Can a dirty panel significantly reduce output?

In typical UK conditions, soiling loss from rain-washed panels is relatively minor — usually 2–5% annually. In unusual situations (near a construction site, bird roost, or under trees) contamination can be much higher. Professional cleaning is cost-effective if panels are visibly soiled, but cleaning alone rarely resolves significant underperformance — check for faults first.

My system hasn't met its predicted output since installation — is that a fault?

Not necessarily. Installer predictions are often made using optimistic irradiance assumptions. Check the PVGIS estimate for your specific postcode, orientation, and tilt — this is a more accurate benchmark than most installer projections. If the PVGIS estimate and your actual generation are broadly aligned, the system is performing correctly even if it doesn't match the installer's sales figure.

Performance fault · All setups

Solar system underperforming

Q: How do I know if my solar system is underperforming?

Compare your actual annual generation (from the monitoring portal) against the expected yield from PVGIS, using your system's panel size, orientation, and tilt. A system generating below 75–80% of its PVGIS estimate warrants investigation. Also look at whether generation has declined year-on-year — some decline is normal (panel degradation of 0.5–0.7% per year) but a sharp drop suggests a fault.

Q: What is normal panel degradation?

Most modern solar panels degrade at around 0.5–0.7% per year. A system that is 10 years old might produce 5–7% less than when new — this is within the manufacturer's warranty performance guarantee. Degradation above 1% per year, or a sudden drop in output, is beyond normal and should be investigated.

Q: What is an MPPT fault?

MPPT (Maximum Power Point Tracking) is the algorithm inverters use to extract maximum power from each solar string. Most multi-string inverters have two or more MPPT channels, one per string. An MPPT channel failure means one string stops contributing to generation — typically halving output on a two-string system. The monitoring portal will usually show one string with near-zero current.

The system is generating — but not as much as it should be. Output has dropped, or it never produced what you were told to expect. Before calling an engineer, it is worth establishing whether the system is actually underperforming against a realistic benchmark, or whether the expectations were wrong to begin with.

Check the benchmark Book a diagnostic

PVGIS gives the honest benchmark
String faults are diagnosable remotely
New shading is a common hidden cause

Confirmed underperformance against PVGIS?

A solar system health check includes a full generation audit, string performance analysis, and a written report identifying the cause and quantifying the generation loss.

Book a Health Check Remote diagnostic — from £75

5.0

13 Trustpilot reviews

Trustpilot Google

I have a GivEnergy system consisting of two batteries, two inverters and a controlling EMS (Energy Management System) which has not worked since Nov 2025. After six months I discovered Solar Tech Support, reached out to them and Ron phoned me back – how often do you get that service? Could not be more helpful – worked directly with me over the phone, outside what I would call normal working hours. Lucid explanations and we were able to discuss the issues and history using camera and email history. As this was a very rare setup, Ron was able to access an EMS expert in the field to confirm the solution. One sunny day in, I am now only paying for standing charge and a few pence for spikes in grid consumption while battery catches up with house demand.

Ian · May 2026 Trustpilot

When my GivEnergy system had an issue, I was completely left without support and had honestly lost all hope. Thankfully, I searched online and found Ron, which completely turned things around. After sending him a message, he responded incredibly fast and called me to assure me that he would get the problem fixed. I really admire his dedicated, supportive nature and his determination to find a solution. With this kind of outstanding attitude and customer service, he has absolutely secured a future customer in me.

Sree · May 2026 Trustpilot

Ron want out of is way to help, nothing was to much. He was very thorough in what he did Very knowledgeable I would highly recommend Ron and his company He did a fantastic job for me. if you have any problems, he'll do his best to help you out and resolve your problem. I wouldn't hesitate to recommend them

Dennis Brown · May 2026 Trustpilot

Ron took me through a diagnostic to confirm my GivEnergy Inverter had a fault. A common one as it turns out with the AC Inverter. As GivEnergy is defunct there is no immediate fix, aside from sourcing 2nd hand replacement. It may be that a fix becomes available over the summer which would make a lot of GivEnergy customers happy (Again)

Tony Deacon · May 2026 Trustpilot

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026 Trustpilot

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026 Trustpilot

Contacted Solar Tech Support in desperation. After explaining the issues I had with my system a diagnosis was made and a solution proposed. Fantastic service, even contacted a manufacturer to arrange replacement parts for me. Great communications, explained all they were doing and what I had to do, clearly and precisly. Followed up to confirm all was ok. Excellent service.

Mr Machin · May 2026 Trustpilot

After GivEnergy went into liquidation, just my luck, my battery started playing up (internal board crashed). Contacted my installer - not interested! Found Solar tech support on a Google search. Sooo glad I found this company! Ron is extremely helpful and has plenty of experience. He soon confirmed what the fault was, and helped me to get my system up and running again. Now moved my GivEnergy account to Solar tech support, and will definitely use again if I have more issues. Unusual to find such a helpful company in these times, no morons reading scripts, just direct contact with the engineer.

Keith Ballard · Apr 2026 Trustpilot

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026 Trustpilot

Ron is a super star. Two months ago my GivEnergy battery failed a firmware upgrade leaving it a brick. My installer couldn't/wouldn't fix it. GivEnergy couldn't/wouldn't fix it. Then they went into administration and all hope was lost. A flurry of emails later and Ron had diagnosed the fault (failed USB flash drive, something I'd suspected) and talked me through resolving it. Two months of nothing resolved in about 3 hours. It's great to work with someone who pays attention to the details, knows that they're doing (not just following a script) and gets stuff sorted without a fuss or up-charging.

Christopher · Apr 2026 Trustpilot

I can add to the list of customers who had already 'given up' on GivEnergy due to their appalling customer service, and that was before they went into administration (their Trustpilot reviews don't lie!). So you can imagine my desperation when, having changed my ISP and my Inverter, predictably, proving to be the only device that didn't connect automatically to my new network, I found zero prospect of any customer support with GivEnergy having called in the administrators just five days earlier! The salvation came from Solar Tech Support. My IT advisor stumbled across their web site and some very helpful tips for beleaguered GivEnergy customers, as well as an offer to provide direct assistance. Nothing ventured, I decided to drop them an E-Mail, with very low expectations based on my experience of GivEnergy customer support. Within an hour Ron had responded with some pin point advice, and after a few exchanges of E-Mails he had nailed the problem, enabling the combined efforts of my IT advisor and solar installer to resolve it and reconnect my Inverter. Thank you Solar Tech Support, and Ron in particular, for coming to the aid of a deserted and despondent GivEnergy customer. Expert, razor sharp advice and first class customer service, even though I wasn't officially a customer.

customer · Apr 2026 Trustpilot

This company are a rare gem, I had a very unusual problem following a failed firmware upgrade on my GivEnergy kit. I then found out GivEnergy were in administration and had dismissed all their support staff! None of the usual fixes to try and restore my inverter comms would work, and I looked everywhere, forums, GivEnergy youtube support videos - even AI couldn't figure it out. My installer was talking about huge sums for system replacements, and being vague / evasive about if they'd even install replacement GivEnergy inverter. Enter Solar Tech Support, reassuring and knowledgeable from the very start, I've learnt loads about my solar system though the friendly chat while my engineer worked as he diagnosed the problem and figured out a fix procedure that I've not found anywhere else - amazing . If you need solar system repairs - especially if you like me have been left high and dry by GivEnergy, I cannot recommend this company enough. Give them a call.

Andy Thomas · Apr 2026 Trustpilot

I sent a message on their website regarding a problem I have on my Givenergy system. Although not supplied by Ronald, I thought it was worth an email. Within the hour on a Saturday, he phoned and we discussed the problem. He logged in remotely and gave excellent advice. I'm too far away for his on-site help but he did diagnose the problem and was happy also to chat through my thoughts about an upcoming solar/battery install I'm planning. Great bloke.... if only he was nearer!

Philip · Apr 2026 Trustpilot

Ian · May 2026 Trustpilot

Sree · May 2026 Trustpilot

Dennis Brown · May 2026 Trustpilot

Tony Deacon · May 2026 Trustpilot

Contacted Ron with a problem and he sorted it out quickly with no problems at all. Very knowledgeable on anything solar/ batteries. I would recommend him to anyone

Phill · May 2026 Trustpilot

I've spoken to Ron a couple of times with issues with my Givenergy installation. Such a friendly knowledge guy very highly recommended. Thank you very much for resolving my issues

michael fairhurst · May 2026 Trustpilot

Mr Machin · May 2026 Trustpilot

Keith Ballard · Apr 2026 Trustpilot

Contacted Solar Tech Support when trying to understand what my Givenergy inverter problem might be and what might be my options. Received good/honest advise which backed up my thoughts.

Hugh Speirs · Apr 2026 Trustpilot

Christopher · Apr 2026 Trustpilot

customer · Apr 2026 Trustpilot

Andy Thomas · Apr 2026 Trustpilot

Philip · Apr 2026 Trustpilot

Step 1 — Establish a realistic expected output

Installer projections are often optimistic. The honest benchmark is PVGIS — a tool from the EU Joint Research Centre that calculates expected solar yield for any location in Europe using decades of irradiance data.

Go to pvgis.ec.europa.eu, enter your postcode, set your panel rated power (in kWp), orientation (azimuth — 0° is south), and tilt angle. The tool gives you an annual kWh estimate that accounts for your specific location and mounting.

As a rough guide, UK systems produce approximately:

950–1,000

kWh/kWp — South England, south-facing, 30–35° tilt

880–930

kWh/kWp — Midlands / North England, south-facing

820–870

kWh/kWp — Scotland / Northern Ireland, south-facing

A system generating 80–100% of its PVGIS estimate is performing well. Below 75% warrants investigation.

Common causes of genuine underperformance

If the system is confirmed below 75–80% of PVGIS, check these.

New shading

Trees that have grown, a new extension, a neighbouring building, or a satellite dish. Even a small shadow on a single panel in a string system can halve that string's output through the "Christmas lights effect".

Failed string or MPPT channel

One inverter MPPT channel or string has failed — from a blown fuse, open-circuit cable, or inverter fault. On a two-string system this typically reduces generation by around 50%.

Panel fault or degradation

Individual panel failure (from hotspot damage, delamination, or PID degradation) reducing output below the expected rate. More common on systems over 8 years old.

Export limiting curtailment

A DNO export limit is actively curtailing generation on sunny low-load days. The system isn't underperforming — it is deliberately limited. Check whether the generation figure hits a ceiling on sunny days.

Inverter efficiency degradation

An ageing inverter operating below its rated efficiency. More common on string inverters over 10 years old where capacitors and switching components have degraded.

Soiling

Heavy panel contamination from bird droppings, dust from construction, or a nearby industrial source. Rarely the primary cause in the UK — but worth checking visually if significant soiling is visible from the ground.

How to identify the cause

Using monitoring data to narrow it down.

Calculate PVGIS estimate and compare

Run your system through PVGIS and compare the estimate against your last 12 months of generation data from the portal. If the shortfall is above 20%, the investigation is worthwhile. If it is within 15–20%, check whether the PVGIS inputs accurately reflect your actual orientation and shading.

Check string voltage and current data

In the monitoring portal, check whether your inverter shows separate data for each string or MPPT channel. On a sunny day both strings should show similar current levels. If one string shows near-zero current while the other is normal, you have a string fault — blown fuse, open circuit cable, or disconnected panel.

Look for a generation ceiling on sunny days

On the sunniest days in summer, does the generation figure plateau at a specific number — say 3.0kW on a 5kWp system — rather than climbing towards peak rated output? If yes, check whether an export limit is set at that figure in your inverter configuration.

Walk around and check for new shading

Go outside at solar noon (midday in winter, 1–2pm BST in summer) and look at the panels from the ground. Check whether any trees, structures, or objects are now casting shadows onto the array. Even a shadow on one panel can drag down an entire string.

Compare year-on-year generation totals

If the monitoring portal shows multiple years of history, compare annual totals year-on-year. A gradual decline of 0.5–1% per year is normal degradation. A drop of 5% or more in a single year indicates a fault event — check the event log for that year for fault codes or equipment changes.

Brand-specific underperformance checks

Each monitoring platform exposes generation data differently. Use the note for your brand to find the right figures for your PVGIS comparison.

GivEnergy

GivEnergy portals show daily PV generation on the Generation page. Compare the daily kWh figure against your PVGIS estimate for the same calendar month. Note that some older firmware versions report generation from the CT clamp rather than the PV input — if your daily figures fluctuate wildly with load, check which measurement source is configured. See the GivEnergy hub for portal navigation help.

Growatt

Growatt's ShineServer portal provides per-MPPT yield data for multi-string hybrid systems. Navigate to Device > Details to compare MPPT1 and MPPT2 daily yield — a significant divergence between strings isolates the underperformance to one set of panels or one MPPT channel, making diagnosis much faster.

Sunsynk / Deye

Use the Sunsynk Connect app History view to compare daily yield across recent weeks. If a single week shows a step-change drop with no weather explanation, correlate with the inverter event log for that date — a firmware update or grid event on that day often explains the change. Sunsynk inverters can also experience MPPT derating in partial shade conditions; a soft reset of MPPT tracking can help.

System not producing Inverter red light CT clamp installed wrong GivEnergy solar not generating Huawei system underperforming SolarEdge optimiser showing N/A Victron MPPT error codes

FAQ

Frequently asked questions

How do I know if my solar system is underperforming?

Compare your actual annual generation against the PVGIS estimate for your location, panel size, orientation, and tilt. A system generating below 75–80% of PVGIS warrants investigation. Also look at year-on-year trends — a sudden drop in output compared to previous years suggests a fault rather than normal degradation.

What is normal panel degradation?

Most modern panels degrade at 0.5–0.7% per year. A 10-year-old system might produce 5–7% less than when new — this is within warranty performance. Degradation above 1% per year, or a sudden drop, is beyond normal and should be investigated.

Can dirty panels significantly reduce output?

In typical UK conditions, soiling loss is usually 2–5% per year on rain-washed panels. Near construction sites, bird roosts, or under trees it can be higher. Cleaning alone rarely explains major underperformance — check for faults first.

My system never met its predicted output from installation — is that a fault?

Not necessarily. Check your installer's projection against the PVGIS estimate — if PVGIS agrees with your actual generation, the system is likely performing correctly and the installer's figure was optimistic. If PVGIS is significantly above actual generation, there may be a genuine fault or shading issue that existed from installation.

What is an MPPT fault?

MPPT (Maximum Power Point Tracking) is how inverters extract maximum power from each solar string. A failed MPPT channel means one string stops contributing — typically halving output on a two-string system. The portal will show one string with near-zero current.

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Confirmed underperformance — get it investigated

A solar system health check includes a full generation audit against PVGIS, string-level performance analysis, and a written report identifying causes and quantifying the generation loss in kWh and £ per year.

Independent — not affiliated with any manufacturer
Health check from £75
PVGIS audit + written report included

Call 07944 877 329 Book free diagnostic