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Old 10-27-2008, 06:57 PM   #1
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12V DC lighting?


I was planning on installing some recessed lighting in the house and was wondering if I shouldn't considering hooking these up to a solar panel with batteries?

I understand that the ROI is essentially non existent but it is a small step in the alternative energy, and as I understand it by passing the inverter is the most efficient way to use Solar power. We currently have our small 12V native stereo hooked up to Solar and it uses a ridiculously small amount of power - enough for us to listen all day on a 3 Watt Solar panel.

Also these lights should look very nice especially compared to CF's...

What I can't quite figure out is what the wattage of say, a xenon bulb that may be equivalent to your average 40 or 60 watt incandescent bulb?

In terms of number of panels/power/size... this is what I came up with:

I figure if we run our lights for 5 hours a night, if there's say 10 of them, it's going to be 50 * wattage, say 10 watts per bulb (may be very off???) = 500 watt hours which will require 200 watts worth of panels (3 hours of sunshine - some loss on the panel from what it is rated vs what you actually get).

As far as battery capacity I understand this is 41 AH (500 watts /12 volts) but not sure how many AH of batteries we'll need to not ruin the battery... I have heard 5x the daily draw but that sounds like a lot (?).

Feel free to point me in the right direction... thanks.


Last edited by pcampbell; 10-27-2008 at 06:59 PM.
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Old 10-27-2008, 10:35 PM   #2
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12V DC lighting?


Here is my take on this.

12vdc is out. Go for 24vdc or 48vdc. The reason is that you can use much smaller wire. With the cost of wire these days 12 vdc is not real popular. My panels are set up for 24vdc. They are 12vdc in series and parallel to get the 24vdc. I have 4 sets of 2 panels in series that are connected to each other in parallel.

The second thing is that a battery system is complicated if you are not familiar with it. Most batteries don't die of old age, they are murdered. This is because the owners are not familiar with battery maintenance and don't use a hygrometer often enough to check the specific gravity. They also allow a bad battery to stay in the system which does nothing but drain the rest of the batteries.

If you are comfortable with dealing with batteries then this might be for you.

There is also the battery storage location. It shouldn't be in your house as they off gas hydrogen which is explosive. It is best to have it in a separate room with good venting. The room should not be hot in the summer as hot batteries are not as efficient and will have a shorter life. Remember how most batteries die.

As you stated the ROI is almost non existent especially in this situation.

If you want to go solar then go with a grid tie system. Less energy in maintenance by you and you won't have to run a low voltage circuit. You can add one panel at a time as you expand your system. Start with either a 24vdc panel or 2 12vdc panels hooked in series to get 24vdc. Get a grid tie inverter and you are in business.

As you add to your system you will get lower and lower energy bills till one day it will be zero.

I can tell you that it feels good sticking it to the man.

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Old 10-28-2008, 07:59 AM   #3
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12V DC lighting?


Great advice, thanks. 24vdc should not be a problem.

I was wondering if its possible to get sealed/maintenance free batteries but I have no really looked into the battery situation. I wanted to first figure out the "truth' behind what capacity of batteries I'll need based on my draw which will likely over a short period of 5-7 hours per day?

I was planning on putting the batteries in the attic, but had also considered the fact that it gets to be 100+ degrees up there in the summer (I think I've got the attic fan set at 110F). In the winter it stays very mild, but then again so does the basement. The upside is to the attic is very easy wiring (since we'd be going from the roof, to the attic, and then to the attic for the overhead lighting) and plenty of room...

New JErsey has put a hold on their Solar rebate thing that made the ROI closer to 20 years which is still pretty crazy.
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Old 10-28-2008, 09:57 AM   #4
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12V DC lighting?


Quote:
Originally Posted by pcampbell View Post
Great advice, thanks. 24vdc should not be a problem.

I was wondering if its possible to get sealed/maintenance free batteries but I have no really looked into the battery situation. I wanted to first figure out the "truth' behind what capacity of batteries I'll need based on my draw which will likely over a short period of 5-7 hours per day?

I was planning on putting the batteries in the attic, but had also considered the fact that it gets to be 100+ degrees up there in the summer (I think I've got the attic fan set at 110F). In the winter it stays very mild, but then again so does the basement. The upside is to the attic is very easy wiring (since we'd be going from the roof, to the attic, and then to the attic for the overhead lighting) and plenty of room...

New JErsey has put a hold on their Solar rebate thing that made the ROI closer to 20 years which is still pretty crazy.
Unless you have a very stout attic I would not be putting them up there. The weight would be way too much for most attics. The heat would be bad and then the off gassing of hydrogen.

If you do go with the attic spread out the batteries since most attics were not meant for all that weight. Also putting them on a weight bearing wall would be better than trying to make a joist carry all that weight.

Then get a fan that is on 24/7. Doesn't have to be a big one, just something to keep the gases from accumulating. It will burn at 4% concentration. It can just burst into flame for no reason and with a hot attic and a fan that can ignite that is a real possibility. Flames of hydrogen are invisible since they burn so hot the light is in the ultraviolet range. But you would never see this as the house would be on fire at this point.

It also mixes with other gases to make very strong acids. In fact excess hydrogen ions is how acid is measured (pH). So you don't want any hydrogen gas sticking around.

Hopefully this has convinced you to keep your batteries in a separate building that would be no big deal if it burned down.

If you do go the battery route get more than you need. The worst thing is to cycle a battery too deep too often.

Gel batteries (maintenance free) are becoming more popular but have a shorter life in most cases.

That sucks about New Jersey not supporting alternative energy. You would think that a blue state would be all over that. Maybe it is just talk for them. I find the red states have the best rebates/tax credits over all.
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