Solar panel replacement - does voltage matter?

dgadee

dgadee

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My cheap at the time 100 watt panel (I think 21v open voltage) is needing replacement and I plan to put up something larger - maybe around 250 watts. I have been looking at technical data for some poly panels and they seem to have voltages of 32v and amp outputs not too much above my 100 watt panel. Do I need to take this data into account when choosing? Or will an MPPT do the translation into more amps at 12v?

I have a MPPT controller at present but will have to upgrade that since present one only handles up to 120 watts.

My thinking is just buy bog standard at low cost and replace as required. Spend a bit more on a controller.
 
dgadee said:
My cheap at the time 100 watt panel (I think 21v open voltage) is needing replacement and I plan to put up something larger - maybe around 250 watts. I have been looking at technical data for some poly panels and they seem to have voltages of 32v and amp outputs not too much above my 100 watt panel. Do I need to take this data into account when choosing? Or will an MPPT do the translation into more amps at 12v?

I have a MPPT controller at present but will have to upgrade that since present one only handles up to 120 watts.

My thinking is just buy bog standard at low cost and replace as required. Spend a bit more on a controller.
Click to expand...


At least buy a decent controller, i'd recommend Victron. My panels are wired in series, so output is typically close to 40v, the MPPT controller is happy with this, my particular controller will accept up to 75v.

As for the voltage/amps question, Ohms law applies here, if the panel voltage was 36v and 3a and the controller dropped the voltage to 12v, the amps would go up to 9a. If you buy a Victron controller you might consider the version with built in Bluetooth, you can then see exactly what's going on and configure the controller to suit your installation. You can also connect the controller to a PC with the appropriate cable from Victron.
 
Thanks. I think I get it now. Looked up panel cost - £96 almost four years ago and now same one is £83. It is mono, so will go for that again.

Will look at Victron, too.
 
OP should spread his search wide for solar panel. The domestic market is huge across the world so that the typical 200w 40v panel is very cheap. (our yacht club has 200 on the roof). Here in west Oz something like 20% of all houses have these panels. I understand that here it is not legal to refit second hand panels so if that follows in UK a house breaker may have panels to burn. I have not seen any panels at 32 volts. I suspect that the 32 volts is at max power point. ie more like 40 v no load. A bit like a 20v panel will give about 16v at best power load. ol'will
 
dgadee said:
What does that give you that a simple display doesn't?
Click to expand...

As well as performance at the time, it displays a bar graph showing hours at bulk, absorption and float, panel output, battery min & max, charge achieved each day, etc. Can also change battery charging and equalisation regime. Mine's the SmartSolar 100/30, blue tooth direct to tablet, not cheap but I think well worth the money.
 
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William_H said:
OP should spread his search wide for solar panel. The domestic market is huge across the world so that the typical 200w 40v panel is very cheap. (our yacht club has 200 on the roof). Here in west Oz something like 20% of all houses have these panels. I understand that here it is not legal to refit second hand panels so if that follows in UK a house breaker may have panels to burn. I have not seen any panels at 32 volts. I suspect that the 32 volts is at max power point. ie more like 40 v no load. A bit like a 20v panel will give about 16v at best power load. ol'will
Click to expand...

Just gone for a Panasonic 245 watt panel. £200 at present. One attraction is width - 800mm - which makes fitting easier on my arch.
 
20180811_160055.jpg 20180819_142629.jpg

Victron Smartsolar MPPT 100/30 with BT gives you detailed visual output for the last 30 days. I also have the Victron battery monitor (BMV 712) which also has BT output.

If you download the android/iphone app "Victron Connect" you can fire it up and explore all the user interfaces and settings for their devices as it has dummy profiles for each device programmed into the app. Try before you buy.

I installed mine in 2018 and it has been excellent.

Most I've got out of my 300W panels in one day was 1,5kWh

Solar300W.jpg
 
Baggywrinkle said:
Victron Smartsolar MPPT 100/30 with BT gives you detailed visual output for the last 30 days. I also have the Victron battery monitor (BMV 712) which also has BT output.

If you download the android/iphone app "Victron Connect" you can fire it up and explore all the user interfaces and settings for their devices as it has dummy profiles for each device programmed into the app. Try before you buy.

I installed mine in 2018 and it has been excellent.

Most I've got out of my 300W panels in one day was 1,5kWh
Click to expand...

I see the advantage but I'm more of a fit and forget person - but will see. I took the Victron battery monitor out of the boat and put in a Smartgauge because the former was impossible for me to understand.
 
Baggywrinkle said:
View attachment 81324 View attachment 81325

Victron Smartsolar MPPT 100/30 with BT gives you detailed visual output for the last 30 days. I also have the Victron battery monitor (BMV 712) which also has BT output.

If you download the android/iphone app "Victron Connect" you can fire it up and explore all the user interfaces and settings for their devices as it has dummy profiles for each device programmed into the app. Try before you buy.

I installed mine in 2018 and it has been excellent.

Most I've got out of my 300W panels in one day was 1,5kWh

View attachment 81326
Click to expand...

I also have a Victron MPPT and am very pleased with it. It does benefit from a high voltage, and high voltage also means less cable loss, so my recommendation would also be to maximise voltage up to that which can be handled by the controller by wiring panels in series, if one has multiple panels. The only reason not to wire in series would be if any of the panels are in shadow at a time when none of the other panels are. The problem then is that the panel in shadow will reduce the total output more than would otherwise be the case.

I have this problem in that two of my four 100W panels are virtually always in shadow and two are in sun, so I have two in series and two in parallel. This means that my 400W maximum 24 hour output is only 1.3 kWh. It's not great for 400W but it's acceptable. :)

Richard
 
You're better off putting a pair of 120w panels in series than putting a single 250w panel on.
 
RichardS said:
Presumably voltage as in #13?

Richard
Click to expand...

I took the advice to go for high voltage and went for one with these specs:

Peak power Wp 245W
Module Efficiency: 19.4%
Voltage at peak power Vmp: 44.3V
Max open circuit voltage Voc: 53.0V
Current at peak power Imp: 5.54A
Max short circuit current Isc: 5.86A
Weight: 15kg

And, as I said, width is about 800mm so easier to fit, though two smaller panels would certainly have worked too.
 
dgadee said:
I took the advice to go for high voltage and went for one with these specs:

Peak power Wp 245W
Module Efficiency: 19.4%
Voltage at peak power Vmp: 44.3V
Max open circuit voltage Voc: 53.0V
Current at peak power Imp: 5.54A
Max short circuit current Isc: 5.86A
Weight: 15kg

And, as I said, width is about 800mm so easier to fit, though two smaller panels would certainly have worked too.
Click to expand...

That all makes good sense to me. :)

Richard
 
dgadee said:
I took the advice to go for high voltage and went for one with these specs:

Peak power Wp 245W
Module Efficiency: 19.4%
Voltage at peak power Vmp: 44.3V
Max open circuit voltage Voc: 53.0V
Current at peak power Imp: 5.54A
Max short circuit current Isc: 5.86A
Weight: 15kg

And, as I said, width is about 800mm so easier to fit, though two smaller panels would certainly have worked too.
Click to expand...

"12v" Panels are commonly about 20v and the advice is often to connect them in series to a MPPT controller. The panel above is already 44v, so no need for series connection :encouragement:
 
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