Frequently Asked Questions about Solar Collector Accessories

We are still preparing products.

But you can look at other categories.

Frequently Asked Questions about Solar Collector Accessories – a comprehensive guide

When a customer chooses a solar collector, they rarely realize that the panel itself is only part of the story. Accessories – mounting frames, fasteners, manifolds, electric backups, sensors – literally form the backbone of the entire system. From experience, I know that accessories are where most unnecessary mistakes occur: an incorrectly chosen mounting frame, underestimated hydraulics, missing seals, an incorrectly sized manifold. The result? The system leaks, the collector moves in the wind, and the output is a fraction of what was promised. This article therefore addresses the most common questions we encounter in practice, based on hundreds of orders each year.

Why are accessories just as important as the collector itself?

A solar collector is essentially just a heat exchanger installed outdoors. To fulfill its function, it needs safe mechanical anchoring, proper hydraulic connection, functional control, and a backup heat source for days without sun. Each of these elements has a critical role. If the collector doesn't have a proper mounting frame, it risks being torn off in the wind (for flat roofs, we typically design for winds of 140–160 km/h, while for pitched roofs it depends on the angle and weight). If a proper manifold and header are missing, collectors connected in parallel won't be hydraulically balanced and will operate with varying efficiency. If we forget the electrical backup, in winter, without sun, the tank won't heat the water to a hygienically safe temperature.

In terms of investment: the cost of accessories typically ranges from 20–40% of the total installation price. Those who cut corners on accessories pay twice – once for the cheap solution and again for repair or replacement after a few months of operation.

Questions about mounting frames – the most common category of inquiries

What mounting frame do I need for my roof type and number of collectors?

This is by far the most frequently asked question, and also the one where customers most often make mistakes. Basic rule: the mounting frame must match the type of mounting surface (flat roof, pitched roof, façade) and the number of collectors you want to install.

For installing two flat collectors (a typical setup for a 3–4 member family with 300–400 liters of tank capacity), the mounting frame for installing two collectors is used. This is a complete mounting frame for in-roof installation on a pitched roof – meaning the collector is installed flush with the roof plane, which is the most aesthetically clean solution and also the most structurally resistant to wind. This mounting frame accounts for the axial spacing of collectors based on their width and has pre-drilled holes for fastening elements.

If you later expand your installation with another panel – a common situation when a customer realizes after a year of operation that the system performs well in summer but doesn't have enough capacity in spring and autumn – there is a mounting frame for adding another collector, which attaches to the existing setup. You therefore don't need to replace the entire mounting system; you just need to install the extension frame. From experience, we recommend: if you're considering expansion within 2–3 years, leave space on the roof during initial installation and choose a mounting frame with expansion capability from the start – you'll save on a second installer visit.

For more on choosing based on specific situations, see the articles How to choose the right mounting frame for a solar collector – flat roof vs. pitched roof and What size and type of mounting frame do I need for my number of collectors in our Knowledge Center.

What is the difference between an in-roof and an adjustable mounting frame?

In-roof installation means the collector lies flush with the roof plane – it essentially becomes part of the roof covering. Advantages: low wind resistance, aesthetics, smaller area exposed to snow load. Disadvantage: requires a perfectly tight connection to the roof covering; for pitched roofs, the angle depends on the roof's slope (ideal is 30–45°). An adjustable mounting frame on a pitched or flat roof allows you to choose the angle independently of the roof slope – typically you can set 35–45° even on a roof with a 15° slope. On flat roofs, an adjustable mounting frame is practically the only option.

What about the weight and load of mounting frames?

A flat solar collector typically weighs 35–55 kg depending on size (2.0–2.5 m²). An empty mounting frame for two collectors weighs an additional 15–25 kg depending on material (aluminum vs. galvanized steel). The entire two-collector setup therefore places a concentrated load of 85–135 kg on the roof. On a pitched roof, this load must be transferred by the rafters; on a flat roof, by the concrete structure. Always check the load-bearing capacity of the roof structure – this can be a limiting factor when renovating older houses.

Questions about hydraulic connection of collectors

What connects collectors to each other and what seals do I need?

Connecting collectors to each other is where beginner installers make the most mistakes. Collectors are connected to each other via direct connections – typically pairs of inlet/outlet on the sides of the collector. This is what the accessories for connecting collectors to each other are for, which include a connecting elbow with correct dimensions, seals resistant to high temperature and antifreeze mixture, and clamping elements.

Key technical requirement: seals must be resistant to temperatures up to 200 °C (during stagnation – when the tank is full and the system stops pumping – the temperature in the collector can briefly rise above 180 °C). Common rubber O-rings from hardware stores are not sufficient for this. Use only EPDM seals designed for solar systems or graphite/PTFE seals.

From experience: we've seen installations where a customer used a common seal from a plumbing installation for a repair. It lasted the first winter, but after the second summer it became brittle and the system started to drip. Since the leak was small and slow, the customer didn't notice for a month that the antifreeze mixture was gone – which caused freezing and cracking of the heat exchanger in the tank during frost. Damage worth several thousand euros due to using an unsuitable seal costing a few cents.

Series or parallel connection of collectors – how does it affect the choice of accessories?

In a series connection, liquid flows through the collectors one after another – the inlet temperature into each subsequent collector is higher. Result: higher outlet temperature, lower flow rate. In a parallel connection, liquid flows through all collectors simultaneously – the same inlet temperature, higher total flow rate, lower outlet temperature compared to series connection. For more on this decision, see the article Series vs. parallel connection of solar collectors – which to choose.

In terms of accessories: with a series connection, direct collector connections and one inlet/outlet to the circuit are sufficient. With a parallel connection of more than two collectors, you necessarily need a manifold and header – without them, you cannot ensure even flow distribution.

Questions about manifolds and headers

When do I need an industrial manifold and header?

For installations of up to 3 collectors, common hydraulic manifolds with copper or brass bodies are usually sufficient. For larger installations – commercial buildings, hotels, apartment buildings, industrial facilities with 4 or more collectors – a stainless steel industrial manifold with ball valves is the right choice.

For such applications, the industrial stainless steel manifold/header set with ball valves – 6/4"x1"; 2-way is suitable, for example. Stainless steel construction is important for several reasons: propylene glycol (antifreeze mixture) can be a mildly corrosive medium at higher temperatures, while stainless steel resists degradation over the long term. Ball valves on each branch allow isolation of individual collectors during servicing without shutting down the entire system.

Dimensions of 6/4"x1" mean: the main (collecting) branch is 6/4 inch (DN40), and the branches for individual collectors are 1 inch (DN25). This size is designed for a flow rate of 3–6 m³/h through the entire manifold, corresponding to systems with 6–12 collectors at a recommended flow rate of 40–60 liters per hour per collector.

What manifold and header materials are suitable for solar systems?

This question is more relevant than it might seem. Antifreeze mixture based on propylene glycol with inhibitors is relatively aggressive toward some metals under prolonged exposure and higher temperatures. Here is an overview:

Stainless steel (AISI 304, AISI 316): ideal material, long-term resistance, no corrosion, medium purity. Higher cost, recommended for larger systems and industrial applications.
Brass: commonly used, good resistance with correctly balanced antifreeze mixture pH (7–8.5). With acidic or overly alkaline medium, zinc leaching can occur. Check the pH of the mixture every 2–3 years.
Copper: excellent thermal conductivity, good resistance to glycol, long tradition in solar systems. Problems arise when combined with galvanized elements – galvanic corrosion.
Galvanized steel: UNSUITABLE for solar circuits with glycol. Zinc dissolves in the glycol medium, forming zinc salts that clog pumps and heat exchangers.

For more on what affects the choice and maintenance of antifreeze mixture, see the article Antifreeze mixture for solar systems – how to choose the right composition and concentration.

Questions about electrical backup – heating elements and boosters

When and why do I need an electric heating element in the tank?

A solar system on its own cannot cover 100% of hot water needs year-round – that's not its purpose. In summer it covers 90–110% (yes, sometimes even more than needed), in spring and autumn 40–70%, in winter 10–30% depending on location and collector angle. For extended periods without sun (typically 5–14 days in summer, longer in winter), a backup source must exist.

An electric heating element is the simplest backup source – directly in the tank, without needing an external boiler. Its 2 kW output is enough to heat a 300-liter tank from 30 °C to 60 °C in approximately 3–5 hours. This is what the 2 kW electric heating element for OKC tanks is used for, sized specifically for tanks of this series.

Strict safety requirements apply when installing an electric heating element: it must be protected by a circuit breaker (typically 10–16 A depending on output), the connection must be in an electrical junction box with a protection rating of at least IP44, and the tank must have a safety valve. The electric heating element is installed into the lower inspection opening of the tank – the reason being that cold water enters from the bottom and the heating element first heats the bottom layer. The upper layer of the tank (where hot water outlet is located) heats up through convection.

Can I install the heating element myself, or do I need an electrician?

Mechanical installation (screwing the heating element into the tank) is relatively simple – it's a threaded connection with a seal, manageable for a skilled layperson. Electrical connection to the 230V mains must be performed by an authorized person (a certified electrician) and must be documented with an inspection report. This is not bureaucratic burden – it's about safety. Faulty electrical wiring of water heating is the source of the highest number of domestic electric shock injuries.

Questions about sensors and control

Where should the collector temperature sensor be placed?

The collector temperature sensor (so-called collector sensor) is installed into a special pocket directly in the collector's absorber – manufacturers have a dedicated position for this, usually at the top of the collector or near the outlet fitting. The article Installing a temperature sensor for a solar collector – placement and connection covers proper placement and connection in detail. Here we'll just emphasize the most important point: the sensor must be in direct thermal contact with the absorber, not just nearby. If the sensor is placed incorrectly, the controller measures the wrong temperature and the system either starts the pump too early (energy loss) or too late (stagnation, overheating).

The tank sensor is placed in the lower third of the tank – measurement in the lower part is critical because the controller needs to know when the tank actually needs reheating. If the sensor were in the upper part, where the water is always warmer, the system would start too infrequently.

Questions about installation and procedure

In what order are the individual accessory elements installed?

The correct installation procedure follows a logical sequence that minimizes repeated work and the risk of damaging finished elements. From experience, we recommend this sequence:

Roof preparation – checking the condition of the roof covering, load-bearing capacity, pipe penetration
Installing mounting frames – anchoring into rafters or preparing ballast blocks for a flat roof. For more on this step, see the article Installing a solar collector mounting frame step by step
Fitting collectors into the mounting frames – without final hydraulic connection
Hydraulic connection of collectors – connections, seals, connecting accessories
Pipe routing – pre-insulated piping (copper or flexible for solar applications) from the roof to the tank
Installing the solar station – pump, safety valve, air vent, flow meter
Installing the manifold/header for more than 2 collectors
Connecting the tank – connecting the solar heat exchanger, installing the electric heating element
Installing sensors – collector and tank sensors, cable routing to the controller
Filling and venting the system – pressure 2.5–3.5 bar, checking all connections
Setting up the controller – temperature differential typically 5–8 K to turn on, 2–4 K to turn off

What are the most common accessory failures and can they be prevented?

From years of experience, we can name the five most common accessory failures that customers call in for service:

Leaks at collector connections – cause: incorrect seals or improper tightening. Prevention: use only recommended EPDM seals, follow the prescribed torque (typically 20–30 Nm).
Clogged flow paths – cause: metal corrosion (zinc salts) or degraded antifreeze mixture. Prevention: correct material selection, regular pH checks and antifreeze mixture condition monitoring.
Pump failure – cause: air in the system (cavitation) or contaminated medium. Prevention: thorough venting at startup, fine filter at pump inlet.
Temperature sensor failure – cause: poor contact, damage from UV radiation (outdoor cable without UV protection). Prevention: use UV-protected cables, insert the sensor correctly into the pocket.
Mounting frame degradation – cause: corrosion of fasteners (common screws instead of stainless steel). Prevention: use exclusively stainless steel A2 or A4 fasteners.

The article Common solar system accessory failures and how to fix them covers troubleshooting in detail.

Questions about expansion vessels and safety elements

Why do I need a solar expansion vessel and not a regular one?

The temperature of the medium in the solar circuit can briefly reach 150–200 °C (stagnation). Common expansion vessels for heating systems are designed for a maximum of 90–110 °C, and their membrane would degrade at higher temperatures. Solar expansion vessels have a special membrane resistant to higher temperatures and are pre-charged to a pressure matching solar systems. In addition, the volume of the solar expansion vessel must cover the increase in the total system fill volume during stagnation – the calculation depends on the volume of the collectors, piping, and manifolds.

Typical calculation for a two-collector system (collector volume 2×3 liters = 6 l, piping volume ~4 l): total fill volume ~10 liters. When heated from 20 °C to 200 °C, propylene glycol expands by ~12%. Required expansion vessel capacity: at least 12 liters plus a safety margin. In practice, we choose an 18–25 liter solar expansion vessel.

Questions about accessory maintenance

How often should solar system accessories be checked?

Recommended inspection frequency:

Every year (in spring before the season): visual inspection of mounting frames and connections, checking system pressure (should be 2.5–3.5 bar when cold), checking temperature on the controller display, checking pump operation.
Every 2–3 years: laboratory analysis of antifreeze mixture (pH, glycol content, inhibitors), visual inspection of seal condition at collector connections.
Every 5–8 years: replacing the antifreeze mixture (even with good analysis results – inhibitors get depleted), checking the condition of the anode in the tank (if magnesium), checking the electric heating element.
After every storm or strong wind: visual inspection of mounting frames and collector condition from the ground or a safe position.

The article Maintenance and replacement of antifreeze mixture in a solar circuit – when and how describes the detailed replacement procedure.

Sizing and calculations – practical examples

Practical example: family house, 4 people, 400-liter tank

Customer from Trnava, family house, 4 adults, existing natural gas boiler, OKC 400-liter tank. Wants to install a solar system and minimize gas consumption in summer.

Solution: 2 flat collectors of 2.35 m² each (total area 4.7 m²), mounting frame for in-roof installation on a pitched roof (38° slope, south-facing, ideal conditions), collector connection accessories and series connection (only 2 collectors, series connection is hydraulically simpler and more advantageous with 2 collectors). 2 kW electric heating element as backup. Result: coverage of 60–65% of annual hot water needs, which, at gas tariff rates and consumption of 400 l/day, represents savings of €180–220 per year. Return on investment for the solar system including accessories: 8–11 years.

Practical example: guesthouse, 20 beds, 4 collectors

Customer from Liptov, mountain guesthouse, season April–October. Hot water need 500–800 liters daily, flat roof, 1,000-liter tank. Here the situation is different: 4 collectors connected in parallel require a manifold and header. The chosen industrial stainless steel manifold/header with ball valves also allows future expansion to 6 collectors without replacing the hydraulics. Adjustable mounting frames on the flat roof, 42° angle. Seasonal coverage: 75–85% of needs. The customer planned to expand with another mounting frame within 2 years – which was possible without touching the manifold, just by installing an additional collector and frame.

Frequently Asked Questions (FAQ)

Do I need to know the exact collector type when buying a mounting frame, or is the number of panels enough?

To choose the right mounting frame for in-roof installation, you need to know the number of collectors and their size – specifically the width and length of the panel. Most flat collectors have standardized dimensions ranging from 1,000–1,100 mm in width and 1,950–2,150 mm in length, but oversized types also exist. Without exact collector dimensions, correct fitting of the collector into the mounting frame cannot be guaranteed. Always specify the collector model or its exact dimensions when ordering a mounting frame.

What happens if I use regular pipe seals instead of solar ones?

Common rubber seals from plumbing installations are designed for a maximum of 90–110 °C and are not resistant to propylene glycol at higher temperatures. In the solar circuit during stagnation, temperature can reach 150–200 °C. A common seal will harden at this temperature, change in volume, and lose its sealing ability. The result is a leak of antifreeze mixture, pressure loss, system malfunction, and in the worst case, damage to the tank or heat exchanger. Always use seals specified by the manufacturer for solar systems (EPDM, FKM, or graphite/PTFE).

Can I connect a solar system to an existing tank without a solar heat exchanger?

No, if the tank doesn't have a separate coil for the solar circuit (a so-called solar heat exchanger), it's not possible to directly connect a solar circuit with antifreeze mixture to potable water. The solar circuit is closed and works with glycol – this must not enter the potable water. If your tank doesn't have a solar heat exchanger, you must replace the tank with a combination tank (with two heat exchangers) or add an external plate heat exchanger. This is a fundamental point that needs to be clarified before purchasing accessories.

How many kilograms of antifreeze mixture do I need to fill the system?

The amount depends on the total system volume: the sum of volumes in the collectors, piping, and solar station. Approximately: one flat collector has a volume of 1.5–3.5 liters, 10 meters of 15×1 mm copper pipe has a volume of ~1.5 liters, a solar station ~0.5 liters. For a two-collector system with 20 meters of piping, the total volume is typically 8–14 liters. Antifreeze mixture is purchased either as a ready-made solution (diluted to -28 °C or -35 °C) or as a concentrate for dilution with water. For temperatures down to -20 °C, a concentration of around 35–40% propylene glycol is sufficient; for regions with frosts down to -30 °C, choose 50%.

Can I combine mounting frames from different manufacturers if they have the same dimensions?

Technically this might work, but we don't recommend it from a safety standpoint. The mounting frame is a safety-critical element – it must be certified as a whole, including anchoring elements and connecting brackets. Different manufacturers may have different tolerances, different anchoring methods, and different guaranteed load classes. If you combine elements from different systems and the collector shifts or tears off in a storm, liability for the damage is legally unclear and the insurance company may refuse to pay. Use complete systems from a single manufacturer.

Do solar system accessories need to be reported to the building authority?

Installing solar collectors on an existing family house usually doesn't require a building permit, provided there's no change to the roof shape or façade elements exceeding a certain size. Under current Slovak legislation (Building and Spatial Planning Act), a simple notification of minor construction to the local building authority is sufficient in many cases. The situation varies by location and building type – for heritage-protected buildings or in heritage zones, the conditions are stricter. Always verify the requirements with your local municipal or city authority before installation.

Conclusion – how to avoid 90% of accessory problems

From many installations, one golden rule emerges: most accessory problems don't arise during manufacturing but during selection and installation. Correct choice of mounting frame for the roof type and number of collectors, using accessories designed specifically for solar systems, following proper hydraulic sizing, and regular system condition checks – these are the four pillars of reliable operation. Investment in quality accessories pays off not only in reliability but also in the longevity of the entire system: a properly installed and maintained solar system operates for 20–25 years without major repairs.

If you're unsure about choosing specific accessories for your situation, browse the entire solar system accessories category or consult our technical department – we're happy to help with a tailored selection for your specific roof type, number of collectors, and tank.

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 advise.