The short answer
The usual causes are dirty panels, new shading, heat, the time of year, or a fault in the inverter or wiring. Start with your inverter app, look for warnings, then check for new shading and dirt. Dirty panels need a clean. Warnings, faults and anything electrical need your installer or a licensed electrician.
Start with the app
Before you look at the roof, open your inverter app or online dashboard. It answers the most important question straight away: is the system producing at all, and is it reporting a problem?
- No production, or a warning message: this points to the inverter or the electrical side. Skip to the section on inverter faults.
- Production is normal-looking but lower than usual: work through the causes below.
To judge whether output really is low, compare similar days. A clear, sunny day this week against a clear, sunny day a few weeks ago is a fair comparison. A hazy day against a clear one is not.
1. Dirty panels
In Malta, this is the most common cause, and the easiest to fix.
- Dust builds up through the long dry summer, from fields, roads, quarries and building sites.
- Saharan dust and red rain leave a gritty reddish film a few times a year.
- Salt coats roofs near the sea, especially those exposed to the majjistral.
- Bird droppings block part of a cell completely, and because cells are wired together, a small dropping can cost more output than its size suggests.
How to check without climbing up: look from a safe spot such as the roof door or a higher window, or take a zoomed photo with your phone. A dull, dusty surface, a dirty band along the bottom edge or white spots from droppings all mean it is time to clean.
Our guide on whether cleaning solar panels increases output explains how to measure the difference before and after.
2. New shading
Shading is the cause most people miss, and in Malta it is common:
- Building work next door. An extra floor, a new block or a penthouse going up can put your panels in shade for part of the day, often only in winter, when the sun is lower.
- Things on your own roof. Water tanks, satellite dishes, a new washroom or stored items can cast shadows across panels at certain times of day.
How to check: look at the panels at different times of day, especially morning and late afternoon, and in winter. Shade on even part of one panel can reduce the output of others on the same string.
If new shading is the cause, cleaning will not help. Talk to your installer about whether moving panels, or adding equipment that limits the effect of shade on the rest of the system, makes sense.
3. Heat
Solar panels work best when they are cool. On very hot days, they produce less than their rating, even in bright sun.
That is why a clear spring day often beats a scorching August afternoon, and why your summer peak can look disappointing. This is normal and not a fault. Good airflow under the panels helps, which is one advantage of the raised frames common on Maltese roofs.
4. Time of year
Output changes through the year with the sun’s height and the length of the day. Winter production will always be lower than summer production. That is not a problem.
The useful comparison is this month against the same month last year, on similar days. If you see a drop year on year, one of the other causes is likely.
5. Inverter and wiring faults
If the app shows a warning or error message, or production stops altogether, the problem is probably electrical:
- An inverter fault or error message. Look up the message in your inverter’s manual. Do not guess what it means.
- A tripped breaker or isolator. Check your distribution board. If it trips again, call an electrician.
- Damaged or corroded cables and connectors, especially on seafront roofs where salt air reaches them.
- A failed panel or optimiser, which some systems can show in the app panel by panel.
Anything electrical is a job for your installer or a licensed electrician. Do not open the inverter, touch cables or junction boxes, or try repairs yourself.
A simple decision path
- Open the app. Warning or no production? Call your installer.
- Compare similar days. Is output really lower, or is it heat or the season?
- Check for new shading, at different times of day.
- Look at the panels from a safe spot. Dirty? Book a clean.
- Still low after cleaning? Ask your installer to check the system.
How often to clean
For most homes in Malta and Gozo, once or twice a year is enough: at the end of the dry summer and in spring before the longest days, plus after any heavy red rain episode. Seafront roofs, roofs near building sites and roofs with a bird problem may need more. See our guide on how often to clean solar panels in Malta, and on whether rain cleans solar panels.
When to call a cleaner, and when to call the installer
- Call a cleaner for dust, salt, red rain residue and bird droppings, especially on raised frames, over roof washrooms or on roofs with low parapets.
- Call your installer or an electrician for warnings, errors, tripped breakers, damaged cables, cracked glass or output that stays low after a clean.
clear.mt arranges solar panel cleaning across Malta and Gozo, and the cleaner will tell you if they notice cracked glass, loose fixings or damaged cables so you can pass it on to your installer.