.

According to some studies, they have the largest heat absorbing area and the highest heat loss of all types of collectors. They are also susceptible to freezing as they have a large exposed area and many small passages.

Solar panel installation: Things to consider

Solar panels for heating water are expected to work in a wide temperature range, which can go from below freezing to about 180 F or even higher. All elements should be made of high-quality materials and capable to withstand higher temperatures during long-lasting sun exposure or lower during the harsh weather. Most panels last 20 years or more.

It is important to know that panels do not store any energy; only a small amount of the heating fluid is inside the riser tubes, so most of the energy is kept inside the solar tank for later use.

Solar water heating systems should have a backup so you can still enjoy hot showers during periods with no sunshine. It is recommended to get a storage water tank that can support the capacity of the system or how much you consume daily.

Is your home suitable for solar panel installation?

Here are the installation tips you need to take into consideration before installing panels:

  • Location. Make sure to install solar panels on the roof facing the south, southwest, or southeast, and tilted at an angle, so that it can receive direct sunlight for most of the day. Avoid areas with shade.
  • Size. The size of your solar panel and the number of them installed will determine how much energy it will receive. The bigger the surface area is, the more solar energy it will absorb.
  • Capacity. Panels come in different sizes and wattage. Get one with a greater wattage because it is more efficient and saves money. And as it needs less space on the roof, it is easier to install.
  • Water storage. In addition to solar panels, which are used to trap solar energy only, you also need a solar water heater system to store/heat potable water. 

Heating water with solar panels: Options

Solar water heating systems often use solar panels to heat the water and tank-type water heaters to store and heat water when needed.

They can be used either in passive systems such as the thermosyphon or active solar heating systems with circulating pumps and controllers. The region where you live and the climate will determine what type is the best for you.

Water can be heated in the direct or open-loop system, so when heated in solar panels, it goes directly into the storage tank for home use.

In cold climates, homes use indirect systems where a mixture of water and antifreeze is used to harness the solar heat and then heat the potable water.


Solar flat-plate collectors are usually consist of:

  • Frame
  • Glazing
  • Absorber plate
  • Riser tubes
  • Insulation


Frames in solar collectors should be strong to resist high winds, heavy rain, snow, hail, and other conditions without breaking or losing functionality.

Most of the time, the shape is rectangular and can come in different sizes, where the most used are 4x8 or 10 feet and 4-6 ft. deep.

The recommended material is aluminum, lightweight but strong, so it can be installed on the roofs without damaging it.

The aluminum channels are a better solution as they come with the designed flanges for easy and convenient installation.

To attach the frame to the rooftops, you can either buy the mounting hardware kit or separate elements, but be careful to buy a long-lasting type, such as stainless steel.

emergency plumber


The front of the collector, glazing is usually made of low-iron, tempered glass, or strong plastic and should have characteristics such as high transmission, non-degradability, strength, and durability. They can either use rubber gaskets or silicone caulk when installing into the frame.

Glass is a good solution for the cover due to its high transmittance and better thermal insulation than plastic, while plastic covers can have a larger area as they are lighter. Also, the window glass is unsuitable as it has high iron content.

Absorber plate

The absorber plate is installed right below the glazing with the 1" gap (recommended). On its top and bottom ends, it has manifolds (headers) made of 3/4" or 1" copper pipes to collect the fluid from the riser tubes. Each riser tube is attached to the copper or aluminum flat fins to transfer the accumulated heat effectively. It is recommended to make the fin-tube connection snug when soldering or welding.

The most important factor when considering the absorber plates is the coating or "selective surface"; it should have a high absorbance and low emittance. They can be made of steel, aluminum, or, most of the time, copper, coated in black paint, black chrome, or copper oxide. Together, they provide a strong, corrosion-resistant assembly with high thermal conductivity.

There are several types of absorber plate/riser tube assemblies, and the selection depends on the particular application:

  • Tube in a flat plate
  • Tubes fastened to an upper or lower flat plate
  • Tubes fitted in a grooved plate
  • The corrugated sheet on a flat plate or riveted together

Riser tubes

The riser tubes are 1/2" diameter copper pipes where the heating fluid circulates. These small pipes can be made with manifolds at their ends or shaped in a serpentine pattern, running continuously from one side of the collector to the other. They are installed a few inches apart (3-6 inches is recommended), and they can freely expand or contract when heated or cooled since they are not attached to the frame.


To keep the captured heat longer and reduce the heat loss from the absorber plate and pipes, collectors are insulated in the back and sides as much as possible. Because of their lower thermal conductivity, the recommended materials for insulations include mineral wool and PUR.

NoteProfessional installation and repair are recommended. Find local plumbers and get FREE Quotes!


Solar panels for heating water are easy to construct and inexpensive to build.

Most big hardware stores, such as The Home Depot and Lowe's, carry all the materials you need to make the panels, or if you prefer plug-and-play systems, you can buy a solar kit.

Solar water heating panels might have higher purchase prices, but they use free and renewable solar energy, providing homeowners with both economical and ecological benefits, which makes them well worth the investment.


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