One Kilowatt Of Solar Makes Electric Cars Greener Than Hybrids

Electric cars beat hybrids on emissions

Electric cars beat hybrids on emissions thanks to additional rooftop solar power

Pop Quiz:  Which results in greater CO2 per kilometre?  An all electric car (EV) or a fuel efficient hybrid?

Answer:  An electric car charged from the Australian grid will result in around twice the emissions per kilometre driven.

Some find this surprising, while others already know Australia’s coal-heavy grid results in grid-charged EVs charged cooking the planet more than hybrids.  Possibly because I briefly mentioned it in this article two years ago.  But we can’t automatically conclude hybrids are environmentally better than fully electric vehicles.  It depends on the situation and there are several factors to consider:

  • Most new car buyers base their purchase at least partially on performance and electric cars can have far better acceleration than the typical hybrid.
  • The Australian grid is getting greener and coal generation has dropped from a peak of around 86% of generation to around 66% today.
  • It requires less than one additional kilowatt of rooftop solar to offset an electric car’s emissions, so they’ll be less than those of a fuel efficient hybrid if they are driven the average distance for Australian passenger cars.

Because many people will buy electric vehicles for their performance, a fuel efficient hybrid often won’t be an appropriate comparison, as the majority of EVs can seriously out-accelerate them.  Also, because buying an electric car often prompts people to install rooftop solar power or increase their current solar panel capacity, this can result in lower overall emissions than purchasing a non-plug-in hybrid.

While I don’t have any statistics on how much extra rooftop solar people are likely to install as a result of getting an EV, I know my boss Finn is looking at installing another 12 kilowatts of solar panels now he has a Tesla S to hoon around in.

Petrol Passenger Car Emissions

According to the Australian Bureau of Statistics, the average Australian petrol powered passenger vehicle only gets 9.4 kilometers to the litre.  This is awful, although a few places, such as Canada where people are in the habit of driving continental siege machines around, still have us beat.  It would be nice if we were improving in this area, but the nation’s vehicle fuel efficiency has been getting worse.

Only 9.4 kilometers to the litre comes to 106 ml of petrol per kilometre.  Burning this results in 244 grams of CO2 per farting out of the exhaust.  In addition to this there are emissions from extracting, refining, and transporting petroleum products.  One estimate is they equal 13% of the exhaust emissions, which makes the average emissions for Australian petrol passenger cars 275 grams per kilometer.

Hybrid Emissions

Finding out the tailpipe CO2 emissions of hybrid cars is easy enough thanks to the Australian Government’s Green Vehicle Guide site.1  I’ve put the information it gave me for the CO2 emissions and fuel consumption of six hybrids below.  These are not plug-in hybrids so they are only fueled by petrol and never charged with electricity.  (Emissions for plug-in hybrids are higher.)  I’ve underlined the grams of CO2 emitted per kilometer for combined cycle — a mix of town and country driving — in red:

Hybrid vehicle emissions comparison

Of these 6 hybrid vehicles 5 are Toyotas.  This is not surprising as Toyota developed modern hybrid cars2 and any hybrid you see probably uses their technology to some extent.  They were expecting the 2020s to be the decade of the hybrid car and my understanding is they were royally pissed off that full electrics stole the crown for “potentially most environmentally friendly vehicle”.  But Toyota has come around and will be selling a full electric car in their test market of China this year.

The emission figures in the graph above only show what comes out of the exhaust.  After they’re Increased by 13% to allow for emissions that result from getting petrol to the vehicle, the lowest emission hybrid results in around 90 grams of CO2 per kilometer.

While it’s possible for non-plug-in hybrids to become more fuel efficient in the future, there’s not much scope for this3 without reducing their performance and most research and development is now going into electric vehicles.

EV Emissions

The exhaust emissions of full electric vehicles are easy to work out.  They don’t have exhausts, so it’s zero.  But EVs do cause CO2 emissions when charged from the grid, as most of that energy comes from fossil fuels.  The good news is grid emissions are falling as renewable generating capacity expands.  This includes rooftop solar, so thanks to everyone who has installed it.

This report says the average emissions per kilowatt-hour for grid supplied electricity in the National Electricity Market — which doesn’t include WA or NT — is 720 grams per kilowatt-hour.  But just like oil there are also emissions from extracting and transporting fossil fuels and this adds roughly 11% to the total, increasing it to 800 grams.

To get emissions per kilometer we’ll need to know how many kilometers an electric car gets per kilowatt-hour.  Here’s how far a selection of electric vehicles travel on one kilowatt-hour of electrical energy from their battery packs according to the Green Vehicle Guide site:

Kilometres of EV range per kilowatt hour of battery energy

km per kWh – according to the government’s Green Car Guide website

There is a fair bit of variation with the Hyundai Ioniq coming out on top.  These distances are only for energy already in the car’s batteries and losses that occur getting that energy in there need to be accounted for.  These can come to less than 10%, but it depends on the battery and how it’s charged and can be much worse.  To keep things simple, I’m just assuming an electric car will travel 5 kilometers per kilowatt-hour of grid electricity.  This makes average EV emissions 160 grams per kilometer or twice that of the lowest emission hybrid.

Sorry! Your State or Territory Is Not Greener Than Any Other

Most people expect charging an electric vehicle in Tasmania or South Australia will result in lower emissions per kilometer because those states generate large amounts of grid power from renewables, but it doesn’t actually work that way.  If a car is charged with mostly renewable grid energy in Adelaide, that means South Australia will either export less clean energy to Victoria or import more dirty energy from there. While there can be a small advantage from charging in a state with high renewable penetration, it doesn’t make much difference.

If you are in Western Australia, which is the only state where the grid keeps its hands to itself and doesn’t touch anyone else’s, emissions per kilowatt-hour of grid electricity are close to the national average, coming in at a few percent lower.

65% Renewable Generation Lets Grid Charged EVs Beat Hybrids On Emissions

Over the last six months of 2019, grid electricity in the National Electricity Market was 78.7% generated from fossil fuels according to the Australian Energy Regulator:

Grid electricity source in Australia's NEM

Looking at the low value for solar power I see it’s not taking into account rooftop solar energy exported to the grid, so the actual figure may be around 75%.

Politicians have told us they’ll do whatever it takes to protect us from the coronavirus and keep the economy ticking over, but the current mob in power have been dragging their heels over global warming, which has the capacity to kill more people and cause more economic damage.  Despite this, we are likely to reach at least 50% renewable generation by 2030 simply because our most crapped out coal power stations will no longer be economical to run by then, even if the government does nothing to prevent them destabilizing the climate or poisoning the air.

Making generation 50% renewable won’t cut grid emissions in half because around one quarter of grid electricity already comes from solar energy, wind, and hydropower.  But because fossil fuel reductions will be concentrated on coal, it should cause emissions to drop by around one-third.  So when we hit that target electric vehicles will still produce around one quarter more emission per kilometer than the most efficient hybrids, but will be about on par with the Toyota Prius V and the Lexus ES 300h.  We may have to wait until the grid is around 65% renewable for typical grid charged electric vehicles to beat the best hybrids on emissions per kilometre.

EVs Out-Perform Hybrids

While it may take a tragically long period for grid charged EVs to beat fuel efficient hybrids on emissions per kilometre, this isn’t a reasonable comparison for the average car buyer.  When most Australians shop for a new car, one of their most important considerations is performance.  If this wasn’t true, most of our passenger cars would have engine capacities of one litre or less4 and someone who bought a car with a big, 1.2 litre engine, like my Hyundai Getz, would be considered a revhead and their significant other would probably consider them irresponsible for having car that costs $40 to fill the tank.

The appropriate comparison for electric vehicles usually won’t be a fuel efficient hybrid because they don’t come close to the performance of most electric cars.  Here’s the 0-100 km/h times for several hybrid passenger cars:

  • Toyota Corolla 7.8 seconds
  • Toyota Prius 9.4 seconds
  • Toyota Camry Accent 8.3 seconds
  • Lexus ES 300h 8.1 seconds

If we compare that to the acceleration times of a selection of electric vehicles, they can do much better:

  • 2019 Hyundai Ioniq electric: 9.9 seconds
  • 2018 Nissan Leaf: 8 seconds
  • BMW i3 BEV:  7.3 seconds
  • Tesla Model 3: Standard Range 5.9 seconds
  • Tesla Model 3 Long Range: 4.6 seconds
  • Tesla S P100-D: 2.7 seconds

While the most energy efficient electric vehicle on the list has slower acceleration than all the hybrids, the rest of the EVs have superior acceleration, with the Tesla S being downright ludicrous.  So the appropriate car to compare to a BMW i3 or a Tesla Model 3 to is not going to be a fuel efficient hybrid vehicle most of the time.  It’s going to be an internal combustion engine car with comparable acceleration, which is likely to have total emissions of around 275 grams of CO2 per kilometer or more.

Under 1 Kilowatt Of Additional Rooftop Solar Makes EVs Greener Than Hybrids

One very simple way to make an EV’s emissions per kilometer lower than a hybrid’s from day one, without having to wait for the grid to get greener, is to install additional rooftop solar capacity.  Just one kilowatt of extra panel capacity will reduce grid emissions by enough to offset the average electric passenger car’s emissions so they’ll be less than a fuel efficient hybrid.  It’s not necessary to directly charge the EV from rooftop solar panels.  The extra solar capacity will still reduce grid emissions even if the car never receives any power directly from the panels.

While it varies according to location, a good rule of thumb is one kilowatt of solar panels will generate an average of around 4 kilowatt-hours a day.  Here are the daily kilowatt-hour averages the the PVWatts site gives for 1 kilowatt of north facing solar in Australian capitals:

  • Adelaide:  4.1
  • Brisbane:  4.2
  • Canberra:  4.3
  • Darwin:  4.4
  • Hobart:  3.4
  • Melbourne:  3.8
  • Perth:  4.5
  • Sydney:  3.8

If one kilowatt-hour of solar electricity is sent into the grid it will reduce emissions by more than the 800 grams of CO2 per kilowatt-hour that results on average from grid electricity use.  Solar energy sent into the grid will very rarely reduce renewable generation and instead reduces fossil fuel generation.  This is because the fuel for solar, wind, and hydroelectricity is basically free and so renewables can outbid coal and gas generation that have to pay for their fuel.5.

Until coal power is driven from the energy market, each additional kilowatt-hour of solar power will reduce emissions roughly equal to the total emissions from mining, transporting, and burning coal; which is around 1 kilogram.6  So, one kilowatt of solar panels will reduce emissions by around 4 kilograms of CO2 per day.

Australian passenger vehicles are driven an average of 12,600 km a year.  This is only 34.5 kilometers a day.  This means the average daily emissions for the following vehicles will be:

  • Typical petrol powered passenger car 9,490 grams
  • Lowest emission hybrid vehicle: 2,760 grams
  • Grid charged electric car that gets 5km per kilowatt-hour:  5,520 grams

So, for the average daily driving distance of 34.5 kilometres, an electric car plus 700 watts of north facing solar panels will result in lower overall emissions per kilometer than the lowest emission hybrid without offsetting solar.  To completely offset the EV’s emissions would take 1.4 kilowatts.  These days only 4 panels are required to provide that capacity.

It Has To Be Additional Solar Capacity

To honestly claim rooftop solar is offsetting emissions from an EV — or any kind of vehicle — it has to be capacity that was installed for that purpose.  Finn, my boss, has had 6 kilowatts of solar panels on his roof for years but doesn’t pretend that includes capacity to offset emissions from driving his new Tesla S, even though those 6 kilowatts produced more energy over the year than his energy efficient straw house consumed before he bought his electric speed machine.

Instead, now that he has an EV, he is planning to install around an 12 extra kilowatts of solar capacity.  That should be more than enough to completely offset the emissions from 6 electric cars charged from the grid.  A number that will increase as the grid gets greener.

I’m not suggesting that it makes sense to install just 1.4 kilowatts of solar panels when you get an electric car.  But I will suggest that when buying a solar system you get the largest one you reasonably can to allow for future electric vehicle purchases.  If you have an existing solar system and get an electric car, you can consider installing an additional system if there is space on your roof.  Alternatively, you can replace a small solar power system with a larger one.

What Does This Mean If I Want To Be Green?

If you really want to be environmentally friendly I suggest you forget about cars and buy a bicycle.  They are even less environmentally damaging than horses.  (Trust me, I know.)  You can use the money you save to install rooftop solar.7  It doesn’t matter if it’s on your roof or someone else’s.  The environment doesn’t care.

If you’re not quite ready to give up on wheeled mobiles and are looking to buy a new car, then given an electric car at the moment is likely to set you back at least $45,000, the greenest way to go about it is either buy a small and fuel efficient internal combustion engine vehicle or a hybrid and spend the difference between that and an EV on solar power.

But if you are a typical new car buyer then, while you don’t want to harm the environment — unless you’re some kind evil dickhead — it’s not going to be the main factor influencing your purchase.  Most new car buyers consider performance to be more important.  And electric cars can provide more of this than any internal combustion vehicle in their price range.  In this case you can buy an electric vehicle, have the high performance you desire, and spend a little extra on a larger solar system to offset its emissions.  The extra solar capacity makes financial sense because it will pay for itself, sometimes in just a few years.

Electric cars are becoming more affordable so there won’t always be a such a large price differential between a low cost hybrid or conventional car and a low cost electric vehicle.  Because electric cars are so simple to make and battery prices are continuing to fall, once mass production brings costs down it should be possible to buy an EV, including its battery pack, for less than a petrol or diesel car.  With luck this won’t take long to happen.  China and India are the most likely locations for it to happen first, but it could occur anywhere.


  1. Even though it’s too stupid to do something basic like just showing emission for all hybrids
  2. Nazi Germany developed a prototype hybrid tank but gave up on it as they were more focused on global storming than global warming.
  3. While there are many things that could be done to further improve fuel efficiency, not many are likely to be cost effective and improvements that are, such as lighter materials, can also be used in electric vehicles.
  4. If Australians didn’t care about performance or air conditioning then most car engines would be 800cc or less.
  5. The cost of brown coal is very low, but all coal power plants have to pay operations and maintenance costs and these are particularly high for Australia’s aging brown coal power stations.  I’m surprised they keep spending money fixing them.
  6. Once all fugitive emissions that result from mining, transport, and methane emitted by coal, this figure is likely to come to more than 1 kg, but I will use the round figure.
  7. You can also consider other environmentally helpful measures such as insulating your home or buying a heat pump hot water system.

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