Navitron Renewable Energy and Sustainability Forum

Energy/Electricity Storage and Use/Grid Connection => Grid-connected Renewables => Topic started by: ecogeorge on September 07, 2019, 08:16:45 PM



Title: PV in Parallel
Post by: ecogeorge on September 07, 2019, 08:16:45 PM
H i folks  -i'm asking something i should know the answer to , but need some reassurance ..........
I have acquired 2 solar panels -each 250w , open circuit voltage approx 38v
i have an inverter (350 w max - 60v input max)
Can i connect these 2 panels in  parallel ? orientation will be vertical and there will be shading on both at different times.
Location of panels is non negotiable .
rgds George


Title: Re: PV in Parallel
Post by: Nickel2 on September 08, 2019, 07:52:48 AM
This topic has arisen before, and I was one of the arguers :fume
The question arose of putting panels in parallel and how they would behave: I was all for inserting a diode  in one leg of each panel to prevent reverse current flow into a shaded panel. Others said it was not necessary to do so.
In the end I opted to go for no-diodes option, contrary to what I believed from tech-college education. It has all worked OK since. :-[
This topic recently arose on a channel that I follow, where I posted my reasoning in the comments. (as nlo114):

<https://www.youtube.com/watch?v=BRMLvzEgvcE&t=4s>

 If the link does not work, here is my comment:
I had a robust argument with a few members of a forum I belong to re. panels in parallel. I advocated fitting a Schottky diode in series with each panel to prevent reverse feeding in shade. The others said don't bother. I conceded defeat and left the diodes out, after a lot of head-scratching.
My logical conclusion goes like this:
1. None of my panels will ever be covered by a totally opaque sheet of anything.
2. The graph on the manufacturers data sheet shows that the voltage output of the panel is almost constant from max. insolation to min. insolation, only the current varies.
3. In almost any light, with no load, the voltage is almost the same, whether unshaded or translucently occluded.
4, Once the panels are illuminated, the MPPT regulates the terminal voltage to what it finds best, always below Voc
5, Therefore, if one panel is fully lit, and the others are cloud/tree shaded, the voltage will stay the same across each panel, but the current each panel contributes to the total will be in proportion the the illumination.
6. With one of my panels behind a tree shadow, and the rest fully illuminated, the Voc of the shadowed panel is higher than the Vmp of the other 5.
7. Connecting the shadowed panel in parallel with the others it's voltage drops to match, and marginally increases the total current by a few mA.
My experiments proved my original argument on the forum wrong, diodes unnecessary unless the shadow is a cardboard sheet on the surface of the panel. I ate humble pie; the money saved was worth a pint, and 25W loss on a cool bright day.
Just my tuppence worth!

So stick 'em in parallel! ;D

Something that turned up though, was the 'Ideal Diode', which was something I had been trying to devise as part of my intended diode-experiments.
Anyone trying to charge 2 lead-acid batteries from one supply without them interacting when the supply is removed, may find it useful. This could apply to RV's, campers, caravans, home battery systems etc. Lower losses than the old-fashioned Lucas split-charge diode unit.


Title: Re: PV in Parallel
Post by: nowty on September 08, 2019, 05:53:08 PM
Probably fine in parallel as the inverter should current limit or power limit. Shading wont matter and Iím in the you donít need a diode camp.


Title: Re: PV in Parallel
Post by: Justme on September 08, 2019, 06:22:08 PM
Its a mute point as you cant fit them in series as you will blow the controller.


Title: Re: PV in Parallel
Post by: TT on September 08, 2019, 10:24:29 PM
Isn't the open circuit volts read under standard test conditions?
My house in scotland doesn't come close to STC, so probably wouldn't achieve 72 volts


Title: Re: PV in Parallel
Post by: oliver90owner on September 08, 2019, 10:35:46 PM
Its a mute point as you cant fit them in series as you will blow the controller.

If one is shaded while the other is Ďoperationalí, in series connection will result in very low production all the time.


Title: Re: PV in Parallel
Post by: Nickel2 on September 09, 2019, 10:20:19 AM
What controller will you be using, and do you intend to expand your system?


Title: Re: PV in Parallel
Post by: ecogeorge on September 09, 2019, 09:20:37 PM
Unsure if this question aimed at me?

First post say parallel and controller max 60v . Chinese joby i already have.
Will not be expanding as controller max 350w.
Its 2 x 250w panels to go on a vertical wall ,will post pics when up.
George


Title: Re: PV in Parallel
Post by: nowty on September 10, 2019, 12:54:56 AM
Thatís fine as you will never get more than 350w from those two panels on a wall.