Parallel or Series???

schew · Apr 10, 2017

Taking the plunge, I purchased two 100w/18v solar panels this morning
https://www.amazon.com/gp/product/B01DXYNGA0/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1

and plan on purchasing this MPPT Controller:
http://www.blueskyenergyinc.com/products/details/solar-boost-3000i

I chose this controller as this was the only MPPT flush mount controller I could find.

My trailer is prewired for solar and as far as I know, all that is needed is to connect the solar panels to the MC4 connectors on the roof, cut out an opening where the "prewired for solar" sticker is and wire in the Blue Sky MPPT Controller.

As of now, I have one 12v battery and may purchase another and wire them in parallel.

If I've understood what I've been reading, it would be best if I connect my solar panels in series as the unused volts will be converted to amps, which will help charge the batteries quicker than if the solar panels were wired in parallel.

Can someone verify my logic, as well my setup?

Oregon_Camper · Apr 10, 2017

With only 2 panels, I think either way is fine. You should test the config on both a day where you have direct sunlight (in series and parallel) and then again on a shady day in both configs.

Your controller can only handle 40 volts, so if you ever decide to add another panel, you'll be forced to wire in parallel.

You should add a power cutoff switch as well (before MPPT controller), so you can turn off solar power when you need to do maintenance.

Finally...remember to keep the panels covered with something while you are hooking everything up. Even indoor lighting will create some power and it will come down the lines.

mlpeloquin · Apr 10, 2017

Wire in series and you will double the voltage and keep the same current. Wire in parallel and you will double the current. At the voltage you stated that the panels output, you would be better served to up the current and wire in parallel. The fully charged battery is 13.5V. The controller will not allow an over charge and the excess voltage will not help. Your 100W panel at 18V output at maximum has 5.55 amps out. See page nine of the Blue Sky Solar Boost 3000i Manual. It states "Multiple PV Modules Must Be Wired In Parallel".

schew · Apr 10, 2017

Thanks for your advice guys. Having read what you have written, would a PMV controller serve me just as well? That MPPT controller is mighty expensive.

mlpeloquin · Apr 10, 2017

schew said:
Thanks for your advice guys. Having read what you have written, would a PMV controller serve me just as well? That MPPT controller is mighty expensive.

Well reading this https://www.victronenergy.com/blog/2014/07/21/which-solar-charge-controller-pwm-or-mppt/ answers the question. You get what you pay for.

Oregon_Camper · Apr 10, 2017

schew said:
Thanks for your advice guys. Having read what you have written, would a PMV controller serve me just as well? That MPPT controller is mighty expensive.

Let's approach this a different way.

Why are you adding solar?

1 - To just add additional power (top off) or do you want to start dry camping and extend your stay without having to use a generator?

2 - To use an inverter and have 120v AC power? Perhaps to watch TV...watch a movie...charge laptop/phone?

3 - Adding a residential refrigerator?

Once we know what your goal is, perhaps we can give you a better recommendation on what hardware fits your needs.

schew · Apr 10, 2017

mlpeloquin said:
Wire in series and you will double the voltage and keep the same current. Wire in parallel and you will double the current. At the voltage you stated that the panels output, you would be better served to up the current and wire in parallel. The fully charged battery is 13.5V. The controller will not allow an over charge and the excess voltage will not help. Your 100W panel at 18V output at maximum has 5.55 amps out. See page nine of the Blue Sky Solar Boost 3000i Manual. It states "Multiple PV Modules Must Be Wired In Parallel".

I searched several times and did not see that statement...????

schew · Apr 10, 2017

Oregon_Camper said:
Let's approach this a different way.

Why are you adding solar?

1 - To just add additional power (top off) or do you want to start dry camping and extend your stay without having to use a generator?

2 - To use an inverter and have 120v AC power? Perhaps to watch TV...watch a movie...charge laptop/phone?

3 - Adding a residential refrigerator?

Once we know what your goal is, perhaps we can give you a better recommendation on what hardware fits your needs.

I would like to have enough stored energy to run each day:
-LED lights for say 5 hours a day/night
-Run the refer in propane mode ( my understanding is that in this mode, electricity is still needed)
-Maybe watch a movie on the flat screen.
-occasional use of the stereo system
- the ability to have the furnace cycle on/off throughout the night if it gets chilly
-intermittent use of the water pump.
-charge mobile devices like phones/tablets

I would fire up the genset for AC, coffee maker, Microwave and such.

Oregon_Camper · Apr 10, 2017

schew said:
I would like to have enough stored energy to run each day:
-LED lights for say 5 hours a day/night
-Run the refer in propane mode ( my understanding is that in this mode, electricity is still needed)
-Maybe watch a movie on the flat screen.
-occasional use of the stereo system
- the ability to have the furnace cycle on/off throughout the night if it gets chilly
-intermittent use of the water pump.
-charge mobile devices like phones/tablets

I would fire up the genset for AC, coffee maker, Microwave and such.

Would you be doing this for >5 days?? Perhaps over a week?

Reason I ask, is a good set of deep cycle batteries (I have 2 Trojan T-1275's) would do everything you're asking, for about 4 days....with no need to for additional charge. These batteries do not come cheap, but you get what you pay for.

Another option you might consider, as it doesn't appear you need a long term power source (ie..>5 days) is a small portable solar solution. My sister has the 120 watt version from Zamp and it is very nice. The nice thing is they can move it into the sunlight where my roof mounted solution mean I am locked in one location HOPE I get direct sun. I'm thinking of adding one of these as a backup for when we camp in deeply shaded locations.

I'd would stick with Zamp or GoPower for the portable solutions.

Zamp
https://www.zampsolar.com/rv-solar-kits/portable-rv-solar

GoPower
http://gpelectric.com/products/portable-solar-kits

schew · Apr 10, 2017

Oregon_Camper said:
Would you be doing this for >5 days?? Perhaps over a week?

Reason I ask, is a good set of deep cycle batteries (I have 2 Trojan T-1275's) would do everything you're asking, for about 4 days....with no need to for additional charge. These batteries do not come cheap, but you get what you pay for.

Another option you might consider, as it doesn't appear you need a long term power source (ie..>5 days) is a small portable solar solution. My sister has the 120 watt version from Zamp and it is very nice. The nice thing is they can move it into the sunlight where my roof mounted solution mean I am locked in one location HOPE I get direct sun. I'm thinking of adding one of these as a backup for when we camp in deeply shaded locations.

I'd would stick with Zamp or GoPower for the portable solutions.

Zamp
https://www.zampsolar.com/rv-solar-kits/portable-rv-solar

GoPower
http://gpelectric.com/products/portable-solar-kits

Sorry, I should have stated that I would like to be able to do this for 4-7 days max, with the genset running occasionally, more so if the AC is needed.
So do you think if I were to get a pair of T-1275 batteries, coupled with the my setup I would most likely be where I want to be?

I've looked at both the brands you mentioned, but neither of those kits offered a MPPT controller, which I understand is superior in utilizing the panels output compared to a PVM controller.
Despite the ability to aim portable panels, for convenience sake I rather have the panels hardwired, always working and ready to go sort of speak, rather than having to setup a portable system and worry about theft.

Oregon_Camper · Apr 10, 2017

schew said:
Sorry, I should have stated that I would like to be able to do this for 4-7 days max, with the genset running occasionally, more so if the AC is needed.

So do you think if I were to get a pair of your batteries, coupled with the my setup I would most likely be where I want to be?

I've looked at both the brands you mentioned, but neither of those kits offered a MPPT controller, which I understand is superior in utilizing the panels output compared to a PVM controller...

IMHO...I think you will be perfectly fine with the portable solution...no need for MPPT with these panels.

Having said that, the panels on the roof...through a MPPT controller....wired to 2 Trojan T-1275's will be FANTASTIC!!

Just think about where you camp....will the location your have your trailer have direct sunlight for a majority of the day? If not....think portable. If yes, then absolutely go roof mounted. They are ALWAYS there...ALWAYS working...and they are not as susceptible to theft.

schew · Apr 11, 2017

Oregon_Camper said:
IMHO...I think you will be perfectly fine with the portable solution...no need for MPPT with these panels.

Having said that, the panels on the roof...through a MPPT controller....wired to 2 Trojan T-1275's will be FANTASTIC!!

Just think about where you camp....will the location your have your trailer have direct sunlight for a majority of the day? If not....think portable. If yes, then absolutely go roof mounted. They are ALWAYS there...ALWAYS working...and they are not as susceptible to theft.

Oregon Camper,
Thanks for your advice. As I have already purchased the solar panels, this is the route I will go. As I do not want to screw into my roof, I'll use 4" Eternabond tape and tape the edges down. In addition to this, I may use doublesided Eternabond tape and tape the underside of the solar panels to the roof as well. Just need to confirm whether or not there will be expansion issues with the roof, tape and panels first.
I'll post some pictures of the project when I can.
S.

Parallel or Series???

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