Green Oversite



The All Electric House

By Bruce Barbour - February 2020

When I walk around new estates it still seems that connecting gas to new houses is still very popular. It seems that builders put this in by default - because that is the way they have done it for the last umpteen years - and it may still be the cheapest in terms of initial build cost. However a number of recent studies have suggested that economically and environmentally it is better to go all electric. I certainly did when I built my new house 3 years ago - a decision that I am very happy with.

Here are two of the reports:
There is also a Facebook group called "My Efficient Electric Home" that might be worth a look - not that I like Facebook. At least you don't have to be registered with Facebook to read this page.
Rather than just relying on the above reports before I go on I will look at why it is worthwhile to go all electric.

Financial: - Gas costs 3.53 to 2.31 cents per MegaJoule (MJ) - AGL Victoria "freedom" tariff inc GST - January 2020. The lower rate is for larger usage. Say electricity purchased from the grid costs 30 c/kWh. This is equivalent to 8.3 c/MJ (30/3.6). I hear you say - this is still more expensive than gas. Yes it is but when you account for the efficiency of use the story changes.

For gas you might have (generously) a 90% efficiency for the very best gas space heater. If using ducted heating or older heating systems this efficiency will probably be a lot less lower - 70% or even lower.  For electricity used by heat pumps (for water and space heating) you should get an efficiency of 300%. This is quite variable - depending on the make and model of the heat pump and also the external temperatures. It could be higher or lower. I will use 300% as an average. Using these factors the usable cost per MJ of gas is 3.92 to 2.56 c/MJ.  The usable cost per MJ for electricity used for heating with a heat pump is 2.76 c/MJ. So heating from electricity is cheaper for all but the highest energy users.

There are other factors that further improve the favourability of electricity. If you have a solar system then the marginal cost of electricity while the sun shines is zero - or if you consider the loss of income from selling that electricity back to the grid, 10.2 c/kWh (Victorian standard solar feed-in tariff). Further, if you have no gas to your house you don't have to pay the quarterly connection fee of approx. $90 ($360 per annum). Most of the commentators that I have read, including AEMO, predict that the cost of natural gas in Australia will increase substantially over the coming years. All in all, electricity is a better financial proposition.

Environmental: - This is less straight forward than the financial comparison. Natural gas - primarily methane - has a carbon content of 0.051 kg(CO2)/MJ. Electricity in Victoria has a carbon content of 1.02 kg/kWh or 0.28 kg(CO2)/MJ (see Note 1). This is 5.5 times the carbon content of natural gas - due to the use of Victoria's dirty brown coal for generating most of the electricity. When the efficiency of use coefficients are applied (90% for gas and 300% for electricity used through a heat pump) the comparison is 0.057 kg(CO2)/MJ for natural gas and 0.094 kg(CO2)/MJ for electricity. Using this analysis gas seems to still have an advantage over electricity generated from fossil fuels in Victoria. However there are a number of factors that make this not so:
  • the extraction and distribution of natural gas leads to what are called (some what mistakenly) fugitive emissions. That is gas - which is largely methane - that leaks into the atmosphere. On occasions as part of the gas extraction and production process methane may be deliberately released into the atmosphere. The industry may also deliberately release carbon dioxide into the atmosphere as often with lower quality gas fields the gas contains a mixture of both methane and carbon dioxide. The carbon dioxide is vented off into the atmosphere as a waste material. This is worse as the gas fields get to their end of use and lower quality gas, and also with newer extraction methods such as fracking. Frankly the size of the release/escape of methane and carbon dioxide during production and distribution is unknown - or if it is known it is not being told to us by the industry. Watch the video for further information.
  • if you use electricity from a roof top solar PV system or you purchase "green power" then the amount of carbon produced from that electricity is much lower (if not zero).
  • And remember I have used the very best gas burning efficiency - it can be a whole lot worse. I have also used a very conservative coefficient of performance (COP) for the reverse cycle air conditioner. The COP for a modern air conditioner can be over 400%.
Note 1: I was surprised that the amount of CO2 from Victorian electricity is still calculated as 1.02 kg/kWh. Over twenty years ago when I was doing a course on renewable energy the figure I was using then was 1.1 kg (CO2)/kWh for Victorian grid electricity. There has been a heck of lot of renewables introduced in intervening 20 years which I would have hoped would have reduced the average carbon content by more than 8 percent. However I can only use the figures published. As more renewables are introduced - as they have to be if we are to have any chance with climate change - and the coal power stations close down - this figure should improve. Ultimately we must be aiming for complete decarbonation of the economy, and this includes natural gas for domestic use. The figures for other states are lower than Victoria, ranging from 0.15 kg/kWh for Tasmania (due to all of their hydro) to 0.81 kg/kWh for NSW making the use of electricity more favourable in other states.

Note 2: If converting an existing house to all electric there are a couple of things to keep in mind. In Victoria especially you should include adding a PV system, if the house does not already have one, or allow for the purchase of 100% “Green Power” – preferably both. If shifting from a gas hot water service the new unit should either be solar thermal or (preferably) a heat pump. To just shift to a storage heated by an electrical resistance element (if these are indeed still available) would be retrograde step (unless this was substantially powered from the roof top PV system). Heat pumps should be used for the main heating functions – hot water and space heating. Resistance (preferably radiant) heating can be used for short term spot heating – say in a bathroom.
One of the issues in Victoria when I was building my new house was that there was a silly regulation in place  that said that if you did not connect gas you had to have a minimum 2kL rainwater tank - I assume that regulation is still in place. So there is an additional cost of a couple of grand to do that if you were not initially intending to have a rainwater tank - but still worthwhile.

If you do go all electric it is best to have a heat pump hot water system - with a reasonable storage tank size. When used in conjunction with a solar PV system with the hot water system set to heat in the middle of the day it works well. The PV should be at least 4 times the size of the energy use of the heat pump so that even in Winter the PV system will generate enough electricity to run the heat pump on the majority of days - so long as other usage is minimised in that period. (In winter I have programmed the air heater turn off at the time the hot water system starts up - at 11am. If there is sufficient sun it will be providing sufficient heating for the house from that time, if not earlier. If not, I will turn the AC heater on a couple of hours later, when the water heater has finished. This is of course not mandatory - you can run them both simultaneously if you need the heat in the house - you will just be using more grid electricity rather than the cheaper PV.)

If you have a good cook in the house it would be worthwhile investing in an induction cook top rather that a cheaper electric cook top. Also make sure any electric oven you purchase does not blow hot air into the room like my model does (making it unusable on warm summer days and inefficient on all other days.  For some reason ovens do not have an energy star rating, which means the manufacturers can get away with lower energy efficiency standards, with efficiency comparison to other brands and models very difficult. But that is another story.) For some reason quite a few of the modern units available blow heat out - so you may be stuck with this "feature".

Also use split RC air conditioning for heating (and cooling) - probably multi-head to allow for zoning which sections of the house are heated. It is more efficient than ducted due to losses in the ducting and more difficulty in zoning. The RC units should use inverter technology - I think most of them do but it is best to check. Inverter technology allows the RC unit to ramp up and down depending on the amount of heating (/cooling) that is needed. The alternative is that the unit is either working at maximum power or switched off on thermostat - an arrangement that is inherently less efficient than an inverter system for RC aircon and allows greater temperature variation in the room.

Think about how the house will be used and install additional doors if necessary to allow zoning.

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