Slimline 100W Solar Panel Fit

[DBK]

I couldn't resist getting the voltmeter out this morning while the sun was shining.

Initially I measured a total of about 36V coming from both panels but when I investigated the voltage coming off each panel the result was a surprise. The old panel was producing 22V but the new one just 14V!

The explanation was because of the low sun a shadow from the satellite dish was across the new panel.

Swinging the dish out of the way I suddenly had 22V from each panel.

I then turned the diesel heater on and this drew a current of at least 8A for several minutes while it fired up. I left things to settle down and a little later with the heater running steadily the current consumption on the meter was down to more or less zero, occasionally going up to 0.5A. So at a steady state the panels seem to be able to keep the heater running despite the weak sun.

At this point the panel voltages were both down to 18V which I understand is the voltage at which they will produce maximum power and where you would expect an MPPT type controller to hold the voltage for highest efficiency.

Turning off the heater the panel voltages quickly went back up to 22V which I guess is almost an open circuit voltage because the controller would have been drawing very little current as the batteries were more or less fully charged with a battery voltage of 13.8V.

Just need to wait for the next trip to see how it all works for real!

 

[Don Quixote]

Unless you cover the panels you will get a false reading as the panels are topping up batteries. Cover panels leave for 20 minutes then take reading from batteries after running the heater for seam period. Then you have a true reading.

 

[DBK]

Unless you cover the panels you will get a false reading as the panels are topping up batteries. Cover panels leave for 20 minutes then take reading from batteries after running the heater for seam period. Then you have a true reading.

A true reading of what? Yes, the batteries were not being charged, I was just looking at the steady state, in the sense the heater was running but there was negligible charge going into the batteries as they were well topped up. From which I deduce the panels were just producing enough to keep the heater running, which from memory is about 4A and that sounds about right as the single panel was producing about 2A last week when it was recharging the batteries.

I won't be able to deduce much more until I live off grid for a few days when I suspect if I run the heater overnight the panels will struggle to replenish the batteries the next day if I am still running the heater.

I may be able to test this next week as I have a trip to make to Carlisle for a funeral.

 

[Don Quixote]

A true reading of what? Yes, the batteries were not being charged, I was just looking at the steady state, in the sense the heater was running but there was negligible charge going into the batteries as they were well topped up. From which I deduce the panels were just producing enough to keep the heater running, which from memory is about 4A and that sounds about right as the single panel was producing about 2A last week when it was recharging the batteries.

I won't be able to deduce much more until I live off grid for a few days when I suspect if I run the heater overnight the panels will struggle to replenish the batteries the next day if I am still running the heater.

I may be able to test this next week as I have a trip to make to Carlisle for a funeral.

A reading of 13.8V indicates that the solar is sullying power and is not the true reading of the voltage of the battery/batteries. with solar off it should drop over 30 minutes to 12.7 or better, but not possible to be sitting at 13.8volts. Thats what I mean by true reading.

 

[DBK]

A reading of 13.8V indicates that the solar is sullying power and is not the true reading of the voltage of the battery/batteries. with solar off it should drop over 30 minutes to 12.7 or better, but not possible to be sitting at 13.8volts. Thats what I mean by true reading.

OK, I understand what you mean. My understanding is a voltage of between about 13.5 to 13.8 when on charge is the float or "maintenance" voltage which effectively keeps it topped up and happy. This is what the controller keeps it at during the day.

The Victron is quiet clever from what I understand as it starts a new charging cycle each day as the sun comes up - literally, it senses the sun and knows a new day has sprung. It has a jumper which you set to select a charging algorithm although it can do a basic charging function if you need it but from the instructions I can't see why you would. This is the only solar controller manufacturer @eddievanbitz recommends and I think I can see why.

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[Don Quixote]

T

OK, I understand what you mean. My understanding is a voltage of between about 13.5 to 13.8 when on charge is the float or "maintenance" voltage which effectively keeps it topped up and happy. This is what the controller keeps it at during the day.

The Victron is quiet clever from what I understand as it starts a new charging cycle each day as the sun comes up - literally, it senses the sun and knows a new day has sprung. It has a jumper which you set to select a charging algorithm although it can do a basic charging function if you need it but from the instructions I can't see why you would. This is the only solar controller manufacturer @eddievanbitz recommends and I think I can see why.

The Victron is a great unit and you will be so pleased with it over time. You are correct with a float charge when they are telling the Victron MPPT controller that they are full, but be aware that after 3/4/5 days of UK sun the MPPT controller will not fully charge the batteries only top keep them up, but with the setup you have I believe you can go for 5/6/7 days in UK without needing to charge batteries fully again. I get round this by running B2B for 20 minutes or moving to new location when not so sunny days, but that would be after 10 or 12 days static and drawing 15/20 amps a day from batteries. Nice to see your setup by the way. Enjoy