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DIY Offgrid Solar

DIY solar with battery backup – up and running!

Update

As of 5/13/2021, I have everything up and running! My DIY solar system with battery backup has produced 5.9 kWh over the last few days. It has been very wet and rainy this spring here in the Front Range of the Rockies and I don’t think we’ve had a full day of sunshine in a couple weeks. In terms of dollars, that 5.9 kWh is worth $0.649. Not much, but knowing I can power the whole house for 6 hours (based on average consumption) is a pretty good feeling. Check out my last post for some detail on how I got the battery bank set up – DIY Solar System with battery backup update.

Battery bank

The battery bank has performed great so far. I am in the process of doing a full discharge test. These cells did each come with a discharge test sheet from Battery Hookup, all showing more than 260Ah (most around 262Ah). Total for the batteries was $1082.

8x260Ah LiFePO4 cell battery bank ready for BMS

Under discharge in the flat part of the curve, the cells are extremely close in voltage. Below is a screenshot of my BMS app (XiaoxiangBMS, which is a super handy app. the fastest I’ve ever spent $6 on the pro version of an app) showing minor discharge current and the cells are within 6 millivolts of each other. It really doesn’t get much better than that.

BMS app (I am not creative enough to name my BMS the U1timatron) showing closely matched cell voltages during discharge

BMS

The BMS is a JBD 8s 100A model I got from eBay that comes with bluetooth monitoring ability. It has worked flawlessly so far. I love it when technology just works. Every setting can be configured. It keeps track of every alarm event. And best of all, it was only $68.

JBD 8S 100A Battery monitoring system (BMS) keeping tabs on my LiFePO4 cells
BMS showing a modest discharge. I’ve taken it to 1200W so far.

Inverter

The all-in-one inverter (inverter, battery charger, MPPT solar controller) is a MPP Solar LV2424 hybrid model. Everything works as expected. I’ve tested all the features successfully. I even got the monitoring software going. The main downside so far to this inverter (and I think this is common) is a relatively high idle power consumption. The BMS reports ~56-60W draw with the inverter on and nothing plugged in. The “idle” power draw decreases as a proportion of the total load on the inverter but it never drops to 0. For example, at 0 load, the inverter draws 60W. At 120W load (based on a questionable Kill-A-Watt), the inverter is drawing 160W, meaning the “idle” power dropped to 40W. This inverter was $665.

Inverter mounted above the battery bank. The solar breaker is to the left.

Solar panels

My $100 each solar panels from Craigslist have been hooked up on and off over the last few days. I haven’t seen more than 480W from the 2 of them combined but they are laying completely flat (they should be tilted towards the sun for maximum power). Overall, happy for the price. I need to get them mounted on the roof.

The main testing location on the south side of our house. They’re basically flat, maybe tilted a degree or two to the south. I haven’t seen more than 480W from them (rated for 2×310=620W) yet but they were cheap so I’m not too disappointed.
Inverter showing the panels putting out 26W on a very cloudy day recently. It has apparently decided that 73V was optimal for whatever conditions were present.

What’s next

My DIY solar system with battery backup is commissioned! Things are functional. Things aren’t located optimally. I need to get the solar panels mounted on the roof and do some tidying around the batteries/inverter. I plan on mounting some drywall above the battery cells to protect from whatever and covering up all the battery terminals. The rear of the cells are covered. The mains are covered. Some of the intermediate terminals are not.

I’m already looking on Craigslist for more solar panels, but I need to 100% finish this project before adding on to it according to my lovely wife (I am sure some of you know exactly what I’m talking about!). With that, I’ll be signing off for the night. The baby is having a very hard time falling asleep tonight. Until next time!

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