Originally Posted by mike
We currently have 2 13-watt CFL bulbs and 2 50-watt heated dog dishes.
The lights are used mostly in winter and would be on max 4 hours a day, the dog dish would be on all the time in the winter. I understand the dishes may be a bit much so they could be left out if a small system could not handle them.
Been away at a wedding so sorry for getting back late.
PD pointed out that the dishes are out for a small system. 2.4KW is a mid sized for off-grid.
I'll do the calc but am basing them on an assumption that the 4 hours is to extend the daylight hours so the chickens will lay more in the winter.
First thing I recomend is to look for some 12VDC lights. They would allow the use a o lighting controller in place of the charge controller and eliminate the need for an inverter. 12VDC CFLs can be found on EBAY.
You will have to rerun thes calcs if the new lights take more wattage.
So 2 - 13W lights for 4 hours.
that's 2 * 13W * 4H = 104WH (WattHours) Load
Now we need to calculate how much your panels need to produce. Most will say 104WH but they forget that nothing is 100% efficient. With off grid
about 66% is normal for a PWM controller and 75% with a MPPT controller.
So 104WH * 1.5 (66%) = 156 WH daily average need produced.
Now divide that by the amount of insolation available. Get the lowest number from above which is December at 1.15 hours.
156WH/1.15H = 135.65W You will need a solar panel of at least 135 watts. A little larger like 150W to 165W would be ok just don't go too far over or that may cause other problems. At 135w you will have excess power in all but the winter months. Also you want one with a VMP of 18V +/-1V.
So first calculation on the battery size. a few things to note about batteries with solar is that you shouldn't use more that 20% of there capacity in a day and should never go below 50% discharge. I now in boats people go past that alot but figure they are only using them a few weekends a year where you'll be using them daily. Be nice to them and they will last.
So we need to divide the Daily WH by the battery voltage then muitply by 5 so we only use the 20% a day.
156WH / 12V * 5 = 65AH minimum on the battery. That would give you2.5 days of usage before they hit the 50% level.
There still is one other thing to check on the battery. They have minimum and maximum charge rates. Typically for lead acid they are between C/8 and C/15 with a preference of being close to the middle. C = AH capacity of the battery. Best to check the spec of the battery manufacture.
So what you need here is to take the amperage of the solar panel and divide it into the AH of the battery. So a 135W 12VDC panel would typically have a VMP of about 8A.
So 65A / 8A = 8.125 and 65A / 15A = 4.33. So your within range with a 65 AH battery. Most marine deep cycle batteries are in the 75 to 100AH range so the would work good. But also remimber that if you over size the panel much abover th 135 you will need to go bigger on the battery.
Just a note that AGMs can be charge up to C/4 but I don't recomend them for beginning systems as this is to be a learning experience and you should use a battery that will teach you how to maintain them.
The charge controller need to be larger than the panel output. I usually oversize them by at least 25% to account for any highlight conditions. Solar panels are rated at 75dF and do puty out more power at colder temps.
So right on the edge of a 10 Amp controller being a little to small. If you can't find a 12 to 15 amp lighting controller a 10 amp will work but might get a spare one just in case.
One can put a bypass switch around the load side of a lighting controller to use when you enter the coop and need light besides the time it allows it. This is the style of controller I'm talking about
. Other's do make them.
So in review your 3 main componets are:
135W 12V panel (min)
65AH battery (min)
12-15A lighting charge controller
I think one should be able to put this all together for about $400 to 600.