Step-by-step installation of a solar system – from collector to tank

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Step-by-step installation of a solar system – from the collector to the storage tank

A solar system for heating hot water is an investment that pays off reliably and in the long term when installed correctly. The problem is that most people only see the collector on the roof and the storage tank in the boiler room – and consider everything in between as "some kind of plumbing work". In reality, the installation of a solar system is a sequence of precisely interconnected steps, where any mistake in the order or in the details can mean either a non-functional system or a serious fault after a few seasons. This article therefore examines the entire process – from preparatory work, through the mounting of collectors, pipe routing, installation of the pump unit, connection of the storage tank, to filling, air venting, and commissioning. It is based on the typical practice of a family house installation, i.e., 2–4 flat collectors, a 200–400 liter storage tank, a typical gable roof.

Preparation and project documentation – what must be ready before you open your toolbox

The first and most often underestimated phase. Many installers arrive at the site with materials, only to find out that they don't know exactly where the pipe will run, what the actual slope of the roof is (not according to the plan), where the distribution panel is, or where the storage tank is located. This prolongs the work and leads to improvised solutions that later cause problems.

Before ordering the materials, it is necessary to know:

Orientation and slope of the roof – the ideal is south ±30°, slope 30–50°. Deviations are possible, but they change the performance calculation and in some cases also the mounting method.
Roof structure load capacity – a flat collector with an area of ~2 m² weighs 30–45 kg, to which snow must also be added. Older houses with light truss structures sometimes require a static assessment.
Pipe route from the collector to the storage tank – length, number of bends, penetrations through structures (roof, ceiling, walls). The ideal route is as short as possible and with the least number of bends.
Storage tank location – the tank must be lower than the collectors (at least 0.5 m lower in a thermosyphon system, in a pump system it is not a condition, but it affects hydraulics).
Electrical connection – the pump unit requires 230 V/50 Hz, the controller also.
Dimensioning – number of collectors, storage tank volume, pipe diameter. If you have not yet resolved the dimensioning, read our article What solar collector power do I need – calculation based on the number of people and consumption and also Dimensioning of solar piping and pump unit – how to do it.

The output of the preparation is a simple sketch – the roof with the position of the collectors, the pipe route with the lengths of individual sections and the layout of penetrations, the position of the storage tank and the pump unit in the boiler room. It does not have to be a CAD drawing, but it must be on paper before the work begins.

Mounting collectors on the roof – fastening, slope and orientation

The physical installation begins on the roof. This phase is demanding in terms of work safety (ensuring access, safety ropes, possibly scaffolding for a larger number of collectors) and requires at least two workers – a collector with an area of 2 m² weighs 35–45 kg and its handling on a sloped roof alone is dangerous.

Fastening of the load-bearing structure

Before any fastening, it is necessary to find the position of the rafters – either using a metal detector (screws/nails), or visually from the attic. Fastening into the rafter through the roof tiles using a roof hook is a standard solution for sloped roofs with hook-type roofing (concrete tiles, ceramic tiles). For flat metal or corrugated roofs, clamps on the corrugation or glued consoles are used.

Roof hooks are always placed directly into the rafter, not into the lathing itself. The minimum depth of the screw insertion into the rafter is 50 mm, recommended is 70–80 mm. Hooks must be in a vertical line (from top to bottom), not shifted sideways – otherwise the rail will not be evenly seated.

Rails (aluminum or steel profiles) are attached to the hooks and form the base to which the collector is fastened with clamps. The length of the rail depends on the number and width of the collectors. For 2 collectors with a width of 1.23 m placed horizontally next to each other, you need a rail of at least 2.6 m, so that there is an overhang of at least 5–10 cm on each side. Collectors are connected hydraulically in series or in parallel – for more than two units, parallel connection is better for balanced circulation. More on this topic can be found in the article How to correctly position and fasten solar collectors on the roof.

Connecting collectors to each other

Modern flat collectors, such as flat frame solar collector IVAR.SOLAR 210 M5 (1230×1696×86 mm, area 2.09 m²), have fittings on the side of the frame with external threads, usually ¾". These fittings are equipped with gaskets resistant to glycol and temperatures up to 200 °C – this is a requirement, standard rubber gaskets are not suitable here.

When connecting two collectors in series, the output of the first is connected to the input of the second using a short coupling (usually part of the collector mounting kit). The input and output of the entire collector field remain open – these are the points where the solar piping is connected leading down to the boiler room.

Solar piping – selection, insulation and routing

Solar piping is not a standard plumbing pipe. The primary circuit operates at temperatures that can exceed 150–180 °C during full solar irradiation and pump stagnation. Standard soft copper or plastic pipes (PEX, PPR) are not suitable for these conditions. Commonly used are:

Hard copper R220 (Ø 15 mm or 18 mm) joined by soldering (not crimping, or only with fittings certified for glycol and high temperatures)
Stainless steel corrugated pipe – flexible, resistant to high temperatures, easier to install in confined spaces
Predesigned double insulated pipe – ideal for long outdoor or unheated indoor runs

A practical solution for solar installation is stainless steel pipe with rubber insulation and cable (2× Ø 16, 10 m). This solution combines both primary channels (output + return) in one bundle with UV-resistant rubber insulation and includes a cable for the collector temperature sensor. This significantly simplifies installation and eliminates the need to separately protect the sensor cable along the route from the roof.

Pipe insulation – why and how

Solar piping in the exterior must have insulation resistant to UV radiation, temperatures of at least 150 °C, and mechanical stress. Rubber insulation (e.g. Armaflex HT, Aeroflex) meets these requirements – standard PE insulation is not suitable for solar piping in the exterior, as it cracks under prolonged sun exposure. Minimum insulation thickness is 19 mm for piping up to Ø 18 mm, in colder areas I recommend 25 mm.

Piping in the interior (from the building entrance to the pump unit and storage tank) can be insulated with standard EPDM insulation, but thermal resistance must still be at least 100 °C. Seals, adhesive for insulation and tape – all must be certified for this temperature range.

Penetrations through the roof and walls

Each penetration through the roof is a potential leak point. On the market there are rubber seals – so-called "kelmacks" or solar penetrations – which are slipped over the pipe before the actual pipe installation and seal the penetration point. The anchoring of the penetration must be waterproof and long-term durable. Never seal the penetration only with sealant or silicone – these materials do not age well under temperature shocks.

Penetration through the wall into the boiler room is sealed with mineral wool and a permanently elastic sealant (not acrylic). The pipe at the penetration point must not be fixed in a rigid way – it must allow for thermal expansion (approx. 1.2 mm/m of pipe at Δt = 100 °C for copper).

Installation of the pump unit and expansion vessel

The pump unit is the heart of the system. It contains the circulation pump, flow regulator (flow meter), safety valve, ball valves for service, air vent and connection for the expansion vessel. In modern units, the regulator is integrated directly into the body.

A good example from practice is solar pump unit IVAR.SOLAR K with regulation IVAR.SOLAR IMTDC. It is a compact unit with integrated differential regulation, which controls the pump based on the temperature difference between the collector and the storage tank. The IMTDC regulator allows setting the start ΔT values (typically 6–10 °C) and the stop ΔT values (typically 3–4 °C), which is the basis for the correct system operation.

Placement of the pump unit

The pump unit is placed:

Always on the return line (cold side from the collector's perspective, hot side from the tank's perspective) – this way the pump does not operate at the highest temperatures and has a longer lifespan
As close as possible to the tank to keep the return loop short
In an easily accessible location for service – not behind the tank, not under the ceiling without a ladder
The pump shaft is always in a horizontal position (pump series with wet rotor are not designed for operation with a vertical shaft)

Expansion tank

The expansion tank is a safety component – it captures the volume of liquid that results from the thermal expansion of the glycol/water mixture when heated. The volume of the expansion tank is calculated from the volume of the system fluid (pipe volume + heat exchanger volume in the tank + collector volume) and the maximum operating pressure. For a standard 2-collector system with ~15–20 m of piping, the expansion tank is typically 8–12 liters.

The nitrogen pre-charge in the expansion tank (set before filling!) must correspond to the hydrostatic pressure of the fluid column from the tank's installation location to the highest point in the system (collectors). Simple calculation: height h [m] × 0.1 = pressure [bar]. If the height from the tank to the collector is 8 m, the pre-charge is 0.8 bar. In practice, it is rounded up to 1.0 bar and a safety margin of 0.2–0.3 bar is added, so the pre-charge = 1.0–1.1 bar.

Connection to the tank – solar heat exchanger and secondary circuit

The tank for a solar system differs from a standard water heater in that it has a second heat exchanger (coiled tube or jacket heat exchanger) in the lower part of the tank. This heat exchanger forms the connection between the primary solar circuit (glycol) and the secondary circuit (drinking water). Both circuits are hydraulically separated – glycol must never mix with drinking water.

The connection is simple, but the order of the connections is important:

The outlet (hot medium from the collector) goes to the lower inlet of the heat exchanger in the tank – thus, the hot medium enters from the bottom up and heats the water in the tank from the bottom
The return (cooled medium) leaves from the upper outlet of the heat exchanger back to the pump unit (return line)

This counterflow principle (hot medium from below, cold medium from above) maximizes the efficiency of heat transfer.

Temperature sensors – correct placement is the basis of regulation

Solar regulation compares the temperature at the collector (T1) with the temperature in the tank (T2). Without a properly placed and functioning sensor, the system cannot know when to start or stop the pump. The collector sensor (T1) is usually placed in a well attached to the collector absorber – this position is specific to each type of collector and is determined by the manufacturer.

The tank sensor (T2) is placed in a well on the tank. The correct height is the lower third of the tank, so the regulation reacts to the actual temperature of the cold water (not the hot layer on top). For this purpose, for example, temperature sensor for well 180 °C; cable 2 m or for less demanding applications sensor for well – PVC cable 4 m; 95 °C are suitable. When selecting the tank sensor, note: a sensor with a max. temperature of 95 °C is suitable only for the tank, not for the collector (temperatures during stagnation exceed 150 °C there).

The T1 (collector) sensor cable follows the same route as the solar pipe – when using pre-insulated double pipe with a cable, the sensor cable is integrated and protected by insulation. The T2 (tank) sensor cable is short and runs directly to the regulator in the pump unit.

Filling, air venting and pressure test

This is the phase where most problems appear – and if done incorrectly, problems will appear only a season later. The procedure is as follows:

Preparation of glycol mixture

The primary circuit is filled with a mixture of propylene glycol and water (never ethylene glycol, which is toxic and unsuitable for solar systems with potential contact with drinking water). The ratio depends on the required frost resistance:

40 % glycol / 60 % water → protection down to -25 °C (typical Slovak winter)
50 % glycol / 50 % water → protection down to -35 °C (mountainous areas)

The mixture is prepared in advance in a container. We never fill the system with pure water – in the case of unexpected stagnation, the water would boil and the piping system would be exposed to temperatures that water cannot withstand.

Filling device

A membrane pressure pump (manual or electric) with a pressure gauge is used to fill the solar system. Procedure:

Close all air vent valves and drain cocks
Connect the pump to the filling cock (usually on the bottom side of the pump unit)
Open the ball valve on the output of the pump unit towards the collector
Pump slowly – fill the system from bottom to top, so that air escapes to the highest point (collector)
Gradually open the air vent at the highest point (usually on the collector or at the air vent valve near the collector) – until liquid flows without bubbles
Pressure test: inflate the system to 1.5× operating pressure (if operating pressure is 3 bar, the test is at 4.5 bar), let it stand for 30 minutes – pressure must not drop
Reduce pressure to operating pressure (typically 2.5–3 bar cold)

Air in the system is the most common cause of weak or uneven flow after startup. If the pump runs after filling, but the flow is low or zero, it is most likely an air pocket in the system. More on this in the article Stuck or weakly pumping solar pump – causes and solutions.

First start-up and regulator setting

After filling and pressure testing, the first start-up follows. This is the moment when you see whether everything works correctly:

Turn on the pump unit manually (bypass the regulator) and monitor the flow on the flow meter – with correct dimensioning, it should be 60–120 l/h for a 2-collector system
Adjust the flow with the throttling valve on the pump unit – too high flow reduces the outlet temperature, too low flow increases the temperature, but reduces the amount of heat delivered
Set the regulator parameters: ΔT start 6–8 °C, ΔT stop 3–4 °C, maximum tank temperature 60–65 °C (to prevent legionella, it is necessary to heat to at least 65 °C at least once a month)
Check all connections for leaks – after heating the system, connections may slightly shift on the first sunny day

Electrical connection of the regulator and sensors

The electrical connection must be in accordance with the manufacturer's instructions for the regulator. Basic rules:

The regulator is powered from 230 V/50 Hz – phase, neutral, protective conductor (PE)
The pump is connected via the regulator's relay – never directly to the grid
Sensor cables are low-voltage (typically NTC thermistor, resistance 10 kΩ at 25 °C) – they are run separately from high-voltage, maximum sensor cable length is usually 30 m without an amplifier
The collector sensor cable must not be run in the same conduit as the power piping – thermal radiation from the piping could damage the cable
All connections in external environments must be at least IP54 protection class

Typical errors from practice – what to avoid

Over the years of installations, certain errors repeat. Here are the most common ones:

Pressure relief valve incorrectly oriented – the pressure relief valve on the primary circuit must be able to discharge liquid. If the discharge hose of the pressure relief valve is led downward and blocked, when it opens, it can cause dangerous spraying of hot glycol.
Storage tank sensor placed too high – the sensor measures the temperature of the hot layer on top and the regulator "thinks" the tank is hot, although most of the water is still cold. The system shuts down almost immediately and the energy yield is low.
Incorrect pre-charge pressure in the expansion tank – if the pre-charge pressure is too low, the membrane in the tank is constantly compressed and the tank performs its function only partially. During thermal expansion, the pressure relief valve opens sooner than it should, and the system loses liquid.
Insulation of the pipe cut during penetration – at penetration points through structures, insulation is often cut or compressed. This location then condenses moisture and corrodes.
Connecting three or more collectors in series – when three or more collectors are connected in series, the temperature difference between the first and last collector is too large, which reduces the overall performance. The recommended limit for a series is two collectors.
Storage tank without a magnetic anode – a solar storage tank operates at higher temperatures than a regular water heater. Without a functional anode, its lifespan is dramatically shortened. The anode must be checked every two years.

Final check and handover of the system

Before handing over to the customer, fill out a handover protocol, where you record:

System pressure cold (e.g. 2.5 bar)
Expansion tank pre-charge pressure (e.g. 1.1 bar)
Type and concentration of antifreeze mixture (e.g. propylene glycol 40 %, protection down to -25 °C)
Regulator settings (ΔT start, ΔT stop, max. tank temperature)
Set flow rate (l/h)
Serial numbers of the pump unit, storage tank and collectors
Date of installation and date of the first planned inspection

The customer should be informed about how the system works, how to distinguish normal conditions from faults, and when to call for service. A good additional reading for the customer is the article Maintenance and service of a solar system – what to check every year.

Most frequently asked questions (FAQ)

Do I need a building permit for a solar system?

In most cases, no. The installation of solar collectors on a family house is considered an announced or even unannounced construction according to the Slovak Building Act (Act No. 50/1976 Coll. in the version of later laws), provided the collectors do not exceed the roof area, do not change the shape of the roof and are placed in accordance with the zoning plan. Specific conditions may vary depending on the municipality and location (historic zone). Always check the situation at the local building office before starting the installation.

How long does the installation of a solar system take on a typical family house?

An experienced team of two installers can install a 2-collector system with a simple storage tank in 1–2 working days. First day: mounting of collectors, piping, installation of the storage tank and pump unit. Second day: electrical connection, filling, pressure test, setting and start-up. More complicated pipe routes, a larger number of collectors or reconstruction of an existing boiler room can prolong the time.

What happens to the solar system in winter when it is freezing?

A properly dimensioned and filled system with a propylene glycol-water mixture (min. 40 % glycol) will easily survive typical Slovak winters. Collectors are not sensitive to frost – the glass cover can withstand mechanical stress. Problems occur only if the system loses liquid (e.g. due to a leak) and only air and some water remain. Therefore, annual pressure and glycol concentration checks are important.

Can I connect a solar system to heating, not just hot water?

Yes, but it is a much more complex installation. A solar system for heating support requires a larger number of collectors (min. 6–10 m²), a large combined tank (buffer tank 500–1 000 l), a correct hydraulic connection to the heat source (boiler, heat pump) and a more intelligent regulator. This application makes sense mainly in well-insulated houses with floor heating (low temperature of delivered heat). More information can be found in the article How to choose a solar system for hot water in a family house.

How long does antifreeze last in a solar system?

Propylene glycol degrades due to high temperatures and oxidation. In solar systems, where stagnation temperatures reach 150–180 °C, the mixture should be checked every 2 years and replaced every 4–6 years or sooner if the pH drops below 7 (the mixture becomes acidic and starts to corrode metal parts). The inspection is done with a refractometer (measuring concentration = frost resistance) and a litmus test (pH). More about this in the article Maintenance and servicing of a solar system – what to check every year.

Is there a difference between flat and tubular collectors in terms of installation?

Yes. Flat collectors are mounted as a single unit – they are heavier and bulkier, but easier to connect hydraulically (connection on the side). Vacuum tube collectors are mounted tube by tube – the frame is relatively light, the tubes are inserted separately, which makes handling on the roof easier, but the actual connection can be more complicated. With a flat collector such as IVAR.SOLAR 210 M5, the installation procedure is standardized and most installers have more experience with it. A comparison of both types can be found in the article Flat vs. tubular solar collector – comparison of types for Slovak conditions.

Conclusion

Installation of a solar system is a technically demanding job that requires preparation, the right materials, and following the correct procedure. Each phase – from mounting the collectors on the roof, through routing insulated piping, installing the pump unit, proper placement of sensors, to filling and setting the controller – has its own rules and common mistakes. The good news is that if the system is properly designed and installed, it will operate reliably for decades with minimal maintenance needs. The first annual inspection after the season will show whether everything is in order – and from that moment on, the solar collectors will quietly and reliably do what they are supposed to: convert sunlight into hot water.

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