solar panels .....

[dapope]

So yesterday we bought a wobblibox..... to go with the two motorhomes..
Its not had 12v properly done in it in the past, and has no air con We are eyeing off a Truama underbed unit as it only weighs 23kg, and we will need to be weight sensitive to stay within the vehicle capacity.
We want to off grid it....surprise surprise...Anyway, the lithium batteries will come out of the swagman.....and I think I can get a shedload of solar on the roof, of the van, as its a poptop, and no stuff on the roof. My question is, the panels I am looking at have a voltage of 23.8v, so am I right in thinking I can effectively double the amperage I am likely to get into the batteries? (and will I be better with MPPT controller?)
My second question relates to the inverter, the trusty W7 knockoff... I am thinking I will just plug the external lead into the 240 output on the inverter, or is that likely to lead to a shocking experience?
Cheers,

[BruceS]

You need to 'match' the panels to the controller or vice versa.
I personally wouldn't touch panels with that voltage as if you ever need to replace any you might find it hard to find similar ones.
12V (nom) panels are usually around 19v or 24v (nom) ones are around 37.7v.
Having said that if you have a 'good' MPPT controller like mine, the limit is 145v so I have 3 hooked in series giving me 119.1v feeding into a 24v controller.

[T1 Terry]

Umm.... if it's a poptop and you plan to cover it in solar panels, who is going to pop the top and close it again each time? Even with air lifters, the weight will need to be perfectly even to stop one corner lifting or lowering before the others and twisting the roof. They are already a very light weight frame design so you can lift them with nothing on there, so the strengthening required to stop it caving in in the middle will make it even heavier.
As far a panel voltage goes, the 23.8v is Vmp or OCV? For an MPPT controller you need all the OCV and Vmp to be fairly close together and the advertised watts to be fairly similar or the lowest/smallest capacity panel will drag the others down to the same amount wasting what ever remaining capacity there was to harvest.

T1 Terry

[dapope]

Umm.... if it's a poptop and you plan to cover it in solar panels, who is going to pop the top and close it again each time? Even with air lifters, the weight will need to be perfectly even to stop one corner lifting or lowering before the others and twisting the roof. They are already a very light weight frame design so you can lift them with nothing on there, so the strengthening required to stop it caving in in the middle will make it even heavier.
As far a panel voltage goes, the 23.8v is Vmp or OCV? For an MPPT controller you need all the OCV and Vmp to be fairly close together and the advertised watts to be fairly similar or the lowest/smallest capacity panel will drag the others down to the same amount wasting what ever remaining capacity there was to harvest.

T1 Terry

thanks Bruce and Terry.
I was thinking matched panels of the semiflexible type, but will do more thinking and measuring anyway..

[T1 Terry]

Good luck with the semi flexibles. We have given up on them entirely now after every fix has not been the golden cure we'd hoped with some failing after being replaced once already. Until someone has had more than 4 of them fitted for 3 yrs without a single failure we will not be advising anyone to use them. We will fit them if they want them, but they will have to buy them so they wear the warranty, we just can't afford to loose any more money as a result of them failing.

T1 Terry

[dapope]

I have some that appear to be delivering still, just not sure how much, they need a good clean. Will see how I go