I need to put together a 12v lighting system

heynow999

Hi All

I am trying to get into the solar business. I met with a builder today and what he wants to do is run some garden lights off of solar power. Basically, it is a small townhouse developement (10 units) and he wants to avoid having to put an extra hydro meter in for a few lights. There are two small areas that need light. I showed him some 3 watt LEDS that are equal to about a 20 watt bulb. I want to put a system together that would run 10 of these 3 watt bulbs.

I am thinking a 75 watt 12volt panel charging an AGM battery through a charge controller. I would need a switch that would make them come on at night. The charge controller would need to shut off the system if the battery gets low. (or would it? would it be ok to just let the battery drain down?) They don't neccesarily have to work all night. It is more for marketing than anything else. I would like some help with sizing and components. How big of a battery would I need How long would a 100ah battery run 10 x 3 watt lights. What is a reliable small charge controller? Wires would be keep as short as possible, maybe 30 feet?

All thoughts are appreciated

Peter

BB.

Re: I need to put together a 12v lighting system

Morning Star makes a couple Landscape lighting controllers (12 and 24 volt):

Sunlight solar lighting controller 20-amp 12 volt
Charge controller and light timer for solar powered lights

We had a similar issue with a small sprinkler system for a small 4-plex I help take care of--Do we get a separate water meter for watering or continue to use the meter from one of the apartments...

In the end, because of city policies (each water connection has taxes and fees to support schools, billing costs, etc.)--it was way cheaper to just give the tenant a $10 credit per month (even in the winter when the sprinkler is turned off)--than to go with a separate meter.

If there is AC power available, and it is done with LED low energy lighting--the total power costs are probably on the order of a couple dollars per month. Just plug in a Kill-A-Watt meter to set the "rate" and show the tenant/home owner--and give then a credit that is 2x the "costs" of power (or whatever makes sense for your situation).

Or, get a used kWhr meter and make the rebate based on the kWhrs / year actually used (with a "thank you" rebate).

30 watts * 12 hours * 30 days * 1k/1,000 * $0.12 per kWhr = $1.30 per month worth of power

It will cost hundreds of dollars to setup a solar system--plus maintenance/battery replacement every 3 years or so...

-Bill

BB.

Re: I need to put together a 12v lighting system

I am sorry--I missed that you wanted to try solar for business reasons... So, to work out what you will need. PV Watts to figure out the amount of solar power for your area. Enter 1 kW (minimum allowed, use to scale later). Derating of 0.77*0.90*0.85 (over all efficiency * batt eff * controller eff)=0.59

Lowest kWhr output is November at 31 kWhrs per month.

Your needs are:

30 watts * 12 hours * 30 days * 1k/1,000 = 10.8 kWhrs per month worth of power

1kW of panels * 10.8 kWhrs needed / 31 kWhr per 1kw of panels = 0.348 kW of solar panels (348 watts) per 12 hours of light in winter

If you want 75 watts of solar panels:

12 hours * 75 watts / 348 watts = 2.6 hours per night (in November)

The above is just a guess--quick rule of thumb calculation--and should meet the basic requirements of your system (scale according to your actual needs).

According to the manual:

Low Voltage Disconnect (LVD)
If the battery falls below 11.7 (or 23.4) volts,
nected from the battery to protect against ha
charges. A one minute delay prevents load d
transients. The load is automatically reconnec
tery voltage recovers to 12.8 (or 25.6) volts.

I am not sure I would use the LVD of the controller to turn the lights off daily (say set them for 5 hours of on time--and in winter, they turn off in 2.5 hours when the battery "goes dead").

AGM would probobly be better in this "type" of applicaiton (running near dead)--but it seems it would be very hard on the battery life.

Battery size--I am not sure that it exactly matters... We would normally recommend 6x daily load:

30 watts * 12 hours * 6 days * 1/12 volts = 180 amp*hour

With a 10% sized array, that would be 18 amps or 18a*17v=306 watt panel...

Rules of thumb--I am not sure how helpful they would be... cut the battery size by 1/2, cut the charge to 5%, and the solar panel minimum would be 76 watts on a 150 amp*hour battery...

But what the heck, overnight is

36 watt*12 hours / 12 volt = 36 amp*hour battery for 12 hours.

36 watt*2 hours / 12 volt = 6 amp*hours per night...



-Bill

heynow999

Re: I need to put together a 12v lighting system

Hi Bill

Yes, I want to supply and install the system. We install solar pool heaters and we are trying to get into PV. We have sold some PV and installed systems on our own homes, but this is a bit out of the ordinary for us.

As for having a meter or not, I know that the hydro company will charge $30 a month just for the meter, even if you just use $1 in energy. That saving alone will more than cover battery replacement. The builder also wants to look green. I know it is green washing in a sense, but the more solar that gets installed, the lower the prices will go..... hopefully.

I appreciate the numbers. I will have to take a good look at them. I guess the whole point is that it is hard to make it work well in November and December. We have a supplier for marine LED fixtures. I will look into the morningstar controller, looks like what we need.

BB.

Re: I need to put together a 12v lighting system

If I was going to make a solid solar based power system... I would look into using the Xantrex Battery Monitor... A service person can just read the display to find out the state of charge--and a couple of the Xantrex models (LinkLite and LinkPro models--that I have looked at--there may be others) have programmable so that it can send out a digital signal (to a switch) to turn of the loads when the power drops below XX% state of charge. When using AGM batteries--about the only thing that will work.

For larger systems it makes sense--but for a smaller system spending USD $250 to $350 for the Battery Monitor itself--makes it difficult to justify.

You may be able to save some power if part of the lighting is motion controlled.

-Bill

mike95490

Re: I need to put together a 12v lighting system

Use the Sunlight Controller, and set to 6 or 9 hrs per night, that will limit the winter hours/drain

BB.

Re: I need to put together a 12v lighting system

Mike,

The bigger issue is that for the number of LED's (Power requirements), the solar panel size desired, and the northern latitude (Canada)--this all adds together to a system that can support only about 2.6 hours maximum (average winter month).

So, the system would either run the battery dead if it tried for 6-9 hours of light per month, or use the LVD to disconnect on the battery hitting a low voltage limit...

And I am not sure how long an AGM or Flooded Cell battery would last if it hit the LVD every night in the winter. A NiCAD battery might perform better--but would be more expensive, contains Cadmium (might be illegal in the application/region), and would probably still need replacing fairly often.

The Digital Battery Monitor with an output that could turn off the loads based on the Battery's State of Charge--would seem to be a nice addition for longer battery life and easier maintenance (just read the meter once a month to make sure everything is working correctly). But it is not a cheap solution.

-Bill