Step-by-step installation of a solar system – what you need to know

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Step-by-step installation of a solar system – complete practical guide

You have decided to invest in a solar system for water heating – an excellent decision. However, between the moment you bring the collectors home and the moment you actually get hot water heated by the sun running through the tap, there is a whole series of technical steps where many mistakes can be made. Not all of them can be corrected without significant costs. In this article, I will walk you through the entire installation process – from roof preparation to the first start-up – as it looks in real-world practice. No sugarcoating, with specific numbers and warnings about the places where people most often mess up.

If you are still in the phase of choosing equipment, first read our article How to choose a solar water heating system for a family home or What solar collector power do I need for my home – installation of a well-dimensioned system is much easier and the result is better in the long run.

What you need to prepare before the actual installation

An experienced installer knows that preparation makes up about half of the success. Customers who leave things to the last minute then wait for materials, hit a chimney where they planned to run the pipe, or find out that their tank doesn't fit where they planned to put it. So start with the following steps.

Project documentation and building permit

For installations where the collectors protrude from the roof plane (for example, free-standing support structures or integrated collectors replacing the roof covering), you usually need a building permit or at least a building notification. Classic collectors mounted in the plane of a sloped roof on a family home usually do not require notification – but always check with the relevant building authority, as it depends on the location and local regulations.

For a combination with a central heating system or when connecting to an existing boiler circuit, it may also be necessary to obtain a statement from the gas company (if you are working near a gas distribution system), and in any case, it is required that the pressure system with an expansion tank and safety valve is designed or at least checked by a person with the appropriate professional qualification.

Material list – what you need to have before you start

Before installation, prepare a complete list of materials. A missing small item – for example, a gasket or the correct type of elbow – can stop you in the middle of the work for hours. A typical list for a two-collector gravity or forced circulation system for a four-person household includes:

Solar collectors (flat or tubular) – typically 2 to 4 pieces, area 4–8 m²
Solar hot water storage tank with a double spiral or solar heat exchanger – volume usually 200–400 liters
Solar station (pump group) with a circulation pump, flow meter, ball valves, and safety valve
Expansion tank for the solar circuit – volume to be dimensioned according to the system content and maximum operating temperature (typically 8–25 liters)
Solar antifreeze – a mixture of propylene glycol and water, concentration according to local climatic conditions (for Slovakia, standard frost resistance is –28 °C to –35 °C, i.e. about 45–50 % glycol)
Solar piping – copper or flexible stainless steel corrugated (corrugated) piping with a stainless steel sheath, diameter typically 18 mm (3/4") or 22 mm (7/8") for longer runs
Thermal insulation of the piping – for external runs UV-stabilized, minimum wall thickness 25 mm for DN 18 piping
Support structure for the collectors – anchoring depends on the type of roof
Solar controller (differential thermostat) with temperature sensors for the collector and tank
Pressure relief valve set to the maximum operating pressure of the system (typically 6 bar)
Drain valve – automatic or manual at the highest point of the piping
Filling and draining set (valves) for filling the solar fluid

Step 1 – Static assessment of the roof and preparation of anchoring

A solar collector with a support structure typically weighs 35–55 kg per piece (flat collectors are heavier, tubular ones are lighter). Two collectors with a structure and piping represent a load of 80–130 kg. This load itself is manageable for most standard roofs, but you must anchor it correctly.

The anchoring must not be only into the roof flashing – you anchor into the rafters or purlins. Before you drill the first screw, find the position of the rafters. You can do this with a magnetic or electronic detector through the flashing, or look from the attic. Rafters are typically spaced every 80–100 cm, so for a typical two-collector width of 200 cm, you usually hit at least two rafters.

Roof hooks are mounted under the roofing – lift the roofing element (tile, shingle), slide the hook under the flashing, and screw it into the rafter with at least two screws with an M8 or M10 thread. After tightening, check the hook for movement – it must not wobble. Then return the roofing to its place, or modify it by cutting if the hook protrudes. Most manufacturers supply hooks in various heights precisely for different types of roofing – thin concrete tiles, high profile tiles, and sheet metal each have their own solution.

Then, aluminum profile tracks (usually two pieces for the full width of the collector field) are attached to the hooks, to which the collectors themselves are fastened using clamping brackets.

Step 2 – Installation of collectors on the roof

Before carrying the collectors onto the roof, plan the entire work. Flat collectors are heavy and large – a typical piece has dimensions of 200 × 100 cm and weighs 35–45 kg. You cannot carry them safely by yourself. At least two people are necessary, and for a larger number of collectors, I recommend three.

Collector installation procedure:

Mount the tracks on the roof hooks and make sure they are level (even on a sloped roof) using a spirit level. The distance between the tracks must match the mounting holes of the collector.
Carry the collectors onto the roof – most commonly through a window in the attic or via a ladder access. Never carry a collector alone without securing it – in the event of a fall, it is dangerous for both you and others nearby.
Place the collector on the tracks and secure it with clamping brackets – each collector must be fastened at least at 4 points.
Connect the collectors to each other – the arrangement can be series or parallel. Parallel connection is more advantageous for most installations (balanced flow, lower pressure), but it requires proper balancing. For 2–3 collectors, a series connection is simpler and functional with proper dimensioning.
Install the air vent at the highest point of the collector field – it must be accessible, as you will need it during the first filling and possibly also during operation.

Step 3 – Solar pipe routing

The solar pipe connects the collectors on the roof with the storage tank in the technical room. This route is one of the most important decisions in the entire installation, as it affects heat losses, the complexity of the installation, and the system's lifespan.

Selection of pipe material

You basically have two options: copper pipe joined by hard or soft soldering, or flexible corrugated pipe made of stainless steel. Copper pipe is cheaper and, with good craftsmanship, can last for decades, but its installation on hard-to-reach routes is challenging. Flexible stainless steel corrugated pipes are much easier to lay through floors, through the attic, through drilled holes – they are inserted like a snake and only need to be bent without elbows. The price is higher, but you save time and fittings.

Never use the following for solar circuits:

Galvanized pipe – glycol aggressively affects it
Standard PE-X or PVC pipe – they are not temperature resistant (a solar circuit can reach 180–200 °C during stagnation)
Standard rubber hoses – they degrade quickly at high temperatures and under UV radiation

Dimensioning the pipe cross-section

For a typical residential solar system with 2–4 collectors and a flow rate of 40–60 liters/hour, a DN 18 (3/4") pipe is sufficient. For longer routes over 15 meters or with a larger number of collectors, consider DN 22 (7/8") to keep the pressure loss at an acceptable level – ideally under 0.5 bar for the entire circuit. Pressure loss depends on length, flow rate, and diameter; if in doubt, calculate it or consult.

Pipe route and insulation

The pipe must be sloped downward from the collectors – at least 1–2 cm per meter – so that the system can be properly vented when shut down and so that steam can condense and flow back during stagnation. If you have a route where a local peak is unavoidable, install an automatic vent there.

Insulate the external parts of the route with UV-resistant and high-temperature-resistant insulation – for example, Armaflex HT or equivalent. The thickness of the insulation wall should be at least equal to the outer diameter of the pipe (1:1 rule). For DN 18, at least 18 mm wall thickness, preferably 25 mm. Insulate internal parts running through unheated crawl spaces, basements, or technical rooms with standard rubber or mineral insulation – UV stability is not necessary there.

Step 4 – Installation of the storage tank and solar station

The solar storage tank is the heart of the entire system. Most modern storage tanks for solar systems have two heat exchanger coils – a lower one for the solar circuit (collector) and an upper one for heating (boiler, heat pump). Some tanks have a smooth shell and an external heat exchanger in the solar circuit.

Storage tank placement

Place the tank as close as possible to the hot water consumption points to minimize distribution losses. Ideally, it should be in a technical room with good access for service. The tank must stand on a solid floor – a 400-liter tank full of water weighs about 450–500 kg. Check the floor load capacity if it is a floor above a basement or a ceiling structure.

The tank must be accessible for checking the safety valve, anode rod, and connections. Minimum distance from the wall at least 30 cm on the anode side – the anode must be regularly checked and replaced (usually every 2–4 years depending on water quality).

Solar pump station (solar station)

The solar station is a compact assembly containing a circulation pump, flow meter, safety valve, ball valves, vent, and temperature sensors. It is mounted on the solar circuit pipe – on the return (cold side of the collector). Most stations are pre-assembled and only require pipe connection and electrical connection of the pump and controller.

Connecting the storage tank to the solar and heating

The solar coil of the storage tank is located in the lower third of the tank – the supply (hot from the solar circuit) is fed from the top, the return (cold to the collector) from the bottom. The upper coil or electric rod is used for heating by the boiler or electricity. Make sure to correctly install the temperature sensors into the immersion sleeves of the tank – one should be at the collector outlet (or in the return near the tank), the other in the lower part of the tank where it measures the temperature of the stored heat.

If you are combining the solar system with a gas or heat pump boiler, see our separate article Solar system in combination with a boiler or heat pump, where hydraulic schemes for various situations are described in detail.

Step 5 – Installation of the expansion tank and safety valve

The expansion tank is crucial for the safety and proper function of the solar system – and at the same time it is a component that is most often underestimated or incorrectly dimensioned in practice.

Why is the expansion tank critical in a solar system

Antifreeze liquid expands when heated – typically by 5–8 % at temperatures up to 100 °C. During stagnation (when the tank reaches maximum temperature and the system stops removing heat), temperatures in the collector can rise to 150–200 °C and the liquid begins to boil and form steam. The expansion tank must accommodate the volume of this steam to prevent the pressure in the system from exceeding the safety valve setting.

The volume of the expansion tank is calculated using a formula that takes into account the total content of the entire system (collectors + piping + heat exchanger), the expansion coefficient of the liquid and the pre-charge pressure of the tank. For a typical system with 2 collectors, a circuit volume of approx. 6–10 liters and a flow pressure of 2–3 bar, the expansion tank volume is 10–18 liters. Always use an expansion tank designed for solar systems – it has a membrane resistant to glycol liquid at high temperatures. A standard heating expansion tank is not sufficient for this!

Safety valve

Set the safety valve to the maximum operating pressure of the system – typically 6 bar. It is mounted on the collector outlet (hot side) or directly on the solar station. The discharge of the safety valve must be directed upwards into a drain, not towards electrical equipment. During each inspection, check that the valve is not clogged – manually press the handle (if it has one) to verify that it opens.

Step 6 – Filling and bleeding the system

Filling the solar circuit with glycol liquid is a moment where incorrect procedure can cost you hours of removing air pockets. Do it right from the beginning.

Preparation of glycol liquid

The solar liquid is prepared by mixing propylene glycol and distilled or soft water. For Slovakia and conditions in Central Europe, the rule is: frost resistance at least to –28 °C, which corresponds to a propylene glycol concentration of approx. 40–45 %. A higher proportion of glycol (50 % or more) increases frost resistance, but reduces the heat capacity of the liquid and increases its viscosity – the pump has to work harder. Always verify the concentration using a refractometer, not just by volume ratio calculation.

Total required liquid volume = volume of collectors + volume of piping + volume of the heat exchanger in the tank + volume of the expansion tank (up to pre-charge pressure) + approx. 10 % reserve. For a typical two-collector system, this amounts to 10–15 liters of finished mixture.

Filling procedure

Carry out the filling using an electric filling pump with a tank. The procedure is as follows:

Close the safety valve (if possible) or direct the discharge into a container
Open all bleeders in the system – on the collector, on the station, at the highest points of the piping
Connect the filling adapter to the drain/filling valve of the solar station (most stations have a pair – one for filling, the other for draining)
Pump the liquid from the bottom up – starting from the tank towards the collector
When no more air comes out of the bleeders and only liquid flows out, close the bleeders
After filling, flush the system (circulate the liquid with the pump for at least 15–20 minutes) while opening the bleeders – air is trapped in the bends of the piping and comes out gradually
Set the operating pressure of the system in the cold state to 1.0–1.5 bar (depending on the height of the collectors above the station and the manufacturer's recommendation)

Step 7 – Connecting the controller and electrical installation

The differential controller (solar controller) is the brain of the entire system. It compares the temperature of the collector and the temperature in the storage tank. When the collector is warmer by the set difference (typically 5–8 °C), the circulation pump is turned on. When the difference drops below 2–3 °C or the tank reaches maximum temperature, the pump is turned off.

Temperature sensors

Proper placement of sensors is crucial. The collector sensor is usually mounted in a special connector at the collector's outlet (or in the back of the collector in a sensor housing) and must be thermally insulated from the surroundings – if left in the air stream, it will measure air temperature, not the collector's. The tank sensor is inserted into a submersion housing in the lower quarter of the tank.

The electrical installation of the controller and pump must be carried out by an electrician or a person with an electrician's qualification. The controller is powered from a 230 V network and controls the pump via a relay output. Solar pumps are usually single-phase, with a power consumption of 15–80 W depending on size.

Step 8 – Commissioning and first inspection

After the installation is completed, the commissioning phase follows, which itself requires sufficient attention – that is why we have a separate article How to set up and commission a solar system, where you will find details about setting up the controller, calibrating the sensors, and the first test cycles.

Here we summarize the basic inspection steps during commissioning:

Visual inspection of the entire installation – no loose connections, all fittings tightened, insulation properly installed
Pressure check in cold state – should be 1.0–1.5 bar, in summer after heating it will rise to 2.5–4 bar (normal)
Flow setting on the flow controller of the solar station – for flat collectors, 30–50 l/h per m² of collector area is recommended, for tubular collectors 20–40 l/h per m²
Controller test – manually start the pump, check that the fluid flows in the correct direction (hot side from the tank to the tank, cold from the tank to the collector)
Check of the safety valve – make sure the discharge is properly elevated
Electrical connection check – temperature sensors properly connected, pump responds to the controller
Test under sunny weather – let the system run and observe whether the tank temperature increases; a standard system under full sun heats a 200 l tank by about 20–30 °C in 4–6 hours

Safety during installation – what you cannot underestimate

Work on the roof belongs among the most risky construction tasks. Serious injuries from falling from the roof occur every year, even among experienced workers. A few rules with no exceptions:

Always use personal fall protection – rope, harness, anchoring point on the roof
Never work on a wet or icy roof
Ladders must be secured and have at least 1 m overhang beyond the roof edge
Materials on the roof must be secured against slipping, even when temporarily set down
Electrical work must always be done with the circuit breaker turned off
Non-freezing fluid (propylene glycol) is mildly irritating in high concentrations – when filling the system, use protective gloves

Common mistakes in amateur installation – from practice

Over years of field work, I have seen recurring mistakes that appear in practically every second amateur installation. I list them so you can avoid them:

Wrong orientation of collectors. Collectors mounted to the west or incorrectly tilted (less than 20° or more than 60°) can lose 20–40 % of annual yield. For Slovakia, the optimal orientation is south ±20°, slope 35–45°.
Insufficient insulation of external piping. Uninsulated 10 meters of external piping can cause heat losses equivalent to 10–15 % of the system's annual production.
Supply and return lines swapped. Collectors are connected in reverse – the pump pumps the fluid in the wrong direction, the tank does not heat up. A common mistake when not checking the flow direction during commissioning.
Missing or undersized air vent. Air in the collector field causes pump knocking and vibrations, reduces flow, and in extreme cases leads to local overheating.
Poor expansion tank – either too small or unsuitable for solar applications. A heating expansion tank without glycol-resistant membrane will start to break down after one season.
Collector sensor not protected from external air influence. The controller receives distorted values and the pump runs or does not run at inappropriate times.
Water instead of glycol. It is not a joke – I have seen a system filled with drinking water more than once. The first winter will destroy the collectors.

When to hire a professional installer and when a skilled handyman can do it

Not every step must be done by a certified expert. A skilled DIYer with technical experience can handle the installation of the support structure, piping, insulation, and installation of the storage tank. What should always be done by a professional:

Electrical installation and connection of the controller (electrician)
Static assessment of the roof, if there are doubts about load capacity
Dimensioning of the expansion tank and system hydraulics (installer with professional qualification for pressure equipment)
Commissioning and final inspection – many manufacturers require this to maintain warranty

Also remember that for some grant schemes (e.g., state subsidies for renewable energy sources), installation by a certified installer and collectors with a Solar Keymark or equivalent certification is a condition.

If you are unsure which type of collector to choose for your home, read the article Flat vs. tubular solar collectors – which type is more cost-effective – it will help you make a decision before purchase, not after.

Solar systems and storage tanks suitable for the installations described in this article can be found in the category Solar systems on atria.sk, where complete sets and individual components are available.

Frequently asked questions (FAQ)

Can I install a solar system by myself without a professional?

The mechanical installation (structure, piping, tank) can be handled by a skilled DIYer with basic installation knowledge. Electrical installation must be done by an electrician. Dimensioning of the expansion tank and pressure testing should be carried out or at least checked by an installer with professional qualification. For maintaining the warranty on the equipment and for the purposes of possible grants, installation by a certified installer is usually necessary – check the conditions with the manufacturer and the grant provider.

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

An experienced two-person team can complete a standard installation (2–3 collectors, 300 l tank, standard piping route) in 1.5 to 2 working days. An amateur installation with first-time familiarization with components, material collection, and possible complications takes 3–5 days. Allow time for sealing drying, initial filling, and first regulator adjustment as well.

What pressure should a solar system have during operation?

In cold state (before heating, in the morning) the pressure should be 1.0–1.5 bar. During operation on a sunny day it rises to 2.5–4.0 bar – this is normal and the expansion tank is dimensioned for it. If the pressure regularly reaches the safety valve setting (6 bar) and the valve discharges fluid, the expansion tank is either too small or has a damaged membrane. If the pressure in the cold state is zero or drops below 0.5 bar, the system likely has a leak.

What happens to the system if I am away for a longer period (summer, vacation)?

This is one of the most important practical problems of solar systems. With full sun and an empty house, the storage tank reaches maximum temperature and the system enters stagnation – the liquid in the collector can start to boil. Quality systems with properly dimensioned expansion tank and safety valve can handle this safely and repeatedly without damage. Stagnation, however, is a load for the glycol liquid and seals – after a season with repeated stagnation, check the pH and glycol concentration. Some controllers have a "storage tank overheating protection" function – the pump starts at night and removes heat. This is an elegant solution, but during the absence of residents, I rather recommend covering the solar system by covering the collectors with a special tarpaulin or manually turning off the pump (the tank will keep the heat for a few days anyway).

Can a solar system be installed on a flat roof or on the ground?

Yes, and in some cases it is even more advantageous – on a flat roof you can optimize the angle of inclination without the limitations of a sloped roof. Special standing structures are used

Do you have a question on this topic?

Having trouble deciding or dealing with a specific situation in your household? Write to us – we are happy to advise.