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Posted by Saki on July 10, 2008, 8:45 pm

We're doing a lighting installation where there is no power and would
like some advice on what Solar equipment we will need. We're total
amatuers, but smart people.

Here's the project:
Run a 15 watt bulb (AC) for 8 hours at night in February in Seattle,
WA where there is often less sun.

1. What equipment will we need on the Solar side?
2. How big of Solar Panel or range of size?
3. What panels do you recommend?
4. What about in the Summer vs Winter? What about for 4 hours?
5. What would approximate costs be for all the Solar equipment?
6. Where should we purchase all of this gear?


Posted by Malcolm \"Mal\" Reynolds on July 10, 2008, 9:54 pm

What are you lighting? How many lumens do you require?

Off the top of my head, I'd suggest you use LEDs for such a low power
setup. You don't actually need AC for light bulbs.

Posted by Eric Sears on July 11, 2008, 2:52 am
 On Thu, 10 Jul 2008 13:45:16 -0700 (PDT), Saki

As Mal points out, you really haven't given enough info.
Nevertherless, working with your figures, a 15 watt flouro bulb
running on 12 volts would use about 1.5 amp-hr each hour. So you need
about 12 amp-hr per day (plus some for losses), for 8 hours.
Since I have no info about your insolation, let's assume maybe 2 hours
of average sunlight in the winter. Probably you would need panels
supplying 10 amps if you really want year-round reliability (20 amp-hr
per day)
To discharge a deep cycle battery to 50% over 4 days (ie 4 days
standby), you would need a battery of about 160 amp-hr capacity.

One suggestion would be 2 x Trojan T105 batteries (220amp-hr capacity
at 12v), 2 X 80 watt solar panels, and solar controller at least 10
amp rating. You would also need a timer working on dc.

Any good battery dealer or solar supplier should be able to give you
some prices - but it won't be insignificant. (Its not much use giving
you NZ prices!!)

Knowing what the light is to be used for might be helpful in making

It sounds like a fairly expensive light.
There are cheaper ways of doing it - it just depends how critical the
light is.

Eric Sears

Posted by bealiba on July 11, 2008, 6:03 am
 On Jul 11, 12:52 pm, phon...@025379386.for.email.address (Eric Sears)

My calculation shows:

Closer to 1.25 for the 15W lamp (15W / 12V = 1.25)
85.11Ah battery minimum capacity (say 100 Ah, this is a common size
battery and would cover the timer as well)
1 X 175W panel
10% daily DOD

What do you think?

Still an expensive light.

Posted by Eric Sears on July 11, 2008, 9:39 am
 On Thu, 10 Jul 2008 23:03:42 -0700 (PDT), bealiba@gmail.com wrote:

Yes, I agree.
I was probably estimating a bit over the top. I guess it depends on
the number of days with low insolation, but the input is approx the
same from the panel.
The fact that the original post also asked "what about 4 hours" leads
me to think it might not be a critical use. In that case, maybe a
smaller panel and battery would suffice - or better still, a smaller
light requirement.  When the post said "a 15 watt bulb" I wonder what
they had in mind? Incandescent?? An 8 watt 12v flouro striplight would
deliver more light, and would require considerably less in panel and
Extra comment from original poster would be useful.

Eric Sears

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