All my electricity is green: my retailer buys RECS sufficient to back my electricity purchases. As such, I don’t care how much electricity I use, except such that it costs me money.

Breakeven analysis is fun.

My house has a twelve year old 160 litre resistive electric hot water service (HWS). General opinion seems to be that a HWS will last perhaps as long as 12 years before failing (my last house had one that was 30 years old and still going strong). It’s currently inside the house (taking up valuable floorspace), and may not survive being moved outside in the coming renovation. I want an instantaneous gas HWS (unlimited hot water at exactly the temperature I dictate), but refuse to use gas.

Instantaneous electric HWS exist and are only about $1000, but require three-phase power (an upgrade costing a surprisingly small $1000, plus electrical work on my side of the divide).  How much power will it consume?  Turns out, the same as resistive heating the water, but it’s all peak electricity.  That pushes its daily cost quite high.  There are other HWS options; reusing the existing tank (free-ish), replacing it with a larger tank (still resistive, $1000), sucking up all the spare electricity from the PV solar system (perhaps $1000), or a heat pump ($3400), and combinations of the above.

I was able to figure out how much electricity we’re using to power our HWS by virtue of it being on a separate meter to the rest of the house – 4.6kWh/day, costing about $0.85/day because it runs off peak. Hot water consumption is expected to increase after the renovations.  It turns out that how much hot water is consumed, and when, is very important for accurately pricing electricity consumption. I’ve a fairly complex spreadsheet modeling current and projected consumption patterns, and the resultant energy requirement timing and costs. We have a PV solar system, which is how I thought I could push our cost of hot water down – heat it from the panels during the day, when electricity is cheap for me ($0.119/kWh).  If your tank is too small (which ours will be/nearly is already) then you’ve got to heat using electricity other than cheap solar electricity.

I calculated the Total Cost of Ownership at the 5 year mark, and the average daily cost of hot water for the various options (note, this is for my projected hot water consumption profile – yours will differ, altering the values):

The heat pump can run off solar using its built-in clock, saving $1000 in diverter costs. You can see that its TCO is a little more than a salvage job on the existing HWS run from solar power, but the daily cost means the heat pump is going to pull away at a mad rate. Hot water that cheap is making me think of grand ways to heat my house.

All my electricity is green: my retailer buys RECS sufficient to back my electricity purchases. When I calculated my household’s Green House Gas emissions equivalence, we pulled in emissions below 15% of that of the average Australian household. In fact, our emissions were down to two sources: our car (7000 km/year @ 9l/100km – emitting a quarter of that of the average Australian household) and our natural gas consumption (20300MJ/year – home heating emissions 57% of that of the average Australian household).  Apparently emissions can vary from 3 to 30 tonnes/year – I’ve calculated my household at around 2.5 tonnes per year at the moment. I think we can do better. How about 1.5 tonnes per year?

I’ve had a poke around the non-hydrocarbon motorised transport market. There isn’t much there for me, cars are north of $50,000, lifespans are limited. If I could buy an electric car for $20,000 that was going to last 20 years, I’d be up for it. Because I can’t, hydrocarbons will continue to be used for this form of transport. Will revisit when car fails, I’m guessing in less than a decade. Besides, I’m pretty convinced “car ownership” will end up being something people did in the 20th century, not the 21st.

We don’t cook with gas; we have an induction cooktop. I hate electric cooking – resistive electric cooking. It’s inefficient, slow, too cold, too hot, ugly and messy and too expensive. I’ve always cooked on gas. Induction cooking has turned me around; it’s everything gas cooking is, without the explosions, burnt-on gunk, poisoning and GHG emissions.  However, it is fussy (it only works with ferrous cookware) but that’s inconvenient, not a showstopper (example: coffee pecolators are almost all aluminium, and those that aren’t have a very small base. The pecolator has to go in a small pot to be used).

Our gas consumption is purely for space heating via a ducted heating system. It costs less than $770/year to heat our house, so an electric replacement will need to be competitive with that. Having run the numbers, I’ve calculated our gas consumption produced 4000kWh of heat in the house each year. Doing that with air conditioners would (assuming 400% efficiency, which is pretty middle-of-the-road) require 1000kWh of electricity. I seem to pay about 30 cents/kWh (if you can figure out what your electricity actually costs you, I’d love to hear what you did to get that number), so that’s $300/year to run air conditioners instead of ducted heating. Payback is less than 10 years if $4000 is spent on adding aircon units.

From an environmental and financial perspective it’s time to ditch gas, so I’m off. Each gas bill raises the daily connection fee.  It’s about $1/day now, so if you don’t use much gas there’s an increasing incentive to use no gas at all. Nearly half my bill is for the privilege of having a gas supply.

But wait! I love wok cooking, and there’s almost no way to wok-fry stuff without gas. What to do? For a couple of years we’ve used a butane camp stove as a stop-gap until we got around to plumbing in our dedicated wok burner, but if we’re cutting off gas we’ll continue living like animals for the rest of our squalid lives! No fear, says my plumber: convert to LPG – like used for BBQ cooking. And so, we now happily wok-fry on gas, which I figure will cost us $30 – $60 a year to refill the bottle. $38 for the LPG conversion kit for the burner, which would have been avoided if I’d thought this all through a couple of years ago when buying the wok burner.

The next problem is: what to do about hot water?