Solar Chicken Coop

[Dave Duerksen]

I am very new to Solar energy. I have been reading and doing some calculations. We have a pretty good sized coop that has about 70-80 chickens in it. I would like to get it off the grid so save on our electricity bill in the winter time. Maybe even eventually do a grid tied system for the farmhouse. I am an electrical engineer so I understand the power side of this quite well. Here are a few details of what we have been using for heat/water de-ice items the last couple winters.

5 - 150W heat lamps 24hrs/day
1 - 200W water container heater base
1 ~ 1500W water tank heater (miniature donkey water)

I really think we could get away without having the heat lamps running 24 hours a day maybe 8 or so. The water icing up is a bigger problem than the heat. The chickens are very hearty in the cold as long as we don't get down in the teens at night. In fact this last winter we never had to use the water heaters. Had a little bit of ice problems but not serious. Last winter it was a lot colder for about 2-3 weeks, that's when we bought the heaters. The Donkey heater was the only one we used. So all that said to ask this?

PS: I also would consider a small wind generator to help out with the cloudy days. We have a pretty decent breeze/wind in Kansas.

From online calculators (wholesale solar) I have come up with 300W panel wattage for 8 hours a day for 6000 Wh/day usage. The thing I haven't figured out is how may Ah of batteries I need. I think I need the inverter efficiency to know how may amps are coming out of the batteries. I am using most of my power at night when not charging. I understand you want no more than 50% DOD and probably more like 70% DOD for lead acid batteries. The calculator says I get 5.33 annual avg sun and 3.83 winter avg. I really think that is a little low but conservative is good. If you can point me to a place to read about this it would be great.

[Rob Beckers]

Hi Dave,

I wrote an article about sizing grid-tie and off-grid systems that could help (it also discusses battery bank sizing): https://www.solacity.com/how-to-size-a-solar-system-that-really-works/

In a more general sense, we tell customers that any time they are turning off-grid electricity into heat they are doing something wrong. It's just too expensive to "waste" like that (and too hard to make in the first place).

Your mention of a single 300W panel producing 6 kWh per day in winter doesn't sound right. Our sun hours over here are not much different from yours (you're sunnier in summer), and a 300W panel produces around 0.4 kWh per average winter day, and double that in summer.

Hope this helps!

-RoB-

[Dave Duerksen]

Hi Dave,

I wrote an article about sizing grid-tie and off-grid systems that could help (it also discusses battery bank sizing): https://www.solacity.com/how-to-size-a-solar-system-that-really-works/

In a more general sense, we tell customers that any time they are turning off-grid electricity into heat they are doing something wrong. It's just too expensive to "waste" like that (and too hard to make in the first place).

Your mention of a single 300W panel producing 6 kWh per day in winter doesn't sound right. Our sun hours over here are not much different from yours (you're sunnier in summer), and a 300W panel produces around 0.4 kWh per average winter day, and double that in summer.

Hope this helps!

-RoB-

I haven't had a chance to read your article yet. Thanks for your comments.

Why do you say it is a waste? In my case I am trying to remove a pretty high cost each month during the winter from our Westar utility bill. The bill is paid by my mother-in-law who is on a fixed income. Our farm doesn't really make that much money to cover those expenses. If I can afford a system to remove that bill then her utility bill will go down in the winter. Eventually I would like to look at a grid tied hybrid system for the house so that we can offset costs in the summer as well.

The system size estimate came from wholesale solar (offgrid-calculator (https://www.wholesalesolar.com/solar-information/start-here/offgrid-calculator)). I did see a problem in my entry of things. I entered 5 - 150W heat lamps for 8 hours a day. The problem was I didn't reduce the sun/hours for winter time. If i enter 3.83 rather than 5.33 hours I get a 2.44 KW system size rather than 1.76 KW system size.

[Rob Beckers]

Dave, alright, let's put some numbers to this and calculate it:

5x 150W heat lamps = 750 Watt, for 8 hours a day = 8 x 750 = 6000 Watt-hours = 6 kWh per day. You're also going to run an inverter, so add 0.5 kWh for that as well (they use power too).

Total energy needs per day = 6.5 kWh

You mention in winter you have 3.83 sun-hours per average day, which is actually pretty decent! Keep in mind that this is for panels mounted at a specific angle, facing south, and with no shading.

With that number we can calculate how much 1 kW of solar panels will produce per average day:

Energy = sun-hours x efficiency = 3.83 x 0.49 = 1.88 kWh/day

The efficiency factor of 49% is a pretty solid average efficiency number from panel to AC, using an MPPT charge controller.

So, to produce what you need, the overall panel size will be:

6.5 kWh / 1.88 = 3.46 kW of solar panels

If you use 300 Watt panels, that works out to 12 panels. These are real-world numbers.

Now, on the battery side the normal sizing is for 3 days of autonomy (no sunlight). In practice this gives you more than 3 days because even overcast days produce some energy. There will be times in winter when this falls short though, and unless losing power is no problem you will need a generator.

Storing 3 days of 6.5 kWh, with the batteries at 50% (and nothing coming in) works out to 6.5 x 3 x 2 = 39 kWh in energy storage in the batteries. For a 48V battery bank that works out to:

39,000Wh / 48V = 813 Ah @ 48 Volt

Let's put some parts to the problem to get an idea of cost:

12x decent 300W panels, at $0.82/Watt (in CAD dollars) = $2,952
1x Samlex PST-1500-48 inverter = $810
1x Outback FM80-150 charge controller = $847
16x Rolls/Surrette S-550 batteries (makes 48V 856Ah) = $6,704

Then there's lots of small stuff like battery interconnects, inverter cables, solar wiring, combiner etc.

Total = CAD$11,313 = USD$8,442 (plus any tax you have locally)

Please keep in mind that this system will not meet electrical code (neither in Canada or the USA), if it is going to get inspected you will need other components, adding quite a bit to the cost.

I don't know what your electricity cost is over there. Here we pay around $0.20 per kWh. Based on that the 6.5 kWh per day would cost right around $40 per month. Say you need to run this 6 months out of the year, that makes $240 per year.

Simple payback time therefore becomes:

$11,313 / $240 = 47 years... (and I'm ignoring the 13% sales tax we also have to pay here).

I'm also ignoring that after 10 - 12 years you're buying your batteries all over again. They are an ongoing cost (a consumable).

This is why I said that any time you are turning off-grid electricity into heat you're probably doing something wrong...

Almost anywhere on this planet off-grid electricity is WAAAAYYY more expensive than what you pay to your local utility. I don't know of many places where off-grid is a cost savings vs. grid-tie.

That said, there most definitely IS a payback for a net-metering (grid-tie) system using solar panels in many places. If your local jurisdiction allows for it. Usually that is the better way to go if you want to save on your electrical bill.

-RoB-