Re: (ET) Solar Cell wattage needed

[William Korthof <wkorthof earthlink net>]

At 09:15 PM 11/7/02 -0600, Bill wrote:
>     Can any of you solar cell charging guys give me a feel for how much 
> solar
> cell output wattage is enough to be of any use for charging or maintaining 
> charge
> on batteries based on your experience? Harbor Freight Tools is advertising 
> a 1.5
> watt 12 volt solar cell for $10. Would three of those be of any use with 
> our

The typical price for good quality, large solar panels is about
$4.00 per watt. Maybe $5.00 per watt for a small order.
I'm thinking about panels that are 50 to 175 watts.

> elec-traks? How many solar cell watts are needed to recharge in a week? 
> Also my
> farm tractor sits outside all winter with its 12v battery. Would 1.5 watts 
> keep
> the battery charged or at least safe from freezing through the winter?

Three 1.5 watt panels would be pretty small.
4.5 watts would output up to 0.075 amps in
full sunlight (maximum).

6 golf cart batteries = 36 V @ 220 amp hours

Average deliverable capacity is probably closer
to 100 amp hours. Maybe 150 Ah.

100 Ah / 0.075 = 1333 hours for a full charge.

In a good sunny location, you might get 5 "full"
sun hours per day average. So figure 267 days.

1.5 watt panels would probably be might be
a good safe winter trickle charge, but no more.

To recharge in a week, you need more panels:
100 Ah / 5 sun hrs / 7 days = 2.86 amps
Three 50+ watt panels would work well, so long
as you actually use the tractor consistently.
But you'd probably want to include a charge
controller (or one per battery) to preclude
over-charging if you used (3) 50 watt panels.


/wk