Solar Panel Configuration

[launchpad]

What a great forum. Excellent content and discussions.
We have a Greenspeed Recumbent Tandem which we take on 9 day Cycle Queensland (Australia) rides. Fully loaded we are around 200kgs. This weight and bad knees don't make the mountains even slightly enjoyable (at least going up). So we have decided to convert it into a pedal assist. One of the good things about the tandem, is we can fit 5 x 50W (light weight, flexible) solar panels overhead. We are using the Genasun GV-Boost to charge a LiFePO4 battery as we go (while the solar panels keeps the sun off us).
My question is about configuration. The Genasun is rated at a Voc of 63V and 8A. The solar panels are 22.2 Voc / 50W. I would have thought I would have 2 pairs in series each pair about 44.4V @ 100W and 2.25 A, running these pairs in parallel. What do I do with the 5th panel? Can I put it in parallel with one of the panels in the series pair (ie a triple, still 44 V but 3.4A) in parallel with the other pair (44.V putting out 2.25A)
Any guidance and thoughts welcome. Thanks, Peter

 

[John in CR]

You can't parallel strings of different voltages like that, and a 6th panel may put you uncomfortably close to recommended limits. With peaks occurring in conjunction with hottest sunniest periods, you want to stay away from limits. Electrics can be wonderfully dependable, but out near the limits is where failures occur especially when you add in higher ambient temps.

If you need the 5th panel for the shade, you might consider using it to charge an extra 12V battery, and use that battery for running accessories like lights, stereo, etc.

John

 

[launchpad]

You can't parallel strings of different voltages like that, and a 6th panel may put you uncomfortably close to recommended limits.

Thanks John. Yeah, don't have room for a 6th panel anyway. I was planning on having both strings at 44V. One would be 2.25A max and with the other being 3.4A (I think).



Would this work with the 5th panel as above? Both the voltage and current should be well within limits?

Peter

 

[ddk]

You can't parallel strings of different voltages like that, and a 6th panel may put you uncomfortably close to recommended limits.

Thanks John. Yeah, don't have room for a 6th panel anyway. I was planning on having both strings at 44V. One would be 2.25A max and with the other being 3.4A (I think).



Would this work with the 5th panel as above? Both the voltage and current should be well within limits?

Peter

nothing would break but you would gain -0- benefits from doing so.
The max current of the series string would still be limited by the 2xP panels

 

[launchpad]

The max current of the series string would still be limited by the 2xP panels

Understood. Thanks. Looks like we will be traveling lighter or use 2 smaller panels instead of the one 50W. Off to do some more maths...

Thanks, Peter

 

[whatever]

as john in cr suggested, use the spare to charge another battery, say you charged up an sla 12-14ahr you could then use an rc charger during the night to recharge some of the lithiums, you would then already have has some energy for the morning start. The rc chargers from memory only go up to 36v, but you can charge from 12v sla to 36v using the rc charger ( or 24v)

 

[launchpad]

Yes, we will use the extra 50W panel as both a spare/replacement for the trike and to charge lead acid or other batteries as suggested. We are going to add 2 x 20W panels in parallel (same Voc as the others) to the front of the solar array on the roof of the trike as they will take about the same area as the spare 50W panel. This will give us 240W max overhead. Once we are up and running, I will post a picture of the setup.
Thanks, Peter

 

[Hwy89]

You could put all 5 panels in series (5X22=110 V) then feed the output through a MPPT charge controller. MPPT (maximum power point tracking) finds the range of peak efficiency from the array then converts the high voltage to the level needed for charging batteries. I know they are available for 12, 24, and 48 volt battery banks and most likely other ranges as well.
Hope this helps.

 

[rjoe]

I would love to see some photos when it's done