Friday, May 10, 2013

Going green: what's the payback?

Going 'green', or installing technologies which lower your footprint, is mostly done by people who are interested more in saving the planet than saving a dollar. This certainly applies to us. The perception for many is that being green is more costly, so I thought I'd show you how going green has lowered not only our ecological footprint but also our bills.

When we recently installed a grey water system it made me reflect on all the things we've done in the last five years. These include solar PV, rain water harvesting, solar hot water, cargo bikes and grey water. I added up the costs of the above and it came to $33,500, which is a lot of money. But how much will these technologies save us in the long run? Well, here are my best estimates:

system cost  savings per year payback (years)
PV $6,500 $600 10.8
solar hot water $3,500 $300 11.7
rain water $10,000 $100 100.0
grey water $4,500 $50 90.0
cargo bikes $9,000 $5,000 1.8
Totals $33,500 $6,050 5.5

There are some surprises in there and I'll explain each one.

First, PV. We have a 1.1 kW Kaneka thin film solar PV system. It generates more or less what we consume (4.5 kWh a day) and we feed in 75% of what we generate to the grid. We are lucky enough to qualify for a now defunct feed in tariff, which means we get paid 48 cents a kWh for power fed to the grid. This makes our bills around -$60 a year (credit) and our bill would be around $550 a year without PV, so we save around $600 a year. This means the system will pay itself off in about 11 years and after that we'll be saving money for another 15-30 years. This was obviously a good investment of $6,500.

Our solar hot system (a Solahart 180L thermosiphon system), cost $3,500 two and half years ago and it saves us around $300 on our gas bill. We boost a little bit between May and October, but this only costs us $20 a year in electricity. The payback time is very similar to PV.

Water is so cheap in WA that there is no way our rain water or grey water systems will ever pay for themselves. Both systems were quite expensive ($10,000 and $4,500 respectively). The 14,000L tank needed lots of digging and piping, new gutters etc to install and is piped into everything (whole house and retic). The Grey Flow system was less expensive and feeds a lawn and fruit trees.We harvest 70,000L of rain water a year and probably about 50,000L of grey water and you can see that the savings aren't great. However this isn't a big deal for us since we see these technologies as more of a society benefit than anything else. The more water we can generate the more water there will be in the dams and the less the need for desalination and ground water use (and the less power used to pump them around).

The bikes have almost paid for themselves already. How can that be I hear you say. Well thanks to the bikes we got rid of our second car, which cost us at least $5,000 a year to run. These are not your average bikes, they're both electric cargo bikes (one is a Bakfiets long, the other a retrofitted electric Workcycles Fr8). They're dutch and they'll probably last longer than me. They get us to work, to the beach, shopping, school runs and more.

So the payback time for all this is five and a half years, not bad eh? Obviously payback times will be different for everyone, depending on the costs and savings involved. However this shows quite clearly that going green can save you lots of money, especially if you invest in areas where you get the best bang for your buck.


  1. Hi Adam,
    I wonder if you would mind giving me some info on the kind of electric conversion motor you used for the fr8, and how you find the motor copes with loads on hilly routes? We are considering the same.
    Many thanks,

  2. Hi Hanna
    The kit is an eZee 36V 14a kit we got from Glowworm Bicycles in Sydney. See this link for the install info:
    The motor goes really well considering the Fr8 is a quite heavy bike and I would definitely recommend it. It's not cheap ($1500 10a, $1,750 14a), but you get what you pay for. I haven't had a single fault in the year we've had it and it gets up quite steep hills well, you just need to drop the gear and put the assist on to full. Just talk to Maurice at Glowworm if you're in Australia, he's knows electric bikes back to front. The install was a fair bit of work so I'd consider getting a factory fitted electric bike if you don't have a bike to retrofit in mind (eg eZee or Whisper).
    Good luck with it, Adam

  3. Great post - My approach to greening our lives was based on this principal - fastest payback first. So far that's meant Solar PV, Solar HWS, E bikes, Wall cavity insulation, Double glazed windows, Wood stove/heater.... but no water tanks yet. That will come soon hopefully. As you mentioned, its more of a broader benefit to general society, but I see it as an important one, so the cash will be splashed - soon. Cheers, Michael from Suburban Digs.

  4. Hi Adam

    Some people baulk at the cost of green technology and will often dismiss it because the pay back periods are too long and therefore not worthwhile investments. But as you point out so well, when added up and averaged out, the returns on the investment made are actually quite good. It is regrettable that people view green purchases as 'investments' rather than 'essential" have to have items that are bought to secure a better future for our families and our society. I am reminded of my father who in his eighties bought a 2.2 kw system nearly 2 years ago. At his age he may never recover the cost but as he said "I'm doing it for the grandkids".