Solar panel and battery requirements

I'm feeling pretty stupid these days. This should be a pretty simple problem but I keep getting different answers depending on the time of day, what I'm drinking at the time, and which online calculator I use.

Basically, I have a 65 watt 110v LED bulb I want to run as a dusk to dawn street light. I figure at the height of winter I might have 6 hours of usable daylight and 16 hours of darkness. I figure at most 3 cloudy days in a row. How much solar power and how large a battery bank do I need?

My calculations have ranged from a 100w panel and a 160 Ah battery being way overpowered to needing 5 100w panels and 300 Ah of battery.

Anybody want to take a crack at it?

Thanks in advance.

Are you sure you are quoting the 65 watts using the actual draw and not the output equivalent?

That sounds really high for an led light.

If it's the actual draw, then I'd personally go with a better led. The reflector design is the most important part, you can get massive light from a small led driver with the reflector lense properly focused.

It would prob be cheaper than going the other way and needing more storage and panels.

They make actual lights with solar, a battery and a lense focused for lightpoles all in one sealed unit.

Sorry can't help on solar needs.

First of all, a 65 watt LED runs you less than 15 watts, so your battery requirements are far less than for a conventional bulb.

a reply to: VictorVonDoom

65 Watt * 16 h * 3 = 3120 Wh energy

You get Ah by dividing Wh by battery Voltage

And as mentioned already a 65W LED will consume about 10-15W

Best way to save energy is to not use energy. Have you suggested using wind power for winter season? There are also windy times during summer, you can take advantage of that.

They should do a combo between wind and solar power. That would be one of the best energy.

a reply to: makemap

AGREED. You can buy a solar powered LED security light on Amazon for $30-$40, that will charge even on overcast days and provide you with near 450 lumens. I have one mounted on my shed in my back lot and it's bright enough for my needs and stays on the entire night, until dawn.

originally posted by: Mandroid7
Are you sure you are quoting the 65 watts using the actual draw and not the output equivalent?

Yeah. I have a pair of 250w bulbs on telephone pole. The pole is rotting out at the bottom and I'm getting too old to climb it. My nephew got a couple of 30 ft. fiberglass street lamps that I'm going to use. I have power at the old telephone pole but I want to install the other street lamp about 100 ft. away and I'd rather not dig a trench if I can avoid it.

The LED bulbs I'm using are 250w equivalents drawing 65w.

originally posted by: makemap
They should do a combo between wind and solar power. That would be one of the best energy.

Drop a heat pump into the ground and you'll be using the four major elements.

originally posted by: makemap
Best way to save energy is to not use energy. Have you suggested using wind power for winter season? There are also windy times during summer, you can take advantage of that.

They should do a combo between wind and solar power. That would be one of the best energy.

I considered adding a wind turbine to the system, but then I've got the extra expense and work of adding another pole for the turbine. Including the added work of securing the turbine for storms or hurricanes. If I have to go through all that I would just a soon dig a trench and run power to the lights.

originally posted by: shawmanfromny
a reply to: makemap

AGREED. You can buy a solar powered LED security light on Amazon for $30-$40, that will charge even on overcast days and provide you with near 450 lumens. I have one mounted on my shed in my back lot and it's bright enough for my needs and stays on the entire night, until dawn.

I want to use these to light up my whole back yard, which is over an acre. I don't think the small kits are going to do it.

originally posted by: moebius
a reply to: VictorVonDoom

65 Watt * 16 h * 3 = 3120 Wh energy

You get Ah by dividing Wh by battery Voltage

And as mentioned already a 65W LED will consume about 10-15W

Yep, that's what I figured on the high end. Taking into account inefficiencies and not wanting to deplete the battery I figure I would need 500w of solar panels and a 300 Ah battery for just one bulb. And I'd be lucky if it lasted 10 years before I had to replace batteries and panels.

Looks like I'll be renting that trench digger and running wire.

a reply to: VictorVonDoom

65 watts is way to high should be less than 30 for 250 watt led equivalent. I used one that draws 27 watts for an outside pole. I bought 150W Off-Grid Solar Panel Kit for 280.00 and it works just fine.

PS it works out to 450-Watt Hours or 37.5 Amp Hours of charge per day.

a reply to: VictorVonDoom

There is a calculator at this site.

Will you be using light sensors to turn them on and off?

Sizing Your Battery Bank

The exact math for sizing your battery system is based on your daily power usage and the battery type. Based on usage of 10kWh per day, here are some examples:
Lead Acid Sizing

10kWh x 2 (for 50% depth of discharge) x 1.2 (inefficiency factor) = 24 kWh
Lithium Sizing

10kWh x 1.2 (for 80% depth of discharge) x 1.05 (inefficiency factor) = 12.6 kWh

Battery capacity is specified either in kilowatt hours, or amp hours.

For example, 24 kWh = 500 amp hours at 48 volts → 500 Ah x 48V = 24 kWh

It’s usually a good idea to round up, to help cover inverter inefficiencies, voltage drop and other losses. Think of this as the minimum battery bank size based on your typical usage. You may want to consider 600-800 amp hours of capacity, based on this example, depending on your budget and other factors.

Battery banks are typically wired for either 12 volts, 24 volts or 48 volts depending on the size of the system. Here are example battery banks for both lead acid and Lithium, based on an off-grid home using 10 kWh per day:
For Lead Acid, 24kWh is equal to:

2,000 amp hours at 12 volts
1,000 amp hours at 24 volts
500 amp hours at 48 volts

originally posted by: dragonridr
a reply to: VictorVonDoom

65 watts is way to high should be less than 30 for 250 watt led equivalent. I used one that draws 27 watts for an outside pole. I bought 150W Off-Grid Solar Panel Kit for 280.00 and it works just fine.

PS it works out to 450-Watt Hours or 37.5 Amp Hours of charge per day.

See? This mistake I made on coffee.

The bulbs are 54w, not 65w.

www.ebay.com... ao%3D1%26asc%3D20160727114228%26meid%3D58948ca969ed4a27b2c3b0a3a7e3700f%26pid%3D100290%26rk%3D1%26rkt%3D4%26sd%3D182531170123%26itm%3D182531170123&_tr ksid=p2060778.c100290.m3507

And, of course, I would need an inverter and a charge controller. The lamp posts I'm using have built in photocells (more current drain). I think solar power for these is just not going to be practical for the winter.

winter temperatures affect battery capacity (lead acid especially) unless they are situated in a
favourable temperature, inside from the elements. all batteries I installed were winterised with
2 inch insulation (kingspan-type) inside a double box with inner on slideout.

below freezing these batteries really struggle to sustain capacity if they are out in the elements.

a deep gel-thixotropic seemed to have improved the lead acid/temperature issue. most batteries I
currently utilise are around the 300-400 amp range.

if you cobble a system together on the cheap, always check second-hand batteries by examining
the plates whilst donning a set of safety gigs. buckled plates indicates the battery has been drawn hard
and fast and will be of no value pdq.

I am currently planning a stand alone system of 14 monocrystalline panels and 1600 amps initially lead/acid
to run a 12 volt led chain with inline blade fuses. radio and charging and inverter 1000w non-pure sine-wave
(cheaper and less robust) to allow use of small hand tools up to 700w.

have you considered a 12 volt system to cut out the inverter and consumption?

f.

I have a 65 watt 110v LED bulb

first problem is you are going to need a inverter or a lot of batteries.

better way is to find ether a 12 or 24 volt LED light system'

www.harborfreight.com...

batteries that are the best for a system like that would be www.renogy.com...

you will also need a LiFePO solar Charge Controller

a reply to: VictorVonDoom

Don't feel stupid. The amount of misinformation flying around these days is pretty high when it comes to energy. But, here's the real scoop:

ETA: Check the addition at the end; I got a little hurried in my calculations.

First of all, you have already spec'd your bulb to 54W, 120VAC. First of all, the power supply in the bulb is not transformer based, so it specifying 50 Hz instead of 60 Hz is meaningless. Don't concern yourself over that detail. All you need is 120VAC in that frequency range, so you will need an inverter. Your wattage is only 54 watts, so a small 100-150W inverter is plenty, and square wave works very well for LED lighting... in other words, you need a very, very cheap inverter to run this bulb. Not so if you plan on using the power for other things besides lighting, now, so recognize that limitation. You can probably use one of those cigarette lighter plug-in jobs.

I tend to figure an inverter efficiency at 80%... typically a little conservative for a square wave, but at these power requirements it's not that big a deal. So you are transforming 12VDC to 120VAC RMS, for a 10:1 voltage increase. That means you will need 10 times the current that is withdrawn, divided by the efficiency, which comes to 12.5 times 1/2 amp, or 6.25 amps of 12VDC power. A single 12V automotive battery will provide about 50 Ahr of power, so that comes out to 8 hours of power. Those ratings are at high current draw, so it should be safe to extend that to 10 hours.

You can drop that 80% and go with straight battery power if you drop your voltage down to 12VDC (possible with LED lighting). You'll also save on inverter cost, since you won't need one. But... from a quick search, the bulb style you spec'd may not be available in 12V. You may have to go with a different bulb arrangement. I don't know how that would affect your end use.

The problem comes in when you have 6 hours of daylight and 16 hours of darkness, and want to design for three cloudy days. There are two ways to look at this:

If you design for cloudy days to still provide enough power to keep the light running, you'll need two batteries in parallel. That will give you about 20 hours with absolutely no power input. The downside is that you will need to increase your solar panels to provide about 4 times the theoretical power needed. If you go with panels designed for 12V charging (about 15VDC output), you'll need 15V times 6.25A times 4, or 375 watts of solar panels. (See below) There may be days when it is overcast enough so even that isn't sufficient, but normally a solar panel will put out 25% of its rating even on cloudy days.

If you want to design for no power during those three days, you'll only need ~100 watts of solar panel (see below)... but your battery needs will skyrocket. Three days is 72 hours, plus the additional 16 hour night means you will need to run for 88 hours without charge. That's 9 standard 12V lead-acid batteries in parallel. You might get by with 8, since even the smaller panels will provide some power during overcast days, but anything less than that will bring you up short.

If it were me, I'd with the former arrangement; batteries are quite expensive. Regardless of which you choose, but especially if you do go with the latter, make sure you diode-protect each battery to prevent one having a dead cell from killing the capacity of the others. Since you're only drawing a little over 6 amps, you can use 6-amp diodes which are not wallet-killers (35 cents each at that link). The current draw will not necessarily be equal all the time between the batteries, so it's a good idea to use diodes heavy enough to handle full current draw, but at the same time, 6 amp is close enough to 6.25 so the chances of overloading the diodes is slim at best.

Make sure your solar panel either has a built-in 12V lead-acid charge controller, or you'll need to get a separate charge controller. The cost shouldn't be too terribly bad since at most you are only looking at 375W. (see below)

ETA: In my haste to reply, I forgot the time differential. You are charging batteries for 6 hours and discharging for 16 at 6.25A. Your charge rate will need to be much higher to compensate for this, on the order of 16/6 or 2.667 times. That works out to a solar panel wattage of around 1000W for two batteries, or 300W for eight. This will not affect the isolation diodes, since they will not be in the charging circuit.

Any other questions, just ask. In the meantime, good luck with your project.

TheRedneck

a reply to: TheRedneck

That's a lot of good information. Much appreciated.

After thinking it over, I'm going to dig a trench and run the power line to the pole. But that doesn't mean I'll be giving up on the solar idea. I'm thinking of going with some sort of grid tie system. I think a 100w panel and a 160 Ah battery would probably be self sufficient in most summer months, and I can always add to that. In the winter and cloudy days, the inverter can kick in and keep the battery charged and the light on.

I couldn't find a 12v 250w equivalent bulb. I'm tempted to disassemble one of the bulbs I have to see if I can modify or replace the driver circuit to work at 12v, but I have too many other projects to worry about that now. In any case, just replacing the 250w metal halides with the LEDs should save me some money.

Again, thanks for the input. If you want to jury rig something, you can always count on a Redneck.

a reply to: VictorVonDoom

If you want to jury rig something, you can always count on a Redneck.

That's why we make good engineers!

The grid-tie system is probably a better idea from my understanding. Just remember, the set-up is more expensive using grid-tie: your have to have a true sine wave inverter designed to follow the phase of the grid. But in the end, if your concern is saving money, it's probably the best route we have for now.

Incidentally, I couldn't find a similar brightness bulb at 12VDC either. If i got really crazy, I'm sure I could find a supplier somewhere that could scrounge up a few, but that could also take days. Just not worth it IMO.

One tip: when you do decide to put in the grid-tie system, allow for future expansion. Get the biggest inverter you can afford and a separate charge controller that can handle multiple panels of varying wattages. The ability to charge multiple banks of batteries with different priorities is a nice plus for expansion too. It'll cost a little more initially, but in the end it will save you money and headaches as solar advances.

Finally, beware of the DIY guys on this one! I have seen so many vids on "How to get rid of your power bill using solar yourself!" that accomplish this, apparently, by burning down the residence, that I lost count. Safety counts! Electricity can be a wonderful servant, but it must be tightly controlled or it'll make a terrible enemy. If in doubt, ask a professional. One of these days I am going to finish the book I started on how to safely and realistically live off the grid... one of these days.

TheRedneck

Solar panels are very important for the use of solar light, so how do you generally choose solar panels?