Zagato
Well-Known Member
If I wire up one 20W panel to another 20W panel does that give me 40W output or is it still 20W but twice as much... if you see what I mean! 
20W + 20W = 40W or just 2 x 20W?
- Thread starter Zagato
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Trundlebug
Well-Known Member
If you wire them in parallel it will be 40w, if in series it will be less. No time to work out & can't remember clearly but I think 10w overall as the resistance is higher
VicS
Well-Known Member
Agreed. Wired in parallel you should be able to draw twice the current and therefore get twice the power ..
Nominally in series you will get the same max current but at twice the voltage so you'd also get twice the power
Phoenix of Hamble
Well-Known Member
If I wire up one 20W panel to another 20W panel does that give me 40W output or is it still 20W but twice as much... if you see what I mean!
Think of Power (W) as volume of water.... if you have 20ltrs and get another 20ltrs, you now have 40ltrs. doesn't matter if they are in series or parallel to Power... still 40ltrs.
Zagato
Well-Known Member
Excellent, thanks for that, I didn't realise 
neilf39
Well-Known Member
Power=volts x amps so you get half the amps in series at 24 volts compared to in parallel at 12 volts. Usefulness depends on whether you need a 24 or 12 volt input. Power available is the same for a given amount of light hitting the panels
Mistroma
Well-Known Member
If you are fitting the normal rigid panels you may well get more output from 2 x 20W panels due to shading. If you shade 5% of one 40W rigid panel the output will be very low. However, shading 10% of one 20W panel and not shading the other still gives full output from one panel.
Obviously both panels can be shaded at the same time but you improve your chances of some output with 2x20W panels. it may well be that actual Ah from 2x20W is quite a bit better than 1x40W, depends on where you are mounting them. Cheaper rigid panels tend to be worst affected by shade.
Obviously both panels can be shaded at the same time but you improve your chances of some output with 2x20W panels. it may well be that actual Ah from 2x20W is quite a bit better than 1x40W, depends on where you are mounting them. Cheaper rigid panels tend to be worst affected by shade.
VicS
Well-Known Member
But don't extend the analogy to include battery capacity. In that case two batteries in parallel double the Ah available but two in series only double the volts not the capacity
alan_d
Well-Known Member
True up to a point, in that it applies to the available ampere-hours (Ah), but the energy available from a battery to do useful stuff is a function of available Ah times the voltage. Thus you would be able (say) to heat the same amount af water to the same temperature using 10 Ah from a 24 volt battery or 20 Ah from a 12 volt battery.
Phoenix of Hamble
Well-Known Member
Yes, because Ah is not a measure of power.... so not comparable.
William_H
Well-Known Member
What you have to be aware of is that solar panels are rated at max voltage times max current. It gives a wattage which is not really achievable except close to it with an MPPT regulator.
So 2 x20 watt panels in series will give an open circuit voltage of 40v. I f you connect that to an MPPT regulator it will happily convert the 40 volts or less to the 14 volts you want for charging 12v battery. If however you connect the 2 in series to a 12v battery direct then you will have more chance of achieving the max current for one panel ie 1 amp especially in low sun shine conditions. You simply waste a lot of power in the cells. If you connect them in parallel then you can get near 2 amps total in good sunshine. You waste the difference in voltage between 20v no load and 14 v battery ie 6 watts in the panel. But the extra voltage is designed to give output into battery when sun is less than ideal.
If that doesn't make sense don't worry just connect them in parallel. (with a regulator) good luck olewill
So 2 x20 watt panels in series will give an open circuit voltage of 40v. I f you connect that to an MPPT regulator it will happily convert the 40 volts or less to the 14 volts you want for charging 12v battery. If however you connect the 2 in series to a 12v battery direct then you will have more chance of achieving the max current for one panel ie 1 amp especially in low sun shine conditions. You simply waste a lot of power in the cells. If you connect them in parallel then you can get near 2 amps total in good sunshine. You waste the difference in voltage between 20v no load and 14 v battery ie 6 watts in the panel. But the extra voltage is designed to give output into battery when sun is less than ideal.
If that doesn't make sense don't worry just connect them in parallel. (with a regulator) good luck olewill
Zagato
Well-Known Member
I was going to wire them up like this minus the diodes and extra negtive lead!
Sunstore are saying it might be better to wire up the panels so that I only have one lead going into the controller, not sure if they mean wire one panel to the other or splice one panel wire into the output wire of the other panel which leads to the controller.
Are the batteries that go into the 1,2, & Both switch described as series or parallel? When asking for battery advice the suppliers don't know. They are assunming both batteries are charged at the same time so recommend similar batteries but surey if it's on positon 1 it will only be charging battery 1!
I'm getting tee'd off with battery research so may just go the easy option which I know works and get two Enduroline EXV90's deep cycle/starter calcium batteries for £175 rather than have two different types in amps etc! Although i think it would be better to get a specific starter and higher amp battery!
Sunstore are saying it might be better to wire up the panels so that I only have one lead going into the controller, not sure if they mean wire one panel to the other or splice one panel wire into the output wire of the other panel which leads to the controller.
Are the batteries that go into the 1,2, & Both switch described as series or parallel? When asking for battery advice the suppliers don't know. They are assunming both batteries are charged at the same time so recommend similar batteries but surey if it's on positon 1 it will only be charging battery 1!
I'm getting tee'd off with battery research so may just go the easy option which I know works and get two Enduroline EXV90's deep cycle/starter calcium batteries for £175 rather than have two different types in amps etc! Although i think it would be better to get a specific starter and higher amp battery!
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William_H
Well-Known Member
Well if it were me I would simply connect each panel with diode built in to each battery. No regulator. You are not likely to do too much overcharging with max 1 amp and a lot less in UK winter. Perhaps some use in summer.
If you go for your diagram and the regulator is able to handle 2 batteries then it should be OK with any sort of mix of batteries.
If you want new batteries I would go for rewire and fit a VSR. Fit a starter battery for the engine and any sort of deep cycle for services.
Throw away you 1,2,both switch and fit isolation switch 1 pole for both engine and service battery. Either buy a VSR that will do emergency engine start paralleling or fit another emergency connecting switch from one bat + to the other.
Just my opinion and many love their 1,2,both switches but VSR makes it all automatic. good luck olewill
If you go for your diagram and the regulator is able to handle 2 batteries then it should be OK with any sort of mix of batteries.
If you want new batteries I would go for rewire and fit a VSR. Fit a starter battery for the engine and any sort of deep cycle for services.
Throw away you 1,2,both switch and fit isolation switch 1 pole for both engine and service battery. Either buy a VSR that will do emergency engine start paralleling or fit another emergency connecting switch from one bat + to the other.
Just my opinion and many love their 1,2,both switches but VSR makes it all automatic. good luck olewill
Zagato
Well-Known Member
I have read this suggestion on other threads Olewill, seems to be an improvement over the 1,2 switch. I don't know what a VSR switch is and wouldn't know how to wire one up etc. Perhaps it's best left for now, I've got so many new things to sort/research before she goes in the water.
