String - inverter configuration

[digital48]

We have 14 panels on a west facing roof wired as two string of 7, and seven panels on a south facing roof, all connected to a Sunny Beam 4000TL.

Looking at the DC readings on the inverter, rather than seeing one (south facing) input high in the morning and the second (west facing) low, then changing to the first being low and the second very high, they both remain with the first low and the second around twice the first.

The only explanation I can think of is that one west facing string and the south facing string have been connected into the second input, and the remaining west facing string into the first input. Is that permissible? Is it ideal?

We're around 20% down on what we would expect to have generated this month.

 

[SolarCity]

When you say DC reading, are you talking about voltages? You don't need much sunlight to produce quite a high voltage - it is the amperage which is more dependant on the light levels.

How much have you produced this month, what panels have you got and what figure were you expecting to generate?

 

[digital48]

I was talking about power. It's practically dark now so I'll have a look tomorrow, get the relevant numbers and come back.

 

[wstevew]

On the inverter there is a breaker protruding from the bottom. Tracker 1 connection is to the left. Tracker 2 connection is to the right. If the 4 wires from the west aspect enter at the same point then they are wired to the same tracker. If they are either side of the breaker then your suspicions are correct.

 

[digital48]

Thanks, but I can't see which wire comes from which string. I just have six wires arriving at the inverter after their trip through a loft and some trunking.

 

[wstevew]

The display shows volts then amps for string 1 then does the same for string 2. The.voltages can be similar but the amps will be higher for the string facing the sun.

I think you would be best to post up what make. And model the panels are and your rough location and how many kWh you have generated for the month and what you are expecting.

 

[digital48]

It's fairly dull at the moment but readings are:
Current 0001: .905A
Current 002: .375A
Voltage 001: 225.58V
Voltage 002: 254.54V
Power 001: 204W
Power 002: 96W

Panels: Canadian Solar 190
Location: Bradford
Power for the month: 49.65kWh
Power expected: 64.5kWh

 

[SolarCity]

The figures look about right for your voltages and current on both strings, but it is still very difficult to say whether the strings are mixed up.

Can you get to any of the plugs of the panels? If you can, switch off the DC isolators and then uplug the connector on a panel on the south facing system. Power it back up and you should be getting 0w on the second input. If you haven't then you know you have problems.

 

[digital48]

Thanks, I'll see if I can get up to one of the connectors.

Are you saying that, if they're connected as I suspect, I have a problem? Would it reduce output?

 

[SolarCity]

Yes, it would affect your output. The good news is that it would be very easy to rectify.

To be honest, your output figures look about right to me though so don't panic.

Make sure you remember to turn the DC isolators off if you're going to do this and remember to turn them off again when you plug them back in.

 

[digital48]

Unfortunately, I can't get to the connectors. Is there an alternative way to check?

 

[SolarCity]

I can't really think of another way unless you can get up to the panels and cover some of them over?

 

[wstevew]

Do you have 2 or 3 dc isolators.

If you have 3 then you should be able to work it out as two of the strings should have a simlar output as they face the same direction.

 

[digital48]

Just one isolator...

 

[wstevew]

Hmmm. That for isolating ac, panels, or both?

I just run your system through my phone app and it says 57kWh for December (birmingham nearest I could find)

1.33 south 25kWh
2.66 west. 32kWh