Use of solar cells for inflight recharging

Does anyone have any recommendations on the appropriate
solar cell technology for in flight recharging of sealed
lead acid batteries? Ie Eg what's the recommended
regulator technology - is it normal to shunt the solar
cells when the battery voltage rises at full charge
to prevent overcharging? This seems a little strange
to me (ie you allow the solar cells to discharge at
high current through a shunt thereby dissapating the
full wattage of the solar cells rather than increasing
the series impedance in the charging line).

Any recommended manufacturers
of regulator/shunt units? Any recomended panel suppliers?

The glider manufacturers, who offer solar panels, only use a couple of
flexible PV panel brands I'm aware of - Stroble (sp?) and one other that
Schleicher has just started installing on new ships.

As far a solar charge controllers go, there's the cheap switching type, the
slightly better pulse width modulated, and the *recommended* Maximum Power
Point Tracking (MPPT) type. The MPPT will also use a pulse width modulated
output.

I've only been able to find one brand of MPPT that is suitable for glider
use. See:
http://shop.altenergystore.com/itemd...D5~eq~~Tp~.htm

Using MPPT can gain as much as 30% more current from a given PV panel array.
This is important where maximum output is needed but there is limited room
for installing more panels. To learn more about MPPT and how it works, I
thing Blue Sky has some good info, see:
http://www.blueskyenergyinc.com/pdf/...Edatasheet.pdf

all the best,

bumper

"Dave Sinclair" wrote in
message ...
Does anyone have any recommendations on the appropriate
solar cell technology for in flight recharging of sealed
lead acid batteries? Ie Eg what's the recommended
regulator technology - is it normal to shunt the solar
cells when the battery voltage rises at full charge
to prevent overcharging? This seems a little strange
to me (ie you allow the solar cells to discharge at
high current through a shunt thereby dissapating the
full wattage of the solar cells rather than increasing
the series impedance in the charging line).

Any recommended manufacturers
of regulator/shunt units? Any recomended panel suppliers?

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

If the charger is simply a "sustainer" you can get by without a charger
controller. That reduces the losses or expense of the conttroller.

If you need to use a controller, it might be noted that the military prefers
to use a shunt charge controller, rather than a series one. The main reason
for this is the controller usually fails open. An open series controller
will not charge. However, an open shunt conytroller will continue to charge
(but not control).

Note that a charge controller is not a regulator. It does not limit
current.

There is a nice section on charge controllers for photovoltaic systems in a
book entitled "Emergency Power for Radio Communications" published by ARRL,
ISBN 0-87259-933-1. It can be ordered at www.arrl.org for $19.95.

Colin

JS wrote:
snip
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.

Bigger is better only if you need the current, otherwise, it's just
bigger and more expensive.

* If you run a radio and vario, and fly less than 5 hours a day and put
out the panel when you land, then reorient it in the evening for the
morning sun, a 5 watt panel will likely be adequate.

* If you run a radio, vario, GPS logger, Ipaq, transponder with encoder,
and fly 6 or 7 hours a day, you'll need that 25 watt panel to fully
charge every day.

5 watt panel ~$100; 25 watt panel ~ $300. I fit the second case, but
opted for a 15 watt panel because I have a large battery, so I don't
have to fully recharge in one day. If I fly 3 days out of 4, the battery
stays charged.

Another option is to have two battery packs, one of which charges while
the other is flying. That charges it during the peak of the day, and so
it doesn't need nearly as big a panel. If you can change packs easily,
it's worth considering, as it's cheaper and more flexible.


--
Change "netto" to "net" to email me directly

Eric Greenwell - Washington State, USA

www.motorglider.org - Download "A Guide to Self-launching Sailplane
Operation"

Dave Sinclair wrote:
Does anyone have any recommendations on the appropriate
solar cell technology for in flight recharging of sealed
lead acid batteries? Ie Eg what's the recommended
regulator technology - is it normal to shunt the solar
cells when the battery voltage rises at full charge
to prevent overcharging? This seems a little strange
to me (ie you allow the solar cells to discharge at
high current through a shunt thereby dissapating the
full wattage of the solar cells rather than increasing
the series impedance in the charging line).

Any recommended manufacturers
of regulator/shunt units? Any recomended panel suppliers?

The main issue for in-flight solar charging is where do you put the dog
goned panel? Rigid panels can only be put inside the cockpit, so a
thin, flexible panel. These are available, but at a jaw-dropping price.
A reasonable alternative to solar charging is to use a bigger battery
(or more of them). You can still charge with solar, but it is on the
ground. That is how I keep my batteries charged in my DG400, and it
really makes a BIG difference. I used to charge them while I was
assembling using the car. The battery voltage would indicate that they
were charged (13.9 V), but they weren't. I would really find this out
if I had any difficulty starting and had to crank more than usually. At
times I would have give up and pull my car over for a jump start (not a
pleasant task when you are by yourself!). Now I have no problem
cranking, even if I have to crank it a lot. And I have plenty of
reserve capacity to start it again after I have landed from a 4-5 hour
flight. And these are 3 year old SLA type batteries. I use a 20 W panel
with a solar charge controller. No need for a fancy MPPT type, because
I have plenty of time to charge the batteries. It is a PWM controller
with anti-sulfating circuitry (I have previously posted the source of
the panel and controller).

Some year I am going to locate a higher engery density battery in the
SLA form factor, such as a lithium-ion or a nickle-metal hydride. But
so far no luck. You can have battery packs made out of individual
cells, but they are VERY expensive and come with no warranty.

Tom Seim
DG400
Richland, WA

Jim,
It is very remarkable you have been able to do this to your batteries
for four years without damage. I wouldn't recommend it for large solar
systems.

However, for an in-flight use, where the pv is basically augmenting the
battery supply a charge controller isn't needed. With longer term
charging & sustaining an inexpensive controller is essential if you
want to get the full life out of the batteries.

Regarding your need for 250 more watts: You might want to do some math
as it looks like you are right on with what you have now. PV's today
are going for between $4 and $6 per watt, so your 250 W would cost you
around $1,000 at the bottom end not including freight, mounting, and
labor. So at $40/year savings it would take you the life of the PV to
earn back your expense, not considering present dollar value or roi on
the $1000 if you didn't spend it.

Sounds like you planned your system very, very well!

"Go" wrote in message
oups.com...

However, for an in-flight use, where the pv is basically augmenting the
battery supply a charge controller isn't needed.

Until somebody forgets that there is no controller and the glider happens
to spend a few days out of the trailer...

I have ruined enough batteries from overcharging to have finally had the
lesson forever drilled into my head; charge controllers are cheap and necessary.

With longer term
charging & sustaining an inexpensive controller is essential if you
want to get the full life out of the batteries.

I agree.

Regards,
Vaughn

Good point.

Vaughn Simon wrote:
Until somebody forgets that there is no controller and the glider happens
to spend a few days out of the trailer...

I have ruined enough batteries from overcharging to have finally had the
lesson forever drilled into my head; charge controllers are cheap and necessary.

Found this while looking for something else. Don't know if the price
is fair.



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