Solar Panel installations final questions

[UFO]

I will be installing solar panels on our Adria Twin soon. There is lots advice on this site - so I am almost there.

I think my battery is 70ah (see photo) - so in future bigger battery(ies) will probably be needed, although we have just about managed for 3 years at all times of the year even without LED internal lights, also now installing LED lights.

100W of solar is good for 100ah of battery I understand. I could buy a 120w panel for £155 or 2 x 80w for £147 - so I will go for the 2 x 80w as the installation is only a bit more work and I wil have plent of capacity for future battery upgrade and more charge in the winter months.160W (2 x 80W) Monocrystalline Solar PV Panel 24v 12v Battery Charger | eBay

(a) To avoid running 4 cables (2 each +ve and -ve) from the roof to the charge controller I have been looking for a connection box / harness but can't find anything. Any ideas?

(b) I realise that if I connect the two panals on the roof the cable from the roof to the charge controller will have to be heavier due to 160W. 80w panal specification is

• Operatine Voltage: 18.0V
• Operatine Current: 4.44A
• Open-Circuit Voltage: 21.24V
• Short-circuit Current : 4.8A

So this means cable with 10amp rating? 4mm solar panel pv cable seems to the common type available and 'rated at 55amp' so this should be ok.

(c) for fixing the panal brackets to the metal roof Sikaflex is recommended. What's the difference between Sikaflex 221 and 252? Which one should I use / does it make any difference?

(d) for preparing the roof Sikaflex cleaner is available. Is this necessary? I would have thought that cleaning with spirit followed by light abrasion would be sufficient.

thank you David

 

[ellisboy]

I use Sika EBT from Screwfix,it's the same but doesn't have the word caravan on it! Just wipe the roof with some solvent cleaner etc.Have you tried eBay for a junction box?

 

[UFO]

(a) To avoid running 4 cables (2 each +ve and -ve) from the roof to the charge controller I have been looking for a connection box / harness but can't find anything. Any ideas?

I have now found some ways of connecting 2 solar panels - a branch connector MC4 SOLAR PV BRANCH CONNECTOR (Y piece) - 1 PAIR | eBay
or a Y cable 1 Pair MC4 Adapter Cable Y Branch Connectors F/F/M And M/M/F For Solar Panels | eBay

 

[ellisboy]

They look good !

 

[Deleted member 3011]

"Rated at 55 amps" in RV-speak means at 55 amps, the cable will start to smoke after a few minutes.

For RV use, it is generally the voltage drop that is more important - most especially between the solar regulator and the battery, but also between the solar panel and the regulator. The first will mean it takes longer to charge the battery up and the second results in wasted power. and keep the run from the panels to the regulator as short as possible.

Mount the regulator as close as possible to the battery (but not usually in the same compartment)

Apart from voltage drop concerns, there is an advantage to running separate wires down from each panel to the regulator. It makes fault-finding easier and if you intend adding panels later then you can double up the panels on each circuit and still keep voltage drop reasonable.

Oh, forgot. Choose the locations for the panel very carefully because the slightest shadow from a vent, hatch, airconditioner, tv antenna falling on the panel can make a huge difference to the amount of power delivered by the panel.

 

[m30]

I used a small waterproof ip rated enclosure (about 100mm x 100mm) from the local electrical factor/trade supplier. I then put a short block of screw connectors inside, which meant I could cut the cables to length nice and tidy. You can shorten the cables and use the connectors you have found if you get the new crimp on terminals, but I think you need a tool to crimp the ends.

Stu

 

[UFO]

"Rated at 55 amps" in RV-speak means at 55 amps, the cable will start to smoke after a few minutes.

Bit cryptic Tony, I never was any good at cryptic crosswords but the heavier the cable the less the voltage drop I guess.

For RV use, it is generally the voltage drop that is more important - most especially between the solar regulator and the battery, but also between the solar panel and the regulator. The first will mean it takes longer to charge the battery up and the second results in wasted power. and keep the run from the panels to the regulator as short as possible. Mount the regulator as close as possible to the battery (but not usually in the same compartment)

Good advice on keeping the cable runs short. What's the reason for not having the regulator in the same compartment as the Electrobloc / battery?

Apart from voltage drop concerns, there is an advantage to running separate wires down from each panel to the regulator. It makes fault-finding easier and if you intend adding panels later then you can double up the panels on each circuit and still keep voltage drop reasonable.

180w of panel will be more than we will ever need so I think I will go with connecting the panels on the roof.

Oh, forgot. Choose the locations for the panel very carefully because the slightest shadow from a vent, hatch, airconditioner, tv antenna falling on the panel can make a huge difference to the amount of power delivered by the panel.

Useful advice thank you.

 

[Deleted member 3011]

What's the reason for not having the regulator in the same compartment as the Electrobloc / battery?

If the electrobloc can handle it, then the regulator will also be OK. That normally will require the batteries to be "sealed" type and my generic advice was based on the possibility that normal flooded-cell batteries might be installed.
Theoretically, even "sealed" types aren't really sealed and there is always the possibility that they will vent under some charging conditions and if that happens it is likely that anything electronic in the same compartment will be damaged by corrosion. Very small risk so normally ignored.

My cryptic comment on cable rating was because this is an area that there are few standards and a cable can be described by several different parameters, most of which are of little use in determining whether a particular cable is suitable for a particular use. In this case "rated at 50 amps" tells you nothing useful. Is it a thick conductor with a low temperature insulation or a skinny conductor with high temperature insulation. No idea of which it is, and in any case the real parameter that is of use in this application is the conductor cross-section area (in square millimetres) because this determines the voltage drop at the given current and that is what is generally the limiting factor in 12V circuitry.

Obviously if the circuit is dragging 100 or 200 amps and the route length is short, the current rating might be a limiting factor, but that is also related to the cross-section of the conductor, the insulation and how it is installed so just the "current rating 50 amps" specification is still not much use to anyone. No point pumping 50 amps through a bit of wire if the voltage drop is 4 volts and the appliance really won't run on anything less than 10V eg a 600W inverter)

 

[Doctor Bob]

Sikaflex EBT - 512 OR 221 ????

Have pulled loads of useful info off the forum about fitting solar panels, starting to order all the different bits needed for my DIY installation. With respect to sticking the panels to the roof the jury favors sikaflex almost unanimously but which one ??? I have come across reference to EBT, 221 and 512 - can anyone advise me which is best to use.

 

[thegoodlookingbloke]

Dream on, if you manage to burn out a bit of 2Amp bell flex with solar panels, you will be my hero for life..

:idea:Experience is something you get minutes after you actually needed it....:dance:

 

[Firefox]

Have pulled loads of useful info off the forum about fitting solar panels, starting to order all the different bits needed for my DIY installation. With respect to sticking the panels to the roof the jury favors sikaflex almost unanimously but which one ??? I have come across reference to EBT, 221 and 512 - can anyone advise me which is best to use.

I used 512 but I think either would do and have both been used successfully in this application. Both have very similar properties by all accounts and I'm not sure of the exact difference apart from sika 221 cures a bit quicker, is a bit stronger, but is not listed as being UV resistant whereas 512 is.