Low voltage system

[kluchtman]

I have a low voltage lighting system around the outside of my house. It started with 20 Watt halogen bulbs but those have been replaced with 3Watt LED bulbs. I have the following transformers running the lights: 1 300 Watt, 1 200 Watt, 1 120 Watt and 1 45 Watt. The 45 Watt runs some sidewalk lights that are on from Dusk to Dawn and all of the others are set to be on for 4 to 5 hours after sundown depending on the season. What I would like to do is set these lights up to a solar charging system. I think it would be easier to just have everything run off of one dusk to dawn photocell and remove the transformers all together. To me it sounds silly to collect enough electricity to power the transformers that are really bringing everything down to the same voltage as the lights.

According to my calculations I am going to need 80 watts of power per hour which is 0.080 Kilowatt hour. Figure 15 hours of light is desired (trying to figure high just in case), then I will need 1.2 Kilowatt hour capability. Now that's figuring that I can remove the transformers all together and run these 12 volt LED bulbs off of a series of 12 volt batteries for 15 hours. Figuring I would have approximately 8 to 9 hours of available charge time, I would need a 200 watt solar panel to charge the batteries to the needed 1.6 Kilowatt capacity.

If I have lost you already then it should be obvious, I am still learning but at this point this is still making some sense in my head.

What I haven't figured out yet is how many batteries would I need to provide this kind of electricity. If I am way out in left field please help straighten me out, but if I am right and someone has the time to point me in the right direction I would greatly appreciate it.
Kurt

[Sunking]

So Kurt answer this question for me and I will help you.

Question:

Why do you want to pay 10 times more for electricity?

You can buy all the power you want from the Power Company for around 10 to 15-cents per Kwh. Anything you take off grid will cost you 10 times that much for the rest of your life. Why would you want to do that?

[Sunking]

I will tell you that you are not even close to what is needed. You are looking at something like a 500 watt system with a 12 volt 500 amp hour battery (the batteries will weigh in around 500 pounds and cost $1000 every few yearsf for replacements). How about $2000 right now up front in cash and $1000 every few years to replace the battery? I will help you and sell you everything you need to make it work. Or you can just pay the POCO $4/month to run the lights 24 hours a day.

What do you want to do?

[Ian S]

Unfortunately, it's a money losing proposition. You've already won the battle by swapping LEDs for the halogens. Maybe you could now consolidate some transformers. To achieve what you want to do with a "small" off-grid solar system it'll average you hundreds of $$ a year in costs to save about $40/yr in utility payments.

[kluchtman]

OK, so I have some more learning to do. So how exactly would this be hundreds of dollars a year?

[inetdog]

OK, so I have some more learning to do. So how exactly would this be hundreds of dollars a year?

Not to go into the numbers, but the biggest costs to factor in are the equipment cost to be amortized over its lifetime and the recurring expense of replacing the battery bank every 2-5 years.

[Sunking]

OK, so I have some more learning to do. So how exactly would this be hundreds of dollars a year?

Batteries are very expensive. For your application around $1000, then in a few years you get to replace it at even higher cost.

[Wy_White_Wolf]

I have a low voltage lighting system around the outside of my house. It started with 20 Watt halogen bulbs but those have been replaced with 3Watt LED bulbs. I have the following transformers running the lights: 1 300 Watt, 1 200 Watt, 1 120 Watt and 1 45 Watt. The 45 Watt runs some sidewalk lights that are on from Dusk to Dawn and all of the others are set to be on for 4 to 5 hours after sundown depending on the season. What I would like to do is set these lights up to a solar charging system. I think it would be easier to just have everything run off of one dusk to dawn photocell and remove the transformers all together. To me it sounds silly to collect enough electricity to power the transformers that are really bringing everything down to the same voltage as the lights.

According to my calculations I am going to need 80 watts of power per hour which is 0.080 Kilowatt hour. Figure 15 hours of light is desired (trying to figure high just in case), then I will need 1.2 Kilowatt hour capability. Now that's figuring that I can remove the transformers all together and run these 12 volt LED bulbs off of a series of 12 volt batteries for 15 hours. Figuring I would have approximately 8 to 9 hours of available charge time, I would need a 200 watt solar panel to charge the batteries to the needed 1.6 Kilowatt capacity.
If I have lost you already then it should be obvious, I am still learning but at this point this is still making some sense in my head.

What I haven't figured out yet is how many batteries would I need to provide this kind of electricity. If I am way out in left field please help straighten me out, but if I am right and someone has the time to point me in the right direction I would greatly appreciate it.
Kurt

Wrong. Daylight is not the equivilant of solar insolation. Depending on your location it is more like 2 to 3 hours in the winter. 2 hours would mean you'd need a 750watt array using an MPPT charger, 3 hours would be 500watts. Battery bank would also have to be in the 500AH range at 12VDC.

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