Solar Sculpture help

Db1966Db1966 Registered Users Posts: 3
I'm working on a metal sculpture that includes an old fashioned street light. My plan is to convert it into a solar LED street light. I've chosen a 50 watt corn LED that will screw into a standard light socket. Below the light is a bench, on the bench sits a large metal robot. Inside the robot will be a flame LED (4 watt) and two blue candelabra c7 bulbs (.5 watt each). All LEDS will turn on at dusk and run off battery power and turn off at dawn, battery recharges.

My questions...

What sized battery is recommended? 6V or 12V? I'm thinking a Lithium Ion...thoughts?
Do I need a 12v to 110v power converter to go from the the battery to the LED's or will the charge controller handle that job?

Any recommendation on a charge controller would be helpful as well. 

And lastly, what sized solar panel can I use that will mount on top of the street that will be small but charge the battery enough?

Thank so much to anyone that can point me in the right direction.


  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    edited February 2 #2
    Welcome to the forum DB.

    Working with solar power, you need to be as conservation minded as possible. And with lighting, the way our eyes work, a 50 Watt vs 25 Watt (otherwise identical LED lamp) is almost impossible to see the difference. So, you may be able to reduce the power usage by a factor of 2 right there.

    Some of the more modern LED lights run at low power (1/3 to 1/10 of full power?) and when a motion sensor is tripped, the light goes to full power--Another method to save energy.

    With LEDs, color temperature and LED design can dramatically affect the apparent lighting intensity. Corn Cob lamps--I am not sure that they are in the top tier of efficiency... And many of the cheap corn cob lamps are driven to fairly high levels (fewer LEDs at with more power--save money on LEDs) and "cheap LEDs" (like T 1 3/4) have very poor heat dissipation (LEDs and phosphers get hot and turn dark in a few hundred hours) vs some of the newer surface mount LEDs with heat sinks (some folks even use copper heatsinks).

    Lastly, there is the efficiency of the LED driver circuit.... LEDs are low voltage (typically around 2-5 volts) but they need a circuit to control the amount of current flow through them. Cheaper installations simply may use a resistor. More expensive (and more efficient/stable switch mode current sources) circuits can be much more efficient.

    The Candle Power Forums is an interesting place to look around. LEDs and driver circuits. Directed mostly towards flashlights, but lots of low power/high lumens/etc. LED and small battery discussions.

    My suggestion is to get a bunch of different LEDs and driver circuits. Experiment to get the effects you need. Then use something like a Doctor Watson DC Amp*Hour/Watt*Hour meter to measure you usage (lots of new meters out there today).

    And figure out how much energy you need (Watt*Hours per day, Amp*Hours at XX Volts per day, etc.). And design a system that will support it.

    On the other side, you can estimate how much energy you can generate with solar... For example, say the largest solar panel you can mount is a 20 Watt panel. And you will be installing near Phoenix AZ with fixed solar array:

    Average Solar Insolation figures

    Measured in kWh/m2/day onto a solar panel set at a 57° angle from vertical (added. -BB):
    (For best year-round performance)


    And you design a system that turns of the LEDs if the battery is discharged. The amount of energy you can harvest would be (long term average) for January would be:
    • 20 Watt panel * 0.61 DC off grid system eff * 4.92 hours of sun (ave January day) = 60 WH per day
    • 60 WH per day / 12 volt battery bus = 5 Amp*Hours per day
    If you want the light to run 10 hours per night, the MOST on time from 1 day of January harvest would be:
    • 60 Watt*Hour per day / 10 hours = 6 Watt average load.
    Anyway, that is how I would start.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Db1966Db1966 Registered Users Posts: 3
    Bill thank you so much for all of that information! Seems like I need to rethink my system a bit before I go any further. And here I thought I could simply hook up some leds to a battery and be good.
  • mcgivormcgivor Solar Expert Posts: 3,020 ✭✭✭✭✭
    Look towards 12V LED lights, keep wattage low, 50 w is a significant load which would require a fairly large battery to power overnight, <10W ~6000K (daylight ) LED 's provide impressive lumen output, they are commonly available at 12V . Once lamps are selected then sizing of their needs can be addressed, remembering keeping wattage low will reduce the overall costs, staying with 12V further reduces cost as no inverter is required. 
    1500W, 6× Schutten 250W Poly panels , Schneider MPPT 60 150 CC, Schneider SW 2524 inverter, 400Ah LFP 24V nominal battery bank 
    Second system 1890W  3 × 300W No name brand poly, 3×330 Sunsolar Poly panels, Morningstar TS 60 PWM controller, no name 2000W inverter 400Ah FLA 24V nominal used for water pumping and day time air conditioning.  
    5Kw Yanmar clone single cylinder air cooled diesel generator for rare emergency charging and welding.
  • BB.BB. Super Moderators, Administrators Posts: 29,359 admin
    You are very welcome DB.

    Setting your expectations is a good start.

    Yes LEDs and batteries are a good start... But if you plan on changing the batteries out every 7 days (take back to the shop and recharge), that is different then "letting the sun" recharge them for you--And planning on your energy budget, etc.

    And you have to look at the "real specifications" / actually do the measurements.... A "50 LED bulb" may take 50 Watts, or it may take 9 watts and be the "equivalent Lumens" of a standard filament bulb.

    If it is a true 50 Watt bulb, a 20 Watt panel will only support 50 Watt*Hours per day:
    • 60 WH per day available energy / 50 Watt load = 1.2 hours nominal in January with a 20 Watt panel.
    Good luck!
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • Db1966Db1966 Registered Users Posts: 3
    Sounds like I need to get rid of the 50w, thats easy as it was only on the list and not purchased. And the street light I'm using won't be used as an actual street light in the sense that it's being used more 'artistically' so it doesn't need to be as bright as a regular street light. I'll look into the <10W  6000K
  • littleharbor2littleharbor2 Solar Expert Posts: 1,377 ✭✭✭✭
    Look for LED lighting with warm white light color. The cool white can be harsh and in the bluish color range. Here's a retro Edison style Led bulb in warm white, found on eBay.

    2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old  but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 700 ah @24 volt AGM battery bank. Plenty of Baja Sea of Cortez sunshine.

  • mike95490mike95490 Solar Expert Posts: 8,340 ✭✭✭✭✭
    is your lighting running 120VAC or 12VDC ?
     If you need 120VAC, look at the small but efficiet Suresine 300w inverter from MorningStar solar. it's not cheap, but rock solid. And if you have long cable runs, you have to go with 120VAC to reduce losses in the long lines.
    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

    gen: ,

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