Solar Driveway Lights

mrnoobmrnoob Posts: 13Registered Users
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!
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Comments

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    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: www.solar-guppy.com/forum/download/voltage_drop_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.
  • mrnoobmrnoob Posts: 13Registered Users
    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.
  • BB.BB. Posts: 25,139Super Moderators admin
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    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.
  • BB.BB. Posts: 25,139Super Moderators admin
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mrnoobmrnoob Posts: 13Registered Users
    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.
  • mrnoobmrnoob Posts: 13Registered Users
    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!
  • BB.BB. Posts: 25,139Super Moderators admin
    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
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 6,440Solar Expert ✭✭✭✭
    Re: Solar Driveway Lights

    I'd look for some LED night light bulbs, or candelabra base 1 or 2 watt bulbs (120Vac)
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Driveway Lights
    mrnoob wrote: »
    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!

    If you still want to go solar, you'll first have to pick out the lights so you know how much your power requirements are. For instance 23 9 Watt CFL's comes to 207 Watts times 5 hours is 1035 Watt hours (not including power factor on the bulbs or consumption of the inverter and wiring inefficiencies). Based on that you'd need about a 300 Watt inverter to handle the bulbs and about 180 Amp hours (or more) of battery to supply the Watt hours. Then you'd need a 336+ Watt array to recharge the batteries. LED bulbs will draw significantly less power (but cost more), so see what you can find.
  • mrnoobmrnoob Posts: 13Registered Users
  • ggunnggunn Posts: 1,972Solar Expert
    Re: Solar Driveway Lights
    mrnoob wrote: »
    Thanks guys!

    So, from what I'm reading maybe I should just continue powering the lights with power from my house?
    From an economic standpoint, yes. If you have the grid available, chances are that by far the most bang for your buck would be to put in a grid tied PV system to offset your electric bill.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Driveway Lights

    2 Watts is better than 9!
    See if you can't buy one first, and try it out; in case it doesn't give enough illumination to suit. Some CFL's claim "as much light as 'X' Watt incandescent" but don't really perform that well. Sometimes the colour temperature is not acceptable either.

    Otherwise:
    2 Watts * 23 Bulbs = 46 Watts. Times 5 hours = 230 Watt hours.
    For that you can buy a very small, inexpensive inverter like a Samlex: http://www.solar-electric.com/sa150wa12vos.html (Not sure how well CFL would do on a cheaper MSW inverter - and you'll probably want to try other things on it. :D )
    And you're down to <40 Amp hours for a minimum battery bank size. You could even use a small AGM type like this: http://www.solar-electric.com/unbamo45agms.html
    Meanwhile, your panel size has also shrunk drastically:
    2.5 Amps @ 14.2 Volts - about 46 Watt panel.

    Basically this is another demonstration of how conservation pays off; reduce the load needs and you reduce the over-all system size. Doesn't matter what you use it for.
  • mrnoobmrnoob Posts: 13Registered Users
    Re: Solar Driveway Lights

    Awesome, Thanks Cariboocoot, great ideas! I guess my only question would be how to hook 14 AWG wire to the inverter.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Driveway Lights
    mrnoob wrote: »
    Awesome, Thanks Cariboocoot, great ideas! I guess my only question would be how to hook 14 AWG wire to the inverter.

    That would depend on how it's wired now. Probably "hardwired" into a timer or photo-electric control?
    You need to disconnect it from the main supply, possibly add a fuse (if none is in the system), and wire it to a "pigtail" with a plug end to connect to the inverter (if you use one of those with outlets).
  • mrnoobmrnoob Posts: 13Registered Users
    Re: Solar Driveway Lights

    Yeah, the lights are "hardwired" to a indoor light switch.
  • BB.BB. Posts: 25,139Super Moderators admin
    Re: Solar Driveway Lights

    LED Lamps do not have a good reputation for long life... I would suggest that you get a few different brands and models--And run them a few months.

    After a few months, pull the bulbs out and look for browning/blackening around the LED's themselves.

    LEDs and their constituents are very sensitive to heat and if the "bulb" has poor heat sinking, the LED's will quickly blacken and fail (or loose output). 500-1,000 hours is a long life for many of these LED's (nothing like the 50,000-100,000 hours usually claimed).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mike95490mike95490 Posts: 6,440Solar Expert ✭✭✭✭
    Re: Solar Driveway Lights

    CFL's often have poor cold weather starting . They may be fine in the summer, but when you get some frost, they may just flicker. And their starting current and power factor may need a larger inverter.

    Or just get some (15) 100' strings of LED holiday lights !! $5 or so on sale. about 5w pre string...
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • mrnoobmrnoob Posts: 13Registered Users
    Re: Solar Driveway Lights

    Thanks everyone for your help! I now have a better understanding and have diagrammed my project.

    6051220007_f961ed8376_b.jpg
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Driveway Lights

    Very good. Only two mistakes: you've grounded the (+) at the panel. Normally in DC wiring the (-) is grounded, the (+) is fused. Which brings up the second error; no fuse on the inverter.
  • Dr. StrangeloveDr. Strangelove Posts: 49Solar Expert
    Re: Solar Driveway Lights

    The positive ground is for cathodic corrosion inhibition. It's the same reason telco DC power is -48V. The standard EE practice of grounding the negative side is fine inside a small box, but when exposed to the elements, can lead to extreme corrosion of the positive potential nodes, proportional to the potential.

    I am unsure why so many solar power inverter/charge controller companies seem hell bent on only negative grounding. A 600V DC positive node - even a nick in insulation or unpotted wire nut, will oxidize quickly.

    Your schematic forgot to include a timer or switch to control the lights - put it on the DC side before the inverter to avoid standby power loss. Or go with a solar charge controller designed for lighting applications like a Morningstar SunSaver MPPT which has a built-in timer and load control when the battery gets depleted.
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Driveway Lights

    If you ground the positive side you fuse the negative. Since the vast majority of DC installs the world over use negative ground without any "cathodic corrosion" obliterating them in their lifetime that clearly is not a real-world concern.
  • BB.BB. Posts: 25,139Super Moderators admin
    Re: Solar Driveway Lights

    From what I understand, the positive grounding is not to protect the wiring,, but to prevent water pipes, gas lines, and other metal/underground stuff from being corroded if there is a break in the insulation--not to protect the wiring itself (wire would be cheaper to replace than a water service).

    For this installation, if a true sine wave inverter is used, typically with isolation from DC to AC circuits--then negative or positive grounding would not matter.

    Looking at how you are going to turn the inverter on and off, and the inverter efficiency at the power levels you choose--will be important.

    Large DC switches are expensive and running an inverter 24x7 even without loads, will waste a lot of power on a smaller system.

    Many inverters have DC inhibit lines which are around 12 volt signal current (low voltage, low current) and is an easy way to turn the inverter on and off (on and inhibit--Inhibit tends to draw a bit of current, but much less than when on).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mrnoobmrnoob Posts: 13Registered Users
    Re: Solar Driveway Lights
    Your schematic forgot to include a timer or switch to control the lights - put it on the DC side before the inverter to avoid standby power loss. Or go with a solar charge controller designed for lighting applications like a Morningstar SunSaver MPPT which has a built-in timer and load control when the battery gets depleted.

    I have this charge controller which includes a timer http://www.amazon.com/gp/product/B003V0AUGU
  • mrnoobmrnoob Posts: 13Registered Users
    Re: Solar Driveway Lights
    BB. wrote: »
    Looking at how you are going to turn the inverter on and off, and the inverter efficiency at the power levels you choose--will be important.

    Large DC switches are expensive and running an inverter 24x7 even without loads, will waste a lot of power on a smaller system.l

    Is there anything on the market that would allow me to put the inverter on a timer? I haven't seen an inverter with a timer. Since I only need power for 5 hours it wouldn't make sense to have the inverter on 24x7.

    In my diagram the charge controller (with timer) is connected to the panel and battery. How will the lights know when to turn off if they are connected to the inverter, which is then wired to the battery? Is the diagram wiring correct for a timer system via the charge controller?
  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Driveway Lights
    mrnoob wrote: »
    Is there anything on the market that would allow me to put the inverter on a timer? I haven't seen an inverter with a timer. Since I only need power for 5 hours it wouldn't make sense to have the inverter on 24x7.

    In my diagram the charge controller (with timer) is connected to the panel and battery. How will the lights know when to turn off if they are connected to the inverter, which is then wired to the battery? Is the diagram wiring correct for a timer system via the charge controller?

    It's a question of what inverter you choose and how much current it draws. Since this is a strictly low-Watt application, you won't be running any 2kW inverter with a potential 200 Amp draw. Something like a 150 Watt inverter is going to draw <20 Amps. It is therefore possible to switch the DC input directly, or control it with a relay. Possible control units include a timer: http://www.solar-electric.com/fldctico.html Or a light sensitive charge controller: http://www.solar-electric.com/sunsolligcon.html (uses the charging panel to determine darkness and turn on lights).

    You may be disappointed with the quality of your $32 charge controller. Just saying. :roll:
  • BB.BB. Posts: 25,139Super Moderators admin
    Re: Solar Driveway Lights

    You have to check the power requirements of the inverter vs the load output of the charge controller (typically anything over 10 amps is less common).

    For a nice TSW 12 volt 300 watt inverter (good for emergency backup power for radio, tv, computer), this one also has a low voltage input switch that you can connect to any 12 volt capable timer (like 'coot's first link).

    That inverter also has a "low power search mode" -- Basically turns on for a few cycles every second or two -- looking for >6 watts of 120 VAC load. When a load is found, the inverter turns on 100%.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • mrnoobmrnoob Posts: 13Registered Users
    Re: Solar Driveway Lights
    You may be disappointed with the quality of your $32 charge controller. Just saying.

    Why might I be disappointed with the charge controller? Quality? Performance? Lifespan?

    Thanks, coot!
  • mike95490mike95490 Posts: 6,440Solar Expert ✭✭✭✭
    Re: Solar Driveway Lights

    Just to stir the pot, you could add another 500' to your feed wire, and feed the light string from the MIDDLE, not the end.

    What does that do for voltage drop ??
    Powerfab top of pole PV mount | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
    || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
    || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

    solar: http://tinyurl.com/LMR-Solar
    gen: http://tinyurl.com/LMR-Lister ,

  • CariboocootCariboocoot Posts: 17,615Banned ✭✭
    Re: Solar Driveway Lights
    mike90045 wrote: »
    Just to stir the pot, you could add another 500' to your feed wire, and feed the light string from the MIDDLE, not the end.

    What does that do for voltage drop ??

    Adds 500' of wire.

    Although I've seen some DC-only installs that "loop" the wire back to the source - the way we do with water lines to maintain even pressure at all taps along the way. Probably not practical in this situation.
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