12v solar light system - help needed

SystemSystem Posts: 2,511 admin
Hi everyone, I'm totally new to this whole idea so I need help.
I want to eventually change all my home lights to 12v MR16 LED bulbs and power them using solar energy. While the house is in a state of (never-ending) remodel I was going to run new light circuits for the upstairs and downstairs and start changing over the fixtures to the MR16 type. The initial plan is to get the infrastructure in place and run the lights off a 12v transformer so that we can get the drywall and ceilings back up and finish the remodel. That way I can worry about the solar part later.
So here is what I’m planning to do. What I need to know is if any of it is a bad idea either electrically or for solar use later on.
downstairs has 10 fixtures using between 15w to 20w CFLs. in order to maintain the same or similar level of lighting I plan to change these to about 18-20 MR16s. first question is will this be needed or should I be able to maintain a similar amount of lighting with just 1 or 2 bulbs per room? What wattage of bulbs do I need?
I was planning run 2 lighting circuits, so half the bulbs on 1 and half on the other, and to use 14-2 wire in a loop circuit to increase its current handling. Do I need more than 2 circuits and do I need heavier wire for the DC even if I run it in a loop?
Upstairs is pretty much a mirror of down so I can just repeat it upstairs.
My biggest worry is if I need to replace 1 15w bulb with 4 or 5 5w or bigger bulbs then what’s the point. Alternatively if one 5-10w LED bulb will do the job but will cost me 80-100 bucks then that’s not going to work for me either.


  • BB.BB. Super Moderators, Administrators Posts: 33,313 admin
    Re: 12v solar light system - help needed

    Since this is going to be a "big" project for you... I would buy one each of your possible solutions (LED, Halogen, CFL, etc.) and connect them with a Kill-A-Watt Meter (if AC) and get a cumulative DC Amp*Hour / Watt*Hour meter for the DC loads:

    wind-sun_2056_7150293Kill-A-Watt AC Power Monitor Meter
    P4400 Cumulative Killowatt-Hour Monitor

    And for the DC meter--take a look at these two (Doc Wattson or Watts UP--disclaimer, I have not used either meter or worked with the vendor):


    The Kill-A-Watt is the only way to go for 120 VAC 15 amp plug-in loads (less than $30). Well worth the money to use around your "grid tied" home to reduce your power bills.

    DC--the RC-Electronics products look to be cheap and very reasonable for DC Amp*Hour / Watt*hour logging.

    The issue is that the lights are so different (LED "colors" vs CFL "colors" vs Halogen true full spectrum--and Halogen can be pretty efficient) and the issues with the circuits that drive the light emitters. Battery system voltage vary quite a bit (in theory, from 10.5 volts to 15.5 volts) and many LED's assemblies/fixtures do not have efficient ballasts (waste power) and may change light levels quite a bit.

    And, since the LED's and CFL's are not "full spectrum (they have two to three colors that "Look White" but many not have good color rendering).

    You need to see how each performs--both electrically, and for your application. You probably will end up with LED's for spot, and CFL's for floods. And perhaps one small halogen if you have exacting color work (fabrics, artwork, etc.).

    And your choices for your "favorite lamp type" may differ with those others in the home/business.

    Regarding AC vs DC wiring... If this is a "small home" (short runs from the battery to the lamp) and the lighting loads are low--you might get away with wiring some 12 volt wiring.

    However, realize that your battery system will output between 10.5 and 15.5 volts (dead to equalization) and that a "12 volt" device will have 10x the current as an otherwise identical wattage 120 volt device (P=I*V)... So, that means that the 12 volt wiring needs to be able to handle 10x the current with only a 1.5 volt drop.

    If this was 120 VAC wiring, you can run the wire pretty far with just 14 awg cable. And have a good 5-10 volts of drop before your AC lighting/appliances would notice.

    For many people, as their needs/systems/homes grow--it ends up being just about as cost efficient to run 120 VAC off of an Inverter and simply buy 20% more panels and batteries to make up for the inverter's lesser efficiency. And, for many devices, the 120 VAC versions are much cheaper and easier to find than their 12 VDC counterparts.

    And, you will probably have to decide what inverter type you will end up using... the very inexpensive MSW (Modified Sine/Square Wave) Inverter or the TSW (True Sine Wave) Inverter.

    My two cents worth... For a weekend cabin, it is hard to beat the MSW for cost. For an off-grid home--then I would highly recommend a TSW (~10-20% of AC devices can be damaged and/or "buzz" when used on a MSW inverter).

    All About Inverters
    Choosing an inverter for water pumping

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • n3qikn3qik Solar Expert Posts: 741 ✭✭
    Re: 12v solar light system - help needed

    For the DC wiring, it may be best to run 10-2 to a center point of your lamp layout. Then run 14-2 from the point to the lamps.

    As BB stated, at 12 volts, it is easy to lose too many volts in the wire.
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