May is the best time to review your photovoltaics - the panels are not yet warmed up to 70°C, the production season is just getting into full swing, and errors detected now will not cost you a single July kWh. In a moment, we'll show you what to check yourself and what you're better off not trying without the equipment.
Why May and not June?
Most PV installation owners review their installation in the summer - when something stops working. This is a mistake. May combines three favourable conditions that no other month has:
- The panels are still cool - can be washed safely during the day without the risk of thermal shock
- Trees in full foliage - only in May you can see the shadow falling on the roof at 11 a.m. and 2 p.m. In March the leaves were not growing, in July the damage has already been going on for 6 weeks
- Ahead of peak production - Any problem detected in May does not rob you of your July energy. Detected in July, it does
Context 2026: With an RCEm of £0.13/kWh, every kilowatt-hour returned to the grid is worth 10 times less than that consumed on site. Dirty panels, a shaded module or an inverter shutting down at midday - these are losses that hurt much more in net-billing than even two years ago.
[1] Wash the panels - but do it right
Dirty panels can produce up to o 20-25% less energy. Winter deposits soot from chimneys on Pomeranian roofs, salty dust from the Baltic Sea and stains are left behind after the melt. Spring is the first of the two recommended washes of the year.
How to wash safely:
- Only in the morning or evening - hot panel + cold water = risk of glass breakage (thermal shock)
- Soft sponge or microfibre cloth, clean water - without abrasives and without pressure washers directly on the panels
- In Pomerania, special attention to salt deposits - Rinse abundantly, do not wipe with a dry cloth: salt crystals scratch the glass.
- Remove bird droppings by soaking gently - dry scraping is a simple way to micro-damage
Cleaning the panels on the roof yourself is possible - but working at height with no experience, no insurance and no safety equipment is a real risk. If you have a pitched roof and an installation more than 4 metres from the ground, it is worth considering having this done together with a technical inspection. One arrival = cleaning + inspection + protocol. Ask for our service offer →
[2] Check the shadow - it's now or never
The trees are in full leaf in May - as they will be in July and August. Stand under the canopy at 11am and 2pm and check that no branch, chimney or new antenna casts a shadow on the panels.
Even one shaded module can reduce the production of the entire string by 30-50% during peak hours. In installations without optimisers, power is limited by the weakest link - one leaf on one panel can shut down a third of the installation.
New branches grow quickly. In Pomerania - especially in the Tricity - neighbouring trees can grow 50-80 cm in a season. An installation that had no shade problems a year ago may look completely different in May 2026. Check the production figures from last May and compare with the current ones - a sudden drop in the same weather = shade or dirt.
[3] Review MC4 connectors and wiring after winter
Winter is a time that the installation spends under snow, in the rain and in strong winds. In Pomerania, the corrosive sea moisture adds to this. MC4 connectors - the connections between panels - are the most common point of failure in older installations.
What to check yourself (without going up on the roof):
- Visible wires at the inverter - that there are no abrasions, no discolouration, no burning smell
- Inverter box - that there is no moisture, rust or signs of overheating
- Inverter application - check the alarm and error log tab for the period December-March
What not to do alone: Do not touch the DC connectors under the panels - the DC system is live all day long when the sun is shining. Inspection of the wiring on the roof and under the panels requires disconnecting the system and working with DC voltage, a task for an SEP-qualified electrician.
If your installation is four years old or more, it's worth ordering a thermal imaging inspection of the connectors at your spring inspection. A thermal imaging camera detects an overheated joint before it becomes a problem - and the cost of such an inspection is a fraction of the cost of a post-failure repair. At SolLab, thermal imaging is a standard part of the service inspection.
[4] Check what's going on under the panels - pigeons are a serious problem
The space between the panels and the roof is an ideal nesting place for pigeons - warm, sheltered from wind and rain, and difficult for people to reach. The problem builds up over years and is invisible from the outside until it is already very serious.
SOLLAB PRACTICE CASE - PRUSZCZ GDAŃSKI
Installation 7 years without inspection. The customer approached us after noticing a marked drop in production in the inverter application. When our team removed the first panels - there were several centimetres of compressed bird droppings mixed with nests and feathers underneath. The DC cables were lying directly in this mass. One of the cables had visible insulation damage. The roof under the installation needed a thorough cleaning before any further service.
Photo 1 Condition at parapet - droppings and nest debris trap moisture and accelerate corrosion. |
Photo 2 Roof after removal of panels - several cm of droppings. DC cables (red) have been lying in this mass for years. |
Photo 3 DC cables under panels - damaged insulation. Droppings contain organic acids that degrade cable coatings. |
Photo 4 SolLab team during clean-up - the intervention required full disassembly, cleaning of the roof and replacement of the DC cabling. |
Why pigeons are more dangerous than you think: Bird droppings contain organic acids (urea, nitric acid) which, when in contact with metal, cause corrosion of frames and handles, and with cables - degrade the insulation. In the case from Pruszcz Gdański, the DC cable was damaged over a length of several centimetres. The DC voltage between the panels and the inverter can reach 600-900 V and is not switched off by any fuse as long as the sun shines.
What to check for yourself:
- Look at the edges of the installation from the ground - whether you can see feathers or traces of bird droppings on the tiles directly below the panels
- Listen to - pigeons cooing under the panels, especially in the morning
- Check inverter application - a gradual, multi-month decline in production in the same weather is an alarm signal
SolLab installs protective netting under the panels on request - both for new installations and for servicing. The mesh, which is mounted on the panel frames, closes off the space under the installation and effectively prevents pigeons from nesting. It is a one-off cost that protects the installation throughout its lifetime.
[5] Configure the inverter for summer 2026
In summer, when many plants are producing simultaneously, the voltage on the local grid can rise above 253 volts. The inverter - according to the standard - automatically shuts down then. On a sunny July afternoon, you can lose 1-3 hours of production and not know it at all.
| Setting up the inverter | What does | When to include |
|---|---|---|
| Function Q(U) | Automatically stabilises the mains voltage by adjusting the reactive power | Always - especially on the outskirts of towns and villages |
| Grid Limitation (70%) | Limits exports to the network | When the network is weak and shutdowns are repeated |
| Export Limitation | Full control over energy output | When you have energy storage - you charge instead of exporting |
How to check if your inverter shuts down for this reason: open the app (Huawei FusionSolar, SolarEdge, Fronius Solar.web, SMA Sunny Portal) → logs/events tab → look for codes: overvoltage AC, grid voltage high, Uac high. If they appear regularly on sunny days between 10am and 2pm - you have this problem.
[6] Set AGD schedules - before the season kicks off
May is the last quiet moment before we enter the full summer season. It's now worth going through the list of appliances in the house once and setting the timers for the hours of 10am to 2pm - this is when the plant is producing at its maximum and the RCEm in summer will be even lower than it is now.
- Dishwasher, washing machine, dryer - timer for 10:00-13:00, each device is 1-2 kWh consumed from its own production instead of being sold for £0.13
- DHW heating - electric boiler or heat pump in solar or noon timer mode
- EV charger - if you have an electric car, switch to charging during peak production hours
- Air conditioning - pre-cooling the house at 12:00 from the sun instead of at 18:00 from the grid
[7] Photovoltaic inspection - check warranty status
There are more than 1.6 million micro-installations, and the vast majority were built between 2019 and 2022. This means that hundreds of thousands of installations are just now coming out of, or are about to come out of, the warranty period. The panel manufacturer's warranty usually lasts 10-12 years, but the installation warranty for many installers was 2-5 years. Many installation companies have closed down - so customers have automatically lost their warranty and installation care.
A technical inspection once every 2-3 years is the best insurance policy for PV installations. It detects problems before they become failures - and is much cheaper than repairing them after the fact. The cost of a professional inspection with thermal imaging is usually the equivalent of 2-3 weeks of production for a 6 kWp installation.
SolLab summer service review - make an appointment in May, get there before the season
The inspection includes a thermal imaging inspection of the MC4 connectors, a check of the inverter and error logs, verification of the DC cabling, a check of the undercurrents and a protocol with an assessment of the condition of the installation. We install pigeon netting on occasion. We service installations from all manufacturers, regardless of who installed them.
Gdańsk - Gdynia - Sopot - Wejherowo - Kartuzy - Tczew - Pruszcz Gdański - and the entire Pomeranian region
FAQ - preparing photovoltaics for summer
When is the best time to wash photovoltaic panels?
Twice a year: in spring (May) and autumn (October). Always wash in the morning or evening - a hot panel and cold water risk thermal shock and glass breakage. In Pomerania, it is particularly important to rinse off salt deposits and soot after winter.
Can I check the condition of the PV installation myself?
Some of the activities - yes: inverter logs in the application, visual inspection of the shade and wiring at the inverter, washing the panels from the ground or a ladder. Inspection of the MC4 connectors on the roof and DC wiring requires an electrical licence and disconnection - a job for a professional.
Why does the inverter switch off in summer when the weather is nice?
The most common cause in the summer of 2026: too high AC voltage on the local grid when multiple PV installations are producing simultaneously. The voltage rises above 253 V and the inverter shuts down automatically according to the standard. Check the logs (codes: overvoltage AC, Uac high) and consider enabling the Q(U) function in the inverter settings or installing energy storage.
How often to do a technical inspection of photovoltaics?
Recommended every 2-3 years, and immediately after any severe storm or hailstorm. Installations older than 4-5 years should have an inspection with a thermal imaging inspection of the MC4 joints. This is particularly important in Pomerania, where marine moisture accelerates corrosion of the connections.
Can pigeons really damage photovoltaics?
Yes - and more seriously than you might think. Pigeon droppings contain organic acids that degrade the insulation of DC cables and cause corrosion of frames and brackets. In the case from Pruszcz Gdański, which SolLab operated, the DC cables had been lying for years in a several centimetre layer of excrement and one of them had damaged insulation - an immediate hazard. Protective netting under the panels is an effective and durable solution.
What to set in the inverter before the summer season?
Above all, make sure that Q(U) - reactive voltage regulation, which prevents shutdowns during mains surges - is enabled. If you have energy storage, set your charging priorities for the hours of 10 a.m. to 2 p.m. Switch your white goods timers to noon, when production peaks.
