How accurate are solar panel output readings?

[Goldfinch1]

Hello

Is it possible for solar panel monitoring to over state the actual power generated by the system? My friend’s 6.4kW system has generated 1280 kWh in the 82 days since its commissioning on 1/12/2022. Extrapolation of this output predicts an annual production of around 5,700 kWh which, according to numerous Internet sources, is about what’s expected for a 6.4kW system in the UK.The thing is, generation to date has all been in winter when output from the panels is generally low. Furthermore, if we extrapolate output for the first 20 days of February, the indicative annual output (with no attempt to correct for more productive spring/summer/autumn days) is approximately 7,500kWh. This is more than the expected annual output. If we applied correction for longer daylight months, this figure would be much higher. The system, located in the SW of England, comprises 16 x 400kW panels arranged in two strings using two Growatt inverters and has battery storage. The placement of the panels is south facing, with no shade. Any thoughts? Here’s hoping our friends have a super efficient system. Thank you.

 

[Amit Bajayee]

Solar panel output readings can be very accurate if measured correctly and with high-quality equipment. However, several factors can affect the accuracy of solar panel output readings, including the quality of the measuring equipment, the placement of the measuring equipment, and the conditions under which the measurements are taken.
To ensure accurate readings, it is essential to use high-quality measuring equipment that is calibrated regularly. The equipment should also be placed in an optimal location to ensure that it accurately measures the solar panels' output.

 

[kvarnanna63]

A 100 watt panel that receives 8 hours of sunlight per day will produce almost 1 kilowatt-hours per day. If we multiply this by 365 days per year, we get a solar panels output of about 365 kilowatt-hours annually. In short, each panel will provide 365 kilowatt-hours each year.

 

[Max105]

A 100 watt panel that receives 8 hours of sunlight per day will produce almost 1 kilowatt-hours per day. If we multiply this by 365 days per year, we get a solar panels output of about 365 kilowatt-hours annually. In short, each panel will provide 365 kilowatt-hours each year.

Sorry, but this estimate is out by a country mile (miles actually).

The estimate for solar generation per annum in central southern UK is 950kWh per 1kW installed. I've got a 12kW system and this rule of thumb has very accurate over nearly 10 years.

So a perfectly south facing 6.4kW system with a matched inverter would be expected to annually generate around 6.4 x 950 = 6,080 kWh per annum.

Similarly using same logic, 100W panel would generate 0.1 x 950 = 95kWh per annum.

Goldfinch1, my 12kW system generated 1097 kWh between 01/12/22 and 28/02/03 and that's measured by FIT meter so dead accurate (I would hope). I'm on the south coast or England. It's not ideal because mine are ground mounted via longish cable and my panels are not over-rated versus the inverter (i.e. 12 kW of panels via 12kW inverter) but even so, as per above, it matches the "950kWh" rule quite closely.

I would say, unless he's had some long periods of very sunny weather that we haven't here, your mate's readings are WAY over-generous. How are the readings generated?

Max