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Solar & EV owners: don’t stress about charging your car directly from the grid when the sun isn’t shining.

The first thing I’ll do in this article is point out it’s difficult to fit caveats into a headline.  The second thing I’ll do now I’m writing the article and have the space to explain is state there are exceptions to the two main points I am about to make, which are:

I will cover some exceptions later in the article, but not now.  Maybe in paragraph 46.  The first thing I am going to do is lay down some ground rules on technology and how far into the future I’m going.

I’m only looking at the relatively near future, which means I’m going to assume home batteries and electric cars will work much the way they do now without any radical changes in technology.

I’ll also assume Australia’s electricity generation will only be around 50% renewable by 2030.  I’m hoping it will be considerably higher, but as I’ve had three failed marriages I have to consider the possibility my optimism levels are slightly above average.

I’m confident my two statements made above will hold true for the next 5 years, but after that it’s possible they will no longer apply.  So in the year 2025, if man is still alive, if woman can survive, they may find… the situation has changed and it makes sense to charge an electric car with a home battery.  But I doubt it.



They are under the impression it is cost-effective to charge an electric car in the evening with a home battery that’s been charged with solar power during the day.

I wish I could join them in this dream world, but I’m afraid I cannot.  This is because, sooner or later, I know that giant carrot in a top hat will show up and start chasing me again.  (He’s the reason I sometimes write these articles at 3:00 a.m. in the morning.)

But another problem — one that doesn’t involve a giant, snappily dressed carrot with muscular legs — is this costs more than simply charging the car from the grid throughout Australia.  This is because:

In addition to these points there are retail electricity plans available now that can — at least potentially — lower the cost of charging an electric car.  These are likely to become more common in the future.

It may seem obvious solar electricity used to charge a car can’t also receive a solar feed-in tariff.  It’s like what my father told me when I wanted to marry two women, “You can’t have your Kate and Edith as well.”  But people who don’t know the ins and outs of solar power and energy storage can’t be blamed for not knowing this.  There are battery salespeople who deliberately ignore it in their spiels about battery savings and then there are those who don’t even understand it’s necessary.  This means they’re advising people without knowing the very basics of how battery payback works.  That’s pretty scary.

The amount of solar feed-in tariff you get depends on your location and electricity plan.  In Perth it’s fixed at only 7.1 cents per kilowatt-hour.1  In Sydney Origin Energy is currently offering a plan with a 21 cent feed-in tariff.  This is more than what they now offer in South Australia.

The lower your feed-in tariff the less it will cost to charge a battery with solar, but the cost will be increased by…

I recently looked at a report from the Canberra Battery Test Centre and estimated, on average, home batteries only provide around 84% of the energy put into them.  If I bump that figure up to 85%, around 1.2 kilowatt-hours will still need to be put into a battery to get 1 kilowatt-hour out.  This means if you have a 7.1 cent feed-in tariff in Western Australia to use one kilowatt-hour of stored electricity will require 8.6 cents of solar electricity, while with a 16 cent feed-in tariff 19.2 cents worth will be needed.

There are also losses when charging an EV’s battery, but if you are going to use an electric car these are pretty much unavoidable, so I’ll ignore them.2

Like most things in life, the more a battery is used the more wear and tear it suffers.  (One of these days my sarcasm is going to be completely worn out.)  There is only a limited amount of energy a battery system can provide during its lifetime, so its cost per stored kilowatt-hour provided needs to be accounted for.  If we consider a Tesla Powerwall 2 — the most famous of home battery systems — and use the following assumptions:

This results in the cost of the battery system per kilowatt-hour of stored energy being 33.7 cents.  As that’s more than most Australians pay for grid electricity it’s clearly not going to pay for itself.  Including the cost of foregone solar feed-in tariff just makes it worse.

To be thorough this figure should also include the cost of capital, but I’m not going to worry about it.  Just keep it in the back of your mind the real cost will be a little worse.

It is possible the cost of batteries will soon come down or maybe it’s possible to just get a really good deal now, so I’m going to assume the cost of a battery is only going to come to 30 cents per kilowatt-hour in most of Australia and only 17.4 cents in South Australia due to that state’s hefty battery subsidy.

If we take the cost of the battery system per kilowatt-hour and add the cost of the foregone feed-in tariff and compare it to the cost of a standard tariff in each capital we get the following:

As you can see, even using an optimistic example, it costs more to charge a car with solar power from a battery than to simply use grid power on a standard tariff in every capital.  The only place it comes close to paying for itself is Adelaide and that’s only thanks to the substantial battery subsidy available there.

Darwin is the worst capital for charging an electric car from a home battery thanks to having the nation’s highest feed-in tariff, while Canberra is the second worse thanks to having Australia’s lowest electricity prices.

While things already look awful, a standard tariff is not the only way to pay for grid electricity to charge a car and other options can make the comparison considerably worse.

Depending on your location there are a number of ways already available to charge a car with grid electricity at a lower cost than a standard tariff.  These include:

Other methods of charging an electric car at reduced cost are likely to become available in the future.  If an EV charger is smart enough it will enable charging when electricity prices are low, zero, or even negative — meaning at times the household will be paid for charging their battery and potentially for consuming electricity in the home.  This graph from Thursday last week shows several periods of negative electricity prices in South Australia on a windy day:

Prices fell to negative 50 cents per kilowatt-hour.  Being able to take advantage of events like this is clearly useful and in two years time it will become possible to pay for electricity in 5 minute blocks rather than having the price averaged over 30 minutes.  This graph shows 5 minute prices on that day:

There were many, brief, 5 minute periods when the wholesale price of electricity dropped down to negative $1 per kilowatt-hour.  EV chargers and home batteries that can make use of these 5 minute settlement periods will have a considerable advantage.  On the other hand, the more storage capacity there is the less often electricity prices will go negative.  We are still in the early days of allowing households to take advantage of swings in wholesale electricity prices and it remains to be seen how much they will help home batteries pay for themselves.

You may not care how much it costs to charge an electric car with a home battery and just want to do it to help the environment.  That’s a great attitude, but not a great idea.  This is because using a home battery is bad for the environment as it increases emissions.

As I explain here, each kilowatt-hour of solar electricity sent into the grid for a feed-in tariff will reduce fossil fuel generation by around one kilowatt-hour.  But because of charging and discharging losses a kilowatt-hour of solar electricity stored in a battery will only reduce fossil fuel generation by around 0.85 kilowatt-hours.  This makes it better for the environment to send surplus solar electricity into the grid than storing it in a battery.  As renewable generation increases and coal power stations are shut down this should change, but unfortunately it’s likely to take Australia more than 5 years to get to that point.

In this section I’ll cover some situations where my contention that charging an electric car with a battery doesn’t make economic or environmental sense may not apply.

Unless there are special circumstances, charging an electric car with a home battery won’t  pay for itself anytime soon and it’s also likely to remain an environmental negative for a considerable time.  However, while it seems unlikely to me, if technology changes fast enough it may make sense within 5 years.

So feel free to go out and buy that electric car without worrying about having enough home-battery storage to charge it every night.

Many years ago now, Ronald Brakels was born in Toowoomba. He first rose to international prominence when his township took up a collection to send him to Japan, which was the furthest they could manage with the money they raised. He became passionately interested in environmental matters upon his return to Australia when the local Mayor met him at the airport and explained it was far too dangerous for him to return to Toowoomba on account of climate change and mutant attack goats. Ronald then moved to a property in the Adelaide Hills where he now lives with his horse, Tonto 23.

That’s a good question. I know in Queensland Ergon allows electric car chargers to be on economy tariffs 31 and 33 provided the charger is hard wired so it can only be used when the economy tariff is available. I don’t know what the rules are off the top of my head for the rest of Australia. I know that according to some DNSP’s terms of use you are not permitted to connect the latest Nissan Leaf to the grid because it has the ability to provide electricity to the grid. (But I doubt that will be enforced provided people are only taking electricity from the grid.)

Powershop has an offpeak 9c inc gst off peak rate from 12-7am for anyone with a registered ev, benifit is also the rest of the house get the rate too, so you can schedule appliances or even top up your home battery for cheap

Lets enjoy the peace before some tiresome twit tells us we are all idiots for even thinking about buying a fancy new electric car when anyone with half a brain could build their own billy-cart for free!

Test-drove a Tesla model S a while back – very impressed – but will have to wait a while until my existing car needs replacement, maybe then go for a Model 3 instead (in WA a good range is mandatory).

….. and my guess would be that YOU couldn’t build a billy-cart… . And might one add that a billy-cart is an infinitely more cost-efficient and environmentally-friendly mode of transport than even a battery-powered Dinky Toy. It’s accepted that it probably wouldn’t impress the neighbours nearly as a much as a multi-thousand-dollar Gee-Whiz-Mobile. …. and as for the much-vaunted ROI on the capital outlay….. the mind boggles as much as loss of capital gains! (Though one supposes you’d buy it on the Never-Never, which would normally cost you 250% of the advertised price-tag. …Can anyone remind me of the olde saying about a fool and his money?

ps…….electric cars were tried and found hopelessly inadequate 100+ years ago, and discarded as a useful option.. I remember Grandma Duck’s one was forever creating problems.

We have just upgraded our solar from 3.2 Kwh to 10 Kwh, turned off our gas heating, and installed a battery with a link to the Reposit power guys in Canberra who manage our export limited system online.

We have gone with a high tech panel heating solution which is definitely not cheap to run compared with RCAC but we dont like blown air heating although it is taking us some time to learn to run efficiently.

Our daily driver is a Nissan Leaf, and because we work part time it gets charged a couple of times per week – some of that is during the day.

We “shop” for green-sourced power through Powershop but we are still drawing big chunks of energy from the grid. According to your analysis we seem to be doing a lot of things wrong, but our saving grace might be that although we cannot control who puts energy into the grid, we can choose who we pay to take it out. Maybe.

Anyway, we are here for the long haul and I have calculated an ROI on our current setup at around 11 years.

One thing we have learnt through our journey is that generating your own power come with a responsibilty to manage your daily life in regard to the weather and your energy requirements (I have never been more aware of the weather since starting this transition).

Keep up the good work and we look forward to hopefully hearing better news about batteries in the future.

You don’t need to to fit caveats into your headlines. All you need to do is pop a “*” (an asterisk) at the end of the headline, just like everyone else does.

There fixed that for you. Saying hybrids easily beat EV emissions is just wrong….You need caveats for your caveats. Emissions are a state by state proposition so if charging 100% from the grid then the comparison changes. Charging with rooftop solar will further alter those calculations.

Top Gear ran a competition for fuel economy around their racetrack, between a Prius Hybrid, and a high-end, very powerful BMW M3. The “deal” was for the Prius to be driven as hard as possible for a given number of circuits, and the M3 to basically follow it around at the same speed (obviously having a very easy time of it). The result – the much more powerful M3 was about 5-10% more fuel efficient. The conclusion – it’s not so much what you drive, but how you drive, that impacts fuel economy. Fuel consumption relates directly to CO2 emissions.

Here in WA, we could fully charge a 62 kWhr Tesla Model 3 “Standard Range Plus” from fully flat using excess Solar generation, for less than $5 of forgone FiT (only 7.135 c/kWhr here, 92 % losses one way). For an advertised range of 460 km, and I’d say virtually zero emissions (ignoring the manufacturing and delivery processes). A little over 1 cent per kilometre travelled, if you assume the capital cost of the solar system is being recovered by other means. Compare this with my near-equivalent I.C. car, which burns about 6.5 litres of fuel/100 km costing about 10 cents per km – producing much CO2 to do so. The EV also has much lower maintenance costs. However – I think you’d have to also factor in the replacement cost of the EV battery with these figures, to get a meaningful cost comparison. As far as emissions go, I’d say it was no contest – although I guess you could still argue that the foregone FiT represents a lost opportunity cost for reducing emissions elsewhere. But, I wouldn’t want to use a battery in between, for all the costs and emissions penalties Ron has presented.

I live in Perth and have a 6.5 kWh solar with Powerwall setup. Our lovely Synergy (the only provider in Perth) refuses to pay for my exported power as they claim my 3 phase power makes it impossible to tell if I’m exporting solar or already imported grid power. They don’t care that the battery isn’t configured to store grid power at all.

So to not hand over power to them for free I need to use as much of my solar generation as possible at home. Therefore I believe charging an EV from solar and battery would make perfect sense.

Wow Kim – that is an interesting issue. I, too, live in Perth, have 6.24 kW nominal panel capacity driving a 3-phase 5kW inverter, but no batteries. In my case, I may be importing on one phase (nett), and exporting on another – but the Smart meter simply takes the total nett power into account – whether it’s a nett import, or export.

Why would they think you would want to import power costing 28.2 c/kWhr to charge a battery, lose 15% of that in battery return trip, and sell it back to them at 85% of 7.135 c/kWhr? And even if you did, surely that is only a benefit to them? Unless they’re concerned about “time shifting” around a Time of Day type tariff – but even then?

I’d write to my local minister, and ask for a clear explanation of their reasons from the State Energy Minister.

Great article but not sure on some of your assumptions here. I had a Tesla Powerwall installed for 12,500 full cost onto my existing 5 year old 5kw solar through Origin at 24 months intrest free without any government incentives which are now readily available in most states dropping the price well below 10k for the 13.5kw battery.

The Tesla Powerwall allows time shifting in the App for those on smart meters to maximize not just solar but off peak power usage topped put from the grid without the need for reposit style or vpp extra cost installs.

Smart meters can also be installed for free in most areas to take advantage of time shifting (i got mine through powershop) in Brisbane free.

At the current time, off-peak is predominately supplied by coal. It may be ideological, but it’s important to some people, and decreased demand will drive the wholesale price of power during off-peak lower.

Export limitations and adding battery to your existing hybrid system allowing you to add extra panels, ie; solaredge SEx000 (non HD-wave series), How much does this affect the calculation?

A short reminder that in July, feed-in tariffs were generally slashed (along with retailer profitability) due to revision of the standing offer plans, and they slashed the “market offer” plans.

In future, I see the price of the FIT being slashed again, and we’ll need to re-visit the evaluation.

So currently, we’re awaiting: 1) Price drops on batteries (stubbornly staying high due to increased demand) 2) Car Chargers supporting feed-in (to make your low FIT + battery per kWh costs less than peak tariffs. 3)

I see you have picked up on Synergy’s (WA) recent 1.75% tariff hike – to 28.8 c/kWhr after tax – at least my system will now pay for itself just that little more quickly (sorry – looking for an upside!).

They also hiked our supply charge by 1.75% – but I did notice they left the FiT at 7.135 c/kWh! Annually, the supply charge is by far and away our biggest nett cost component.

Very thought-provoking. We have 6.5 kW panels and 6 kWh batteries, in WA. My plan was to plug the future EV car into the house when the house batteries were full (usually the early afternoon). The cost would be the forgone (pathetic) feedin tariff.

So (as Ronald reminds us) if home batteries are currently uneconomic how do electric cars stack up ? How long before you are back in the black driving one (not counting one you can claim a business tax deduction – just a home user) ?

Would like to see a detailed running cost comparison to the average home fuel powered vehicle. If anyone has see a layman’s comparison already done then would appreciate a link.

“The total cost of ownership of some electric vehicles in Australia could match that of their petrol and diesel equivalents as soon as next year, according to BloombergNEF, and – with the right policies – the share of new vehicle sales could reach 50 per cent by 2030 as targeted by Labor.” See: https://thedriven.io/2019/04/30/total-cost-of-evs-in-australia-may-match-petrol-cars-by-next-year/

The post includes an illustrative graph showing the projected declines in the total cost of ownership of BEVs from 2017 through 2029. Whether that is likely to be accurate remains to be seen – who knows?

Battery electric vehicles (BEVs) are already operationally more energy efficient (73%), compared with hydrogen fuel-cell electric vehicles (HFCEVs – 22%) and power-to-liquid fuel internal combustion vehicles (P2L-ICE – 13%) – in the terms from energy generation to final drive to wheels. See: https://twitter.com/transenv/status/899976235794788352?lang=en

Posted Jul 16 at Bloomberg is an article headlined “Fossil Fuels Are Far Less Efficient Than Previously Thought”, by Luke McGrath. The article is sub-titled:

“Fossil fuels, long regarded for their high-energy return on investment, are not as efficient as once thought. In fact, their final yields are not much better than those of renewable options, according to a new study.” See: https://www.bloomberg.com/news/articles/2019-07-16/fossil-fuels-are-far-less-efficient-than-previously-thought

The study referred to in the Bloomberg post is here:https://www.nature.com/articles/s41560-019-0425-z

Meanwhile, petroleum fuel prices are likely continue to rise. “Resources and Energy Quarterly – June 2019” (published Jul 1) includes on page 64:

“The introduction of a low-sulphur bunker fuel standard for international shipping in 2020 may put upward pressure on the price of crude oils that refineries use to meet the standard, and downward pressure on crude grades typically used to make the (current standard) high sulphur fuel oil (Box 8.1).” See: https://www.industry.gov.au/data-and-publications/resources-and-energy-quarterly-june-2019

Also see: https://www.reuters.com/article/us-imo-shipping-usa-refiners/new-marine-fuel-rules-to-boost-diesel-prices-for-at-least-a-year-analysts-idUSKCN1TB2CJ

However our RAC in WA has undertaken some quite detailed analyses for a broad range of both electric and i.c.engine vehicles of various types, to fully compare total vehicle cost-of-ownership – although done for WA, I think this may well answer your question.https://rac.com.au/car-motoring/info/buying-a-car/running-costs If you go down to near the bottom of the article, you can download in PDF format the details for a range of electric cars, and SUV’s, people movers, etc.

““how long is a piece of string”! you ask…… Any lateral thinker would tell you it’s twice the length as it is from the middle to one end.

Just don’t move house too soon or you may still be paying for a system you don’t own. We are %70 off grid. We could not afford to buy the size battery bank in lithium but have 12 x 530 ah agm and panels which power our house 24/7 except for electric oven, welding and occasionall dryer. Hot water is off peak $45 per quater so solar h/w not viable.

Oh come on now Richard! You KNOW that that’s Billy-Cart-Age technology! What WILL the know-all neighbours say?

It’s one thing to buy a Triple A Grade rated battery from the absolute best manufacturer of such battery in the entire world (whoever that may be).

According to this 9 News item published just a few hours ago at:https://www.9news.com.au/national/industry-unprepared-for-nsw-solar-plan/46acee24-66ee-4ea2-b83c-73e1a300f24e

“High installation rate with an unprepared workforce, poor training, poor auditing scheme leads to injury/death/reputational damage,” the document, seen by AAP, said. There is also a significant risk of medium- to low-income families being “enticed” into loans they may not be able to pay back. ”

– Australia’s leading energy retailer can’t even organize the installation of new electricity meters without stuffing it up.

– There’s manufacturers around who can’t even make electric scooters for kids that won’t catch fire (see https://au.pcmag.com/ninebot-by-segway-minipro/59406/lime-remotely-kills-2k-scooters-that-may-catch-fire)

– Audi has just recalled its new EV due to ‘fire risk’ (see https://www.thetruthaboutcars.com/2019/06/audis-first-electric-vehicle-recalled-over-fire-risk/). One would think they would have learned from Tesla’s experience (Tesla can proudly make claim to being first in such events)

– State Governments (such as Queensland) that change the rules every12 months or so on just about everything connected with solar installations.

Seems naive to me to expect that anything different from the above will happen in the rather infant EV and home battery market, given the state of affairs that exists at the moment with what’s already around.

So, waiting at least 5 years as Ron suggests seems very good advice to me. At least that way you might well avoid the possibility of ending up with the solar equivalent of a ‘My Little Gumnuts Wet Bag’ ( see: https://www.catch.com.au/product/wet-bag-woodlands-wonderland-large-3909573/?st=2&sid=wet%20bags&sp=3&asp=3&aqi=30a54b67aeb1c6e19111ac364c752a52 )

Hopefully, in 5 years time, we’ll have sorted out the problems that already exist (including grid related issues), rather than adding yet another layer of even more complex ones on top of things.

I’ve been looking how we could get “off grid” for some time now – but for us it’s just way too uneconomic.

What do you mean “70%” off-grid? Do you still pay the daily supply charge, to allow you to run the oven, welder, etc., when necessary?

If I was to spend the money and buy an EV, I would install a Stand Alone system solar/battery/inverter/EV charger. That would enable charging whenever I wanted, and not effect my FiT. Possibly make use of some of the excess in the house/garage.

And for a domestic Standalone Solution (PV – Battery – Inverter) – 15 KW+ PV is the sweet spot (plus 20 KW 1/3 Phase Standalone Inverter). A comparably sized Battery Bank can vary in both chemistry and capacity a bit, and Permanent System Autonomy Smart Load Control Logic is essential.

Charging an electric car with a grid-connected solar-battery is worse for the environment than simply charging it from the grid.”

Is there any reason you omitted the third and most obvious answer?? —> (Google): Charging Electric Cars with Solar Power. SolarEdge released a new solar inverter that charges EVs for a more efficient energy transfer. Owning an electric car that is charged by a solar power system is an excellent way to ensure your transportation is both cost-efficient and emissions-free.

Well of course it aint necessarily so. If you are not connected to the grid & a connection costs $50-100k! I still aim to use solar (daytime) charging though.

Howdy Ronald I’m interested to hear what you think about the “greenest” way to charge an electric car.

We just bought a Kona EV which has a pretty large battery, so we don’t need to charge it often (once or twice a week). We’ve also got 6 kW of solar which exports much more than we need to charge the car.

So we’ve got a couple of choices- a) only charge the car during the day when we’re exporting solar; or b) only charge the car at night and purchase 100% accredited greenpower

I figure that option (b) is probably the greenest (although the most expensive): let’s say I export 100 kWh/week, and my car needs 40 kWh/week to charge it, I get: option a) The grid is supplied with 60 kWh/week of renewable energy from my solar, vs

option b) The grid is supplied with 100 kWh/week of my solar, plus a further 40 kW of accredited greenpower, i.e. 140 kWh/week. That means an extra 80 kWh/week of non-renewable that I have displaced from the grid.

But maybe it’s not as simple as that, because option (a): I’m adding energy when there’s already a glut of solar power available that can’t be used or stored, which makes it harder for solar farms to make moneyhttps://www.abc.net.au/news/2020-01-28/solar-profits-threatened-by-nem-rules-killing-investment/11903706 option (b): I’m consuming power at night when renewable energy is in shorter supply, hence increasing the demand for non-renewables and improving their profitability.

ah – just realised that I phrased that last part badly; what I meant was: But maybe it’s not as simple as that, because for option (b) I’m adding extra energy to the grid when there’s already a glut of solar power available that can’t be used or stored, which makes it harder for solar farms to make moneyhttps://www.abc.net.au/news/2020-01-28/solar-profits-threatened-by-nem-rules-killing-investment/11903706 And I’m consuming more power at night when renewable energy is in shorter supply, hence propping up the demand for non-renewables and increasing their profitability.

Of the 2 options (b) will result in the least emissions. While you are correct this will very slightly push down electricity prices during the day and discourage the building of new solar farms, this effect may be countered by low daytime electricity prices during the day resulting in more coal generators leaving the market, so I wouldn’t worry too much about that side of things. But if you want to help take strain off the grid and help reduce grid over voltage issues, then charge your car in the middle of the day.

I’ll mention that low off-peak rates and or controlled loads will become available in the middle of the day in the future. For example, I’m in Queensland at the moment and here it is normal for the off peak hot water systems to be turned on during the day. So you could end up charging your car at a cheap rate in the daytime.

Richard consider installing a Specific Circuits Off Grid [Standalone] System for your EV and add some other circuits [possibly pool filter or HWS etc] with duty cycles that suit daytime PV Power sources only.

Of course if needed, these circuits [or some of them] can be switched back to Grid supply via COS if required at any time.

This is a common commercial factory scenario where the business in mainly a day time operation and therefore efficiently suits an Off Grid Solution; but the same logic applies to domestic premises also.

Importantly you can install an Off Grid [Standalone] System at your premises as well as having an On Grid System already in place and the Off Grid System qualifies for STC’s at the PV nameplate value.

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