FAO Ian - Gridfit 250?

jmackle - The figures for 2 x 110 watt Navitron panels would suggest that they were made for the Gridfit 250.

When the panels are performing to peak output, the Gridfit is within its optimum power band.

Your numbers are fine but the way you got to them a little suspect.

(One of the potential issues of using unbranded products from China is that things can and do change from shipping batch to batch - so check that the items you have report the same electrical characteristics.)

In an earlier thread, Mickey reported HIS 110 watt panels as Voc = 22.0v, Vmax = 17.50v. Lets assume yours are the same.

For a 110 watt panel the current at optimum voltage = 110/17.5 = 6.3 amps.

If you put 2 panels in series, you will get 17.5 volts x 2 = 35 volts BUT THE CURRENT WILL STAY AT 6.3 amps.
(If you put them in parallel, then the voltage would be 17.5v but the current would be 12.6 amps.)

So you can epect the series panel output to be open vircuit voltage of 44 volts, working voltage of 35 volts, and a current of 6.3 amps.

The Gridfit 250 will handle this with ease and you should expect to see something like 200 watts (which is the maximum continuous output of the Gridfit 250 despite the "250" in the name) when the panels are going full belt.

Even though the 44 volts "open circuit" appears to be comfortably within the Gridfit 250's tolerance, it is maybe a little tight (but OK!). Some panels actually have a higher voltage output when first new - sometimes as high as 15% above the spec - and can last for a few weeks. I used to understand why this was, but I am afraid I have forgotten now.

Another point is that panels are specifeid at a "standard" insolation of 1kW per m2. However, the incident sun intensity varies very considerably in the UK. Many people regard 1 kW /m2 as the maximum they will likely see but there were occasions in UK this summer when the incident solar insolation was GREATER than 1 kW / m2 - and therefore the panels will output more - and the safety margin we thought we had is less than we thought.

However, if the inverter is working well and providing power to the grid, there is almost no danger that the voltage will rise excessively. It is only in a powerout situation (startup) that the voltage could rise to a worrying level. Having said that, the Gridfit 250 has a very good high voltage rejection mode that allows it to cope with modest overloading without issue.

Also be aware that the Gridfit 250 has a low tolerance to high(ish) grid voltages. Theoretically, it should handle grid voltages of up to 241 volts AC rms. Observations would suggest that the Gridfit sees anything over about 237 volts AC rms as a fault condition and failsafes. This is part of its anti-islanding detection but I see it as probably the unit's primary weakness as it is quite normal for UK voltages to exceed 237 v AC rms - resulting in low productivity.

In summary : Everything will be fine.

I hope this helps.

Regards,
Ian