On Mon, 14 Jul 2008 08:13:20 EDT, "Paul" wrote:


"Phyllis and Jim" wrote in message
...
I wonder if you can get enough power from a photo cell without paying
an arm and a leg?

How powerful is your pump?

Jim


Kinda depends on how much arms and legs go for in your neck of the woods.
I've a Sequence pump that uses about 120 watts. A 400 watt inverter ($30)
would easily run it. Car battery, maybe $75 or so.

Except a car battery won't work. Batteries found in cars are
typically designed to provide a high current for a relatively brief
time (cranking) whereas what is needed is a lower current for a
relatively long time (like a golf cart). At 120 watts at 120v that's
1 amp, at 12 volts that will be a 10a draw. Most car batteries can't
handle that, as a matter of fact, most "deep cycle" type batteries
won't handle that. What will probably be needed is a several
batteries in parallel to provide that much current overnight.

Now here's where the body
parts come in. On ebay, 123 watt solar panels go for $660 each and I'd need
two of them, figuring that the sun only shines 1/2 the time, but the pump
runs 24/7. Maybe 3 would be better to allow for cloudy days and system
losses.

You'd need two of them even if optimal conditions were present 100% of
the time. Remember, the batteries have to be recharged from the
previous night's use while supplying power to the pump at the same
time during the day. Furthermore, even on bright, cloudless, sunny
days the photovoltaic cells are only going to provide full power for
just a few hours at best. There will be some output during morning
and late afternoon, but nowhere near the 120 watts needed. 3 panels
sounds quite optimistic.

Throw in a charging regulator,

This will be essential, and matching the regulator to the type of
batteries you have (so as not to overcharge or something harmful to
the life of the batteries) is critical, if battery life is to be
maximized.

and we're in the 2 kilo-dollar
neighborhood.

Probably a lot more.

That's more than arms and legs go for around here. It doesn't
sound feasible for anything larger than say a whiskey barrel size water
feature.
Paul

You have to have a real interest in photovoltaics right now to make
this work. It is very expensive up front, and most folks cannot
justify the expense on simply economics. Granted, there are
exceptions where this is an economic alternative to being "on the
grid," but for most folks getting power from the electric company is
still the way to go, high energy prices notwithstanding.

Galen Hekhuis