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The installation of a solar water heater is a solution to get some of its domestic hot water at a lower cost. It allows you to benefit from free energy and save up to 30% on your bill.

Installation of a solar water heater

Necessary material

  • Solar thermal panels
  • Buffer tank ECS
  • Isolated tubes
  • Temperature sensor
  • Circulation
  • Expansion tank
  • Electronic regulator
  • Copper tube
  • Copper and brass solder fittings
  • Plumbing and sealing seals
  • Lead sealing strip
  • PVC evacuation tube
  • Siphon
  • Vannes

Difficulty: 4/4
Cost : € 6,900 (excluding boiler)
Time: 2 weeks
Equipment: meter, spirit level, flat wrenches, pipe cutter, power strip pliers, drill, screwdriver, welding machine, handsaw, hammer, harness, roof ladder, scaffolding

Solar thermal collectors are used to recover solar energy to heat a water / glycol / antifreeze mixture, called heat transfer fluid. Via a closed circuit and exchangers, this fluid is used to heat the water contained in a hot water tank.

Double heat production for added security

Thanks to suitable metal structures, the sensors can be installed on a flat roof or on a sloped roof, in an integrated way (our building site) or above the roof. In this house near Paris, the owners decided to heat the water in the bathroom thanks to this device. To mitigate the possible lack of sunshine, a wall-mounted condensing boiler, used for heating, was connected to the hot water tank. The balloon put in place here (Aquasol de Weishaupt) has four hydraulic connections to connect the A / R pipes coming from the sensors and those connecting the boiler. A sensor continuously measures the water temperature and switches on the boiler via the controller if the temperature is too low for DHW production. This type of installation, carried out by an authorized RGE Solaire professional, is eligible for the energy transition tax credit (ISCED) and allows deduct 30% of the expenses (materials, materials and equipment) as soon as the work is done by an RGE certified professional.

Aid and subsidies under certain conditions

It is also possible to obtain various grants to finance all or part of the project (Anah, eco-voucher region, municipal aid) or to subscribe to a Eco-Ready loan at zero rate. To benefit from it, the assembly of these various files of request for help and financing is to be deposited before the beginning of the works.

Principle of operation of a solar water heater

The operation of the solar flask

  • The refrigerant circulates in a loop between the hot water tank (6) and the thermal sensors through a circulator (4).
  • The panels are equipped with a sensor that continuously measures the fluid temperature and sends this information to the controller (2).
  • When the preset temperature is no longer obtained, the sensor sends the information to the controller which transmits it to the boiler (1).
  • It starts then and, thanks to a set of automatic valves, sends to the buffer tank a supplement of hot water.
  • The boiler stops sending hot water as soon as the preset temperature is reached at the outdoor sensor of the solar panels.

Diagram of installation of a solar water heater

1. Boiler
2. Regulation / programming
3. Solar panel
4. Circulator
5. Expansion vessel
6. DHW preparer with exchangers
A. Heating
B. Domestic hot water

Laying roof panels

Remove the tiles

  • Start by removing the tiles where the solar panels must be installed.
  • Store nearby for the end of the work.

Screwing cleats for thermal sensors

  • After having checked the future alignment of the sensors with the mechanical tiles, screw the cleats (27 x 47 mm) intended to support the thermal sensors on the counter battens of the roof.

Screw the cleats

  • To ensure a good hold of the solar panels, the end of the cleats is pre-drilled and screwed diagonally into the counter-battens at slow speed to prevent any splintering of the wood.

Install the solar panels on the roof

  • Position the two panels on the roof.

Adjust the spacing between the sensors

  • Adjust the spacing between the sensors using the polystyrene profile supplied.

Screwing fasteners

  • Check the positioning, screw the fasteners now the panels, then install the supports allowing the installation of the sealing profiles.

Thermoplastic probe connection

  • Connect the heat sink temperature sensor to the location provided on the solar panel.

Connect the thermo-plunging probe

  • Retract the other end of the cable into the attic for later connection to the controller / programmer.

Connect the hydraulic hoses

  • Bring out the two pre-insulated hydraulic hoses on the roof and connect them to the solar panels.
  • If possible, work in pairs to avoid damaging them.

Connect the pipes to the thermal sensors

  • Using a pliers and a spanner, connect the two pipes to the thermal collectors according to the installation instructions.

Glue the insulation around the pipes

  • Check and if necessary glue the insulation around the pipes.

Screw the lead strips for sealing

  • At the bottom of panels, screw the lead strips to seal.

Guarantee the good flow of rainwater

  • In the lower corners, add a section of battens, then place a section of overlapping lead strip to ensure proper flow of rainwater.

Nail the aluminum curbs

  • Set up the aluminum curbs on the sides of the solar panels, nailing their brackets to the battens.

Installing the covers

  • Then install the covers that close the sealing profiles at the front.
  • They slide sideways, then clip themselves.

Reinstall the tiles

  • Reposition the peripheral tiles from the bottom.

Insert the rubber seal

  • On the periphery of the sensors, insert the rubber seal into the grooves at the junction of the covers and panels.
  • Be careful to ensure tightness.

Connection of circuits

Tie the boiler and the balloon

  • After installing the DHW tank and the circulator, make the connections between the boiler and the tank, then those between the solar collectors and the tank.

Connect the hoses

  • Connect the panel hoses to the hot and cold water valves of the hydraulic circulator by installing the necessary fittings and gaskets.

Wall mounting of the expansion vessel

  • Fasten the expansion tank to the wall.
  • Connect it to the cold water, after the pressure gauge, connecting the metal hose in connection with the circulator.

Connection of insulated pipe sections

  • Measure and cut two sections of insulated metal tubes.
  • Connect them to the valves of the hydraulic circulator using a wrench.

Screw the inlet and outlet valve onto the hot water tank

  • Screw an inlet and outlet valve onto the tank, then connect the two pipe sections from the circulator.
  • Replace the insulation.

Weld the copper tubes

  • From the boiler, make a copper outlet on hot and cold water.
  • Mount the blank connections to the balloon and braze them.

Soldering copper tubes and fittings

  • Solder the last copper fittings and allow to cool.
  • Connect the brass connections of the copper tubes to the preparation tank from the boiler.

Install a siphon drain

  • Add a double-entry drain trap to the cold water system, which empties the hot water tank and the boiler's internal tank if necessary.

Install the siphon

  • From this siphon, whiten the PVC drainage system up to the Y connection equipped with a reduction.
  • Degrease, sand and glue the fittings and tube over them.

Hydraulic circulation connection

  • Make the electrical connections of the outdoor sensor of the solar panels on the regulator.
  • Connect the hydraulic circulator to the mains. All that remains is to put back the electricity.


Video Instruction: Racold solar water heater