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Thread: Building an off grid solar lighting system?

  1. #1

    Default Building an off grid solar lighting system?

    Hi all,

    I could use some help with this project.

    A friend asked me to install some security lighting on his house, he wants it to be solar a solar powered LED system. The system will consist of a 9 bulb/fixture system that will be motion activated. The max load if all 9 bulbs were on at once ( which they rarely would be) is 270W. All of the fixtures and electrical will be professionally installed and run to a standard breaker box (OFF grid). From there it will be up to me to power it.

    I contacted a supplier who quoted me around $4000 for the system. I am pretty sure that I can put one together for less than that, but I want to be certain I know what I am doing before I get started.

    I need to make sure I am creating a balanced system that is able to handle the load requirements, and also that there is not something I have over looked.

    I realize that I need

    1. Panels
    2. Batteries
    3. charge controller
    4. inverter

    Any suggestions are helpful.
    In Him (Jesus Christ) was life; and the life was the light of men. And the light shineth in darkness; and the darkness comprehended it not.
    Shorty C/D M*glites

  2. #2
    Flashaholic* AnAppleSnail's Avatar
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    Default Re: Building an off grid solar lighting system?

    Quote Originally Posted by vestureofblood View Post
    9 bulb/fixture system that will be motion activated.
    Max load if all 9 bulbs were on at once ( which they rarely would be) is 270W.


    I contacted a supplier who quoted me around $4000 for the system.

    I realize that I need

    1. Panels
    2. Batteries
    3. charge controller
    4. inverter

    Any suggestions are helpful.
    In Missouri, you get a lot of sun. How often do you have a run of cloudy days, though? That helps determine the batteries needed.
    How well do solar cells work there (A 100-watt-rated panel gets xxx watts)?
    How much power do the motion sensors take? Do they run during the day?

    I have some questions though: Voltage of system? (This helps us get your conversion losses and wire losses).


    270W for an 8 hour night is 2160 Watt-hours, which gives us a rough estimate for 'maximum power use in one go.' I'm told that with most battery systems, you want no more than 50% depth of discharge to maximize cycle life, so we want around 4 kWh of storage... which is:

    330 A*h at 12v, or 165 A*h at 24v.

    And you'll want to recover somewhere between 0 and 2160 watt-hours in a day with the panels, charge controller, and conversion and line inefficiencies. What's the expected usage? That'll help you find how low you can go in that range. How many watts do y'all get out of a 100-watt solar panel in MS? A system that gets 250 W averaged over 8 hours will be overkill; and probably run all 9 bulbs all night every night.

    What kind of light patterns are they, or are the bulbs fixed? Whose are they, and what voltage do they run at?
    My biggest light-hog is my camera.

  3. #3

    Default Re: Building an off grid solar lighting system?

    I would skip the inverter and run everything DC.

    Motion-activated and short "on" times would really reduce costs of batteries and solar cells. Just one deep cycle marine battery and a basic 20-Watt solar charger with regulation might be enough. If each bulb is 30 watts, and the bulbs are triggered 100 times per night and stay on for 1 minute after motion is sensed, that's only 50 watt-hours of consumption. A decent sunny day might generate 20W x 6hrs = 120 watt-hours. A well-designed solar panel would still provide something useful on a cloudy day if there's enough cells in series to exceed battery voltage, and it's possible that the lights would only be triggered 10 times per night.

  4. #4

    Default Re: Building an off grid solar lighting system?

    Quote Originally Posted by AnAppleSnail View Post
    In Missouri, you get a lot of sun. How often do you have a run of cloudy days, though? That helps determine the batteries needed.
    How well do solar cells work there (A 100-watt-rated panel gets xxx watts)?
    How much power do the motion sensors take? Do they run during the day?

    I have some questions though: Voltage of system? (This helps us get your conversion losses and wire losses).


    270W for an 8 hour night is 2160 Watt-hours, which gives us a rough estimate for 'maximum power use in one go.' I'm told that with most battery systems, you want no more than 50% depth of discharge to maximize cycle life, so we want around 4 kWh of storage... which is:

    330 A*h at 12v, or 165 A*h at 24v.

    And you'll want to recover somewhere between 0 and 2160 watt-hours in a day with the panels, charge controller, and conversion and line inefficiencies. What's the expected usage? That'll help you find how low you can go in that range. How many watts do y'all get out of a 100-watt solar panel in MS? A system that gets 250 W averaged over 8 hours will be overkill; and probably run all 9 bulbs all night every night.

    What kind of light patterns are they, or are the bulbs fixed? Whose are they, and what voltage do they run at?
    We do have good sun here. I would say a "run" of cloudy days here is fairly uncommon.
    I dont know how much juice the motion censors use. The lights would probly come on periodically in the day if something passed in front of the censor.

    I am thinking the default setting of most of the lights will typically be OFF. A high estimate to me would be expecting 4 hours use total for the system per night. There will probly be a switch set up for at least a few of them so they can be turned on for constant for other use, but not all of the lights would be running at once. I would like him to be able to run 2 lights for an 8 hour period if needed.

    At this point I am open to either a 12 or 24V system. The bulbs are going to be off the shelf so if anything happens to them he can just go pick up a replacement. I was thinking of using bulbs similar to this.
    http://www.lowes.com/ProductDisplay?...llow&cId=PDIO1

    Quote Originally Posted by PerryScanlon View Post
    I would skip the inverter and run everything DC.

    Motion-activated and short "on" times would really reduce costs of batteries and solar cells. Just one deep cycle marine battery and a basic 20-Watt solar charger with regulation might be enough. If each bulb is 30 watts, and the bulbs are triggered 100 times per night and stay on for 1 minute after motion is sensed, that's only 50 watt-hours of consumption. A decent sunny day might generate 20W x 6hrs = 120 watt-hours. A well-designed solar panel would still provide something useful on a cloudy day if there's enough cells in series to exceed battery voltage, and it's possible that the lights would only be triggered 10 times per night.
    The only problem I have with going DC is that the bulbs and fixtures are designed for use with 120V AC. If there is a simple way around that too I'd be for it.
    In Him (Jesus Christ) was life; and the life was the light of men. And the light shineth in darkness; and the darkness comprehended it not.
    Shorty C/D M*glites

  5. #5
    Flashaholic* Walterk's Avatar
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    Default Re: Building an off grid solar lighting system?

    Its too wide a question to answer in a forum.

    Mastervolt and Victron have splendid brochures about how the lay out would be of an off-grid system, consisting of consumers, cells, converters and chargers. That would be a good start. After that you should find yourself information on solarpanels and converters.
    And by all means; do the math seriously beforehand. Pretty easy with the example calculations found in the brochures.

  6. #6

    Default Re: Building an off grid solar lighting system?

    You need to ask your friend what is his goal in going with solar panel vs the grid. Is he trying to save money via solar? Continue to power the security lights if power is cut off from the grid? etc.

    If he is trying to save money from using solar, the time to break-even from this investment may be too high.

  7. #7

    Default Re: Building an off grid solar lighting system?

    He wants to use solar so that even when the power is out his security lights still work. Saving money on the electric bill would be a plus too but not the primary reason.
    In Him (Jesus Christ) was life; and the life was the light of men. And the light shineth in darkness; and the darkness comprehended it not.
    Shorty C/D M*glites

  8. #8
    Flashaholic*
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    Default Re: Building an off grid solar lighting system?

    When you got a $4000 estimate/quote, you're getting about $2000 worth of equipment, and $2000 of labor and know-how. So, of course you can do it all yourself for less, and/or get a lot more for your money.

    Motion activated means lights will only be on an hour or so each night. This will allow you to go smaller than what you think.
    I get about 10 3-minute activations on one of mine for the front yard, and maybe 2-3 activations on the sides of the house, and maybe 1 activation in the back yard. With your 9 locations, you need to guestimate the worst case scenario situation(all on for 12 hours). Once you know that, it'll be easy to pick components.

    DC lights are highly recommended. You don't want to run power wasting inverters from a battery pack. There are plenty of LED DC flood lights, LED bulbs,... available. For that independent outdoor lighting project, use AC only if you must.

    A single 100w+ 24v solar panel. Check your local solar panel stores. If you can't find any, Ebay has many to choose from. The bigger you go, the better off you are. 100-300w run $4-$2 per watt delivered. The smaller panels tend to go up in the dollar/watt ratio. So, I'd go as big as possible.
    If the 9 bulbs are motion independent and rarely all on at once, I'd start with just a 4-pack of series wired GC2's with Hydrocap's. SamsClub and Costco usually have the 6v battery for <$100 each. A couple of series wired 12v Group-31 deep cycle marine batteries should suffice too. Owner needs to 'maintain' batteries by topping off as needed.
    A 15-20a 24v solar charge control with lighting control. Check Morningstar, Futurlec, or EPsolar. MPPT cost $250-$350. But, you can get a decent PWM controller for <$80.
    No inverter!!!! If you must invert, find something with 2000w+ of clean pure sine wave power. You might need to run a water pump, computer/internet, tv/cable, charger, or refrigerator with it in an emergency situation. With the crazy weather caused power outages, you might just end up running an extension cord to that 'lighting inverter' for 'home' usage.

    Wildlife have been known to kill batteries from those little solar recharged hardware store security motion lights. But, I'll still recommend the Maxsa-80 and Maxsa-100 which work pretty good for not so busy night locations. Just pick up a dozen, and you won't have to worry about solar panels, batteries, inverters... http://www.maxsainnovations.com/solar_motion_lights.htm
    A single point of failure in your home brew panel/charger/battery/inverter system will disable ALL your lights. With several independents, you'll have 'most of them' working when needed. Also, buying a single Maxsa, or equivalent, allows you to test each location for activations and expectations. HomeDepot and Lowes have similar individual solarcharged/battery/LEDlight systems for <$150.

    Is grid tie an option? Going independent solar/battery will waste any surplus power that can be used to feed the grid to reduce e-bill.
    If you need lighting in a loss of grid situation, consider computer uninterruptable power supplies too.

  9. #9

    Default Re: Building an off grid solar lighting system?

    Ok, I am almost convinced that DC 12V is the way to go, but then what about the fixtures? I need ones that can be powered by only 12V. I am also having trouble finding any suitable 12V bulbs that are for outdoor use. All of the outdoor ones I have found that are 12VDC are LEDs mounted in a pre existing fixture.

    Do you happen to know where to find either of these deadrx?
    In Him (Jesus Christ) was life; and the life was the light of men. And the light shineth in darkness; and the darkness comprehended it not.
    Shorty C/D M*glites

  10. #10
    Flashaholic*
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    Default Re: Building an off grid solar lighting system?

    More details. What AC lights have you tested that are acceptable? What type of bulb are you looking for? light output? range?

    Ebay has plenty of DC LED light bulb choices. AC motion sensors can be converted to DC if you have electronic experience. Pull the transformer and bridge rectifier from it.
    Last edited by deadrx7conv; 08-03-2012 at 03:44 PM.

  11. #11
    Unenlightened
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    Default Re: Building an off grid solar lighting system?

    The battery capacity will impact more than reliability.

    Make sure that you have about 8 days of reserve storage to maximize the life of the battery. Battery life is largely determined by how deeply you cycle the battery each night. Ideally, you want to limit the depth of discharge to 20% (including periods of bad weather). Cycling the battery at a deeper rate decreases the battery life at an accelerating rate.

    We design our systems to this criteria and consistently deliver 5-7 year batter life. You pay more up front, but save money over the life of the system.

  12. #12
    Unenlightened
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    Default Re: Building an off grid solar lighting system?

    This is something i've been considering on building myself. Not something as big as the OP, but I'd like to light up my backyard with some lights. I'm such a newbie when it comes to all this off grid stuff, so i'd like to see the approach the OP uses. I built a small off grid light to light up the inside of a tool shed that works pretty well. One issue I had was finding some DC bulbs, anyone know of reputable place that sells some, besides ebay?

  13. #13

    Default Re: Building an off grid solar lighting system?

    1) Unless you have solar incentives and can take advantage of it for this system, you will never ever save money off running from the grid.

    2) If all your friend wants is his system to work during power outages, then I would ditch solar and just have 5 days or so of battery backup and have a transfer switch to run off the batteries/inverters. Use good quality AGM batteries and your friend could get 10-15 years out of the batteries if they are only used infrequently.

    3) Consider running only half the lights off the backup and you will save added money on the batteries, probably a better way to go.

    4) Don't go with the 2000 watt inverter. The 2000 watt inverter will have a large static load no matter if the lights are on or not ... at least if you need to power 120VAC motion detectors.

    5) You could consider a 12V motion detector an use this to turn the inverter on. That would eliminate the larger static load from motion detectors and the like.

    If you want to run this purely off solar, it is going to be expensive to do it right and make it reliable. I am guessing that 4,000 did not have 2,000 of mark up.

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