Aaron Yarbrough

larry kidd wrote:It got down to about 20f last night and I never insulated or heated the batteries. Lost power about 2:30am took till about noon to get the cells warmed up to about 35f or 2c and got power back online. Spent the better part of the day after that wrapping the cells with heat tape for pipes and put insulation under and over , still need to go back and insulate the sides. Used 30 feet of heat tape with a 90w draw. It has it's own thermostat on at 35 off at 50 if I remember correctly.

That's good to know. I thought lithium batteries would just not charge at low temps. I didn't know discharging would be affected as well. My batteries are in the same insulated enclosure as my inverter and it seems like the inverter puts off enough heat to keep the battery above warm.

So, to give everyone some closure on this this thread I completed this project a couple of weeks ago (just in time to claim the solar tax credit). Here are the details:

I ended up replacing my Magnum charge controller/inverter. That decision ultimately came down to the relatively low inverter power output (4400 watts). I want to have the option to use induction cooktops in our home/cabin and in the guest cottage (Currently, both have propane ranges). I didn't completely math it out but I felt the cooktops combined with the convection oven and the HVAC systems systems would be too much for the Magnum inverter. The new Sungold inverter can output 10000 watts.

I now have two strings of modules  increasing my generation from 3.8 kW (12 modules) to 6.5 kW (18 modules). I ended with 6 extra modules (3 old(320W) & 3 new(400W))

While assembling the 16 kWh Lithium Iron Phosphate battery I broke one of the terminals on one of the EVE cells. I couldn't find a welder to reattach it so I drove to Houston (~200 miles) to pick up a replacement cell.  While I was at the warehouse in Houston I bought a fully assembled 15 kWh Lithium Iron Phosphate battery. This was a day after I had found out one my FLA batteries had a bad cell (See previous post) so the latter purchase was a bit of panic buy. It also seemed like a good opportunity with the volatile tariff situation to get a low cost battery and not have to pay shipping.

Here's a vlog from the upgrade project:


Addendum:

As projects beget projects I found myself with extra solar panels, an extra brand new Lithium Iron Phosphate battery(see above), some functional 6V FLA batteries,  and a used but perfectly good inverter/charge controller so I built a solar/firewood storage shed. And because I feel like I have to justify owning a chain mortiser (and more so because I like the aesthetic) I made it (hybrid) timber frame. I also have been wanting to play around with linear actuators so I installed an adjustable pitch racking system on the roof. Here are some vlogs from that project:

Beginning construction


There are some intermediary videos but here is the wrap up:


Next steps involve learning how to safely climb trees do a little surgical canopy pruning to provide to deshade the modules in the afternoon.

Thanks to everyone who commented for all of the tips and advice.



   

Jackie Lei wrote:Yes, LiFePO₄ batteries really are a big step up. I’m also planning to upgrade, I’m looking at a 16 kWh LiFePO₄ battery for my home loads. The price is surprisingly low, just a little over $1,200. A friend recommended this battery manufacturer to me since I’m not very familiar with LiFePO₄ products myself.

This is the battery I’m considering. Could you help me take a look and let me know if the lifespan can really reach 10 years?

I usually wait for Will Prowse to test and break down a battery before I buy it.

I am just south of Austin. I installed some cooling tubes about five feet deep for an earth sheltered structure. My results were not great. In the beginning, the air temperature in the tubes was pretty consistently in the mid 70s but once I started pulling air through they warmed up significantly. As summer wore on the base temperature in the tubes crept up into the mid 80s. Also, my run wasn't long (~25 feet) so I'm sure that was an issue as well.

If you're going to dig, I think you would be better served by building a walipini-like sunken greenhouse.

Fore reference, here's an explanation of how I built my cooling tubes:

David Baillie wrote: Lithium is a game changer as well as you can get full array production since they have low resistance to charging unlike lead and you don't waste time at the high voltage low amperage low production absorb stage. It has forced solar designers to change their ways as we now maximize panel numbers due to low panel costs as our first priority. On the down side you are usually best to repanel completely so you can maximize your strings and the all in one inverters are terrible at lead acid charging as they lack a proper 3 stage charging profile.

We woke up with no power a few weeks ago. One our 6V FLA batteries had a bad cell I think. Fortunately, I had recently received a lithium battery kit and was almost finished assembling it so we we didn't have to limp along for long. The difference between the FLA battery bank and the Lithium Phosphate one is amazing. We're still getting summer temperatures here(two months out from the winter solstice) and I'm running two mini splits, a convection oven, an induction cooktop two fridges and it seems like I can't run the battery out of power. Then with 2-3 hours of full sun it's back to 100% charge. I ordered more solar panels which I will still install but it definitely appears like the weak link of my system was my battery.

 

If the shed is on pier and beam blocking off the crawlspace to keep the wind out will help keep the space warmer.  

Is the shed foundation pier and beam? If so you could cut out the plywood subfloor to access the joist bays to put in mineral wool batts. It's not too tricky especially if the plywood was put down with screws.

John Carr wrote:
I should have mentioned that I'm in the northeast, only an hour and a half from the Canadian border. My water inlet pipe has to be down at about 5' to avoid freezing, so I'm hesitant to make an exterior housing, even if insulated. The water's coming in on the north side of the house so I have to battle the cold where it emerges from the trench.

I'm thinking of putting in a small 'basement' within the edge of the foundation (maybe 5'x5') that I can access through a trap door in the inside floor to turn off the water. But maybe this is not necessary? Otherwise I can just run it up from the trench through the soil, and maybe since it's within the perimeter of the foundation it's not in danger of freezing? I would just insulate the foot or so from the underside of the floor down a foot or two into the soil.

Our frost depth here is about 2 inches so hopefully someone with more cold climate experience will chime in. In a really cold climate I would run the water pipe below frost depth into the building footprint and stub it up in an interior wall.  

John Carr wrote:
how do I run the water inlet and septic outlet through the rubble trench foundation? Do I just put it among the rubble and hope it won't get crushed? Or do I need to build a small "basement" from concrete block or something to house the water inlet and outlet?

I would run a 3 inch waste water line through a piece of 4" pipe in the area around the trench to protect it.  For the water inlet you could do something similar but with a long sweep 90° elbow through the grade beam or build an  insulated exterior housing and run the water line in through the wall.

If you keep water away from your foundation(by having large roof overhangs, installing gutters, and grading  the landscape to move water away from the foundation) I think you will be fine not using geotextile fabric or drain pipe. I've installed drain pipe on the two rubble trench foundations I've done and I'm pretty sure it just gets crushed anyway. As an alternative to geotextile you might consider using burlap instead. It will break down eventually but should help initially to keep sediment out of your rubble trench.  Hopefully, by the time it the burlap is compromised you have the roof on and the soil around the site has stabilized so incursion isn't as much of an issue.