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Old 27-03-2017, 19:12   #1
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Two 70W solar panels on one 140 Genasun?

Hey just looking to pick somebody's brain in regards to solar panel setups.

My wife and I are looking to install (6) 70-watt solarland panels on our boat and they will be mounted together in pairs. Two on each side of the boat, and two on top of the bimini. For each pair of solar panels we were thinking of utilizing (1) 140w Genasun controller. So three Genasuns, and 6 panels. Does this sound like an efficient setup? We are very new to solar, so if anyone has any advice we are very receptive.
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Old 27-03-2017, 19:31   #2
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Re: Two 70W solar panels on one 140 Genasun?

Long as you are paralleling high voltage panels, like 27-30V, not putting a pair of "12V" actually 17-19V in series, since that controller doesn't want 32+ volts total.

The lower-end Victron MPPT, like 75/15 would give more flexibility on inputs, MPPT's efficiency is better and wire runs smaller gauge at the higher volts
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Old 27-03-2017, 22:12   #3
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Re: Two 70W solar panels on one 140 Genasun?

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Long as you are paralleling high voltage panels, like 27-30V, not putting a pair of "12V" actually 17-19V in series, since that controller doesn't want 32+ volts total.

The lower-end Victron MPPT, like 75/15 would give more flexibility on inputs, MPPT's efficiency is better and wire runs smaller gauge at the higher volts
John - Do you mean getting a victron controller for each solar panel or a 75/15 for each pair instead of a Genasun? We were going to just run each pair of panels in parallel, because of the thought of minimizing shading issues. Is this worth doing? Or is it more advantageous to just go up to a 140w panel? Many thanks for the reply!
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Old 28-03-2017, 01:36   #4
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Re: Two 70W solar panels on one 140 Genasun?

you need to know the Voc of the 70W panels. If they are full size cells (low-voltage) panels, then putting in series will be fine for the GV10. If they are cut-cell (17+V) then putting in series will be too high voltage for the GV10 input..

Yes, if high voltage you can parallel them to a GV10, however if you're going to run all the wires anyhow, why not use two GV5 controllers instead of one GV10? You'll have less losses in partial shading this way (one controller per panel). The cost of two GV5 isn't much more than one GV10.
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Old 28-03-2017, 05:12   #5
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Re: Two 70W solar panels on one 140 Genasun?

Yes ideal for shading is one controller per panel.

In that scenario, if low-volts sometimes a good PWM will actually be more efficient, and cheaper, but the market has gone so MPPT crazy it's more difficult to identify the good ones.

Going to 24V will help with the wire sizing, but then adds expense out at the other side, have to add converters for 12V devices.
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Old 28-03-2017, 05:35   #6
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Re: Two 70W solar panels on one 140 Genasun?

Or separately, series the three pairs so each provides 24v to a Victon 15/75 and let that convert it down to 12v.

The problem is there are two many choices and no best answer.

Just pondering over the same problem with 2x80w panels or 1 x 150w panel. I think the best answer is the KISS approach with 1 x 150w panel. Its cheaper, fewer wires and if it goes wrong down the line probably easier to diagnose the fault

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Old 28-03-2017, 05:54   #7
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Re: Two 70W solar panels on one 140 Genasun?

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Or separately, series the three pairs so each provides 24v to a Victon 15/75 and let that convert it down to 12v.

The problem is there are two many choices and no best answer.

Just pondering over the same problem with 2x80w panels or 1 x 150w panel. I think the best answer is the KISS approach with 1 x 150w panel. Its cheaper, fewer wires and if it goes wrong down the line probably easier to diagnose the fault

Pete
That would be 75/15, volt capacity first, then amps.

Yes, that line gives great flexibility, but most recently we were talking about optimizing for partial shading.

​On that topic, I am looking for US retail suppliers of (or willing to ship in) gear using the new embedded "MPPT on each cell string" ICs from Maxim.

Jinko "Eagle MX" is one line, others mentioned on Maxim's site are Trinapeak, and "ET COM"?
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Old 28-03-2017, 09:36   #8
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Re: Two 70W solar panels on one 140 Genasun?

Hi,
What are the dimensions of the 70w & the 140w panels?
My 265w panel is 38.7 x 64.5 size matters ie; more watts per sq" the better.
IMHO fewer panels = less wiring & fewer connections ergo less to go wrong.
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Old 28-03-2017, 13:31   #9
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Re: Two 70W solar panels on one 140 Genasun?

400 watts in total sounds about right i would use 1 large mmpt controller circa 50- 60A for a 12v setup Most controller designers assume you will have only 1 controller per battery bank. Also consider a system to keep the panals always rightangles to the sun it makes a huge difference to the AH you get per day. After a 6500 nm voyage this year forget about any other form of charging such as wind or hydro in the tropics Solar is the only thing that really works its easy to install and its hardy and will give you by far the least amount of trouble. I have tried everything else. Use 8d agm batteries and the largest mains charger and alternator you can afford. A small diesel genset is also very worth having. Hope this helps
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Old 29-03-2017, 15:45   #10
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Re: Two 70W solar panels on one 140 Genasun?

Great input guys! Thanks for the advice. I'll look into the Victron controllers as well. I've watched a good video that simulated shading of solar panels and I was surprised to see what a little shade would do, given why we are breaking up the space with many smaller panels.
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