Solar setup

[Pamelala]

Advise on Solar Setup would be greatly appeciated as we are going round in circles but this is what we have so far.

We have 3 solar panels 250 watt ( Pmx 250w- Vmp 30.3v - Imp 8.24A - Voc 37.9V - Isc 8.85A) which we are connecting in parallel. The run from the furthest panel to combiner box is 5.5metres (that includes the 4mm2 cable attached to the solar panel which is about 1 metre long) so we intend to use 6mm2 cable from the MC4 connectors. Would that be ok or can the run be longer?

 

From the combiner box to the mppt controller (outback 80 flexmax) we have a 3metre run and we intend to use 16mm2 cable. Would this be ok?

 

From the controller to batteries which is around 1metre we will use 25mm2 cable. Is that ok?

 

Now we are wondering what size fuse to use and if we need some sort of isolating switch? Can we get fuses suitable for this job at car spare places?

 

Also will this set up accommodate a further 4th solar panel in the future if necessary?

 

The panels are attached to steel roof of the boat via aluminium brackets do we need to earth the panels?

 

Many thanks for any help.

[Scooby]

i have 3 x 165 panels and 1 x 100w panels all connected in series the panels have 4mm2 cable to the mc4 but then i have 6mm2 from that, upto 12 metres from the batteries to furthest panel. It sounds a bit stupid having 4mm and then using 16mm2 and 25mm2, wouldnt you expect the panels to have 16mm2 rather than 4mm2, i have used 6mm2 all the way to the batteries, runs pefectly with 595 watts connected to 60 amp reg,

[matty40s]

i have 3 x 165 panels and 1 x 100w panels all connected in series the panels have 4mm2 cable to the mc4 but then i have 6mm2 from that, upto 12 metres from the batteries to furthest panel. It sounds a bit stupid having 4mm and then using 16mm2 and 25mm2, wouldnt you expect the panels to have 16mm2 rather than 4mm2, i have used 6mm2 all the way to the batteries, runs pefectly with 595 watts connected to 60 amp reg,

I would have used a larger cable from controller to batteries if installing that system.

The OP is minimising voltage drop to the nth degree nothing wrong with that.

 

A fuse between the controller and batteries is needed on the positive side, 100A if you have an 80A controller.

Isolator switches are not a must, however, can help if you need to do any work on your electrics or test batteries etc.

You don't need to earth the panels.

[smileypete]

Typically in that setup the three panels would be in series (daisy chain) to the outback, using say 6mm² solar cable. 25mm² cable from outback to batts will accomodate up to 80A no problem.

 

The controller manual should state the fuse size, use eg. a 'megafuse', ideally a decent brand like Littelfuse, must go in the positive near the batts but not in the batt box itself.

 

I think most people connect directly to batts via a fuse and without an isolator. Before working on batt, controller wiring etc isolate the panels by unplugging an MC4 connector, then remove controller fuse.

 

If the controller has screw terminals, terminate the bare cable ends with 'bootlace ferrules' to suit the wire size off Ebay or an electrical distributor, squish them on with pliers to keep them in place.

 

Adding another panel probably means reconnecting the panels in parallel with MC4 splitters, but that's not too tricky, best cross that bridge if and when you come to it.

 

cheers, Pete.

~smpt~

Edited July 11, 2014 by smileypete

[Pamelala]

I would have used a larger cable from controller to batteries if installing that system.

The OP is minimising voltage drop to the nth degree nothing wrong with that.

A fuse between the controller and batteries is needed on the positive side, 100A if you have an 80A controller.

Isolator switches are not a must, however, can help if you need to do any work on your electrics or test batteries etc.

You don't need to earth the panels.

 

Thank you so much for the information you sent in your message and it's very reassuring that you think the cable sizing and runs are ok. Many thanks. Kind regards.

[Pamelala]

Typically in that setup the three panels would be in series (daisy chain) to the outback, using say 6mm² solar cable. 25mm² cable from outback to batts will accomodate up to 80A no problem.

 

The controller manual should state the fuse size, use eg. a 'megafuse', ideally a decent brand like Littelfuse, must go in the positive near the batts but not in the batt box itself.

 

I think most people connect directly to batts via a fuse and without an isolator. Before working on batt, controller wiring etc isolate the panels by unplugging an MC4 connector, then remove controller fuse.

 

If the controller has screw terminals, terminate the bare cable ends with 'bootlace ferrules' to suit the wire size off Ebay or an electrical distributor, squish them on with pliers to keep them in place.

 

Adding another panel probably means reconnecting the panels in parallel with MC4 splitters, but that's not too tricky, best cross that bridge if and when you come to it.

 

cheers, Pete.

~smpt~

 

Thank you for your comments, most useful.

 

The chap we bought the solar panels from advised us to run the panels in parallel to a combiner box because of shading from trees etc so that if one panel was in shade the other two would would continue producing power as normal. What do you think of this idea? Is there a reason why it's typical to run the panels in series?

 

You are right I've just looked at the wiring diagram from outback on the internet and they do suggest 80Adc Maximum Circuit Breaker on the positive cable to the batteries. I had missed that!!!!! On the instructions that came with the controller it just said 'dc disconnect'. Would it be the same as adding a fuse or do I have to get a circuit breaker?

 

Many thanks, kind regards.

[smileypete]

Thank you for your comments, most useful.

 

The chap we bought the solar panels from advised us to run the panels in parallel to a combiner box because of shading from trees etc so that if one panel was in shade the other two would would continue producing power as normal. What do you think of this idea? Is there a reason why it's typical to run the panels in series?

 

You are right I've just looked at the wiring diagram from outback on the internet and they do suggest 80Adc Maximum Circuit Breaker on the positive cable to the batteries. I had missed that!!!!! On the instructions that came with the controller it just said 'dc disconnect'. Would it be the same as adding a fuse or do I have to get a circuit breaker?

 

Many thanks, kind regards.

 

The shading problem happens on houses with chimneys, trees too, so most (all?) panels have 'bypass diodes' fitted. If a panel gets shaded its bypass diode allows the current from the others panels to literally bypass the panel, so the output of the others isn't affected. Probably worth checking with the supplier or google details for the panel to check they're fitted.

 

I'm surprised Outback recommend a 80A breaker for a 80A controller, if a 4th panel is added it may be pushing 80A at times in spring and summer. Could be worth emailing them and asking if a 100A megafuse will do, I agree with Matty that 100A would be the way to go.

 

If they do really want a breaker try an ebay search worldwide for eg. 'bussman 100 breaker' or 'blue sea 100 breaker'. Might need to get one from the states for £30ish, there are cheapo ones for around £10 but probably not worth it.

 

Some of these type breakers have a manual trip facility which is handy to isolate to work on the wiring or if there's some sort of problem. Eg:

 

http://www.ebay.co.uk/itm/Bussman-DC-Circuit-Breaker-100-Amp-Surface-Mt-185100F-/370337024562 (surface mount)

http://www.ebay.co.uk/itm/Blue-Sea-Waterproof-12-24v-100A-Main-Circuit-Breaker-New-/251566490330 (panel mount)

 

cheers, Pete.

~smpt~

Edited July 11, 2014 by smileypete

[Pamelala]

The shading problem happens on houses with chimneys, trees too, so most (all?) panels have 'bypass diodes' fitted. If a panel gets shaded its bypass diode allows the current from the others panels to literally bypass the panel, so the output of the others isn't affected. Probably worth checking with the supplier or google details for the panel to check they're fitted.

 

I'm surprised Outback recommend a 80A breaker for a 80A controller, if a 4th panel is added it may be pushing 80A at times in spring and summer. Could be worth emailing them and asking if a 100A megafuse will do, I agree with Matty that 100A would be the way to go.

 

If they do really want a breaker try an ebay search worldwide for eg. 'bussman 100 breaker' or 'blue sea 100 breaker'. Might need to get one from the states for £30ish, there are cheapo ones for around £10 but probably not worth it.

 

Some of these type breakers have a manual trip facility which is handy to isolate to work on the wiring or if there's some sort of problem. Eg:

 

http://www.ebay.co.uk/itm/Bussman-DC-Circuit-Breaker-100-Amp-Surface-Mt-185100F-/370337024562 (surface mount)

http://www.ebay.co.uk/itm/Blue-Sea-Waterproof-12-24v-100A-Main-Circuit-Breaker-New-/251566490330 (panel mount)

 

cheers, Pete.

~smpt~

Hi

I checked with the panel supplier and the panels do have bypass diodes in the junction boxes. Is the advantage of connecting the panels in series rather than in parallel that we use less cable and no combining box or are there other advantages?

 

I have emailed Outback so I will await their reply with interest.

 

Many thanks for your help. Kind regards.

[Justme]

The big advantage with panels in series is the higher string voltage has lower losses & you can use thinner cables for the same wattage. Plus the start up voltage is reached earlier in the day & stays till later in the day. As we all know a long charge is needed to get to that magic 100% SOC. Not an issue in summer but in winter it will really help.

 

Bi pass diodes are not the great solution they are made out to be. However neither is wiring in parallel.

 

 

Shade is to be avoided as much as possible.

[Pamelala]

The big advantage with panels in series is the higher string voltage has lower losses & you can use thinner cables for the same wattage. Plus the start up voltage is reached earlier in the day & stays till later in the day. As we all know a long charge is needed to get to that magic 100% SOC. Not an issue in summer but in winter it will really help.

 

Bi pass diodes are not the great solution they are made out to be. However neither is wiring in parallel.

 

 

Shade is to be avoided as much as possible.

 

Thanks for the information. Looks like we will be thinking about linking in series now. You can see how clueless we are when it comes to solar power!! Kind regards

[bargemast]

Thanks for the information. Looks like we will be thinking about linking in series now. You can see how clueless we are when it comes to solar power!! Kind regards

 

Your not the only ones, I'm still pretty clueless myself too, and waiting for the arrival of 2 250w panels to arrive.

 

Good luck, and success with your installation.

 

Peter.

[Pamelala]

Your not the only ones, I'm still pretty clueless myself too, and waiting for the arrival of 2 250w panels to arrive.

 

Good luck, and success with your installation.

 

Peter.

Good luck with yours too. We have found it so confusing but have gained some sound knowledge from the answers we have had on here. We did speak to the electrician who did the wiring on our boat this morning to ask if we had a shunt to run cables through as on the controller guide. We had so that was good news. All just goes over my head I'm afraid, electricity is so complicated, a steep learning curve. He said run the panels in parallel!!! So parallel or series that is the question!! It seems each way has it good points. Amps or volts??? We will get there one day I'm sure. Then the sun will disappear!

[bargemast]

Good luck with yours too. We have found it so confusing but have gained some sound knowledge from the answers we have had on here. We did speak to the electrician who did the wiring on our boat this morning to ask if we had a shunt to run cables through as on the controller guide. We had so that was good news. All just goes over my head I'm afraid, electricity is so complicated, a steep learning curve. He said run the panels in parallel!!! So parallel or series that is the question!! It seems each way has it good points. Amps or volts??? We will get there one day I'm sure. Then the sun will disappear!

 

Cheers Pamelala, I've studied the questions and answers on the solar subject on here for a while aswell, but for me things are so much easier if I can see how it's all done in reality. I've bought a supposedly good MPPT 60Amp regulator, not half as good as your Outback 80 Amp, but as I'm rather limited in what I can spend, this one will have to do for my installation.

 

Maybe in the near future they will invent (bizzard maybe ?) moonlight-panels aswell, and from then on life will be much cheaper with no gennies to run anymore, although it won't be easy to find enough space on the roof.

 

Peter.

Edited July 12, 2014 by bargemast

[peterboat]

I have 900 watts of solar flexible glued down panels running in series, at times on the control panel I see 150 volts from the 2 controllers I have 25mm tails that are very short running into the buss bars via fuses. The cables running back to the batteries from the buss bar are very large.

 

Peter