installed some compact fluorescent fixtures, now thinking of making them solar powered.

[ozarkjeep]

I added some can lights to my sons room, and a nearby bathroom.

4 fixtures, 13 watts per, 52 watts total, at 120 V thats .4 amps.

Im thinking 2 golf cart batteries, and 50-75 watt solar panel, a charge controller, and small inverter, could run those lights, and several more, easily.

say I have 12 of those lights total in my house, 156 watts total, 1.3 amps at 120 Volts AC

then when the power was out, I would have lights as well as saving the miniscule amount of electricity they would use.

I guess I would have to figure out the cost per KW/hour, vs the system cost.

Batteries = $150 ( 2 trojan T105)
Solar panel = $300 50 watt, 2.99 amps max output
inverter = $40 Aims 400 watt ( expansion room for 20 more CF light fixtures)
charge controller $35 handles up to 6 amps of solar panel, again, room for expansion

So $525 for free, and un-interuptable lighting in my house, for likely several years ( given the VERY light load on the batteries)

am I figuring things right here?

has anyone done a project such as this?

156 watts, say for 8 hours per day, thats 1248 Watt hours, or 1.248 KW-hours per day ( is my math correct hmmm?)

so say electricity is $0.10 per KWhour here in Arkansas, so, im saving $0.1248 per day, saves $44 a year in electrical costs, so it would take almost 11 years to pay off the system, the batteries would have to be replaced during that time frame most likely at a cost of $150 again.

so its not so much a savings thing as it is a backup, in case of power failure type of thing.

thoughts?

 

[Corey]

Looks about right to me. Don't forget that your inverter may eat 30-50% (or more!) of your power, so size batteries accordingly. Also, you mentioned an 11 year payoff - but I wouldn't be surprised if you aren't buying new batteries long before then - which will tack on more years to the payback. Overall, it's a neat idea - and like you said, has merit for backup power as opposed to cost savings.

One possibility I have considered would be using solar / battery, but then running some of the new white or soft white LED's directly off the battery. This saves some complexity with the inverter, etc but would add it to the wiring side as you would need a separate 12V system. Then the cost of that offsets the inverter cost. Although in a real SHTF situation, you have more power going directly to light as opposed to heating up an inverter, but you can't plug any other 110V appliance in. So not much of a 'win' either way.

Corey

 

[kevinlp]

are you really going to have all 12 lights (156W) on for 8hr per day. anything less and the payback time extends even further.

 

[Andre B.]

I added some can lights to my sons room, and a nearby bathroom.

4 fixtures, 13 watts per, 52 watts total, at 120 V thats .4 amps.

Im thinking 2 golf cart batteries, and 50-75 watt solar panel, a charge controller, and small inverter, could run those lights, and several more, easily.

Snip

156 watts, say for 8 hours per day, thats 1248 Watt hours, or 1.248 KW-hours per day ( is my math correct hmmm?)

Snip

thoughts?

About 9 more panels and 6 more batteries and you will be a lot closer.

 

[ozarkjeep]

probably not, and again, I wasnt really looking at it as a cost savings measure, but more of a backup thing.

Im thinking now of a smaller system, with dedicated lights ( ONLY for power outages) , smaller panel, smaller battery, smaller cost.

are you really going to have all 12 lights (156W) on for 8hr per day. anything less and the payback time extends even further.

 

[ozarkjeep]

How do you figure?

do I really need 9 panels making 3 amps each per hour of sunlight?

your response is a bit vague to be of any value to me, would you please elaborate?

I added some can lights to my sons room, and a nearby bathroom.

4 fixtures, 13 watts per, 52 watts total, at 120 V thats .4 amps.

Im thinking 2 golf cart batteries, and 50-75 watt solar panel, a charge controller, and small inverter, could run those lights, and several more, easily.

Snip

156 watts, say for 8 hours per day, thats 1248 Watt hours, or 1.248 KW-hours per day ( is my math correct hmmm?)

Snip

thoughts?

About 9 more panels and 6 more batteries and you will be a lot closer.

 

[eba1225]

Ozark,

Looks about right to me. I was looking at a system that would provide power to the house that was grid tied. My payback was in the order of 12 yrs without batteries.

Erik

 

[Andre B.]

How do you figure?

do I really need 9 panels making 3 amps each per hour of sunlight?

your response is a bit vague to be of any value to me, would you please elaborate?

Just using the looks about right method of engineering, based on living in Wisconsin.

Conditions have to be just right for PV panels to make full rated output. Hazy sky, clouds, dust on the panels, the angle of the sun, the temperature of the panels all reduce the energy output.

Using your first energy in/out numbers.

156W 8Hours a day means that the 75W panel would need to make full output for 16.6 hours per day, without considering storage or inverter efficiencies. I would guess that even on a good day you will be lucky to get 4 hours which means you would need 4.2 panels. Now add in the efficiencies and the fact that there will be days with no significant sunlight that will drain the batteries more and will have to be made up when the sun comes out again, and you are up around 10 panels. Even then you will need to charge the batteries now and then from a generator or in your case the grid.
You do not want to leave lead acid batteries in a discharged state for long periods of time (weeks or even repeated periods of a few days) that is what causes the sulfates to form hard crystals and be unavailable for charging. AGM batteries are better in this regard but compared with GC batteries are much less tolerant of over charging and way more expensive. With GCs you can add water but with AGMs once they vent you cannot easily put the water back, some have had some luck drilling holes into each cell but it is just a guess as to how much water to put in.

The bigger battery pack is so you can make better use of the PV panels, and comparatively batteries are almost insignificant in cost.

Now if you are willing to only use what energy is available and switch back to the grid (the lights and/or to charge the batteries) when it is not you can get by with however many panels you have.

Unless you know batteries, in which case you can likely get by with a volt and amp meters, you should consider a battery monitor. The least expensive one I can think of at the moment is this one.
http://www.bogartengineering.com/trimetric.htm

 

[ozarkjeep]

you are right that panels dont make full power for very many hours per day, but the panels on my other solar project do make SOME power from sun up to sun down.

ive got another solar powered project, and when I run the 4 compact fluorescent lights on it, the monitor shows less than an amp draw, and anytime there is at least an amp from the panel, the battery voltage does not drop at all.

This led me to believe that the CF lights can be run on a 2-3 amp panel with some battery backup for night time.

In retro spect, 8 hours per day is way over what the lights would be used. about 4 hours is more likely the case.

regardless though, I will likely continue to rely on the generator for power outages, as the investment $$$ and time/wise just really isnt worth it.

Andre, you have made me want to do it now though, simply to show that it can be done.

 

[TMonter]

Don't forget the power factor and ballast on the lights.

 

[Sandor]

Use 12 volt CFL's and skip the inverter.

 

[ozarkjeep]

Im not sure what you mean here?

the ballast is built into the light, and I assume its accounted for when the bulb is sold as a 13 watt bulb with an edison type base?

not sure what power factor is.

Don't forget the power factor and ballast on the lights.

 

[ozarkjeep]

that is a great idea, when I looked a few years ago, those lights were $60 or so each though.

have they come down in price?

Use 12 volt CFL's and skip the inverter.

 

[Sandor]

Looks like less than 14 bucks.

(broken link removed to http://www.nolico.com/saveenergy/12_volt_marine_cfl.htm)