AC or DC LED Lighting for off-grid solar

[kunal]

I'm working on Solar powered Lighting system for a number of off grid training centers.
The application is mainly for LED lights. The question is whether to go for DC or AC fixtures. Solar systems would generally be 600W - 1000W (12V). Furthest lights would be 60 feet from the batteries.

[russ]

Hi Kunal - Welcome to Solar Panel Talk!

Let us see what kind of replies come.

Russ

[greenHouse]

Kunal,

AC inverters are their own source of waste and should be avoided if at all possible. Since LED lights are very small loads, one of the better reasons to stick with AC -- higher voltage, lower current, less voltage drop and waste in the wiring -- is irrelevant.

The only remaining question is whether or not you want to have AC power available as a convenience item. There are small sine wave inverters on the market -- the Morningstar SureSine 300 is a sweet unit with a very low standby power draw (I measured it at around 3.5 watts) -- or you could have some 12 volt "power ports" ("cigarette lighter") jacks installed and allow people to bring their own square wave inverters.

[Mike90250]

I'd go with DC lights for RVs. The ones with resistors, are much less efficient than ones with internal current drivers. Some regular flurscent fixtures are more efficient than LEDs

Will your 12V system be solar charged ? Could cause problems at different points in the charge cycle when battery voltage is 15 or 16 volts - automotive & RV lights are not designed for that range.

[greenHouse]

I'd go with DC lights for RVs. The ones with resistors, are much less efficient than ones with internal current drivers. Some regular flurscent fixtures are more efficient than LEDs

Will your 12V system be solar charged ? Could cause problems at different points in the charge cycle when battery voltage is 15 or 16 volts - automotive & RV lights are not designed for that range.

This is another argument for using LEDs since they tend to have a much wider range of acceptable input voltages. Anything with a filament is going to be designed for a fairly narrow range of voltages, at least on the higher voltage side.

[Sunking]

Need to be really careful with LED's, especially inexpensive DC models as they tend to use linear shunt regulators for the drivers.

So here is the problem with any shunt regulator device input current = output current. So for example a popular LED made by Cree is XL series and the current runs between .75 to 3 amps @ 3 volts. So use any current between .75 to 3 amps and do a little math fun At .75 amps @ 3 volts the light uses 2.25 watts. Catch is the input voltage is 12 volts @ .75 amps = 9 watts. So at 260 Lumens @ 9 watts = 28 Lumens per watt. That is just about what a incandescent is rated at.

But even with that said using a buck/boost DC driver, the efficiency of LED fixtures runs 50 to 70 Lumens per watt which is no better than CFL's at a fraction of the cost, and falls way short of T5 and T8 Florescent lighting of up to 105 Lumens/watt. LED's still have a long way top go, but I think they will get there, just not now.

[greenHouse]

It's for this reason that G-d invented series wiring

[Sunking]

It's for this reason that G-d invented series wiring

Other than educated in electrical, who is going to understand and know how to optimize the method? I digress.

[john p]

1W Cree 12V MR 16 replacement type draw 1.68 watts.. I like the light out from them it appears to me and everone else that sees them say colour is good. You need to be able to mount that at least 9 ft between ceiling and floor.. They make fantastic outdoor security lights as if mounted so that they have long throw they cover a very wide area for very little power use.

[greenHouse]

Other than educated in electrical, who is going to understand and know how to optimize the method? I digress.

Considering how many times "wired in series" is used in a renewable energy forum, my guess is that just about everyone understands the concept. And considering how much discussion of "voltage" also happens, I'm guessing 75% or more people grasp the concept well enough to do something with it.

And if they don't, they can ask the same as they always seem to.

[greenHouse]

.

I choose DC

The choice should be made based on total installed cost, plus cost of operation. Remember that with low voltage DC, you may be limited as to parts =and= you may need heavier conductors. There are many low power inverters with efficiencies in the 95+ percent range, and while converting back to low-voltage DC at the LED will result in more loss, the efficiency of many LED lights is likewise in the 95+ percent range.

[Mike90250]

Welcome back Julie - Long time no see.

[greenHouse]

Welcome back Julie - Long time no see.

I've been working on a new commercial monitoring product. I'm hoping to start going head-to-head with Deck and Draker.

Now that the overweight dog has been snatched up (Fat Spaniel was bought by Power One or whomever -- I forget), I think I'm in an excellent position to take some of the business they likely left behind.

[Sunking]

Now that the overweight dog has been snatched up (Fat Spaniel was bought by Power One or whomever -- I forget), I think I'm in an excellent position to take some of the business they likely left behind.

Good luck Julie.

[russ]

Right! Go for it tiger!