EV charging @ home: What you need to know
As electric vehicles become more and more prevalent in our society, electricians need to know how to install the appropriate battery technology. Smart Energy Lab general manager Glen Morris writes.
So, you’re in the market for an electric vehicle (EV), one that will make you a stranger to service stations (except when nature calls) and save you money by turning your surplus solar into cost free kilometres.
But there’s a catch, when the sun is powering your home solar system, you’re out and about, maybe at work or just getting to know your favourite retail shops again. Your precious solar is ‘leaking’ out to the grid for little financial benefit when it could be topping up your EV.
You need a battery!
Selecting the right size storage battery for afterhours charging requires a few considerations. What will be the maximum AC demand from the AC charger built into your EV? (the ‘thing’ on the wall that plugs you into your EV is actually just a fancy socket outlet with smarts, called Electric Vehicle Supply Equipment or EVSE for short). Its job is to supply single or three-phase power to your EV and using pilot pins, tell the EV that you’re plugged in and not allow you to drive off with the cable connected.
The battery charger built into EVs varies in their features. Some provide a three-phase charger (though this is less common) that can delivery around 11-22kW to your EV’s battery pack. Most current model EVs only have single phase chargers typically rated at 7-7.4kW.
So called ‘fast charging’ generally refers to direct DC charging from a grid connected rectifier that can supply 400-800V DC to your vehicle’s battery at rates up to the 100s of kilowatts. These cost as much as your car and are generally only found at public charging stations.
To use a case study based on my own EV (Kona Electric) which has a single phase 7.4kW charger built in, I would be wanting a storage battery/inverter system that can supply up to 7.4kW of power exclusively from the stored energy in the battery. The capacity of the battery is really a decision based on how much surplus solar power you have, how much energy you use on a daily basis when driving your EV and whether you need some reserve capacity for unexpected blackouts.
My daily drive is typically 80km using about 14kWh of EV battery energy, thus a storage battery with a bit more than this (allowing for less usable capacity than the theoretical maximum capacity) would suffice for after sunset charging.
If fast AC charging isn’t required, then the extra cost of getting an EVSE installed ($2,000-$3,000) can be avoided by using the supplied 10A 240V equipment that came with the Kona. Though this will only ‘trickle’ charge at 2.4kW, to replenish the daily driving use of 14kWh will only take around six to seven hours. This also means that the storage battery/inverter system doesn’t need to be sized for a peak demand of 7.4kW, instead only 2.4kW, thus cheaper.
Here at the Smart Energy Lab, we have a range of EVSEs from basic (supply AC power only) to so called ‘smart chargers’ that can monitor when there is surplus solar energy flowing to the grid and divert it to the EV’s battery, as well as ensuring a target state of charge of the EV is reached by a certain time of day irrespective of the source of energy.
Some of these ‘smart chargers’ can directly interact with their attached storage battery to optimise renewable energy charging as much as desired.
For those EVs that have three phase chargers (11-22kW) built into the vehicle, we have a three inverter (synchronised three-phase) system with three 10kWh high voltage battery packs attached to supply up to 30kWh of stored energy to the EV, even after sunset.
Sizing solar PV for EV charging is an equally subjective decision. Ideally it should be able to produce as much on an average day as the EV consumes, however, this “average day” will vary with the seasons and here in Melbourne the monthly solar radiation average varies by a factor of three from mid-winter to mid-summer.
Practically speaking, the more solar PV the better and available mounting locations is usually the limiting factor. To give some typical examples based on the my daily driving requirements (14kWh/day), approximately 6kWp of solar panels would cover the average monthly mid-winter solar production to that of the vehicle’s use.
Soon we’ll be trialling the first approved vehicle-to-grid (V2G) inverter/EVSE system in Australia. This has only just become possible with the update of our inverter standard AS/NZS 4777.2:2020 to prescribe the connection and protection requirements of V2G systems connecting to the utility grid.
So, what’s all the fuss about V2G?
Considering most EVs have an onboard battery of 30-100kWh, it’s likely to already be the biggest battery you will ever have at home. V2G means that you can use the power in your EV to supply your home and even export to the grid when the price incentive is present.
With the reforms of our electricity regulations, it has become possible for small batteries to be aggregated into large virtual batteries, that via real time controls can participate in the Frequency Control Ancillary Services (FCAS) market, where the spot price can be astronomical even for small amounts of energy delivered just when the network needs it.
Suddenly your little EV sitting in the garage or carport is earning you money trading energy (even charging on demand can be profitable). Forget crypto mining… just plug your EV in and watch the FCAS and NEM markets as you sip your evening beverage.
Follow this link to see live market pricing.