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My first grid-tie system - 2.5kW?

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Long timer lurker finally taking the solar plunge. I live in Cape Town in a smallish townhouse in a complex. Our complex is bulk metered by Eskom (100kVA 3-phase for complex split to 12 units among the three phases). Each unit has a iTron prepaid meter. For some reason, despite being single title units, our complex is submetered. I have relentlessly tried with Eskom to get a conversion done so that each unit is supplied directly be Eskom, and so that we can "enjoy" the lower block tariffs, but the red tape has been prohibitive. 
Recently, our reseller informed us that they will be changing their tariff model and our flat rate will increase to R3.00 inc. per kWh. For simplicity I'm going to just to use the word "unit" from here on. 

I've decided to take a little money saved from not travelling during Covid and spend it on "my first little solar install". My constraints are a budget of about R20 000 to R30 000 (max) and a viable unshaded flat-roof space of about 7m x 4m.

My daily average usage is about 15kWh. I've been actively tracking my electricity usage (LED pulse metering on prepaid meter using Arduino and SQL database at 1 minute interval) since I moved in, so I have a good grasp of my usage.

Considering that cost is an issue and I'm mainly working from home for the foreseeable future, I'm considering going grid-tied for now just to help me lessen my Eskom usage during daytime. I contacted my reseller and asked them about grid-tie. They explained that I should avoid any backflow since I will pay for the energy pushed back, but that the meter has tampering-detection disabled and that it should not trip if there is the occasional few seconds of backflow. If it does trip, they normally swap out the meter. Please note that there are other units connected to the same phase as I am, and the electrical infrastructure inside the complex is owned by us, so it is unlikely that the phase will ever flow back to the Eskom meter. 

OK, so a little bit about my usage. Here is a chart of my usage during a typical day. My average usage during is about 450W during working hours, with the occasional peak of the geyser and the kettle. 



Here is also a table showing my current usage between the hours of 09:00 and 16:00 and how much of that a 1.5kW, 2kW and 2.5kW grid-tie system would be able to cover of my usage (given ideal conditions). To explain it a bit better, I've taken my Eskom usage at 1-minute intervals and then capped it at 1500W, 2000W and 2500W to get an idea of how many units each wattage will be able to cover. 


I can probably get away with using a small system (<1kW), to cover most of my average daytime load currently, but I'm considering the following to get a little bit more bang for the buck.

  •  Go with a 2.5kW grid-tie inverter and 7x 365W panels (2555W)
  • Replace 3kW geyser element with 2kW element. 
  • Install Geyserwise unit and set to only heat to 65C between 12:00 (noon) and 16:00. Geyser should still be around 50C by 8:00 morning shower time. 
  •  Shift a few high-usage appliances into daytime (dishwasher, washing machine etc).
  • My hope is to consume about 5 units a day from PV, so that my annual savings will be about R5500 (1825 units @ R3). Also meaning about 5 years to break even.

I'm considering the following setup:

  • 7x Canadian 365W panels - Series connection
  • Solis Mini 2.5kW 4G Grid Tie Inverter + Warranty extension + Wifi stick + CT clamp
  • K&N DC Disconnector (Single string 25A 450V)
  • 4mm Solar wires, MC4 connectors and tools, flexible PVC conduit
  • DIY mounting structure with 30deg tilt.
  • DB board add: Mains breaker, 15A breaker + electrician to sign off

Lastly, my proficiency with these things I would rate at a 5/10. I'm mainly a firmware and electronic PCB designer so I'm accustomed to <24V. My highest achievement unlocked with higher voltages was to add a breaker in my DB board.

What do you guys think? Am I on the right path? I'll post a few drawings of my intended setup later in the week.

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