After coming up with a plan for energy reduction and eventual back-up, the actual planning got underway. In terms of the electrical system, I had to figure out a way to the the installation in a scalable manner. Best to get the bulk of the preparation work done up front, rather than doing a lot of modifications later.
The Electrical Design
The “final” plan for the electrical system looks like this:
Following a lot of comments on forums and doing a fair amount of research, I decided on a Hybrid solution for the PV installation. This will allow for energy production via solar, use of batteries for backup, coupling a generator at a later stage and use of the grid without the option to feed back to the grid. Grid feedback was a brief consideration, but with the regulations being unclear at this stage and the likelihood of it costing more to export than it’s worth, that idea was quickly scrapped.
My choice of inverter was a 4kW/5kVA Hybrid with built in MPPT charge controller and pure sine wave output. The chosen unit (a re-branded Axpert MKS 5kVA) allows for a maximum solar input of 3kW which, based on my current load profile, would be sufficient for electrical supply during the day with enough spare capacity to charge the batteries. For batteries, I have chosen to install a 200Ah bank consisting of 4 x 100Ah batteries series connected to give 48V and then parallel connected with a second string to give 200Ah. Based on my expected loads, this should be more than sufficient as back-up during periods of Eskom load-shedding.
The inverter will power all the household loads excluding the geyser, stove and pool pump. These would eventually be replaced with green or energy saving alternatives.
In order to make this work, I would need to re-wire the existing electrical distribution board and install a new distribution board for the new installation. Easier said than done as the existing DB is and external unit on the wrong side of the house! This would mean re-directing the existing circuitry to the new DB that will get installed in the garage.
To make matters worse, the existing DB looks like a dogs breakfast.
Trying to make sense of that mess would take a bit of thought. I’m still amazed that the installation got a Certificate of Compliance when we bought the house – there is wiring with damaged insulation, labeling is wrong and circuits are mixed. As for the 40-year old circuit breakers still being able to trip on overload or short circuit, I wouldn’t bet on it! If nothing else, the planned re-wiring would make the installation safer.
The Solar Hot Water System
While looking at the complete system, I continued researching my water heating options, either evacuated tubes or a dual element powered by PV with utility as backup.
Based purely on initial cost, I have decided to retrofit an evacuated tube system to my existing geyser. Something like this from Sustainable:
Pricing isn’t too bad at around R12,500 as a DIY option.
The dual element system worked out to around R 18,000 with the largest cost being for the PV panels required to make it work. I really like the PV option, but with space being a bit limited on my roof, and my budget being a bit tight, the retrofit tube system is the way to go for me.
I’m sure with a bit of shopping around I’ll be able to find what I need for a decent price. I’m not interested in the Eskom rebate (or whoever is offering it these days) because as far as I’m concerned, the only ones who benefit are the installers.
I’m planning on doing the installation myself (with a lot of help from my more knowledgeable friends) to save some money and learn a new skill at the same time. Watch this space!