Solar panels - parallel or series?

[Homestar]

Looks like st some stage soon I'll be getting 5 x 95 watt solar panels which I was then thinking of running into an MPPT charger such as a Victron 100/50 or similar.

Being an Electrician I'm thinking I should wire them in series as the controller can handle 100 volts (I'm assuming here the open circuit voltage will be around or just under 100 volts with the panels connected in series here but haven't got the panels yet to check this).

So, for the solar gurus, is this the correct way to go? Thinking that doing this will reduce voltage drop and allowing charging to continue down to a lower light level as a higher voltage will be maintained on the input for longer.

Thoughts/theories?

[weeds]

I’m no guru but sound good to me....

What brand/type of panels??

[Homestar]

I’m no guru but sound good to me....

What brand/type of panels??

No idea yet - they are a few years old and I probably won't have them for a couple of weeks. I'm not expecting them to perform like new but they should be good for a while yet by the sounds of it.

[Eevo]

Thinking that doing this will reduce voltage drop and allowing charging to continue down to a lower light level as a higher voltage will be maintained on the input for longer.



im not sure if this will reduce voltage drop.
but im thinking it will decrase resistance though your wires.
less amps = less resistance which is useful on hot days.

[Homestar]

Hadn't thought about lower conductor temp that may be possible in a positive temperature coefficient conductor by lowering the amps.

[bee utey]

My suggestion is to go series-parallel, keep the panel voltages to under 60V where contact isn't a safety hazard. For 36 cell units OC voltage will be slightly higher than 20V especially in cold weather. Five panels is of course an awkward number to do that with.

[Markf]

Looks like st some stage soon I'll be getting 5 x 95 watt solar panels which I was then thinking of running into an MPPT charger such as a Victron 100/50 or similar.

One of the reputably better regulators around.


Being an Electrician I'm thinking I should wire them in series as the controller can handle 100 volts (I'm assuming here the open circuit voltage will be around or just under 100 volts with the panels connected in series here but haven't got the panels yet to check this).

Panels of around 100W tend to have an open circuit voltage (Voc)of between about 18V and about 25V so you may, or may not, be on safe ground. The only way to be dead set certain is to measure Voc.



So, for the solar gurus, is this the correct way to go? Thinking that doing this will reduce voltage drop and allowing charging to continue down to a lower light level as a higher voltage will be maintained on the input for longer.

Thoughts/theories?

Series connection will certainly reduce I2R losses over parallel connection given the same wire size.

[austastar]

Hi,
If I have understood what I have been told, there is also the fact that shade on one panel will lower the output of a series array more than a parallel array.
Not that you have much choice with five panels.
Cheers

[Milton477]

I have always thought that parallel was better when panels could be in partial shade. If wired in series, the one in the shade pulls the others down & the output is less than if they were in parallel.

[Homestar]

Ah, hadn't thought about the shade on one panel affecting the whole system. I could easily go with 4 panels and do a series parallel setup.

[DeanoH]

Double the voltage, half the current and quarter the losses. You can't beat series connection though 5 panels is an 'awkward' number of panels.

Assuming 1/. that the panels are nom. 12v the Voc will be approx. 22v. and 2/. DC battery voltage is nom. 12v then 5 panels will give a theoretical 110v DC so theoretically 10% over voltage for the Victron 100/50. If these are older degraded panels then may be a bit down on Voc but is it worth risking a $400 solar reg ? With panels and battery (load) permanently connected (no fuses/no switching), Voc will probably never happen but IMO not worth the risk so why not a Victron 150/35 which costs the same as the 100/50 ?

Aah ha I hear you cry :), what about the DC side of things 5X95 = 480 watts or 40 amps @ 12v but realistically 35.5 A @13.5v so a theoretical < 1.5% over nominal max current. I could live with that. In practice this will seldom if ever happen especially with older 'less than optimal' panels even if perfectly aligned. I'm yet to see a panel that can actually deliver max stated current but, again theoretically, given a typical Melb western suburbs clear, cold winter morning it's theoretically possible. Quality solar regs like the Victron don't come with a built in suicide pact, if they're running too hot they'll just move the MPPT point to reduce the load/heat and live happily ever after.

IMO you're better off to go with the Victron 150/35 in this example as it wont be 'spiked' with excess voltage and is well capable of handling a theoretical 1.5% (or greater) overload.

Deano :)

[rangieman]

Isn,t Damien a solar Guru [tonguewink]

[DeanoH]

I have always thought that parallel was better when panels could be in partial shade. If wired in series, the one in the shade pulls the others down & the output is less than if they were in parallel.

This is why in a series setup you'll have a reverse biased diode across each panel as well as a forward biassed diode in series with the lot to avoid the smoke, flames etc from accidental reverse polarity connection. I haven't been there for a while but the BP Solar site had a good write up on this. Note. many panels come with this protection already supplied. The 12v BP panels I used to work with were two 6v panels wired in series and had 3 diodes fitted, 2 reverse biased across each 6v 'panel' and one forward biased. When series connecting we shorted out the forward biased diodes in all but one panel as 0.6v X no of panels was a significant voltage loss in the scheme of things.

Deano :)

[DCX15Y]

Looks like st some stage soon I'll be getting 5 x 95 watt solar panels which I was then thinking of running into an MPPT charger such as a Victron 100/50 or similar.

Being an Electrician I'm thinking I should wire them in series as the controller can handle 100 volts (I'm assuming here the open circuit voltage will be around or just under 100 volts with the panels connected in series here but haven't got the panels yet to check this).

So, for the solar gurus, is this the correct way to go? Thinking that doing this will reduce voltage drop and allowing charging to continue down to a lower light level as a higher voltage will be maintained on the input for longer.

Thoughts/theories?

Definitely in series.
This will produce nearly half a kilowatt an hour and might be too many panels if you are just charging a couple of car batteries?

[Homestar]

Will be 300 to 500Ah of deep cycle batteries. Depends on what the van weighs and what GTM I register it as. Will know in a couple of weeks both of these things. :)

One good thing about registering a classic van in Vic is that they just ask what the GTM is - the axles are rated to 2,000Kg so that's what I'll tell them. Hoping the van currently weighs around 1,600Kg which is fairly typical for a van of that size for its year.

[DCX15Y]

Will be 300 to 500Ah of deep cycle batteries. Depends on what the van weighs and what GTM I register it as. Will know in a couple of weeks both of these things. :)

One good thing about registering a classic van in Vic is that they just ask what the GTM is - the axles are rated to 2,000Kg so that's what I'll tell them. Hoping the van currently weighs around 1,600Kg which is fairly typical for a van of that size for its year.

In a 12V system that would be 3.6kWh to 6kWh. You would never want to discharge them more than about 30%, so that would give you 1-2kWh for long battery life. If you are cycling around that amount, then it will recharge in four of five hours of solid sunlight, so seems about right. If you go to 24V then double everything (including the battery weight).

[Homestar]

Will be 12 volts, and power draw will be well within the capacity of the batteries. Exact system layout is still unknown as I haven’t got the van to where an check out where the batteries can live and still don’t know the weight. 😊