Having used photovoltaics at home for 4 years with no regulator
between the 1250W array and the batteries, I can say this works if
there is always a load on the batteries.Not a problem with a house.
Recently installed a Blue Sky MPPT 48V 30A controller to add
efficiency. I still need to add another 250W of PV, as my electric bill
is nearly $40 this year...
Bumper's suggested controller will work great in a glider if you're
leaving it tied down outside for days. It's highly unlikely that the PV
panel will produce enough current to overcharge the battery in flight.
Without a charge controller, use a zener diode in series with the
panel.
You can pick up flexible PV panels on E-Bay. Search for flexible
solar panel or powersheet. A 5W powersheet will be about $80-100 US.
You could probably fit 12V 10W behind the canopy, above the spar.
If you're recharging the batteries on the ground pre/post flight, use
at least a 25W panel (the bigger the better), and a charge controller.
Jim