Off-grid in the suburbs

off grid

One ReNew reader has used his electric vehicle to take most of his energy consumption off-grid. He explains how he did it.

I was keen to increase the size of my PV system as my house was using more energy than the system produced in winter. This meant I was importing energy from the grid at 29 c/kWh (100% GreenPower, I hasten to add!).

I was also keen to experiment with going off-grid. I considered going completely off-grid, but that would mean losing the perceived reliability of supply from the grid, requiring a leap of faith for a suburban consumer like me.

Off-grid economics

My solution, instead, was to install a separate off-grid PV system. I now have two PV arrays with separate inverters, one connected to the grid and one off-grid, with the house running (mainly) on the off-grid system.

The idea of going off-grid with battery systems was featured in ReNew 128. One article suggested that price parity with a grid connection is yet to arrive, particularly in metropolitan areas, as PV may now be cheap but batteries are still expensive.

However, I already had a good-sized (8 kWh) lithium ion battery in my plug-in Prius conversion. I was able to use this battery for my off-grid system, with it providing around 6 kWh storage at 75% depth of discharge. So, even though I live in metro Melbourne, the economics worked out well for me.

Technology needed

My system required some technology: I purchased a 4 kVA Ecotronics unit from Commodore Australia that does it all. It is a MPPT (maximum power point tracking) PV controller, battery charger, AC inverter and grid UPS all in one (see Products, this issue).

It is designed to run off a 48 volt battery, the same as my Prius PHEV conversion system battery. The conversion system, from Enginer in the USA, uses a 48 volt battery and a DC–DC converter to step the voltage up for the Prius’s drive system.

The Ecotronics unit can also automatically revert to grid power if there is not enough sun or the battery is low. It can even be set up for load levelling—i.e. charging the battery bank on night-rate mains power then supplying power during the day. However, with a relatively high night-rate tariff (19 c/kWh), the economics for this are marginal for me—a 10 c/kWh saving over the day rate of 29 c/kWh.

The Ecotronics unit simply connects to the Prius conversion’s 48 volt battery via a large Anderson connector (a high current rated two-pole connector popular in DC systems). When not running the house loads, the Prius battery can either be charged from the Ecotronics unit’s built-in battery charger or the charger that came with the Prius conversion kit.

Read the full article in ReNew 130