Adding Extra Solar Panels

[Barra]

Back on the boat in a few weeks and adding more solar is the next project.

Current set up -

4 x 85 watt panels mounted 2 in series either side of the boom on the coachroof then paralleled into a single 20 amp PWM controller

Works OK. I get up to 18 amps when there is no shading from the boom or sails onto one side or the other. With shading to one side i get total shutdown on that side ie from 18 amp to 9 amps. So not ideal underway which is when I need more juice.

Plan is to add an extra 2 x 100 watt panels (one to each side of the boom again) and due to difficulty getting to the existing panel wiring this will be kept separate.

So intended set up -

4 x 85 w panels changed to MPPT controller (keep same wiring of 2 in series to parallel)

2 x 100 w (19voc) panels into second MPPT controller. (The ones im looking at have 3 strings of 36 cells per panel)

Questions

1. Is it worth changing the PWM controller to MPPT on the existing panels in the hopes of getting some gain when the boom shades one side?

2. Whats the best way to wire the new panels - series or parallel - given the shading issue I have? ie double the volts from in series in the hope the MPPt will be able to get some output from the shaded panels? Wiring this way will be harder than parallel logistically so I would want to see some gain to drill the extra holes etc


thanks for any thoughts or similar experiences

barra

[autumnbreeze27]

I have 8 X 100W panels wired to a MPPT 60amp controller, each side of the top are wired separately in series. I did series to keep the wire size down and help with shading.

I've been pulling 2.1kw/day with the boom centered (ie: lots of shading)

If I had to do it over again, I would buy 4 cheap 20-30amp MPPT controllers and have each pair run to it's own MPPT. Then I could just carry one or two cheap spares.

I might buy 4 of them as spare in case the mppt-60 dies on me.

I do like the pretty graphs and web server of the morningstar.

[Barra]

Thanks for the reply Autumnbreeze.

That seems like a pretty good result for the MPPT with the same wiring set up as me either side of the boom. Besides the crazy price of a 60 amp controller why would you go for multiple smaller ones?

Redundancy or is it somehow more efficient? I would have thought multi charge sources from 4 MPPT controllers would get in each others way like multiple alternator regulators sensing the others volts at the battery resulting in 1 backing off current? Dont seem to hear about that with solar though....?

With my install of the extra 100 watts either side of the boom what would you recommend for the wiring - these 2 extar panels in series or parallel/

thanks

[Albro359]

Have you got diodes across those panels in series and across the solar cell groups in each panel ? If not, that will help with the partial shading issue by not shutting everything down.

[Barra]

Originally Posted by Albro359

Have you got diodes across those panels in series and across the solar cell groups in each panel ? If not, that will help with the partial shading issue by not shutting everything down.

The existing panels were on the boat when i bought it. They are hard stuck to the coachroof and wired through embedded conduits so no way to tell exactly what ive got in the way of diodes behind those stuck panels physically at least.

The panels are mounted long ways athwartship so the boom shade probably affects any internal panel strings at pretty much the same time by shading one end of the panels simultaneously.

Plan is to play around with covering up bits of each panel and try and work out whats exactly happening that way.

My understanding was that if i replace the PWM controller with an MPPT this would help with the shading issue at the controller stage regardless of diodes though?

thanks

[Albro359]

An MPPT controller will do better than a PWM controller when you have a much higher input voltage then the output voltage you need, but if you have a string of series connected cells partially shaded, the whole string will shut down (Unless you have a diode across each cell, which is generally not the case)...if all the strings are partially shaded as you say then the whole panel is shut down.....MPPT won't help you there

[nimblemotors]

Putting the panels in parallel can help with shading.
Just MPPT alone is better, but not by much.
See my other thread, you can use 8 of the miniMPPT controllers
to put all panels in parallel going into your existing MPPT controller.

The miniMPPT would let you add any extra panels, just adds to the current, up to the limit of the charger MPPT.

Originally Posted by autumnbreeze27

I have 8 X 100W panels wired to a MPPT 60amp controller, each side of the top are wired separately in series. I did series to keep the wire size down and help with shading.

I've been pulling 2.1kw/day with the boom centered (ie: lots of shading)

If I had to do it over again, I would buy 4 cheap 20-30amp MPPT controllers and have each pair run to it's own MPPT. Then I could just carry one or two cheap spares.

I might buy 4 of them as spare in case the mppt-60 dies on me.

I do like the pretty graphs and web server of the morningstar.

[Barra]

Originally Posted by Albro359

An MPPT controller will do better than a PWM controller when you have a much higher input voltage then the output voltage you need, but if you have a string of series connected cells partially shaded, the whole string will shut down (Unless you have a diode across each cell, which is generally not the case)...if all the strings are partially shaded as you say then the whole panel is shut down.....MPPT won't help you there

Yep so this goes to my wiring dilemma for the 2 new 100 watt panels im planning to add - 1 each side of the boom is all i can fit and if i wire these in parallel then i will get one working most of the time but not 2 and only 16 to 18 volts (ish).

If i wire these 2 new panels in series then i get higher volts say 36 when both in the sun for an mppt controller to work with but the shade on one side is going to drop that down to something lower. Maybe due to the cross shade issue it will be a complete shutdown of that shaded panel.

Obviously adding these panels in series to the existing ones would be best but thats not practicable at all.

So which way to wire these 2 panels??

thanks