So, you’ve got your electric vehicle (EV) and now you're on the hunt for the best energy plan to keep it charged up without breaking the bank. You’re not alone! Many EV owners dive into this quest, seeking advice and tips from fellow enthusiasts, often ending up with a flood of opinions and even some referral codes for potential savings.
At Charge HQ, we understand the importance of this search. After all, it’s the difference in cost between drawing energy from the grid and utilising your own solar power to charge your EV that drives the savings.
I set out to do some analysis of the more commonly promoted EV energy plans and quickly found myself down a rabbit hole so deep that this discussion of why finding the best energy plan for EVs is hard, is the only outcome of my work.
To be fair, this applies more broadly to all energy plan comparisons in Australia.
Why is it so hard?
A home energy load profile represents the pattern of electricity consumption by a household over a specific period, typically measured in hours, days, weeks, or months. It provides insights into how much energy a home consumes at different times of the day and on different days of the week or seasons.
Energy plans in Australia come in two main flavours - anytime and time of use tariffs. More recently demand charges are being applied to each of these.
Load profiles vary enormously from one home to the next and this variation has a significant impact on the annual cost of energy.
Take two real-world examples from homes in Sydney with EVs, using the Average Daily Load Profile provided by Ausgrid.
Home A has 15 kW of solar, a home battery and isn’t very energy efficient with well above average annual energy use. Even with the home battery, there’s significant grid use in the morning and evenings. The EV is charged from excess solar and topped up from the grid overnight.
Home B has 6.6 kW of solar, a home battery system and is quite energy efficient. Over the course of the year, the home battery meets almost all overnight energy demands. The EV is predominantly charged during the middle of the day from a mix of rooftop solar and grid energy (when renewable contribution is high).
Home A uses a lot of energy during the peak period (and can’t shift it) so will be very sensitive to the peak pricing. Home B on the other hand which meets most of its energy needs from solar and a home battery, will be less affected by peak period prices. Energy prices in the middle of the day combined with daily access charges will dictate the total energy bill.
Every home is different, and all of the following factors can have a major impact on your load profile.
It’s a long list and it’s not complete. It’s really hard to understate just how much variation this long list creates in the load profiles from one home to the next.
From an energy bill perspective, the load profile is based entirely on energy used from and exported to the grid. There are a few different sources of this data:
If you just want to compare the cost of energy using different retail energy plans, interval data from your energy retail or distribution network will work.
These data sets only know your net grid imports and exports. They don’t know about your solar production, home battery behaviour, or when your movable loads such as an electric vehicle were using power.
If you want to compare the cost of energy plans which encourage you to use energy differently, and you have home solar, a battery, or an EV you’ll need their individual contribution profiles. Combined with your grid data they’ll help you form a view on how much your energy use may change and at what times of day. We’ll look at this in more detail later.
Once you have your load profile data, say for the last 12 months, you can combine this with the different energy plans to compare what your cost would have been on each of the different plans.
For a flat rate or any time plan you need:
For a Time of Use plan, you need:
For each of these tariff periods you need to know:
Note that the time of day can vary by:
The time windows are influenced by the distribution networks but they’re not rigidly set by them, energy retailers are free to provide plans with custom periods. So the time of day each tariff period applies to may need to be adjusted for each energy plan being compared.
Off-peak historically referred to the cheapest energy tariff overnight but this is now changing. Off-peak can be the middle of the day or it could be the overnight. If the energy plan also includes a “super off-peak tariff”, then it will often be the cheapest period. Some energy plans will offer an “EV off-peak tariff” or an “EV charging window”- this can be cheaper with retailer A, but it may also be more expensive than “off-peak” with retailer B.
The two main sources of tariff data are the energy retailer and the Energy Made Easy site.
In both cases, you’ll often need to do some digging to piece together the details for each tariff.
Take the Ovo EV Plan on the Energy Made Easy website. The summary table is missing both the “ev off-peak” and “ev super off-peak” periods which are the core features of this tariff.
You’ll find details of these periods on the “special” tab.
Other limits such as the 5 kW panel limit in NSW for this plan aren’t listed on the Energy Made Easy website but are covered in Ovo’s market contract terms.
I’m using Ovo only as an example here, a similar situation repeats on other retailer websites.
If you’re comparing two energy plans where the highest prices and lowest prices occur at the same time of day, your analysis can rely solely on your historical data.
In many cases, particularly with EV plans this won’t be the case. For example, the cheapest time to use energy each day may be
For each plan, you’ll adopt a different pattern of EV charging (and home battery control) to obtain the cheapest energy bill.
To accurately compare the plans, you need to adjust your historic energy usage load profile by making some assumptions about what you think it will look like under the new plan.
You can use EV charging history data from apps like Charge HQ as a starting point, or use average annual driving distances combined with average wh/km to work out EV energy use.
Now that you have your energy data, details of the tariffs you want to compare, and some data to inform how your load profile might change, you can build your own model in Excel or Google Sheets to compare them.
It’s a bit of work but it’s the only real way of making an accurate comparison.
Before starting down this rabbit hole I thought that there would be a website or online service that could do this for me. Something that would import my energy data, and compare all of the plans available exactly as they applied to me.
I’ve had a look and haven’t found anything that does a thorough job, including:
Having completed the process and built my own model, and seeing how complex it is, I’m less surprised that there’s no service to do this for me. It would be a difficult product to build and maintain with reliable results.
I analysed both Home A and Home B described at the start of the article, for Home A there was about a 10% saving available by choosing the best energy plan. Over the course of a year if I valued my time it wouldn’t have offset the cost of building the model.
Home B on the other hand uncovered some more substantial savings from switch energy plans, enough to justify the work, but there are more fun things I’d rather be doing!
Finding the right energy plan for an EV owner is hard!
