Never been one to let the carrier drop

I wanted to write a little bit about what I’ve chosen to do for my solar battery bank because I think that the popular approach is less safe than what I’m doing.

Note that I am running a 12 volt system – but you could use this same approach for higher voltages. You would need to have breakers or fuses for midpack string equilization as well if you did. Feel free to ask me about this.

What I’ve done is first put a fuse on the positive terminal of every battery – this is a marine fuse, direct attaches to the battery post. Then I have 2 10 AWG wires going from each battery to ground, and 2 going to the battery breaker for that battery. Each battery has a 40 amp breaker.

The intention here is that if a battery were to get severely out of balance, it’s breaker would trip during charging because it would get a unreasonable amount of charge current. Every month or so I check to make sure I have no tripped breakers.

Beyond that, if a battery were to have a short circuit fault in it’s BMS, the fault current would be limited to what that battery could supply. I have seen many people advocating 4/0 or bus bars between batteries in 12 volt systems and I think this is potentially quite dangerous – especially in a large pack such as mine. (I have 12 280 AH batteries, for a total of 40kW of stored energy – if each battery contributed 250 amps of fault current, this would make for a eye popping 2500 amps.. I would be pulling bits of battery off the ceiling, not to mention that would be a very difficult arc to quench)

I would like to encourage DIY solar folks doing a battery bank to consider using my approach (many little wires, one breaker per battery) rather than the more popular (big bus bars between batteries) approach.

So, finally after many months of slowly nudging the project along, my solar lithium battery boxes are done. I’ve done a load test with a space heater, and nothing other than the space heater got even remotely warm. I am feeling victorious 😉

There’s many little bits of the project left to do – I need to hook up something to maintain the old lead acid pack, in case I decide to use it for something, I want to add lighting to each battery box, and a alarm light, and of course the battery box heaters – which are already in place and all the wiring is pulled for, but I need to connect up the relays and drill a hole for the 110 cable to go into one of the boxes.

But, still, I am running off the lithium batteries. This is a major milestone.

So, earlier in the year, when COVID was just starting to ramp up and also when coincidentally I was in the midst of about as manic as I let myself get these days, I – in perhaps a moment of unreasonable paranoia – decided I wanted a backup generator. Except, I wanted a backup generator that would actually be useful if social unrest or other issues resulted in gasoline being difficult to get. (Not that many gas stations have backup generators, so even just a city-wide blackout could the cause this, and we’ve certainly had our share of blackouts since moving to this house, including one !5-day! outage)

So, I did what seemed the most reasonable thing to me at the time, which was buy a bunch of solar panels, some lead acid batteries, and a couple of big inverters.

It has been working pretty well – my basement’s been running off it since March, I think, and I haven’t run out of power yet – however, at the moment the panels are just lying in the front yard. If my math is correct, this is only giving me 30% of the power i’d get if they were on a two axis tracker.

So, I’ve been slowly working through various designs to try to figure out how I want to do tracking with them. I’d like to do something cheap-ish and DIY, and I’m fine with the east/west axis being manual but I want the RA axis to be automatic. I was pondering something like a drawbridge with a winch, but lately I’m again favoring the idea of using a couple of large bearings (I like the idea of using wheel bearings and wheel hubs from a car for some reason) and a gear motor. But it may change designs again. I’ve been suffering from a certain extent of laziness surrounding it. Some of my problem is that I am not really that great at using 3D modelling software – I really need to sit down and learn, but I’m not really sure which software I want to use. I am increasingly thinking I need to buy a desktop application for this as I tried using several different web based solutions and all of them had serious performance issues. I do not think 3D modelling is really something that’s well suited to being a web app, especially in the post-flash world. Of course, maybe part of the problem is just my lack of 3D modelling skill..

Anyway, winter is coming, so I should probably put a little more effort into this. It’s easy to generate enough power to run your basement in the summer in Seattle.. we have very long sunny days. The winter, with it’s very short, cloudy days, is likely to be a good deal more challenging.

One thing that is very sasisfying about having thrown together a solar array – beyond that it worked on the first try and I was able to easily set up a raspberry pi to track energy in and out of various things – is that I can use it to charge my EV. Whatever wars we get up to over oil are therefore that much less my fault. It’s possibly the most effective protest of the US war machine I’ve ever come up with.

So, i’ve decided to stop waiting for the government to make some sort of ‘green new deal’ happen and put my money where my mouth is. It also helps reduce my paranoia to know that I will have backup water and power supplies if the government (who provides both things in the city of Seattle) experiences some sort of outage or other difficulties. So, I’m putting out 3.5kW divided as 1.6kW of monocrystalline and the rest amphorous (the idea here is to make power in both sunny and cloudy conditions). Realistically I expect to see maybe 1kW output except high noon on the brightest parts of summer, but that is still enough to keep my fridge and freezer running, and I can also add a grid intertie inverter to reduce my power bills when I’m not using the array for backup power or to charge my electric car.

I’m also putting in 10kW of backup energy storage, which can be charged either via the grid (I’ve got a 40 amp charger) or via the solar array. I will likely also experiment with solar towers and solar tracking. Those of you who know me know I often have hobbies-for-a-year – this is my hobby for 2020.

I am also adding numerous rain barrels to store rainwater and a 12 volt pumping system that can be used to pressurize my pipes via a water filter from the rainwater, as well as some 12 volt emergency lighting.