We are encouraging questions from readers about electric vehicles, and charging, and whatever else you want to learn. So please send them through and we will get our experts to respond, and invite other people to contribute through the comments section.
Our second question comes from Will, who asks:
Following the article on charging an EV from a battery such as a powerwall, have you any further comments for my situation living on a rural property totally off grid?
We don’t have enough capacity in our solar system to charge an EV. (4.25 kW panels. 6kVa inverter, 600Ahr batteries).
What are the best options, a dedicated solar system for charging the ev, or expanding the existing system? Would a dedicated charging system need its own batteries and inverter, or are there other suitable combinations for charging from the sun?
Our expert Bryce Gaton writes:
A good question Will.
Off-grid living and electricity provision have in the past been a difficult mix, but with the proliferation of cheaper panels, 240V inverters and reliable battery systems – the issue has much reduced.
It is still an issue for the typical current limited off-grid domestic supply when adding a high-demand item, be it an electric oven or an EV. However, an EV, unlike an oven, can be ‘demand managed’ both for time of charging as well as current draw.
So, the first issue to consider is EV charging time – if it can be done during the day and you have enough solar panels to charge your off-grid batteries, provide basic household demand AND enough left to slowly charge the EV, then choosing the right EVSE is the only consideration.
I will come back to off-grid EVSE (electric vehicle supply equipment) selection a bit later.
If you want to charge the EV overnight, then battery size selection will also need to be added to your consideration list.
If your EV electricity use added to your existing household electricity consumption exceeds your generation capacity: then you’ll need to add additional solar PV (or wind, micro-hydro, steam or, heaven forbid, diesel generation) to your growing consideration list.
So, having covered off on the gamut of items that adding an EV to your off-grid household – and assuming you have now solved the generation and or storage issues it created: the final issue to deal with is “how do I charge the EV given I have fluctuating electricity generation/maximum load considerations?”
A normal EVSE (electric vehicle supply equipment) has a fixed maximum delivery current. Usually this is either 16A or 32A.
An EV drawing even 16A can seriously compromise (or even shut down) a normal off-grid system when the sun goes behind a cloud or a large electrical item in the house turns on, adding to the load created by the EV.
Consequently, you will need to install an EVSE that can sense the PV or other electrical generation and ‘throttle back’ the charging rate depending on the changes. Thankfully, there are now a couple of EVSEs coming onto the market that can do just this.
One is the Zappi unit that is now being distributed in Australia by Evolution Australia EV supplies.
Another potential system is currently being developed by Delta Systems here in Victoria – see press release here.
A simpler alternative is to install an EVSE that can be manually switched to different current levels. Several portable (Mode 2) EVSEs are currently available, and even some newer Mode 3 ones have this capacity.
You can also buy a kit solution to construct your own mode 2 or mode 3 EVSE with switchable current levels along with WiFi and other features – but be warned, it can be a complicated thing to build and program and little less in cost to buying the ready-made Zappi or Delta Mode 3 EVSEs.
Hopefully that answers your question Will!
If others have suggested responses, please add in the comments section below.
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