Solar system installation step by step: what you can do yourself and what must be done by a professional

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Solar system installation step by step: what you can do yourself and what must be done by a professional

A solar system isn't rocket science, but it isn't a simple DIY job either. Over years of practice, I've seen dozens of installations – from exemplary work to cases where the homeowner successfully handled the support structure and saved a few hundred euros, to disasters where an amateur-soldered solar circuit required a complete rebuild after two seasons. So I'm not writing this article to discourage you or to push you toward DIY at all costs. I want to give you a realistic overview of what installing a solar system involves, where the real risks lie, what you can handle without special equipment, and where you simply cannot go without a professional – and not because of bureaucracy, but because of physics and safety.

If you're still deciding on the specific system, the number of collectors, or the tank volume, first check out the articles How to choose a solar system for a family house: output, number of collectors and tank volume and What solar system output do I need: calculator based on number of people and hot water consumption in our Knowledge Center. Planning the installation only makes sense once you have a clear idea of the system.

What a typical solar system contains and why it matters for installation

Before we get into the procedure, we need to clarify what the system consists of. This directly determines which phases are DIY-friendly and which are not.

A standard system for a family house consists of five functional units:

Solar collectors – flat-plate or tube collectors, most commonly 2 panels for a 3–5 person household
Support structure – adapted to the roof type (pitched, flat, facade)
Solar tank – bivalent, usually 200–300 liters
Solar station – pump group with controller, expansion vessel and safety valve
Solar circuit – copper or stainless steel piping with thermal insulation, filled with antifreeze mixture (propylene glycol)

Each of these units has a different installation character. The support structure is predominantly mechanical work. The piping requires soldering or press-fitting with pressure testing. Connecting the tank to the household hot water system is plumbing work. Wiring the controller is electrical work. And commissioning – filling, venting, setting parameters – is professional diagnostics.

Phase 1: Preparation and planning – what you must resolve before the first screwdriver

Technical survey and structural assessment

The first phase is purely paperwork and analysis, yet many underestimate it. Before any order or installation, you need to know:

Roof load capacity: Two flat-plate collectors with structure commonly weigh 80–120 kg. On a pitched roof with a standard rafter structure this usually isn't a problem, but on an older roof with damaged rafters, a flat roof with a light metal sheeting, or a garage roof slab, it can be critical. A structural assessment isn't just a formality – it's your insurance.
Orientation and tilt: Optimum is south ± 30°, tilt 30–50°. Deviations are workable but affect output. More on this in the article Solar system for pitched vs. flat roof: which to choose and what it means for installation.
Shading: Chimneys, ventilation outlets, neighboring trees – anything that at least partially shades the collectors during the day significantly reduces output.
Pipe routing: Where will the solar piping run from the collector to the boiler room? Every extra meter means heat losses and additional material. The ideal route is as short as possible, with a minimum of penetrations through structures.

Permits – when are they needed?

This is a question we get very often. Simple answer: collectors mounted on an existing roof within the roof plane (i.e., not protruding beyond the roof surface) in the vast majority of cases do not require a building permit – it's a simple structure or building intent for which a notification is sufficient, or sometimes not even that. A more complex situation arises with flat roofs with superstructures, facade installations, heritage-protected buildings, or installations in protected landscape areas. Always check the current status with the relevant building authority – rules may vary by municipality.

Phase 2: Installing the support structure – the most realistic DIY part

Installing the support structure is the phase where a skilled and responsible homeowner with experience working at heights can genuinely save on technician's work. Most systems supplied as a set include a structure adapted to the specific roof.

Pitched roof – installing hooks and rails

On a pitched roof, the collectors are anchored using roof hooks that are installed directly on the rafters under the roofing. Procedure:

Determine the rafter layout – usually every 70–90 cm. The hook must always sit on a rafter, not just under the roofing.
Uncover the roofing at the installation point (lifting or temporarily removing a few tiles is enough).
Screw the hook to the rafter – at least 2 screws 6×80 mm, ideally stainless steel.
Put the tiles back and seal the hook penetration (most hooks have an integrated lead or rubber gasket).
Install horizontal rails on the hooks according to the collector spacing (usually 1,400–1,500 mm).
Ensure alignment with a spirit level in both axes.

Working at heights requires fall protection. On a roof with a pitch over 20°, do nothing without a rope and anchoring equipment or scaffolding. This isn't a cliché – every year in Slovakia several fatal falls occur precisely during amateur roofing work.

Flat roof – ballast structure or anchoring

On a flat roof you have two options: a ballast structure made of concrete slabs, or anchoring into the roof structure. The ballast option is gentler on the waterproofing but requires calculating the structural load (concrete slabs 300×300 mm commonly weigh 9–11 kg each, for two collectors you need 8–12 pieces). Anchoring is more stable, but you must penetrate the waterproofing, which requires thorough sealing and ideally the presence of an experienced roofing technician.

Specific product examples with solutions for both roof types: Vaillant auroSTEP VSL S 250/2 T is designed for a pitched roof and comes complete with a full rail structure and roof hooks. For a flat roof there's the Vaillant auroSTEP VSL S 250/2 F variant, which has a different base type adapted for a flat roof surface with adjustable tilt. Both sets are complete – they include the tank, collectors, station and control system.

Phase 3: Installing the tank – physical but manageable work

The hot water tank (200–300 liters) is heavy. An empty tank weighs 70–120 kg depending on design, filled with water it's 270–420 kg. Placing the tank in the boiler room or utility room is purely physical work, but requires at least two people and a well-thought-out procedure – typically tilting the tank on its side, moving it through the door, and standing it up in place.

The tank must stand on a flat, load-bearing floor. A boiler room's concrete floor is usually suitable without further measures. On a wooden loft floor or in an attic, the structure should be checked – 400 kg on an area of 0.3 m² is a significant point load.

Don't forget the service space around the tank – at least 60 cm on the anode side (the protective magnesium anode is replaced regularly, usually every 2–4 years depending on water hardness) and at least 40 cm on the connections side.

Phase 4: Solar piping – this is where professional work begins

This is the phase where most DIY enthusiasts hit their limit. The solar circuit is not an ordinary water installation. It operates with temperatures up to 180°C (collector stagnation temperature in summer when the tank reaches maximum), with an antifreeze propylene glycol mixture and a pressure of 2–4 bar. Poor installation here doesn't just mean a leak – it can mean corrosion damage to the entire system, tank failures, or pipe bursting during stagnation.

Pipe material – what to use and what not to

The solar circuit is made exclusively of copper (Cu) or stainless steel (inox). Plastic pipes – including PERT/AL/PERT or PEX – are unsuitable for the solar circuit due to the high temperatures (stagnation temperature can easily exceed 150°C). This rule cannot be bypassed even with special types of plastic. Copper Ø18 mm is the standard dimension for a two-collector system with a circuit length up to 15 meters. For longer routes or more collectors, consider Ø22 mm.

Soldering copper in the solar circuit must be hard soldering (temperature above 450°C, silver solder), not soft soldering (tin solder). Soft solder cannot withstand the thermal stress of the solar circuit. In practice this means you need an oxy-acetylene set or a professional gas torch with sufficient temperature, protective gas (nitrogen) to prevent oxidation inside the pipe, and experience with hard soldering. An alternative is press-fit or screw fittings certified for solar circuits – these don't require soldering, but must be certified for temperatures of at least 200°C and pressure of at least 10 bar (even though normal operating pressure is 2–3 bar, the safety valve is set to 6 bar).

Pipe insulation

Solar piping, especially in areas exposed to UV radiation (on the roof, at roof penetrations), must be insulated with UV-stable insulation. Standard black Armaflex insulation without UV stabilization degrades in sunlight within 2–3 years. Use special solar insulation (EPDM or Armaflex HT Solar) with a thickness of at least 19–25 mm on the outdoor section and 13 mm inside the building.

Phase 5: Installing the solar station and tank – professional plumbing work

The solar station (pump group) is usually installed in the boiler room as close to the tank as possible. It contains a circulation pump, flow meter, check valves, safety valve, filling fitting and pressure gauge. Mounting it on the wall and connecting it to the tank and circuit is plumbing work that requires knowledge of hydraulic schemes and experience with pressure testing.

The tank must be connected to the solar circuit (heat exchanger in the tank), to the cold water supply, to the hot water supply, and to the backup heat source (boiler, electric heating element or heat pump). Each of these connections has its own specifics – safety valve on the cold water side, circulation, check valves. When customers install a tank without experience, the most common mistake is the absence of a safety valve on the cold side (risk of tank explosion) or incorrect directional connection of the heat exchanger (the solar zone gets connected to the boiler heat exchanger instead of the solar heat exchanger, and vice versa).

For sets with an integrated tank and collectors, such as Protherm HelioSet FES2 250 BM or Protherm HelioSet 2.250C HT, hydraulic schemes and installation instructions are included directly with the set and are clearly laid out. Still, the final pressure test, filling and setup remains work for a certified installer.

Phase 6: Electrical wiring of the controller – electrician only

The solar controller (differential thermostat or digital control unit) controls the operation of the circulation pump based on the temperature difference between the collector and the tank. Wiring the controller includes:

230 V power supply (fixed connection from the fuse box or a socket with a protective conductor)
Connecting temperature sensors (NTC sensors, mostly low-voltage 12 V, but the route must be kept separate from the mains wiring)
Power supply and control of the pump
Possible connection to the boiler or heat pump (bus communication or potential-free contacts)

Electrical work on fixed wiring is, under current Slovak legislation, the job of a qualified electrician. This isn't just a formal requirement – incorrect wiring can cause fire, short circuit, or electric shock injury. Moreover, without an inspection report of the electrical installation, the insurance company may not pay out in case of damage.

Phase 7: Filling, pressure testing and commissioning – professional only

This is the final and most critical phase. The solar circuit is filled with a propylene glycol and water mixture in a ratio corresponding to frost protection (most commonly 40–45% glycol, protection down to -25°C). Before filling, a pressure test is performed with air or nitrogen at 1.5 times the operating pressure, minimum 6 bar – the pressure drop over 30–60 minutes is monitored. Any drop indicates a leak that must be found and fixed before filling.

Filling is followed by venting – the solar circuit must be freed of air bubbles, otherwise the pump cavitates and the system doesn't work. Venting is done using a special procedure (so-called flushing), most often with a filling pump with feedback. If air remains in your solar circuit, you'll hear noise and the system will have reduced efficiency or be completely non-functional.

Setting the controller – delta T (the temperature difference at which the pump turns on and off), maximum tank temperature, overheating protection – is also a professional configuration task. Incorrect settings can lead to tank overheating, unnecessary pump wear, or insufficient use of solar energy.

Combination with an existing system – boiler or heat pump

Most family houses have a solar system as an addition to an existing boiler or heat pump. Correct interconnection is key to the efficiency of the whole system. This topic is covered in more detail in the article Combining a solar system with a boiler or heat pump: how to properly interconnect the systems. Briefly here: the tank must have a two-zone heat exchanger or must be hydraulically connected so that solar energy primarily heats the lower zone of the tank, and the boiler or heat pump only tops up the upper zone when solar production is insufficient. Incorrect connection, where the boiler and solar system "compete" for the same zone, leads to the boiler covering demand that the solar system could have covered on its own – and the return on investment worsens.

If you're looking for a compact set where the collectors, tank and station are designed as one functional unit, check out the Solar System No. I S – a versatile solution suitable for typical family houses.

Typical mistakes from practice that are costly to fix

Over years of working with solar systems, the same mistakes keep repeating. The most common ones:

Pipe route too long without sufficient slope for venting: The piping must have at least a 0.5% slope toward the vent valve. Air gets trapped on horizontal sections and the system cavitates.
Missing or weak insulation on outdoor piping: Heat losses on uninsulated outdoor piping in winter can wipe out the entire morning gain from the collector.
Undersized expansion vessel: During summer stagnation, the entire volume of liquid in the collector evaporates and needs somewhere to expand. A vessel that's too small leads to the safety valve opening and glycol escaping – the circuit can be practically drained several times per season.
Incorrect flow rate in the solar circuit: The flow rate is set using the flow meter in the station – the optimum is usually 40–60 l/h per collector. Too high a flow rate reduces efficiency (the liquid doesn't have time to heat up), too low causes overheating and stagnation.
Not following manufacturer instructions: Each manufacturer has specific requirements for controller settings, tank temperature, and glycol type. Ignoring them can void the warranty.

Costs and real savings: what you can save with DIY and where it's not worth the risk

Installation of a solar system by a professional company commonly costs €600–1,200 including labor (excluding materials), and can be more with a more complex pipe route, multi-story houses, or an unfavorable layout. Where you can realistically save with your own work:

Installing the support structure and rails – savings of €150–300
Physically placing the tank and collectors on the structure – savings of €80–150
Digging and backfilling for underground piping (if the route goes through the garden) – savings of €50–150

Where DIY brings a bigger risk than the savings: hard soldering of copper (mistake = replacing the whole circuit), pressure testing (equipment rental + expert knowledge = the savings evaporate), filling with glycol (wrong ratio = freezing in the first winter, collector damage). Calculate realistically: saving €200–300 on the structure is reasonable. Trying to save €300 on the piping and risking €2,000 in damage isn't a smart deal.

Documentation and warranty conditions – what not to forget

After completing the installation you must have:

Pressure test protocol for the solar circuit
Electrical installation inspection report (from the electrician)
Proof of filling and type of glycol used (with pH value and date)
Manufacturer's warranty certificate for the tank and collectors
Operating manual for the controller and tank

You'll need these documents when applying for a subsidy (if available), in the event of an insurance claim, and when selling the property. Without the pressure test protocol, most manufacturers won't honor warranty claims. More on preventive care and annual checks can be found in the article Maintenance and servicing of a solar system: what to check every year and when to call a technician.

Frequently Asked Questions (FAQ)

Can I install the entire solar system myself, without any professional?

Technically yes for some phases, but not fully from a legal and warranty standpoint. The electrical wiring of the controller must be done by a qualified electrician who issues an inspection report. The pressure test and filling can technically be done yourself, but most manufacturers (including Vaillant and Protherm) make the warranty on the tank and collectors conditional on installation by a certified service organization. So you'd lose the warranty on expensive components, which is a much bigger risk than the cost of a professional.

How long does professional installation of a solar system take?

A standard two-collector system on a family house is installed in 1–2 working days. It depends on the pipe route, roof type, and boiler room accessibility. Simple jobs (tank in the boiler room directly below the collectors, short pipe route) can be handled by a team of two technicians in one day including commissioning. More complicated jobs – for example piping running through multiple floors, through a basement, or involving intervention in the existing boiler hydraulics – can take a full two days.

Do I need a building permit to install solar collectors?

In the vast majority of cases, no. Collectors on a pitched or flat roof of a family house are standardly classified in Slovakia as a simple structure or minor alteration of an existing structure and don't require a building permit. Exceptions apply to heritage-protected buildings, some protected landscape areas, and cases where the collectors significantly change the silhouette or mass of the building. We always recommend checking with the local building authority before installation.

How much glycol is needed in the solar circuit and how long does it last?

The amount of glycol depends on the circuit length and collector size. For a two-collector system with piping up to 15 meters, count on a total circuit volume of about 6–10 liters. The mixture is usually blended at a ratio of 40% propylene glycol and 60% water, giving protection down to about -24°C. As glycol ages it loses inhibitors and becomes acidic, which corrodes the aluminum parts of the collector and the copper piping. Replacement is recommended every 5–8 years, or whenever the pH drops below 7 or the density doesn't match the standard. More in the article Common solar system faults: overheating, air in the circuit, insufficient water heating.

What happens if the solar system has nowhere to put the energy in summer – does it overheat?

Yes, stagnation is a real phenomenon that always occurs when the tank reaches maximum temperature and the pump shuts off. The liquid in the collector overheats above the boiling point (at 1.5–2 bar that's around 120–130°C) and starts to vaporize. The steam pushes the liquid back into the piping and expansion vessel. A well-designed system handles this without damage – the expansion vessel must be correctly sized and the safety valve must not drip at every stagnation event. Systems with a cooling function – where the controller runs the pump at night to release excess heat into the tank – minimize this problem. More in the article Solar system in winter: how it works at low temperatures and how to prevent the circuit from freezing.

Is it more advantageous to buy a complete set or assemble a system from individual components?

For most family houses, a complete set is clearly more advantageous. The manufacturer guarantees hydraulic and thermal compatibility of all components, provides clear installation documentation, and the warranty covers the whole unit. Assembling a system from various components from different manufacturers only makes sense for large or atypical installations where standard sets don't meet the output or layout requirements. Sets like Protherm HelioSet, Vaillant auroSTEP, or the Solar System No. I S are designed precisely to eliminate this problem and simplify both installation and servicing.

Conclusion: a realistic view of DIY vs. professional installation

Installing a solar system isn't a black-and-white matter. It's a project where an intelligent combination of your own work and professional assistance can bring real savings without compromising safety and quality. The support structure, physical work placing the tank, running cables and pipes before covering them – these are phases where a capable homeowner can meaningfully contribute. Hard soldering of copper, pressure testing, filling the circuit, electrical wiring, and commissioning – these are phases where a professional isn't a luxury, but the foundation for a functional and safe system.

Investing in quality installation pays off faster than you might think – a properly functioning system can cover 50–70% of annual hot water consumption, while a poorly installed system with leaks, air in the circuit, or incorrect settings can operate long-term at just 20–30% of its potential. And that's a difference that matters not only in euros but also in satisfaction with the investment. Questions of payback and available subsidies are covered in more detail in the article Frequently asked questions about solar systems: return on investment, subsidies, permits and connection.

Do you have a question on this topic?

Can't decide or dealing with a specific situation in your household? Write to us - we're happy to help.