Installing additional solar - DIY?

[Wh05apk]

We currently have a 120w panel and a victron 75/15, we use about 5-600wh per day so would like another 200w or so as we have plenty of roofs pace. We have 246ah gel batteries, and use the van a lot throughout the year, mid summer 120w can just keep up, but would like to have enough for 8-9 months of the year. Do the cables from each panel need to be fed through to the controller separately, or can I have a connection on the roof, saving feeding through and breaking the seal?
Also are the panels literally just stuck on with sikafix?

 

[tonyidle]

As long as the panels have the same voltage output (on the panel label or measure it disconnected) you can connect them on the roof + to + and - to - . In other words in parallel. Just make sure the controller can handle the combined current (amps).

They are stuck to the roof using Sikaflex (no screws needed). Just follow the Sikaflex instructions regarding surface preparation. Bear in mind that some of the best-priced (per Watt) panels at the moment are 250W because they're the size used for domestic solar installations.

 

[Richard n Ann]

Solar panels are usually 19v so you'll need cable down to the regulator that can handle 17a continuously.

Our 150w solar has 8 screws into the roof and also bonded. It's up to you but I would never just rely on adhesive alone.

 

[Wh05apk]

Looking at the vitreon 75/15 we have it should handle 220w, so thinking may just go with an additional 100w for now.

 

[tonka]

Ref the fixing. Only every just sikaflex my brackets onto the roof. Done 4 panels on various vans and never had any issues.

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[Wh05apk]

Fixing is my concern, might be tempted to use sikaflex, but then use a safety cable.....

 

[tonyidle]

Fixing is my concern, might be tempted to use sikaflex, but then use a safety cable.....

I would guess that most panels you see on mhs are simply attached with adhesive. If you have ever tried to remove correctly applied Sikaflex (there are other excellent PU adhesives) you wouldn't worry about a panel detaching.

 

[Richard n Ann]

Depends what van you have. Our coachbuilt has a thin skin of aluminium on the roof. When the sun beats down on it, it expands and ripples up clearly showing it's not connected to whatever is beneath. I wouldn't want the panel banging up and down with the wind under it while driving.

 

[Wh05apk]

Looking promising, how do I "splice" into the existing cables, I have seen mc4 connectors referred to, I gather these have built in diodes in to prevent current flowing between panels, is it just a case of cutting existing cables and connecting through these, and can they be used externally?

 

[Sundowners]

If you have the solar panel plug connections you can get two into one plugs so you don't need to cut any wires-------- I think they are the mc4 plugs you mentioned

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[PhilandMena]

Oddly enough, I have just put another Solar Panel on the roof and as a result of bad planning on my part have 4 solar panel corner brackets that are brand new and unused. These require no screwing into the roof, just bonding with Sikaflex and screwed to the side of the panel with self tapping screws. If your interested, you can have them for two thirds of the price I paid for them , plus postage. I'm happy to put pictures up so you can see what's on offer.

 

[Sundowners]

If you use something like sikaflex do it before a skin forms on the surface------ so get everything ready to go before you put the 'glue' down.
I have done the three panels on our van just with an alternative to sikaflex and check security every time I wash the panels------about three years on and still VERY secure. Our previous van had a thin ally sheet roof that was not fixed to roof timber so I glued and screwed it-------- it was very difficult to remove without ripping the roof sheet!!

 

[tonyidle]

Depends what van you have. Our coachbuilt has a thin skin of aluminium on the roof. When the sun beats down on it, it expands and ripples up clearly showing it's not connected to whatever is beneath. I wouldn't want the panel banging up and down with the wind under it while driving.

On the face of it I'd agree. But to screw to anything other than the skin you would have to first screw a sub frame to the battens within the roof (having found where they are!) then screw the panel to the subframe. Doing that would also constrain roof expansion and could well lead to other problems. A panel glued to the skin is heavy enough to sit still.

 

[tonyidle]

Looking promising, how do I "splice" into the existing cables, I have seen mc4 connectors referred to, I gather these have built in diodes in to prevent current flowing between panels, is it just a case of cutting existing cables and connecting through these, and can they be used externally?

The diodes aren't in the connectors - you'll find them inside the termination box on the back of the panel.

 

[tonyidle]

If you use something like sikaflex do it before a skin forms on the surface------ so get everything ready to go before you put the 'glue' down.
I have done the three panels on our van just with an alternative to sikaflex and check security every time I wash the panels------about three years on and still VERY secure. Our previous van had a thin ally sheet roof that was not fixed to roof timber so I glued and screwed it-------- it was very difficult to remove without ripping the roof sheet!!

The method I use is to pre-position the panel (with mountings attached and roughened ready for adhesive) then masking tape around the mountings about 6mm clear of them. Move panel to one side & prepare the areas you have marked with tape ready for the adhesive. Fully coat these areas with a 3mm layer of adhesive then lift the panel into position (easier with a helper). Gently wiggle the panel until adhesive has squeezed out around the edges of each mounting - but don't overdo it as you need a couple of mm under the mount. Use a gloved finger to form a neat fillet around the mounts. Remove masking tape.

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[DBK]

When I added a second 100W panel I wired them in series. I did this because the existing cables were a bit thin and by wiring them in series I could keep the current the same but just doubling the voltage, Victron also recommend series connection. This disadvantage is if one panel is shaded the overall drop in power can be greater than if they are wired in parallel but I'm happy to live with this. If it is so sunny we have to park under trees there should still be enough power generated.

I fitted a waterproof junction box from Screwfix onto the roof and used this to make the connections. It also give me the opportunity to easily add a third panel at some time.

 

[Richard n Ann]

I put aluminium channel down first so the solar panel can be changed easily if it fails. The panel then bolts down to it with special 8mm channel nuts known as 'zebs' (because some have springs on )

 

[Silver-Fox]

Looking promising, how do I "splice" into the existing cables, I have seen mc4 connectors referred to, I gather these have built in diodes in to prevent current flowing between panels, is it just a case of cutting existing cables and connecting through these, and can they be used externally?

The diodes are on the panels on mine.
I presumed the connectors were just that, connectors.

I have connected two panels together on the roof to one pair of feed cables to the controller.
I shortened the cables on the panels, couldn’t see the point of long cables coiled up on the roof.

 

[Lenny HB]

For connecting them on the roof you just need MC$ branch connectors you can get them in 2 way, 3 way etc.

I prefer to use aluminium brackets 2 down each side and one at each end. I use Sika 291i its a marine adhesive sealant with a much higer bonding power, a few quid more but safer IMO.
If using plastic brackets it's very important to make sure the Sika you use is compatible as some types are not.

 

[Hettie's Crew]

I was thinking about adding a second panel.
We have a Poly 150-180 panel (not exactly sure what wattage until I look underneath).
A Votronic MPPT 350 controller, chosen because we thought we may add a second panel and twin Exide ES900 G80 gel batteries. I was going to add a 100-150w Mono panel.
I thought it would be simply joining the wires on the roof, +to+ -to -
Is there more I should be considering?

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[Lenny HB]

I was thinking about adding a second panel.
We have a Poly 150-180 panel (not exactly sure what wattage until I look underneath).
A Votronic MPPT 350 controller, chosen because we thought we may add a second panel and twin Exide ES900 G80 gel batteries. I was going to add a 100-150w Mono panel.
I thought it would be simply joining the wires on the roof, +to+ -to -
Is there more I should be considering?

Should work fine providing the cables going down to the controller are at least 4 mm sq.

 

[Minxy]

I was thinking about adding a second panel.
We have a Poly 150-180 panel (not exactly sure what wattage until I look underneath).
A Votronic MPPT 350 controller, chosen because we thought we may add a second panel and twin Exide ES900 G80 gel batteries. I was going to add a 100-150w Mono panel.
I thought it would be simply joining the wires on the roof, +to+ -to -
Is there more I should be considering?

Nope, just as Lenny says, you need to make sure the existing cable going down to the controller is capable of taking the 'input' from the 2 panels.

I considered getting a higher input cable when I installed 2 x 100w panels on our camper but as each came with long cables anyway I ran all 4 down (2 x pos and 2 x neg) and twisted the ends together before slot them into the + and - inputs of the controller, then tightened them up, works fine.

 

[Hettie's Crew]

Should work fine providing the cables going down to the controller are at least 4 mm sq.

I bought some 4mm squared from an auto electrical place and the wires from the panel are fatter.

 

[Lenny HB]

I bought some 4mm squared from an auto electrical place and the wires from the panel are fatter.

Two reasons, Solar cable is double insulated as it is designed for house installations so the over all diameter is larger than a single insulated cable.
More importantly Auto cable is sized by the overall diameter including the insulation, so 4 mm auto cable is probably ony 2 mm sq copper.

The cables going to your regulator look way under size.

 

[Richard n Ann]

Two reasons, Solar cable is double insulated as it is designed for house installations so the over all diameter is larger than a single insulated cable.
More importantly Auto cable is sized by the overall diameter including the insulation, so 4 mm auto cable is probably ony 2 mm sq copper.

The cables going to your regulator look way under size.

Yeah I read that the car industry cable size is the outer diameter so that the size of holes and cable runs etc can be calculated more easily

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[Lenny HB]

You don't need to go over the top with cable sizing, ideally 3 % voltage drop but IMO 5% is fine.
In the summer and your panels are delivering say 10 amps a 5% drop would reduce the output to 9.5 amps which is not going to worry you in mid summer.
In winter when you need most power but the panels are only producing 3 amps a drop of 0.15 amps is not really going to worry you either.

 

[tonyidle]

Yeah I read that the car industry cable size is the outer diameter so that the size of holes and cable runs etc can be calculated more easily

Not in my experience:

Broken Link Removed

 

[Hettie's Crew]

The cables going to your regulator look way under size.

I find that difficult to accept, the overall diameter of that cable is around 6mm and it’s the standard cable from the panel that Photonic Universe say is 4mm2.

 

[Lenny HB]

@tonyidle

 

[Lenny HB]

I find that difficult to accept, the overall diameter of that cable is around 6mm and it’s the standard cable from the panel that Photonic Universe say is 4mm2.

I was looking at the ones going to your batteries, however they look a bit bigger in your enlarged photo.

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