Professional solar cleaning: costs, frequency, and pure water technology

The Unger pure water system: technology, comparisons and best practices

The development of renewable energies is one of the important energy policy choices made in many countries, including France. Beyond individuals, many businesses have chosen, or been required, to equip themselves with photovoltaic panels for electricity production.
Thus, for several years now, all new buildings exceeding 1000m² have been required to include solar panel or green roof coverings on 33% of their surface area. Discover our full range of professional pure water cleaning equipment for windows and solar panels . Unger is a leading manufacturer in this field, offering a very wide range of products covering all your solar panel cleaning needs.

Introduction: Why clean solar panels?

The electricity production of a photovoltaic installation depends directly on the transparency of the modules. Studies conducted by various European manufacturers and laboratories show that progressive fouling can reduce efficiency by 10 to 30% , depending on the environment and the period of maintenance failure.
The main contaminants responsible for this loss of performance are: mineral dust, bird droppings, pollen, sea spray, industrial deposits (soot, hydrocarbons), and limescale deposits left by insufficiently demineralized water. Some regions may be more affected than others, with sandstorms from North African countries, particularly in the southern part of France, as well as pine pollen deposits (sticky green dust).

The Unger Pure Water System: An Overview

Unger is a German manufacturer specializing in professional cleaning tools since 1964. Its range dedicated to window cleaning, warehouse cladding washing, and solar panel cleaning relies on pure demineralized water technology delivered via a telescopic pole. This system is particularly well-suited for technicians working on roofs, parking lot shade structures, or large sloping surfaces. Unger technology is currently the most advanced and, above all, the most comprehensive professional range on the market. Unger has also become part of the American Bissell group.
Find all the ready-to-use pure water cleaning kits at Voussert for an immediate start to your business.

Components of the Unger HiModular system

• HiModular telescopic pole: made of fiberglass or carbon fiber, variable height (3 to 15 m depending on the model), lightweight and rigid. Find the entire range of nLitre carbon HiMod poles and Unger professional nLite carbon poles at the best price.
• Wash head with semi-circular brush: soft nylon bristles suitable for encapsulated surfaces. Integrated rinsing via central nozzles.
• Flexible connection: hose integrated into the pole, length up to 30 m, recommended pressure 2-4 bar.
• Unger nLITE filtration unit: compatible with reverse osmosis and resin, connected upstream of the pipe, available in fixed or mobile trolley version.

Operating principle

Water from the mains or a reservoir is filtered upstream (sediment pre-filter, activated carbon), then passes through the demineralization module (reverse osmosis or resin). The resulting water, with a TDS (Total Dissolved Solids) level below 10 ppm, is delivered to the brush head. There, it naturally absorbs dirt and evaporates without leaving any limescale or organic residue.
Water quality is monitored using an electronic TDS meter (digital pen): a reading must be taken before each project. A TDS level above 15 ppm at the filter outlet requires replacement or regeneration of the filter module.

Comparison of filtration systems: reverse osmosis vs. resin

Two technologies are used in practice to produce the pure water needed for pole cleaning. Each has a distinct technical and economic profile that should be evaluated according to the context of use. Unger's DI hydro-power filters are highly mobile and available in various production sizes. Unger's reverse osmosis filtration systems, on the other hand, are reserved for large-scale cleaning projects, and while their mobility exists, it is less intuitive than that of the DI range.

Summary comparative table of pure water filtration systems

Reverse osmosis (RO): detailed analysis

Benefits
• Production of water of consistent quality regardless of the initial hardness of the network.
• Less manual intervention: the membrane can withstand large volumes without close monitoring.
• Suitable for sites with fixed connection: industrial installations, solar farms, car park shade structures.
• Unger nLITE Ion system available in integrated reverse osmosis configuration + polishing resin to achieve 0-1 ppm.

Disadvantages
• Significant water discharge (also called “concentrate”): up to 50% of total consumption, restrictive in areas with water restrictions.
• Sensitive to frost: semi-permeable membranes do not tolerate temperatures below 4°C.
• Limited throughput for small portable units: not suitable for rapid interventions on small sites.
• Higher initial investment cost.

The Unger DI filter deionizing resin: detailed analysis

Benefits
• Ultra-compact system: Unger DI filters fit directly onto the trolley or in the trunk of a utility vehicle.
• No discharge: 100% of the water is recovered.
• Immediate commissioning: no assembly or preheating time.
• High instantaneous flow rate (30 to 80 L/min depending on the column): ideal for large areas treated quickly.
• Low TDS output (< 1 ppm): superior quality to standard reverse osmosis without post-polishing.

Disadvantages
• Resin lifespan directly linked to water hardness: in TH > 30°f zones, resins are depleted rapidly (sometimes in a few days).
• Frequent replacement without pre-treatment: high recurring cost if the local water is very hard.
• TDS check required before each use: depletion is progressive and invisible to the naked eye.
• Used resins require specific management (chemical regeneration or controlled disposal).

Configuration recommendation

Recommended maintenance frequency

The cleaning frequency of photovoltaic panels cannot be standardized nationally: it depends on the immediate environment of the installation, the tilt of the modules, the time of year, and the level of performance loss accepted by the customer. The table below provides a professional reference guideline.

Indicators that trigger an urgent intervention

• Bird droppings localized on more than 2% of the active surface of a module (localized shading effect = potential hotspot).
• Measured production loss > 5% compared to the reference curve (monitoring via inverter).
• Visible accumulation of dust or foam (areas with a low slope < 10°).
• Presence of limescale deposits following a previous intervention with poor quality water.

Typical calendar for temperate zones (metropolitan France)

• February-March: Post-winter spring cleaning. Removal of winter deposits (moss, emerging lichens, early pollen).
• June: Pre-summer cleaning. Optimization for the period of maximum production (summer solstice).
• September: Post-summer cleaning. Removal of pollen residue, insects, and summer dust.
• December (optional): visual inspection and cleaning if significant deposits related to the heating period (combustion areas nearby).

Maintenance cost estimate

The estimate below relates to the activity of a specialized service provider performing cleaning services on behalf of third parties (individuals, professionals, power plant operators). The figures are indicative and should be adjusted according to each company's specific cost structure.

Profitability and customer pricing

For a customer rate between €0.08 and €0.20/Wp (installed peak watts) depending on the installation size, the profitability of a professional service is achieved as soon as the managed panel fleet exceeds 50 kWp. The added value is justified by: traceability of the intervention (TDS report, before/after photos), the absence of risk of scratching (pure water + Unger half-round brush), and visual inspection of the cells (detection of micro-cracks, traces of hot spots).

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