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EV charging: the best source
EV charging
Electric vehicles are getting more and more popular as an alternative to internal combustion engines. Instead of stopping at the petrol/gas station the EV owner has a range of options in which to choose and effectively there are 3 x modes of charging:
- Mode 1: charge at home with portable unit, plug into dedicated AC socket
- Mode 2: uses an AC EVSE* , hard wired in the house, dedicated circuit
- Mode 3: DC charging, the EVSE is a high powered AC-DC charger, not found in homes
*( electric vehicle supply equipment)
Portable chargers
Most of the portable chargers available are single phase with varying outputs and there are some that can use three phase AC.
The single phase units have capacities up to 15A plug with a larger than normal earth pin but there are heavier duty options around. Some have a screw fitting, the more industrial ones but you will have a socket that matches.
The 15A units are versatile in that they fit into standard power points but you will need a 15A to 10A converter. The issue is that the charge time on these units is long with a max of 3.5 kW output.
Fixed chargers
Same as portable units except they are housed in a purpose built enclosure mounted on a wall and is wired directly to the house switchboard.
Come in single and three phase from 7.2 kW and 22 kW. Cables can be built in or portable with pros and cons with both approaches.
For more information I thoroughly recommend an article in Renew issue 156 by Lance Turner that goes into great detail concerning the different methods of charging, the pros and cons, potential network interference in the future and great buyers guide
We will be concentrating on. . . .
All energy usage should be looked at from the perspective of a T.E.M.S approach ( Total Energy Management Strategy) and in the examples presented we make certain assumptions concerning the EV’s battery capacity, the owner’s drive profile, domestic charging access, solar contribution and more.
Will be looking a a range of options from full peak grid charging to a solar off peak charging strategy
The assumptions. . . .
So before getting stuck into it we have to make certain assumptions which are:
- Customer has a EV, battery capacity of 100 kWh, drives around 400 - 500 kM per week
- Rapid charge is not an option for this customer so will be relying on home charging
- Customer has a 5 kW solar system at their home
- Has a peak and off peak tariff arrangement
- Peak Monday: Friday 7am - 10 pm
- Off peak: Friday 10:01 pm till Monday 6:59 am
- Peak costs: $0.30/kWh and off peak $0.14/kWh
Charging option 1: just from peak grid power
In this situation the customers tops up over a few nights after solar production hours and turns off charging before the off peak tariff kicks in:
- Total charge needed to replenish the battery is *80 kWh/0.85 = 94 kWh
- Max current he can extract is 15A so 15A * 230V = 3.45 kW
- Takes 94/3.45 = approximately 27 - 28 hours to achieve full charge
- Total cost per week is $28.20
- Per year is $1466
- After 10 years assuming 2% increase in electricity per year will cost $16,056
- Total km’s covered = 260,000
*never full discharges all the battery capacity
Charging option 2: just from off peak grid power
In this situation the customers tops up just during off peak periods, either after 10 pm and before 7 am Monday - Friday, on the weekend or a combination of both:
- Total charge needed to replenish the battery is *80 kWh/0.85 = 94 kWh
- Max current he can extract is 15A so 15A * 230V = 3.45 kW
- Takes 94/3.45 = approximately 27 - 28 hours to achieve full charge
- Total cost per week is $13.16
- Per year is $684
- After 10 years assuming 2% increase in electricity per year will cost $7,493
Charging option 3: from peak and off peak
In this situation the customers tops up just during peak and off peak with a 50:50 split:
- Total cost per week is $10.34
- Per year is $538
- After 10 years assuming 2% increase in electricity per year will cost $11,774.89
Charging option 4: solar and off peak on weekends
Now the only time the customer can utilise his domestic solar system is on the weekends but there are few assumptions that have to be made to make this example realistic:
- The ability of the 5 kW system to service the 3.45 kW load is restricted to 3 hours/day
- So the total contribution from solar is 6 hours/week ( just on the weekends)
- The other 19 hours is from off peak grid electricity
So, per week is $9.24, per year $ 480.48, after 10 years assuming 2% increase in electricity per year will cost $5,261.12
Charging option 5: solar all the way or. . . . .
Now the ideal scenario is for the EV’s battery to be charged completely from a renewable energy source but, unless the owner has access to onsite charging, which indeed may be the case, the direct contribution from solar will be limited to the weekends and this assumes that they won't be driving the car at all!
There is another option and that is a correctly sized solar system in conjunction with an energy storage solution. Let’s assume that the customer has a larger solar system and a Tesla Powerwall and intends to charge from it.
Charging option 6: solar and batteries
In this option the customer’s EV will be charged directly from three sources and in no particular order:
- Solar
- Off peak electricity
- Battery storage during evening peaks
So we will have to make some assumptions in regards to the contribution of each.
Charging option 6: solar and batteries, continued
We know that we can directly charge on the weekend and contribute 6 hours/week to the EV battery load. This leaves 19 hours of contribution from the other two sources:
- Solar on the weekends; 6 hours
- Off peak electricity; 3 hours
- Battery storage during evening peaks, 2 hours/day Mon - Friday, total 10 hours
Total cost per week is $1.45, per year this is $76 and after 10 years assuming 2% increase in electricity per year will cost $825
Conclusion
As more and more consumers start purchasing EV’s strategies will need to be developed in regards to usage and also charging regimes. Relying on purely peak grid power will not only cost the owner but put undue stress on a power system that is already fatigued.
Using a combination of solar, cheap grid power and storage results in the cheapest yearly costs but we haven’t factored in the purchase price of these renewable energy systems.
A prudent approach involves a cost benefit analysis of all approaches tempered by financial realities, drive profiles and access to off peak grid and renewable energy sources and storage options.
Be warned; EV’s are here and they are not going away!
If you’d like to see more of what Greenwood Solutions get up to in the real world of renewable energy, solar, battery storage and grid protection check out the following pages:
https://www.greenwoodsolutions.com.au/industry
https://www.greenwoodsolutions.com.au/commercial
https://www.greenwoodsolutions.com.au/commercial/customer-stories
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