Solar panels system for lighted sign off grid

easytim · June 2010

I'm wanting to build a solar system with batteries to run an electric sign off grid.

The LED sign draws 5.53 AMPS and runs on 120 V I want the sign to run for hours or 14 hours off grid each night. That's 608 watts being used for the LED sign per hour being used.

I live in St. Louis, zip code 63016. I know this will be costly but this is exactly what I want to do, no matter what the cost.

Its almost like running a toaster in the middle of the woods every night for 14 hours.

Can somone please tell me how big of a system will I need. I have some idea, but I'm not sure about a lot of things. It's a lot of power to need everyday, even during the winter months. The charge time in December is very short and I will need a large system to make my charge in 3.5 hours or 4 hours of useable sun light charge time..

If someone would steer me if the right direction it would surely help, Thanks

What will I need to make it all happen

Cariboocoot · June 2010

Re: Solar panels system for lighted sign off grid

The simple math answer:

608 Watts * 14 hours = 8512 Watt hours.
(Or four times what my whole cabin uses.

)

How do you get that much power out of PV? Not easily.
The up side is the fixed load of less than 1000 Watts. The downside is the time you need to supply this for. At 24 Volts you'd need 354+ Amp/hrs *2 (at least) = 708 Amp/hrs. That's a lot. Then you have to charge it, which calls for at least 35.4 Amps of current @ 28.8 Volts = 1020 Watts, minus the usual derating would be approximately 1275 Watts of panels. So that's 6 or 7 big panels ($4000) plus a charge controller ($150) and a lot of battery ($2500 worth) and a small inverter ($450). Total: $7000 and change.

This is not a precise solution to the question, just a rough idea of what you're in for.

Still sure you want to do it?

icarus · June 2010

Re: Solar panels system for lighted sign off grid

Simple(est) math for off grid systems. Take the name plate rating of a system, divide by 2 to account for all system/battery charging loses, multiply that number by 4, the number of average hours of "good" sun. (Seldom can one expect more than 4 on any annual basis)

Using Coot's calc, 8500wh/4=2150*2=4250

So you would need ~ 4000 watts of PV and batteries. That said, you would need ~ double that to allow for some reserve. So, 8 KW of PV, off grid might cost say $8/watt installed for a grand total of ~$64,000 Even at that, you are going to have to count on replacing your batteries every 3-10 years, depending on what batteries you buy, at perhaps 1/3 the cost of the total system, say $21,000.

Good luck and keep in touch,

Tony

Kamala · June 2010

Re: Solar panels system for lighted sign off grid

What kind of LED sign is this. LEDs are intrinsically low voltage DC devices. You might gain some small advantage by trying to modify the sign to run directly from DC, but I don't think it will be enough to justify the cost. Marc and Tony have it pegged.

I will say that your 608W is a little off. 5.53A @ 120V is 664W. Over 14H this becomes 9.3KWH. Lets call it 10KWH.

You are certainly in the scores of thousands of dollars to make this a sustainable system.

K

easytim · June 2010

Re: Solar panels system for lighted sign off grid

Yes, I'm going to do this.

I should ask for more of a break down on exact sizes of things, I want to make sure its a go for sure,I far as I can see yes,yes,yes.

BB. · June 2010

Re: Solar panels system for lighted sign off grid

Using the PV Watts website, assuming 1kW of solar panels (even number), 0.52 overall system efficiency, fixed array near St. Louis Mo:

"Station Identification"
"City:","St._Louis"
"State:","Missouri"
"Lat (deg N):", 38.75
"Long (deg W):", 90.38
"Elev (m): ", 172
"PV System Specifications"
"DC Rating:"," 1.0 kW"
"DC to AC Derate Factor:"," 0.520"
"AC Rating:"," 0.5 kW"
"Array Type: Fixed Tilt"
"Array Tilt:"," 38.8"
"Array Azimuth:","180.0"

"Energy Specifications"
"Cost of Electricity:"," 7.0 cents/kWh"

"Results"
"Month", "Solar Radiation (kWh/m^2/day)", "AC Energy (kWh)", "Energy Value ($)"
1, 3.60, 59, 4.13
2, 4.22, 61, 4.27
3, 5.09, 78, 5.46
4, 5.40, 77, 5.39
5, 5.67, 80, 5.60
6, 5.83, 78, 5.46
7, 5.86, 80, 5.60
8, 5.50, 75, 5.25
9, 5.33, 73, 5.11
10, 4.83, 72, 5.04
11, 3.53, 52, 3.64
12, 3.02, 48, 3.36
"Year", 4.83, 835, 58.45

So, depending on the season, you get between 48 to 80 kWH per month per 1 kW of solar panels. Assuming you want 14 hours per night at 10kWH in December:

10 kW per day * 30 days * 1/48 kWH per month per 1kW array = 6.25 kW of solar panels

So, 14 hours of light in winter (you would still have days of bad weather which the solar system will not keep up) you would need 6,250 Watts of solar panels.

Battery wise, we typically say 3 days of no sun and 50% maximum discharge for longer life, assuming 48 volt battery bank:

10,000 WH of load * 3 days * 1/0.50 discharge * 1/48 volt bank = 1,250 AH of 48 volt batteries

If you have utility power available--you could do it with grid tied power... For about 1/4 the price of hardware and no battery maintenance.

Out west, we do have solar powered signs... But they tend to use much less energy and probably only operate a few hours per night. Conservation would be your friend here.

-Bill

AntronX · June 2010

Re: Solar panels system for lighted sign off grid

Are LEDs used to simply light the sign or there are moving graphics processors involved? If there are only LEDs, then you need to rewire LED's to run directly on 48V DC. This will save you 30 - 50% of solar panels and batteries. Are you concerned about theft of equipment? Roughly, without modifying the sign, you will spend $10,000 on panels and batteries alone.

mike95490 · June 2010

Re: Solar panels system for lighted sign off grid

easytim wrote: »

I'm wanting to build a solar system with batteries to run an electric sign off grid.

The LED sign draws 5.53 AMPS and runs on 120 V I want the sign to run for hours or 14 hours off grid each night. That's 608 watts being used for the LED sign per hour being used.....

YOW !! 600W of LED's !
Do you have to wear welding goggles near the sign? SPF 50 ?

Thats 8.4KWh for a 14 hour run. x6 for the battery size, for 3 days running to 50% discharge in winter, low light hours. A 50KWh battery is needed, @ 48V, that's 969Ah of battery. Call it 1,000amps for easy math.

For recharge, you need to have enough solar to 500a x 1.5 in a 4 hour day. That's 187A @56V for recharge, or 10,472w of solar PV, and about 4 charge controllers to manage it.

Sure you can't run an extension cord to it?

System2 · June 2010

Re: Solar panels system for lighted sign off grid

I thought that LED's were supposed to "sip" electricity, not guzzle!

I think that AntronX is on to something. LED signs do not have every diode constantly ignited; there are complex programs controlling a system in which various diodes are constantly firing. From a distance, the lovely sight of scrolling text appears.

I can't imagine that any diode in the average side-of-the-road LED sign has spent more than half of it's life "on." If this is the case, the required wattage may end up being a lot less than 600W.

icarus · June 2010

Re: Solar panels system for lighted sign off grid

LEDs do indeed "sip" electricity. It just seems that the OP is planning on using a S*#T load of them.

Tony

BB. · June 2010

Re: Solar panels system for lighted sign off grid

Also an issue of the right tool for the right job...

LED's, CFL/Florescent, Metal Halide, high pressure sodium, etc. all are very efficient (lumens per watt).

The dividing lines are how are they used (area lighting, or point source like in a sign) and color (white light with "red filter" vs red LED)--all affect the end power requirements.

-Bill

Solar panels system for lighted sign off grid

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