diy solar

diy solar

Help with off-grid cat colony

cayz

New Member
Joined
Dec 28, 2021
Messages
5
Location
Delaware
Good Afternoon.

I'm "new" to the whole solar power "thing", although I've been a veteran tinkerer for decades. But, I've come up with a real head scratcher, and before I throw more money at things, I'd like to get the opinion of this group...

This is what I have - A 10x10 shed, with several nooks & crannies (like litter box corner, cat tree corner, and the Cattic. No hookup to power. Literally in the middle of a farmer's field
Needs:
1) Provide a small night-light above litter box corner - when it gets dark, you can't see your hand in front of your face if you are in the shed. The cats need SOME light - 5W?
2) Provide Human Lighting when the volunteers show up to clean, feed & water. In at least 3 locations (Litter box Corner, Cattic, Main Room). Enough to see clearly.
3) Power my Solar Heating Fan (this *should* be a wash, but more on that later).
4) Battery MUST be sealed (AGM) - no out-gassing, least susceptible to fire, etc. The shed is no where near humans, so SAFETY is the biggest concern.

The problem is that #1 needs to run up to 13 hours a day during the depths of winter, and #2 for an hour or two per day.
And, as is typical for the NorthEast USA (I'm in Delaware), there may be 4-5 days of no appreciable sunlight in a row.

#3 - Solar Heating - this is a simple system that should not draw down the battery charge at all - a painted-black box has a temperature probe inside it. Once the temperature reaches 80, it turns 2 fans on (one in the box (push) and one at the end of 15' of duct work to a 1 gallon water jug in the shed (pull). Once the temperature in the box goes below 70, it turns the fans off. My thinking is that the only way the box will get hot is if the sun is shining brightly, which should give me enough amperage to provide power to fans. And yes, it works very well - I actually have to have a cut-off so when it hits 80 inside the shed, it turns the system off. 80degrees in the shed, 30 degrees outside.

Given just the "Needs", do you think I should be able to do this on a single 12v battery?

I'm going to post in the first comment what I currently have, and maybe someone can answer why it doesn't work.
 
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Ok, so given all of that, this is what I've cobbled together, but it still doesn't last more than 2 days, which I really think I must be missing something here...

Renology 100W panel - angled around 60degrees, pointing south, at the far end of the "property", which is in full sun. 40' 10ga wire running to:
Epever 30A MPPT controller, EPever Elog01 and MT50, so that the volunteers can snap me a photo of the MT50 when there is a problem, and the Elog01 gives me historical data.

Battery: Die Hard Marine Battery, Group 31M, 825 CCS, 100 Ah. Purchased July 2021.

Load Side:
2 digital timers: https://smile.amazon.com/gp/product/B012FSL2GK - each using <2 W
____Timer #1 turns on Litter Box Lights at dusk, off at dawn - I re-set the timing quarterly.
________18inchs of LED tape. 18 LEDs.
____Timer #2 turns on the HVAC - in the Winter, it turns on the Solar Heating System
________2 Inkbird thermostats: https://smile.amazon.com/gp/product/B019I3YCFS (each <3W)
________2 Computer Fans but only when sun is shining - (each < 1 amp)
Mechanical 1-hour timer feeding "Staff Lights" - https://smile.amazon.com/dp/B01M0I7F3I - so a volunteer comes in, turns the timer all the way around, and gets 1 hour of light. Most of the time, they are done in 1 hour. I'm usually there longer, so I twist it around a second time (2 hours / day).
Oh, the Epever MT05 and Elog are also "Load" items. I would hope they are low power usage.

The MPPT is set up with AGM 100Ah settings, with the default settings - it lets the battery discharge to 11.1V (temp compensated) before dropping the load. It won't restart the load until the power is over 13.2 (I think that is what RaisRcv is). The control parameters are attached.

It can charge the system within 60 minutes from a load-off situation - I've seen it pushing 15+V @ 5+A on a bright sunny day, but I'm thinking it is charging it too fast, or maybe not to the proper level. What I'm seeing recently is the Battery State of Charge going from 100% when it is sunny out, to 45% within 10 minutes once the sun goes back in, according to the Epever Elog.

When I first got the battery, the SOC would go from 30%-50% during the day (this is when I first got and installed it in July '21), but within a week, it was getting fully charged (100%), but dropping to 60% overnight.

Now that I'm writing all this, and getting all of the data into one place - does it sound like the battery is performing the way it should?
Is there a better battery that I can get that won't break the bank?

Thanks.

James
 

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  • ControlParameters.txt
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OK, a few thoughts from someone running small AGM systems:

1: a 100w panel is nowhere NEAR enough. Go read through My Napkin Math Thread and see what I've found there. The short of it is that 200w of panel couldn't compensate for the cloud cover and a 5w draw, and I added in a 200w panel in parallel to my 100w panel for my 7w driveway lights. You're going to need a LOT more solar to top off the batteries every day. Add up your wattage and hours so you know how many watt-hours you need per day, then divide that by how many hours of average sun you get, then double that (or triple) for weather and imperfect sun angle.

The MPPT is set up with AGM 100Ah settings, with the default settings - it lets the battery discharge to 11.1V (temp compensated) before dropping the load. It won't restart the load until the power is over 13.2 (I think that is what RaisRcv is). The control parameters are attached.
2: With AGM and FLA batteries, anything lower than 12.1v is damaging the batteries, at 11v you're destroying them inside. There's something wrong with those parameters if it's letting you go down to 11v.

3: Are you aware that with FLA and AGM batteries you can only use 50% of the listed Ah? Anything less than 50% (or 40% on the really top-of-the-line golf cart versions) will damage the batteries quite quickly and you'll lose capacity.

When I first got the battery, the SOC would go from 30%-50% during the day (this is when I first got and installed it in July '21), but within a week, it was getting fully charged (100%), but dropping to 60% overnight.
That's a combination of not enough solar panel (only getting 20% recharge in a day) and damaged batteries (not holding the charge), and you've seen that here too:
Battery State of Charge going from 100% when it is sunny out, to 45% within 10 minutes once the sun goes back in,
If it's dropping that fast then the batteries have been damaged beyond repair. If you were to drop in another battery in parallel you would nerf the whole system as the bad battery is going to control all the charging (Battery SOC, voltage) but the new guy is going to be doing all the work (it has amps still) but never getting charged. As an example, when I added in the 200w panel to my driveway lights it topped my batteries up right quick, and then they died that night. I got less than 2 amp hours out of the 15Ah batteries I had in there because I had nuked my batteries with low state of charge damage.

So,
1: do the math or rig a shunt and figure out what your total watt-hours usage is per day.
2: Get a LOT more panel involved
3: Dump the battery and get a few new ones installed in parallel.

If you know what your actual watt-hour usage is, that will tell you how much solar panel and battery you need. If you can get that number to us we can help with all the mathing. A basic shunt/meter is like $40 or less on Amazon and is a really useful tool to have.

And #4, the MOST IMPORTANT THING OF ALL!!!! Bring out more wet food human! :)
 
Hey, Thanks @Rednecktek for all of the info.
1) I had tried to get the amount used a couple of years, but I think I bought the wrong thing:
DC Power Monitor - https://smile.amazon.com/gp/product/B017FSED9I - it only gave me the instantaneous usage.
Would the logs from the Elog help? Again, I'm a tinkerer, and Comp-Sci, but not EE, so...
Is there a better recording device you would recommend?

2) The Renology panel is 5 years old; is it likely due to be replaced? But, as I said, I had several times in the 6 months when I was getting 80+Watts. Even in December, I was getting 30W of power. I don't know if that is "good" or "bad", and if bad, is Renology still the best? Are there "almost as good" ones at a cheaper price (this is a cat colony, not a palace - all this will be out of my personal pocket.... )

3) Getting two 12V and running them in parallel, like - to - to input -, + to + to input + (24 V)?

3b) Did I make a reasonable choice for the battery? I had had a local-brand Group 31 Marine Battery that finally died in June 2021
(Hmmm, shortly after I put the new MPPT system in to replace a blown PWN in Dec 2020)...
But, as much as I cringed when I bought the new MPPT system (~$200), the batteries are Real killers - $250 each.
Any recommendations for "good" ones?

3c) It does sound like I have the parameters all wrong for the MPPT... Was getting the Epever MPPT a bad choice? I followed the defaults, since I didn't know any better...

4) And yes, the cats love the Solar Heating System - in addition to keeping the water from freezing, I store about a week's worth of canned food in the in-shed "Hot Box" (insulated milkcrate with the duct running into it, a 1gallon waterer, and 2 stacks of wet food). So, not only does the heat system warm up the entire shed, but their wet food is often "toasty" (the outside heat generator can reach 150deg!). They LOVE their wet food all heated up!
 
Hey, Thanks @Rednecktek for all of the info.
1) I had tried to get the amount used a couple of years, but I think I bought the wrong thing:
DC Power Monitor - https://smile.amazon.com/gp/product/B017FSED9I - it only gave me the instantaneous usage.
Would the logs from the Elog help? Again, I'm a tinkerer, and Comp-Sci, but not EE, so...
Is there a better recording device you would recommend?
I've never worked with the Elog, so I have no idea what it's going to tell you. What you're looking for is an average watt usage, usually over a week or so to make sure the numbers even out and you can get an accurate average. What I see a lot of people using is A Battery Monitor and AiLi is the most common version used, but they're all the same pretty much. It's cheap and should do the job and I hope some other people can recommend other versions that are cheap as well. The big key is to have accurate usage numbers. The napkin math may say 400wh per day, but when you throw a shunt on there and find out it's actually 520wh/day, well that extra 120Wh is like 10Ah which is 20% of your battery's usable capacity!
2) The Renology panel is 5 years old; is it likely due to be replaced? But, as I said, I had several times in the 6 months when I was getting 80+Watts. Even in December, I was getting 30W of power. I don't know if that is "good" or "bad", and if bad, is Renology still the best? Are there "almost as good" ones at a cheaper price (this is a cat colony, not a palace - all this will be out of my personal pocket.... )
A lot of people see Renology as a dying company, but them, HQST, Rich Solar, etc are pretty much all the same panels so it doesn't really matter as long as your VoC is about the same as to not piss off the charge controller.
3) Getting two 12V and running them in parallel, like - to - to input -, + to + to input + (24 V)?
Parallel you add the Amps, Series you add the volts. With the MPPT controller you can throw 360w on there, but you should be fine with 4 of the 100w panels. The big key is to not push the MaxPV Input Voltage of the controller with the VoC of the panels. Most 100w panels are about 20v-ish VOC, so 4 in series would be 80-ish volts. If you had the physical ability (roof or mounting frame shape) you could make a 2s/2p setup facing one pair east-ish for morning sun and another pair west-ish for afternoon sun. Yes, you'll make a little less power at one time, but you'll be making it for LONGER time, no net gain.
3b) Did I make a reasonable choice for the battery? I had had a local-brand Group 31 Marine Battery that finally died in June 2021
(Hmmm, shortly after I put the new MPPT system in to replace a blown PWN in Dec 2020)...
But, as much as I cringed when I bought the new MPPT system (~$200), the batteries are Real killers - $250 each.
Any recommendations for "good" ones?
The battery choice was fine, it's how the poor things were abused by being under charged (not enough solar) and over discharged (below that 12.1v limit) that really hurt them. I've heard a lot of good things about the Costco 6v golf cart batteries being a good cost/usable amp hour so that might be worth looking into. Unfortunately with the freezing temperatures you get out there, LiFe's aren't really a cost effective option. :(
3c) It does sound like I have the parameters all wrong for the MPPT... Was getting the Epever MPPT a bad choice? I followed the defaults, since I didn't know any better...
Nah, EPEver is a decent mid-tier brand so no faults there. I suspect that the AGM Pre-set is designed for the ultra-heavy-duty-golf-cart-industrial batteries that can take the hit easier, and your bulk and float voltages are probably right or real close enough, it's more the setting for the LOAD port cut-off voltage. You can always download the manual and set up a manual charging profile and set where the LOAD ports shut off. Not usually difficult, just a little time consuming, but once it's done it's done forever.
4) And yes, the cats love the Solar Heating System - in addition to keeping the water from freezing, I store about a week's worth of canned food in the in-shed "Hot Box" (insulated milkcrate with the duct running into it, a 1gallon waterer, and 2 stacks of wet food). So, not only does the heat system warm up the entire shed, but their wet food is often "toasty" (the outside heat generator can reach 150deg!). They LOVE their wet food all heated up!
Wait, they get WARM wet food!!! Spoiled! Don't tell my cats, they might go on strike. :)
 
One thing you can do is head over to my How Low Can You Go thread and play around with the JRC site. It's a fill-in-the-blanks thing where you input your array size, Watt-hours load, battery bank, etc and it'll give you a graph showing how many "dead battery days" you'll likely have with your system. Then start playing with the panel wattage and battery capacity until you don't have any more of those "dead battery day" bars. There are a few examples in that thread to give you a reference as to what you're looking at.
 
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