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Forget the solar array and 12V storage batteries. That 150 watt (120 volt) would equate to more than 1500 watts at 12 volts. Couple that with the power loss through the inverter and you wouldn't get enough power to run the light for very long.... if at all. There may be a EE on the forum who can take this a little further but I think even if it worked marginally... you would be setting yourself up with some serious maintenance issues. Take the deal from the CO-OP. At least when there is a problem, you can call them.

Even though an EE I can't answer your questions (waaaay into extra-high-voltage var specialty)...but what I can tell you is that unless you are up for a great deal of "educational experience" I'd not go with the panel thing. Solar can be a maintenance nightmare.

Now, what I want....is a parabolic-solar-powered water distiller. Seems like it should be simple; water here in the desert is *terrible* and downright poisonous; only solution is to buy distilled, which I am. Undersink RV system just kept breaking and I got tired of paying to fix it. So I started wondering, what with all the sun we get here, why we don't have a solar-powered house-sized distillation system available, that is just a simple array of parabolic mirrors aimed at the boiler. It's a no-brainer. BUT...no such thing. You'd have to buy the zillion dollar panels, the converters, blah blah blah....so I keep buying distilled.

MA

I pay the 11 bucks per month. They replace the bulb and fix the "electric eye" switch when it goes bad. I think the cost and maintenance of all the equipment and batteries you would need would exceed the monthly charge. If I had my absolute druthers, I would prefer to have a separate usage meter and switch on the pole so I could pay for my exact use and be able to turn the light off if I so desired. There are times when I'd like to get the telescope out and shut the light off.

For yet another option, Google: backyard nuclear reactor.
Yes, it's real.

dgpretzel wrote:.... On balance, I would suggest that, although the concept is great, this particular instantiation of it will
likely cost you more than you think, and these specific components are not the best for this application.....

That's sort of what I said earlier. Your analysis is going to come up waaay short considering Bloke's original request was to power a 150 watt sodium lamp.... NOT an 80 watt one.

NOTE TO JOE.... remember that movie 'Soylent Green' where the fellows were pedaling a contraption to generate electrons to drive a light?... maybe you could consider putting those kids to work on a tandem!

Vapor lamps require AC, which means inverting from 12 volts. The inverter is a failure point. The solar panels only produce their nominal rating when aim at a full sun, and then only when they are clean. They need to be cleaned regularly. Also, the cheaper solar panels use a plastic cover that is not UV stabilized and clouds over time, reducing output even more. Those I know who use them on their motorhomes don't expect half their rating in practice.

You will also need quite a sophisticated charge controller for your panels to keep from ruining the battery in fairly short order.

The battery specification that counts is the reserve minutes. The amp-hour rating works, but it is a rating based on a 20-amp draw until the battery has used up 80% of the charge (it will damage batteries to discharge them further very often). The charge controller needs four stages, a quick charge when the battery is discharged, a soak charge, a trickle-charge, and an anti-sulfation cycle. Good ones are hundreds of dollars when specifically designed for solar panels. A cheapie battery charger that just puts out one voltage either won't charge it fast enough or it will boil it out once charged. And without an anti-sulfation cycle, it will kill the battery in a matter of months.

And then there's the load. An 150-watt vapor lamp will pull the lamp load plus the ballast load, at least 200 watts. Wattage stays constant, but current changes, with inversion. So, 200 watts at 120VAC is still 200 watts at 12 volts, but it requires 10 times the current--16 amps in this case. A 16-amp load will discharge the typical 12-volt-deep-cycle battery in less than 5 hours. You could improve that by getting two 6-volt deep-cycle batteries and running them in series. The favored brand for these is Trojan, and the T-105 is a 6-volt golf-cart battery, and two of those will provide an honest 200-amp-hour capacity. They would probably light an 150-watt vapor lamp from dark until midnight (using a timer instead of a photocell). Those batteries are about $125 each. Just for general note: If you get deep-cycle batteries at Tractor Supply or something similar, get true "deep cycle" and not "marine starting" batteries. The former are design for relatively low current drains and are quite durably made. The latter are slightly beefed-up automotive starting batteries. Been there, done that.

But charging those batteries would require pumping those 180 (or so) amp-hours back into those batteries during each day, even on cloudy days. At 12 volts (you'd actually need closer to 14 volts out of the panel to charge the batteries quickly), a 4-hour charge would require 45 amps current, which is 540 watts. So, even if you got 80 watts out of a panel, you'd need six of them, even if they worked perfectly.

You will have to replace those batteries every four or five years, even with a high-quality multi-stage charger/maintainer.

So, it seems to me you are into $700-800 in stuff just to have a hope of making it work, even with everything working as specified (which it won't, especially after a few months). And when you considering having to replace those panels and batteries every few years, you'll exceed $10 a month easily. And if you own it, you'll have to maintain it.

Sometimes it really is cheaper to rent something than to buy it.

Rick "who knows how much solar chargers and batteries for construction signs cost, and you can add a digit, at least, to the above prices" Denney

bloke,
just get one of those jockey statues, the ones holding the lamp, a 60 watt bulb, and a really long 16 gauge extension cord. A lot cheaper, you can even put a 13 W CF in it and use less power. 'course, the light isn't quite the same quality.

Or, just sneak into your neighbor's house sometime, hook up the 220 into their electric clothes dryer, and off you go.

Oh, I'm not particularly electric knowledgable. But I did watch a guy working on a streetlight this morning, for about 15 seconds.

Big Tesla coil will light flourescent bulbs at a distance.
It will impress your neighbors too.

bloke wrote: - I could tap into the public water line for some hydro-electric...

Please, Please, Please - go with that one and let us all know how it works out.