TL;DR:

  • Most inverter manufacturers include a monitoring app — set it up on day one and check it weekly in summer, monthly in winter
  • The key metric is specific yield (kWh per kWp): compare your system against UK regional averages to catch underperformance that would be invisible just from looking at generation numbers
  • Shade, dirt, a failing module, or a faulty inverter can all cause significant generation loss — often silently, with no visible fault indicator

Your solar system generates the most money and carbon savings when it runs at full output. But most homeowners install a system and then barely look at it for years, only noticing a problem when an installer mentions it during a routine visit. That’s a shame, because the monitoring tools available today make it genuinely easy to catch problems early.

What Your Inverter App Tells You

Every string inverter sold in the UK for the past decade includes some form of monitoring. SolarEdge, Fronius, SMA, Solis, Growatt, Enphase — they all have apps. The data is there; you just need to use it.

The basic metrics to track:

Daily generation (kWh): How many units of electricity your system produced today. Compare this to similar days in previous years. A sunny June day in the south of England should produce around 4.5—6 kWh per kWp of installed capacity.

Specific yield (kWh/kWp): Total generation divided by your system size in kilowatts peak. This is the right number to compare against benchmarks. A 4 kWp system generating 20 kWh on a day is yielding 5 kWh/kWp. This normalises for system size so you can compare against neighbours and regional averages.

Performance ratio: Actual generation versus theoretical maximum given the day’s irradiance. Good performance is typically 75—85%. This requires irradiance data from your inverter’s weather station integration or a local sensor, so it’s not always available.

Grid export vs self-consumption: If you have a smart meter or energy monitor, how much of your generation went to the grid versus being used in the home. This affects your economics but not system health.

Comparing Against UK Benchmarks

The best way to spot underperformance is to compare your specific yield against regional data. Tools that provide this:

PVOutput.org: A community platform where UK homeowners log their generation data. You can see systems in your postcode area and compare daily and monthly yields. If you’re consistently 20% below similar systems nearby in the same weather, something is wrong.

OpenWeatherMap or Solcast: Solar forecasting tools that estimate expected generation for your location based on irradiance. Some inverter apps (SolarEdge, for example) integrate this directly.

Your installer’s annual report: Many installers offer yearly performance checks. Ask for an expected vs actual comparison.

A rough seasonal benchmark for a south-facing 30° pitch system in the UK:

  • January: 0.3—0.6 kWh/kWp per day
  • April: 2.5—4.0 kWh/kWp per day
  • July: 4.0—5.5 kWh/kWp per day
  • October: 1.5—2.5 kWh/kWp per day

These vary significantly by location. Systems in Cornwall will outperform Scotland; east/west-facing systems will produce less.

Common Faults and Their Signatures

Partial shading: If a tree, chimney, or new building is casting shade over part of your array, you’ll see generation dip at specific times of day when the shadow falls. String inverters are particularly vulnerable because one shaded panel pulls down the whole string. Panel-level optimisers (SolarEdge, Tigo) or a microinverter system (Enphase) can mitigate this.

Soiling and debris: Bird droppings, lichen, moss, and general grime can reduce generation by 5—15% if panels haven’t been cleaned in several years. The British climate does a reasonable job of self-cleaning with rain, but not perfectly. If you notice a gradual decline over months that isn’t explained by weather, cleaning is worth trying.

Panel degradation: All panels lose efficiency over time, typically 0.5—0.7% per year. After 10 years, expect your system to produce around 93—95% of its original output. Faster degradation is a warranty issue.

Inverter faults: Most inverters log error codes when they fault. A brief morning fault that clears is usually fine — inverters don’t start up until they have enough voltage, and on cloudy mornings they may briefly fault before settling. Persistent error codes, or an inverter that’s offline for hours mid-day, needs attention.

Failed optimiser or microinverter: If you have a panel-level monitoring system (SolarEdge Power Optimisers or Enphase IQ microinverters), you can see each panel’s output individually. A panel producing significantly less than its neighbours — or nothing — points to a failed optimiser or microinverter. These can be replaced under warranty within the first 12—25 years depending on the product.

Setting Up Alerts

Don’t rely on checking the app manually to catch problems. Most monitoring platforms let you set up email or push notifications for:

  • Daily generation below a threshold
  • Inverter offline for more than X hours
  • String output deviating from expected

For SolarEdge users, the monitoring portal lets you set up alerts under Alerts > Alert Rules. For Enphase, alerts are configured under Settings > Notifications in Enlighten. Fronius Solar.web has a similar alert system.

A simple rule — “alert me if generation is more than 30% below forecast on a clear day” — will catch most significant faults within a day of them occurring.

When to Call Your Installer

Call your installer (or the inverter manufacturer’s warranty line) if:

  • The inverter is offline and won’t restart
  • You have a persistent error code that doesn’t clear
  • You can see individual panels offline in a panel-level monitoring system
  • Generation has dropped more than 20% compared to the same period last year, after accounting for weather

For string inverters without panel-level monitoring, a meaningful generation drop that isn’t explained by weather or shading warrants an on-site inspection — there’s no way to tell remotely which panel or string is at fault.

The good news is that solar systems are generally reliable. Most problems, when they do occur, are caught quickly if you’re looking at your monitoring data regularly. Five minutes a week in summer is enough.