Solar iluminated advertisement

mi_cin
mi_cin Registered Users Posts: 8 ✭
in Off Grid Solar & Battery Systems #1
Hello guys,

I have another solar related question. I would like to build an independent LED iluminated advertisement. The led lights are about 200W. How do I configure a battery/panels set so it can work during Polish winter? The night is even 14h long... The lighting will work only during the night, so the batteries can be charged during the day.

Thanks
mi_cin
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #2
    Re: Solar iluminated advertisement

    I'd say "forget it".
    200 Watts constant for 24 hours is 4800 Watt hours. That's 200 Amp hours @ 24 Volts, meaning at least 400 Amp hour battery bank (think two parallel strings of four "golf cart" batteries: 220 Amp hours @ 6 Volt).
    Then to recharge it you'd need maximum panels because of the very short hours of sunlight in Winter. You are at about the same Latitude as I am: 52 degrees North. The Winter light gets down to a mere 6 hours around Dec. 21st, and much of the time it's cloudy. You could count on about 2 hours daylight. So you would need like 2800 Watts and an MPPT controller just for that 440 Amp hours @ 24 Volts.

    So you'd end up having to expand the bank to handle multiple days of no sun and expand the panels accordingly.

    Really expensive way to power a sign.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #3
    Re: Solar iluminated advertisement

    Conservation will be your friend here... Look at getting some good quality LED spot/flood lamps to light the advertisement. And keep the back ground (and or text) bright/contrasting colors (less light required to make a readable display if it is white/light colors vs lots of dark greens and browns).

    I would think you could get down towards 20 watts pretty easily (5 watt LEDs can be surprisingly bright). Now, with 1/10th the power requirements, an off grid power system makes a lot more sense.

    Also, you could look at traffic in the area of the advertising... Perhaps you only need lighting from 6pm to midnight and again a couple hours in the morning... There may not be enough traffic between midnight and 5 amp to be worth the power.

    And if the traffic is very light (10-20 minutes of no traffic in the middle of the night), you might even look at motion detectors.

    Lastly, the power system needs to be designed to avoid taking the batteries "Dead"--That will usually shorten the life of the battery bank dramatically (to 1 year or even a few weeks of useful life if taken dead). So, to account for periods of bad weather, you should have some sort of state of charge detector that allows the lights to be turned off automatically if there is not sufficient sun to keep the system charged. Note that "simple" voltage monitoring of lead acid batteries is not terribly accurate for determining state of charge--but may be "good enough" for your needs.

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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  • mi_cin
    mi_cin Registered Users Posts: 8 ✭
    #4
    Re: Solar iluminated advertisement

    Hi guys,

    Cariboocoot:
    The ad doesn't have to be illuminated 24/7. Just during the night. So I assume that if I want to cover the longest night at 21 Dec which takes 14 hours I will use 0,2kW * 14h = 2,8kWh = 2800Wh. It's 116Ah @ 24V. So when I make it double (in case of poor weather conditions) I will get 233Ah. So its almost half of your calculations for 24/7 running time.

    So can I count that I need also half amount of panels, so 1400Wp?

    BB.:
    Then, if I cut the LED power by half (what is possible) can I divide values counted above by 2?

    mi_cin
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  • Cariboocoot
    Cariboocoot Banned Posts: 17,615 ✭✭✭
    #5
    Re: Solar iluminated advertisement

    Short answer: yes. :D

    The amount of power needed is the load Watts multiplies by the time. If you only need the sign on half the day you only need half the power and everything scales down accordingly.

    The biggest problem is still the need for an over-sized array to provide enough recharging during the very short and often cloudy Winter days.

    I believe Bill was suggesting you use a standard sign which could be illuminated by even less Wattage supplied by more conventional CFL or LED flood lights.
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  • BB.
    BB. Super Moderators, Administrators Posts: 33,613 admin
    #6
    Re: Solar iluminated advertisement

    Yes, cutting power in 1/2 would cut the overall usage by 1/2 too...

    Regarding lighting. LED's tend to be focused more than other lighting (less light lost due to "floodlight effect". And understanding of how the human eye works. The eye is a "logarithmic" device. In other words, it is not like we perceive many physical things--For example a person that is 2x taller than the child next too him is a huge difference. For the eye, a 2x (or 1/2) difference in lighting is barely perceivable. A 10 to 1 difference is a large difference and the lower powered (or lighting effect) would be overwhelmed by a 10x brighter light/reflective surface.

    So--It is very easy to cut power usage by 1/2 with just less wattage on sign. Add the efficiency of LED lighting and good optics/reflector on fixtures, and you should be able to reduce power usage to near 1/10th pretty nicely.

    Given that solar power is expensive (roughly 10x the cost of off grid electricity vs utility power when you take all costs into account--battery replacement, the initial cost of hardware, etc.)), the extra work/expense to reduce the power used by lighting should be more than justified by the reduction in solar power used.

    If you can, try to obtain several different good quality LED fixtures and experiment with lighting on an existing sign (or in your yard) of your shop and see how it works for you (and other things, say if the sign is mounted high, try lighting from above rather than from below and see if the natural reflection of light improves the brightness to the eye (the "glossiness"/reflective properties of the material/paint/print surface will have an effect too).

    -Bill
    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
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