A while ago the Fully Charged show featured a great device called the Zappi, which can charge an EV using surplus solar:
This is pretty amazing for EV owners who also have solar PV.
It means that instead of exporting surplus energy at a reduced rate ($0.12/kWh) it is possible to avoid importing energy at a higher rate ($0.25/kWh). This can effectively double the benefit of having solar PV by boosting self consumption.
However as of writing, the Zappi V2 is $1,395 (for example, from EVolution here).
Is it possible to create a software virtual plug to charge an EV using only self-generated solar PV?
Charging the EV using only rooftop solar costs $0.12/kWh. This is the opportunity cost of the feed-in tariff which would would otherwise be earned for feeding energy into the grid.
Charging the EV using grid power alone costs around $0.25/kWh.
Depending on the proportion of PV generation at a given time, the effective cost per kWh may be somewhere in between.
What if we can turn on the charger only at times when the solar is generating 100% or more of what the EV will use?
A custom software program could query net solar export and control a smart plug to generate savings.
|Mitsubishi Outlander PHEV|
|Envoy S Metered Solar house monitor|
|TP Link HS110 Smart Plug|
- Cheaper EV charging (approximately 50% savings)
- No need to manually enable / disable charging when:
- Weather is variable
- Household consumption is high (e.g. boiling a kettle or running the dishwasher)
- Weather is variable
Things to consider
These are also some risks to consider when designing a DIY software control:
- The PHEV plug safety instructions say not to plug anything in between the wall socket and charger plug – i.e. where the SmartPlug should go.
- The PHEV charger expects to be plugged in and left alone – will it be happy with power being enabled / disabled?
Another thing to consider… is it worth buying a Smartplug to do this?
Assuming the plug can be purchased for a reasonable price (for example $40 including shipping from here) and weekly EV charging from nearly empty, the plug pays itself off in <1 year:
|Opportunity cost / lost export ($/kWh):||0.12|
|Saved expense ($/kWh):||0.25|
|Net saving ($/kWh):||0.13|
|kWh savings to pay off:||307.69|
|Average charging session (kWh):||8.00|
|Number of charges:||38.46|
See Part 2 for an approach to implement this solution in Python…