For this type of renovation to be appealing to everyone, it has to make sense economically. On this page we’re documenting all financial aspects of our sustainable build, contrasting the costs and savings with a “normal” build where possible, and outlining the methods and techniques we’ve developed to save money.
As part of that I’ll be displaying a series of calculations to show homeowners where the savings can be made and where the pain points are, starting with solar solution. The water solution is still being costed and I still have to finish the calculations for the building etc., but once they’re done I’ll put it all together so you can see what the total cost/benefits are for going completely off the grid. But first let’s look at solar.
Let’s begin with a solution that uses electricity from the grid and doesn’t use a battery. This is the solution most people will probably go for given it’s more cost effective than including a battery (as you’ll see in the calculations where I do include a battery). At the moment my bill is estimated to be around $800 a year for electricity and $160 a year for gas. I have also assumed that I won’t have to pay for gas and electricity connections at $340pa and $396pa respectively, a feed-in tariff of 10c per kWh. My electricity provider charges me 27.4c per kWh.
Roland and his team of solar experts have estimated that I will use about 12kWh a day (I actually use around 7kWh a day) and that I should be able to generate about 23kWh a day. Of this I will directly consume around 5.7kWh per day with the rest (7 – 5.7)kWh coming from the grid. I will be able to export around (23 – 5.7)kWh to the grid every day.
So my annual savings will be:
= 2,038
This chart shows the cumulative net cash flows discounted back to today’s dollars for each year over 15 years. In the first year I would incur a loss equal to the cost of the system less the annual savings. By year 4, my annual savings would have accumulated to a number greater than the cost of the system. So my payback period is 4 years. A great result!
With this solution I’ll be generating more electricity so I’ll be able to feed more into the grid. I should be able to generate about 26kWh a day. Of this I will be able to export around (26-5.7 = 20.3)kWh to the grid every day and will directly consume around 5.7kWh per day with the rest (7 – 5.7)kWh coming from the grid. So then my annual savings will end up being:
So my annual savings will be:
=2,149
The payback period is in year 7.
As before, this solution should generate about 26kWh a day. Of that 26kWh, I will directly use about 5.7kWh during the day, with 6.3kWh going into the battery, (26-5.7-6.3 = 14)kWh going to the grid and 6.1kWh being consumed from the battery.
So my annual savings will be:
= 2,047
This solution is expensive! And the payback period is LONG! So if the economics are more important than energy security, then this is probably not the solution for you.
I’m still working on the water solution and we aren’t sure how much the system will cost yet. But we will have the numbers very soon!
I’ll be doing a full projection of costs and savings for the “total solution” which will include:
I have some preliminary estimates of the total solution below but I need to do more work on the costings, especially for the water solution. At this early stage I estimate that by year 7 I will break even and then I will be making money on my solution without a battery. A really great result! The battery continues to be prohibitively costly. I’m planning on staying in the house for a long time, but maybe not 17 years.
The next step is to do some variations on the assumptions, (i.e. inflation, electricity feed in tariffs etc). I’ll post them to the site so you can get an idea of how these variables impact the cost effectiveness of going off the grid
There are two parts to the renovation. The off-grid part, and the building part. My plan is to detail the costs of the pre-fab and recycling against a “normal” build. I’ll then add those to the projections above.
Beyond reduced living costs and reducing my carbon footprint there are other benefits from incorporating sustainability into a home. (Laquatra, 1986) documents the improved re-sale value from improved thermal performance and (Jackson et al., 2009) show how adopting renewable energy adds to a home’s value. Domain has written that energy efficient homes can sell for as much as 10 per cent more.