Here’s a photo of my DIY McGyver-style power wall:
This installation has grown bit by bit over time. I’m in South Africa and on a very tight budget. A few years ago when we had two to four hour power cuts three times a day a friend gave me a Multiplus 24/800/16 for my birthday. I had two 12V deep cycle lead acid batteries at that time (salvaged but still serviceable) so at least we had a a glorified UPS to keep the lights and TV on during the frequent blackouts.
Then, when I had a little more to spend, I replaced the lead acid batteries (now completely worn out) with a 2.8kWh LFP one. When some more money came in I added four PV panels and a SmartSolar. Later still I added a Phoenix 24/1600 inverter to power the fridges and freezers that we have. (We’re out in the sticks and we make one big shopping run a month.) The water pump for the rainwater harvesting and backup tanks (very necessary since we have municipal water one day a week if we’re lucky) also run off the Phoenix. This necessitated the addition of another 2.6kWh battery.
Both batteries are housed in the box underneath the power wall (normally covered with the lid standing to the left of it). The DB box on the right holds the DC breaker and surge protectors for the PV panels; the one on the left houses the AC breakers. The switch at bottom right is the KETO battery disconnector which houses two 125A DC fuses. The batteries are BlueNova 26V 2.8kWh LeFePO4 models.
The idea was to have enough power to significantly reduce our power bill (fridges, freezers and the TV are a major component of our monthly usage) and to be resilient against power failures since the national infrastructure is being held together with sticky tape and paperclips. To save money I installed everything myself. Yes, I did the homework to make sure it’s done the right way, and while I am not a licensed sparkie I do have a background in electrical engineering, I do know the difference between AC and DC, and I have had basic training as an electrician when I was still young and good-looking. So I’m confident that the installation is safe.
I’m using the AC Input Control settings on the Multiplus to supplement power from the grid if the PV panels don’t get enough sunlight. Through a lot of measurement and some trial-and-error I have worked out at what clamping voltage the batteries have dropped to about 30% SOC, at which point the Multiplus begins charging and switches the TV, the kitchen fridge and the lights from the inverter to the grid. At 10 amps charging current this just keeps the SOC at 30-40% until the panels provide more power. At 80% SOC the Multiplus stops charging and switches back to inverting mode. I figure this is the optimum to maximize battery service life.
Note that the Multiplus appears to calculate the SOC by integrating its own charging current and inverter output over time. This works well if the Multiplus is the only device connected to the battery, but with a SmartSolar and additional Phoenix inverter in the mix this goes right out the window, so switching AC Input on and off by voltage is the only option. Judging the SOC by the clamping voltage of the batteries only is of course not 100% accurate, but for my purposes it’s good enough and I can’t justify the expense of a Cerbo and Smart Shunt. I’ve had this running for several months now and it works quite well.
I’m about to add a relay box with a timer to switch the water pump at the backup tanks to the inverter during daylight hours, and to the grid between sunset and sunrise. (Except when there’s no grid power, in which case the relay will automatically revert to inverter-only mode.) The box is still sitting on the table in front of the battery enclosure but hasn’t been mounted yet. The reason for this relay is that if we want to run the dishwasher and have a shower in the evening the pump is just a little to much and drains the batteries to a point where the charger kicks in at around four in the morning.
This illustrates the main drawback of using the Multiplus AC Input Control settings for grid supplement power: it’s either on or off and there’s no way to charge proportionally to keep the batteries at a certain SOC. The batteries will be charged at whatever charge current settings I have put in, but only stop charging when the SOC is at around 80% (judging by voltage). This means that sometimes, if the gods of sunlight and electricity are particularly unhappy with me, it is possible for the charger to kick in early and charge the batteries from the grid to about 80% SOC during the night, so that by sunrise the batteries are almost full and I’m not getting a lot of cost savings out of my PV panels. It is also possible for the batteries to be drained to 30% SOC and then for the grid power to fail, in which case I will have to hook up my trusty old generator set. However, spreading the loads sensibly and playing with the Multiplus charging current settings (still an ongoing process) can go a long way to optimizing everything.
I fitted the SmartSolar with a fan (an aluminium enclosure containing two laptop cooling fans powered by the salvaged laptop power supply mounted below the SmartSolar) because on sunny days the case gets far too hot for comfort. I’m not quite happy with those fans; they’re too noisy. I also mounted the MK3 dongle against the wall. (The Multiplus doesn’t have Bluetooth.) I’d like to replace it with a VE.Bus Smart Dongle, but I can’t justify that expense for what is essentially just a luxury. Plugging in the laptop also works, and I’ll make do with what I have.
So anyway. Here’s my McGyver-style power wall. I’m moderately proud of it and quite happy with the way it does the job. 
Bummer.