With the electric vehicle revolution kicking into gear, it’s time to talk about why getting your energy infrastructure sorted sooner rather than later is a smart move.
In this article, we’ll demystify electrical network capacity and maximum demand, and shed light on the roadblocks that might impact your ability to install your favourite home EV charger in the future.
We’ll also show you how solar panels, batteries, and smart EV chargers can help overcome these limitations and improve your overall energy management strategy.
Why You Should Know About This
If you don’t plan on moving for the next few years, there’s a strong chance that a brand-spanking new electric vehicle will call your garage home at some point. But when the time comes, you might not be able to simply call up the local sparky and install your EV charger of choice.
Limits To Network Capacity
The capacity to operate various electrical loads on your property is constrained by the size of your switchboard and consumer mains. Additionally, upstream in the electrical distribution network, there are further limitations, such as the capacity of local transformers1, distribution feeders, substations, and ultimately, the overall mix of generators supplying electricity.
So, what’s that got to do with you? Plenty! The grid is a work in progress and is constantly being maintained and upgraded. At any given time, each local street transformer will collectively supply the connected houses with a limited amount of power.
This is the distribution transformer in my street, which supplies power to my house and about 50 others nearby. I hope it will have enough juice to fill up my EV when I’m rich enough to afford one, along with all my neighbours.
Electric vehicles are power-hungry and are rapidly multiplying in numbers. Although each state has its own rules governing the installation of home EV chargers, it’s pretty much on a first-come, first-served basis. This ad hoc approach isn’t sustainable and will likely have to be managed more closely in the future. That means tighter regulation.
Let’s Talk About Maximum Power Demand
Although you can’t swap out the low-voltage transformer on your street for a bigger one, you can do things on your own property to potentially increase electrical capacity or at least manage what you have more effectively.
Maximum demand is a term that represents the peak load or the maximum amount of power that needs to be supplied to meet a consumer’s electricity demands at any given moment. It is measured in kW (kilowatts), not kWh (kilowatt-hours). *Bashes head against the wall repeatedly*.
In Australia, an electrician is required to consider the whole installation’s maximum demand when installing any new electrical equipment into your house. It says so in the book they swear allegiance to – AS/NZS 3000:2018, the Wiring Rules.
There are many ways of doing this, and each has its benefits. Here are two of the most common methods used for a domestic installation:
Calculation Of Maximum Demand
In this method, the maximum demand is estimated by summing all the individual loads in an installation. Some loads have a diversity factor applied accounting for different usage patterns. The electrician will do calculations based on tables in the rule book.
There may be a scenario where the electrician says – due to maximum demand limitations, an upgraded switchboard and larger consumer mains cable must be installed to meet the extra demand of a home EV charger. This might entail changing a single-phase supply to three-phase.
Although it sounds like an expensive option, the plus side means you would have increased electrical capacity and be more likely to use your charger and other energy-intensive appliances at your preferred time of day (subject to network rules).
Limitation Of Maximum Demand
For this method of defining maximum demand, a circuit breaker may be used in place of or in conjunction with the main switch to limit the current draw for the whole installation. Job done!
This is a much cheaper option because it only involves the installation of the main switch/circuit breaker. The downside is that it puts the onus on the customer to manage any loads that may cause the new circuit breaker to trip in an overload event. As far as capacity is concerned, you’re in the same boat as before the EV charger was installed, only now you’ll have to watch your usage patterns very carefully.
As in the calculation method above, there may be instances where an electrician will decide that the limitation method isn’t suitable for defining maximum demand when installing equipment. There may not be enough headroom due to other high current loads, or the switchboard may be too crowded or old. It may be time for a switchboard and/or mains cable upgrade.
Out with the old (left) and in with the new (right) three-phase switchboard with plenty of room for solar and EV charger. Image: Safety Switch Electrical Fremantle
Overcoming Capacity Limits
On the surface, capacity limits might look bad, making life more uncomfortable than it needs to be. I disagree. A bit of tough love makes us think a little deeper about what energy actually is, and the way we use it. The Electricity Grid 2.0 is a smart grid, and if you’re smart too, you can use it to overcome most capacity constraints.
Real-time Consumption Monitoring
A real-time consumption monitor can be your best friend for managing maximum demand. You can easily stay under the threshold that may trip your main switch/circuit breaker by keeping an eye on your power consumption as you use it. It will soon become apparent which appliances are the power-hungry ones, and you can adjust your usage patterns to suit.
It helps if you know the current ratings of all your electrical equipment. You’ll find them either stamped on the appliance’s nameplate or the data sheet that came with it. This is usually searchable on the internet. Simply type in the brand/model followed by ‘datasheet’ of ‘specifications’. Look for power or current ratings, then do your sums.
Rooftop Solar Panels
Fortunately, most rooftop solar power system owners are well-versed in solar energy self-consumption. They have been beaten into submission by the slow erosion of feed-in tariffs over the last decade, and now, for financial reasons, it makes sense to use solar power in real-time when it’s available.
This has a knock-on effect of reducing maximum demand on your incoming grid supply. For example, your EV charger operating near full load might draw most of its demand from solar and the rest from the grid, thus helping to stay within your main switch limits. It’s a win-win situation. But what happens to maximum demand when the clouds roll over? Enter the smart devices.
Smart EV Chargers
Many home EV chargers have automatic features that allow you to take the guesswork out, enabling you to stay comfortably within your maximum demand limits. These are many and varied and will require EV charger research on your part to get the right solution. Features such as dynamic load balancing, power sharing, and scheduled charging are worth looking out for.
Some chargers have a ‘solar only’ mode, which tracks and uses the surplus solar electricity that might otherwise be exported to the grid. If not enough solar energy is available, the charging is paused or throttled. These are usually pre-configured with thresholds to avoid unnecessary intermittent stop/starting that would damage/wear out contacts and hardware components.
Power Management Systems
Various home energy management systems, including DIY home automation, can intelligently prioritize and manage power allocation within your property. The sky is the limit with these devices, and it is a big rabbit hole if you choose to go down it!
Among an almost endless list of automatic systems designed to save you time, which, in order to implement, actually chew up much more time than they were designed to save, is a useful one called ‘load shedding’. These systems can automatically reduce non-essential loads when your EV charger is used to ensure you stay within your property’s maximum demand threshold.
Home Batteries
There are many reasons for installing a home battery, and one that is often overlooked is the ability to act as a buffer, allowing you to draw from it during peak demand periods, and avoiding overloading your electrical system. This can arguably be factored into a financial case for installing a battery versus another expensive option – upgrading your switchboard/mains capacity.
Your battery may have an app configurable mode such as ‘grid support mode’ that prioritizes the battery to support the grid during high demand, adding more capacity. In addition, it could be integrated with a home power management system to optimise energy usage and stay within capacity limits.
In Finn’s recent video, two Tesla Powerwalls were configured to never overload the 63A main breaker by monitoring the incoming power and throttling the 10 kW of battery charging in real-time.
Charge Ahead Of The Regulatory Curve
Electric vehicles are hungry beasts, and they are breeding like rabbits. The limits of our electricity infrastructure are becoming apparent, both on our collective properties and within the broader distribution network. Utilities are taking steps to address these limitations, but there are also several ways to proactively increase or manage your own capacity. I’d say it would be a safe bet to stay ahead of the regulatory curve and get your infrastructure sorted now.
Footnotes
- Some of the electricity utilities have network capacity mapping tools online, which show the location of transmission lines, distribution lines, and capacity of various assets. These maps are of limited use to the average Joe but are worth a look to see if your area might be constrained. Western Power and Essential Energy are two that I could find. ↩
About Kim Wainwright
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I see rationing of vehicle charging time slots in our future.
All to reduce required grid but more particularly local distribution backbone investment
And use of smart meters to detect likely infringement of maximum permitted power draw other than during the allocated slot.
Slots will be rationed by price. 7 to 9 pm in the evening will be very expensive in some suburbs.
And midday will be relatively cheap esp in summer in suburbs with lots of solar on rooftops as that does not require major grid investments and will soak up the duck curve excess power generation.,
We are heavily involved in the roll out of EV chargers across the fleet of businesses we have solar installed on and this issue raised by Solar Quotes is one many people are not talking about. As detailed in Kim’s blog careful planning needs to be completed to be sure the facility has the current carrying capacity to supply the additional load when needed.
One option we think has merit is to have the charger on power poles at certain points on the existing road and grid. This does create it’s own challenges and then ownership and who makes the profit comes into the equation.
Class A Energy Solutions has determined that particular sites are more suited than others and advice the customers on a case by case basis. Taking into account power factor correction is another conversation to reduce the demand freeing up capacity for EV chargers.
Always such great articles. On charging, I wonder if with a proliferation of both generation and storage options (including big batteries in cars), both residential and commercial, we’re still trying to use an accounting method for charging that’s heavily location-based? For example if you’re generating big exports of a day when you’re not home, why can’t a person charge elsewhere, using that exported amount as a type of credit? It seems bizarre that they have to be physically located at their home, to be able to access energy that’s shared across the whole grid.
I’ve recently moved to amber electric to take advantage of their variable supply and Feed-in tariffs that follow the NEM. I signed up without realising that they couldn’t support my battery with their smartshift system so I had to start managing my battery myself.
I’ve had a 5kWp PV, sonnen 10kWh battery for 5 years. Also a Tesla car for 4 years. I’ve also been using Home Assistant for about 5 years.
Started with amber by:
1/ charging at 3am for the morning rush
2/ discharging at full rate when a feed-in tariff spike was detected.
Electricity costs didn’t meet my expectation or come close to my previous VPP plan so I started looking for what others were doing.
Came across a system called EMHASS which is an add-on to Home Assistant and manages energy flows. It takes a 24 hour forecast of solar production, FiT, ST and consumption history and calculates a plan to use deferable loads like pool pump, car charging, hot water etc to soak up excess grid energy at very low and even negative prices. Also when to charge and dischage the battery to an arbitrage system. I now get to charge the car for 3 hours a day at 3 c/kWh and get a negative electricity bill. Since setting it up I get anout 80 cents profit per day. Will be interesting to see how it goes in summer.
I’ve always said, and I’ll repeat it here, that for a vastly disperse country like Australia, PHEVs are the correct way forward. We keep our cars for 10 years on average. And need to get better at reducing our CO2 emissions. Now!
As stared here, our electricity grid and infrastructure are going to need massive, decade long upgrades to be able to cope with the demand of EVs.
1. PHEVs bring Zero CO2 transport for the average daily commute of 36 kms available to the masses, with just a standard 2kW 230v 10amp wall outlet in 7 hours overnight. The manufacturers (Mitsubishi being the leader in this field with PHEVs since their essentially unchanged Outlander drive since 2014) have done the math!
2. PHEVs have Zero Charge anxiety on the occasional out of town trip.
If the goal to move to EVs is to reduce CO2, then why not 90% reductions with PHEVs now, than just a handful of blinkered BEV die-hards early adopters?
The average Australian wants to do the right thing. They’re too smart to jump into BEVs with all the Charge Anxiety issues one is then bagged with. Note the long queues buying (50% CO2 reduction) HEVs!
And would prefer their taxes to go into home loan and rent reductions instead of a near impossible rushed electricity grid.
In Victoria, I understand the government has ruled that from next year, properties with EVs must go on to a variable rate. Obviously this is being done to discourage EV owners from charging at peak times. I am trying to configure my Zappi charger and finding it very confusing.
Hey Tim!
I work in myenergi support in Aus, I just saw your comment here and thought I’d chime in!
It’s pretty easy to configure your Zappi to charge off-peak, simply set your Zappi to ‘ECO+’ mode, ensure that it’s set to 100% green via your app, and then set a scheduled boost based on your off-peak tariff times, and if your car is plugged in and ready when the schedule is active, it’ll charge!
I’ve seen some really amazing deals from companies like OVO and AGL offering 8c/kW which is unreal.
Hope that helps! Feel free to get in touch if you want any more info or advice!
You can get us directly at [email protected]
Dear Alex
Thank you for that. I have found the Zappi very reliable but have not got beyond stop and fast charging. I think I made a mistake in having the home electrician install it and in the future if you have a service I will probably have you come and wire it into the Tesla Gateway and set it up so I can charge from solar without the battery or at night on low tariff. I do not have an app. I will try again from the keyboard on the unit. I tried the other night but it started charging straight away and I suspect I only had it set to eco and not eco+.
Kind regards
Tim
I freely admit, I’m close to ignorant on matters of this nature. Our switchboard has what looks like a fuse perhaps, labelled ‘SPD/MPD 80A’. Does this mean the max the house can draw at any one time is 80 amp before power is cut?
Hi Brian. The fuse labelled SPD/MPD 80A is to protect the network’s service equipment from fault current. SPD = service protection device. MPD = meter protection device. The maximum that your house can draw is governed by the sum of the circuit breakers in your switchboard, which, due to a diversity factor, is unlikely to be as high as that sum appears, or ideally as high as your 63 A main switch. It’s also possible that your main switch is also a circuit breaker, in which case 63 amps would be the maximum current your house will draw before tripping the circuit breaker/main switch and cutting power to your house.
Brian Bycroft,
SPD/MPD 80A = Service protection device (SPD) and/or meter protection device (MPD) with 80 Amp HRC rating.
This fuse sits between the grid supply, one each per supply phase, and the electricity retailer’s service meter, and is normally sealed by the electricity retailer (or network).
The SPD primary function is for network protection and installation isolation. The MPD primary function is for the retailer’s energy meter protection and isolation.
The SPD/MPD fuse does not replace the installation’s main switch, usually a Circuit Breaker rated between 50 A and 63 A (per phase).
The maximum current an installation can draw continuously is dependent on the installation’s Main Circuit Breaker rating – NOT the SPD/MPD fuse rating.
Brian,
Your current should be below 80amps, about 18KW, that’s more than my house draws even with my EV charging at 7KW.
Cheers
Bill
Hi Kim – great article thanks.
I appreciate the answer is likely to be “it depends” but for a typical single phase house what’s the typical maximum power allowed before tripping under the Limitation Of Maximum Demand approach?
Hi Gareth. Using the limitation of maximum demand method simply means using a circuit breaker as a main switch and so limiting the current draw by tripping when it goes over the current rating written on the circuit breaker. In WA where I live, a single phase property must use a 63 amp breaker as a main switch. The voltage is 240 volts, so 63 A x 240 V = 15 kW power. This figure is more of a guide though because it also depends on other factors such as the type of load, surge current, and power factor etc.
I have had EVs for the past 5 years, and rarely have had to charge fast at home. For most of us a 10A GPO (power point) is enough, should be enough if your daily commute is say 100km.
We have crossed the Nullarbor and driven from Perth to Broome, then you need fast charging (if you can get it), so maybe save your electrician’s money for fast charging:)
There may be some other reasons to install a more powerful charger, in my case I was a shift worker, home a lot in the daytime, so I could soak up my excess solar.
Also if your Electricity supplier offers a discount for EVs charging in the early hours, mine (Western Power) offered a cheap rate from 11pm to 4 am (I think), which may not be long enough for adequate charge.