I am building a new house and am going to install 7.4kW of PV with a 5kW inverter, and a Tesla Powerwall 2 (with 13.5kWh usable storage).
In my current home I have 3.4kW of PV and a DIY PV diverter based on the EmonTX shield + Robins diverter sketch. It works great.
However I am wondering if the addition of a battery might allow me to simplify things and remove the PV diverter. My plan is as follows;
- add a relay or timer to control my HWC element (3kW)
- at 12am’ish turn on the HWC element for 2 hours
- during this time any excess solar will be soaked up by the HWC
- and any shortfall will be covered by the battery
- by starting at 12am the battery should have had a chance to charge up a bit
- once the HWC is up to temp, or 2 hours is up, any excess will go back into the battery
- at 4am turn the HWC element on again for a few hours (if needed)
- I get cheap night rates so this ensures I have hot water in the mornings
The general idea is to simplify the system by removing the diverter, and just using the battery as a buffer for when solar is limited, or the house load spikes.
I have a few other ideas also; by having two elements in the HWC (middle and bottom) and checking the solar forecast each morning…if high solar expected turn on the lower element, in order to maximise the amount of hot water, and if low forecast turn on the middle element, so we have enough for the evening but don’t risk discharging the battery too much if the solar is limited.
Anyone considered this approach? Have any thoughts about whether it is a good/bad idea?!