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Thread: Solar Driveway Lights

  1. #1

    Default Solar Driveway Lights

    I'm a noob beginning my first solar project and have two questions:

    I have 23 existing lights spanning 1400 feet down my driveway that are wired to my house with 14 gauge wire. I'd like to intercept the line running to my house and tie it in to my solar setup. Reusing the existing wire will save me time and money since it's already connected and buried. What should I do with the ground wire? The charge controller only has +/-. Is the existing 14 gauge wire suitable for this project?

    I'm planning on using 2watt LED light bulbs for each of the 23 lights. I've purchased this 85 watt solar panel and this charge controller. What type of battery would you recommend?

    My hope is that this setup will power my driveway lights every evening for 5 or so hours.
    Thanks!

  2. #2

    Default Re: Solar Driveway Lights

    Welcome to the forum.

    Do you know the Voltage of the existing lights? Chances are they're 120 VAC if they're still bright at the end of 1400 feet of 14 AWG wire. That's going to be a problem if you try to switch to low Voltage LED lights powered by battery. You will also need to know the current rating of the lights.

    Then you need to plug the data into a Voltage drop calculator like this one: http://www.solar-guppy.com/forum/dow...calculator.zip

    I can tell you in advance that even with very low Amp LED's you're not going to have much left of 12 or 24 Volts by the time you reach the end of 1400 feet of 14 gauge wire. Like about nothing.
    Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  3. #3

    Default Re: Solar Driveway Lights

    Thanks Cariboocoot!

    I'm pretty sure the existing lights are 120 VAC. I'll double check when I get home. Would I be better off running new wire down the driveway? If so, what type? And thanks for the calculator link.

  4. #4
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    19,641

    Default Re: Solar Driveway Lights

    You can also use a generic web based voltage drop calculator... And to send 1 amp 700 feet (say 12 volts, 12 watts, 1 amp) is ~4.3 volt drop...

    4.3 volt drop at 120 VAC or 3.6% loss (and that would be 120 VAC * 1 amp = 120 watts) is a lot less of a problem than 4.3 volt drop at 12 volts (36% voltage loss at 1/10th the power levels).

    There are lots of options for landscape lighting (AC, DC, different DC voltages, etc.)... So--Conservation (LEDs) is a great start, but you (and us) need to know the details of your loads too.

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  5. #5

    Default Re: Solar Driveway Lights

    You'd need to know the Voltage of the new lights as well; if they're 12 VDC or 24 VDC. It's going to be a problem either way as that is a very long run for such low Voltage. A quick estimate shows 24 VDC running 2 Amps total load would need 6 AWG wire for the 1400 feet. That would be really, really expensive.

    A couple of options: replace the lights with independent solar units (check carefully to be sure they're bright enough and will last 5 hours) or change the existing ones for 120 VAC LED units if you can find them. Then if you still want to experiment with solar you could power them from a small inverter.

    Basically, your wire run is a killer for low Voltage.
    Four 175 Watt panels, OB MX60, 232 Amp hrs, OB 3524, Honda eu2000.

    Ohm's Law: Amps = Volts / Ohms
    Power Formula: Watts = Volts * Amps

  6. #6
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    19,641

    Default Re: Solar Driveway Lights

    You are probably correct that those lights are 120 VAC... Sending low voltage DC any distance will usually require very heavy copper cable to do the job.

    In your case, going with some sort of 120 VAC LED or small CFL type replacement bulb may be the only practical (cost effective) solution. And drive that from your home power, or use a small/efficient 120 VAC inverter to drive the line (more costs).

    Otherwise you may end up needing to rewire with 2 or 2/0 copper (or aluminum) cable to get decent 12 volt power at the end of your run. Probably way more work than it is worth.

    Especially if you have AC Grid power already. Off grid power (solar+battery) will cost around 10-20+ times as much power kWH vs grid power for most people (including costs of battery replacement every 3-8 years, new controllers/inverters approximately every 10 years or so, etc.). And you need to monitor the battery bank state of charge too... Take a battery bank dead even once (bad weather, failed timer, failed solar panel electrical connection, etc.) can kill the bank and require replacement. Making an "unattended" system bullet proof (turn off lights before batteries die, for example) can add significant costs/complexity too.

    Focusing on conservation is usually the best place to invest your money. It reduces your costs every month for decades to come (life of appliance/product).

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  7. #7

    Default Re: Solar Driveway Lights

    Thanks guys!

    So, from what I'm reading maybe I should just continue powering the lights with power from my house?

    FYI, the driveway is heavily wooded, so powering the lights individually with solar is not a an option.

  8. #8

    Default Re: Solar Driveway Lights

    Or, I could add a cheap inverter to my setup and use small CFL bulbs for each light. Do you have an inverter recommendation? And, should I use two 6v golf cart batteries, or a "deep cycle" with my setup?

    Thanks so much guys!

  9. #9
    Join Date
    Mar 2006
    Location
    SF Bay Area (California)
    Posts
    19,641

    Default Re: Solar Driveway Lights

    It all depends on your desires... Saving money, being lighter on the environment and such... Conservation (smaller lights, more efficient lights, even motion detector lights, etc.) is better all the way around.

    If it is for fun and/or personal education, by all means do the research and design. See what you come up with.

    We have a FAQ thread with lots to read. Both about specific solar projects (small, large, emergency backup, etc.) as well as lots of other sources of information regarding conservation and alternatives to generating electricity (solar thermal is frequently the best "bang for the buck" -- Although, many solar thermal projects are great DIY projects, they are usually plumbing in nature--leaking pipes, failing pumps, replacing tanks every ten years, etc. all make for lots of self education and use of personal time).

    Working Thread for Solar Beginner Post/FAQ

    -Bill
    20x BP 4175B panels (replacement) + Xantrex GT 3.3 inverter for 3kW Grid Tied system + Honda eu2000i Inverter/Generator for emergency backup.

  10. #10
    Join Date
    Sep 2006
    Location
    Willits, CA
    Posts
    5,401

    Default Re: Solar Driveway Lights

    I'd look for some LED night light bulbs, or candelabra base 1 or 2 watt bulbs (120Vac)
    http://tinyurl.com/LMR-Solar
    http://tinyurl.com/LMR-BigLug
    http://tinyurl.com/LMR-NiFe

    Grundfos 10 SO5-9 with 3 wire Franklin motor (1/2hp 240V 1ph # 214505 ) on a timer for 3 hr noontime run - Runs off PV
    Powerfab poletop PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe battery | 15, Evergreen 205w "12V" PV | Midnight ePanel || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT

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