Solar panel paralleling.

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A friend of mine has purchased several solar panels, some are 14V at 1
A, some are 24V at .5A , he has quite a bunch of them of them and
wants to charge a 12V 250VA lead acid pack. He actually has 5
different panels with significantly different ratings. So the
question becomes, in dealing with the different voltage ratings,
parallel them or should I build a polyphase inverter and charge a
inductor for each panel and dump them sequentially so each panel runs
at maximum current without fighting each other. Any ideas so he gets
the max bang for the buck? He started the project before consulting
me, or I would have had him purchase one large panel instead of a pile
of random junk.

Anybody worked this problem before? What happens when you wire a
half amp panel in series with a one amp panel?

Its been 15 years since I have had to do current source math, so I'm a
bit rusty,

Steve Roberts

 

[Rheilly Phoull]

A friend of mine has purchased several solar panels, some are 14V at 1
A, some are 24V at .5A , he has quite a bunch of them of them and
wants to charge a 12V 250VA lead acid pack. He actually has 5
different panels with significantly different ratings. So the
question becomes, in dealing with the different voltage ratings,
parallel them or should I build a polyphase inverter and charge a
inductor for each panel and dump them sequentially so each panel runs
at maximum current without fighting each other. Any ideas so he gets
the max bang for the buck? He started the project before consulting
me, or I would have had him purchase one large panel instead of a pile
of random junk.

Anybody worked this problem before? What happens when you wire a
half amp panel in series with a one amp panel?

Its been 15 years since I have had to do current source math, so I'm a
bit rusty,

Steve Roberts

Might be best to series the lot and use a swmps to charge the batteries,
the primary current from the panels will be limited to that of the
lowest rated one.

Rhielly P

 

[James Arthur]

A friend of mine has purchased several solar panels, some are 14V at 1
A, some are 24V at .5A , he has quite a bunch of them of them and
wants to charge a 12V 250VA lead acid pack. He actually has 5
different panels with significantly different ratings. So the
question becomes, in dealing with the different voltage ratings,
parallel them or should I build a polyphase inverter and charge a
inductor for each panel and dump them sequentially so each panel runs
at maximum current without fighting each other. Any ideas so he gets
the max bang for the buck? He started the project before consulting
me, or I would have had him purchase one large panel instead of a pile
of random junk.

Anybody worked this problem before? What happens when you wire a
half amp panel in series with a one amp panel?

Its been 15 years since I have had to do current source math, so I'm a
bit rusty,

Steve Roberts

The solar panels' max power output is gotten at roughly
2/3rds their open-circuit voltage.

If the 14v panels are really 14v open-circuit you'll
only get a fraction of their rated current charging a
12v battery.

In series, the output current is limited to that of the
*weakest* cell or panel.

So, an easy, ugly, wasteful, solution is to connect the 14v
panels in pairs, then parallel the lot (pairs and 24v panels).
Maybe wire or'd with diodes, if you're going to be nice
about it.

Or, for efficiency, parallel the like-voltage panels, then
make maximum power point tracking (MPPT) converters/chargers
for each resulting voltage, e.g. 14v, 24v, etc.

(graph of MPPT principle here:
http://store.altenergystore.com/Ove...y-Solar-Boost-6024Hdl-60A1224V-WDisplay/p248/)

The solar panels are usually so expensive you can't afford to
waste 'em; converters beaucoup might make sense.

Cheers,
James Arthur