Just curious how everyone's solar and/or batteries did/is doing during this last freeze. I'll start. Mine didn't.
Let me preface this by pointing out I am heating and cooling about 4,000 sf and of that about 3000 sf has 10 ft ceilings. So, if you compare to typical 8 ft ceilings and go by cubic feet it's closer to 5000. That's a lot to cover with the size system I have. (System size in my signature.)
Last Saturday night it only got down to around 35 degrees but when I got up my batteries were down to 16%. With predicted temps in the mid-teens and little sun I realized this is not going to work. So rather than fight with it I just switched everything back to grid. My thinking was run it all on grid with the whole house gen as primary backup. Then get my batteries back to 100% and let them sit there as secondary backup. This turned out to be a good decision.
The two worst days here were Monday and Tuesday. I used 160 kwh and 180 kwh respectively. Any solar contributions would have been a drop in the bucket. Now, I know I'll get some of the typical responses about such massive usage but reference the square footage I'm heating above. It just takes a lot of BTUs, even with a very efficient home and heat pumps. From my perspective it wasn't bad. Last year during the Jan '23 freeze and similar conditions my usage was 230 kwh on the worst day and I wasn't heating the garage then, which is another 440 sq ft or thereabouts. The Mitsubishis get all the credit on that reduction - I'll circle back to that.
This was my first winter freeze since switching most of the house over to solar so it was definitely a learning experience. What did I learn? Not really anything I wasn't expecting but perhaps still a wakeup call. If I ever truly wanted to be close to off grid I'd need to add more panels and a LOT more batteries. My little 60 kwh bank doesn't even come close. While I could certainly lower the thermostat and do some other stuff to cut my usage quite a bit, I don't see any way to get down to a level that would allow the current system to cover my needs. I was already planning on bumping the batteries up to 120 kwh. Now I'm leaning towards mimicking
@timselectric's plan and going closer to 200 kwh. I wouldn't even consider this if it weren't for the ongoing drop in battery prices. I'm starting to think it's doable. It likely still wouldn't carry me through a cold spell like this one, but it would get a lot closer.
The other part of the equation is production. Let's face it - when it's cloudy all day for days adding a bunch more panels may not have much of an impact and there's certainly an issue of diminishing returns on that investment. I do need to add more, if only to cover the summer needs. I was close to covering the needs in the summer, even when it was over 110 F. So I'm still thinking adding another 7k or so of panel production would be a good move. The negative is the only place I would be willing to add them is the north facing roof of the shop. Even though there is little slope on the roof, in the winter those panels are going to be anemic in production.
Back to the heat pumps. I was once again impressed with the Mitsubishi. Not only because the consumption was less but they kept the house toasty throughout the freezing temps. Last year we had some 10 year old Luxaire units that ran 24/7 and still the bedrooms wouldn't hold above about 62 degrees. This year the house stayed around 72 degrees and the garage was at 70 with very little in the way of problems. I did see a drop Wednesday morning when it was still 16 degrees on one of the units for about 3 hours. I talked to my HVAC buddy who installed them and we decided it was likely in a heavy defrost cycle. That seems likely since it eventually recovered, but it was warming up outside at the same time so I'm not 100% sure on that. Even during this the inside temp only dropped about 4 degrees in the bedrooms serviced by this unit. I'm gonna call it a huge win on upgrading to the high efficiency heat pumps.
Other than that, we didn't have many issues. I had a hot water line freeze up but I managed to get it thawed and re-wrapped then let the water drip. Also had a line freeze that supplies water to one of the pastures but it didn't burst so I got that thawed and did a little work on insulation so hopefully it's good. I still haven't switched back to solar since it's supposed to be cloudy and back down in the 20s at night Friday and Saturday nights. If it's okay with y'all, I'm done with freezing temps for this winter. Spring can come along anytime now and I'll be happy!
One other note on my batteries. I've had a problem with two of them not getting back to 100% for months now. Something like 87-88% and only three lights on the panel. With them sitting idle and soaking for a few days they are all back to four lights. I need to hook up my laptop and see what the actual level of charge is, but the float charge seems to have helped them.
I feel like DIY solar is still a little bit of the wild west and we're all learning as we go. I can't help but think the time, effort and money we're all putting into it now will only help us and others going forward.
So how did you do during the freeze? Any good stories? Any suggestions or comments?
Stay safe and stay warm out there.
