Reading your solar inverter app: what the numbers mean

Most rooftop systems now come with an app that shows what the panels are making. Many owners look at it for the first week, see numbers they are not sure how to read, and then stop. That is a pity, because a minute a week with the app is the cheapest way to catch a problem early. This guide explains the main figures, what normal looks like in Tricity, and when to pick up the phone.

The main figures

Apps differ in layout, but almost all show the same few numbers.

• Power now (kW). What the panels are delivering at this moment. It rises through the morning, peaks around midday and falls in the afternoon. On a clear day it follows a smooth curve; clouds make it jagged.
• Today’s generation, or yield (kWh). The units made so far today. This is the figure to watch, because a unit (kWh) is what your bill counts.
• This month and this year (kWh). The same, added up. Use these to compare one month with the same month last year.
• Total generation (kWh or MWh). Everything the system has made since it was installed.
• Status. Normal, standby at night, or a fault, often with a code.

A hybrid system adds more:

• Battery level (%) and whether it is charging or discharging
• Home use, or load (kW), what the house is drawing at the moment
• Grid (kW), whether you are taking power from the grid or sending it out

What normal looks like here

The best check is units per kW of panels per day, averaged over a month. By our estimate for shade-free panels in Tricity:

So a 5 kW system averaging about 23 units a day in April, or about 15 in January, is working normally. A clear day can be well above the average and a cloudy or foggy one well below it. Our guide to how much solar produces in each month has the monthly figures behind this table.

Why power now never reaches the panel rating. A panel’s rating is measured in standard test conditions, at a cell temperature of 25°C. On a roof in Tricity the cells run much hotter, and heat lowers output, so a 5 kW system usually peaks well below 5 kW, especially in May and June. That is normal.

The app and your electricity bill

The app shows what the panels make. Your bill shows what crosses the meter: the units you imported from the grid and the units you exported to it. The difference between the app’s figure and the export is what your home used straight from the panels. In Punjab, PSERC’s rules also provide a separate generation meter, whose reading should be close to the app’s total. Our guide to net metering in Punjab explains how the bill is worked out.

Readings that mean you should call

• Zero generation on a sunny day. The inverter is off, a breaker has tripped or there is a fault. Do not open the DC or AC boxes yourself.
• The app shows a grid fault or high-voltage error, especially around midday. The inverter switches off when grid voltage goes outside its limits. Your installer can check the settings, and persistent high voltage is a matter for the electricity board.
• A month well below its normal range in clear weather, or well below the same month last year. Our guide to why solar produces less lists the causes in order.
• One string far below another, where the app shows them separately. That points to shade, a faulty panel or a connector on that string.
• The app stops updating. Usually the Wi-Fi has changed or the data logger has lost its connection, not a fault in the system. Reconnecting it keeps your history complete.

A simple routine

• Once a week, glance at the last seven days. A sudden drop on clear days is worth a look.
• Once a month, note the month’s total and compare it with the same month last year.
• After a dust storm or a smoggy spell, check whether a clear day after cleaning produces more than one before. If it does, dirt was costing you units. Our guide to solar maintenance through the year covers when to clean.

How we use the app

With the 4-Year Care Shield included with every home system from us, we review your generation each month and call you if a month comes in more than 15% below where it should be. At handover we set up the app on your phone, show you these figures on your own system, and make sure the data logger is on your Wi-Fi. Our guide to choosing a solar inverter covers what to look for in the monitoring when you buy.

Common questions

How many units should my solar system make in a day?

In Tricity, on average about 3 units per kW of panels a day in December and January, and about 4.4 to 4.7 from March to May. So a 5 kW system makes roughly 15 units a day in mid-winter and 22 to 24 in spring, more on clear days and less on cloudy ones.

Why does my 5 kW system never show 5 kW in the app?

Because panel ratings are measured at a cell temperature of 25°C, and panels on a hot roof run much hotter, which lowers their output. A peak well below the rating is normal, especially in summer. Watch the daily units instead.

What is the difference between kW and kWh in the app?

kW is power at this moment, like a car's speed. kWh is energy over time, like the distance covered. Your bill counts kWh, which are units, so today's and this month's kWh are the figures that matter.

My solar app has stopped updating. Is the system broken?

Usually not. Most often the Wi-Fi password or router has changed and the data logger has lost its connection. The system keeps working and the inverter's own display shows that it is running. Reconnect the logger so the history stays complete.