Diagram of Michael Mobbs' Sustainable House Energy Monitoring System

“Here’s to it, and to it again. If you ever get to it to do it, and don’t do it,
may you never get to it to do it again.”

I’m 65. It’s unlikely during my lifetime  I’ll get back the money I’ve spent this year going off-grid.

Due to saving over $3000 a year I have got back much more than the $48,000 I spent going partly off-grid in 1996 (19 years x $3000 = $57,000).

But I’m confident that the sale value of my house (The Sustainable House), and other homeowners with off-grid features, whether just energy efficient appliances or such, is higher, too.

The running costs, or “liveability” of a house, is now figuring more strongly in both the minds and the pockets of house owners, buyers and the real estate industry.

Liveability is the key to higher prices and faster selling times, according to Cecille Weldon of the Centre for Liveability Real Estate. The centre is solely focused on training and promoting real estate agents to sell sustainable housing.

Michael Mobbs heading off-grid

Cecille says there are over 400 real estate agents specially trained to sell houses with sustainable items. She says the agents are now advocates who can sell sustainability features in the sale price and cut down the time to sell. For a list of the real estate agents go here.

This Burr is about the costs I’ve paid to go off-grid for electricity, along with costs for some other off-grid products and electricity use rates that apply to related projects.

The cost of going off-grid is directly affected by two things:

  • the amount of electricity used through the year – the higher the use, the higher the cost
  • the amount of sunlight which can be harvested at the site – the more sunlight, the lower the cost

Using very rough estimates based on projects I’m consulting on for consumers and businesses, and without doing a complete survey of all products on the Australian market now, the relationship between the amount of daily electricity use and system cost is in this range:

Daily average electricity use           Purchase cost (panels, inverter, batteries)

5 – 7 kWh                                                    $15,000 to   $35,000 – save ~ 4-10 tonnes air pollution

10 – 15 kWh                                                $25,000 to   $55,000 – save ~ 8-20 tonnes air pollution

These costs will bring an end to your electricity bills but they will also lose any savings you’re achieving from feed in tariffs and the savings you make by using your own solar electricity, which is not reflected in your bill (and which most people forget to consider.)

I’ve been working in the off-grid market and observing prices since I installed my solar grid-connected system in 1996. This year I’ve seen the costs of going off grid decline more rapidly than the decline of the price for solar panels; my rough estimate is battery prices in Australia this year have reduced by about 5 per cent with about 15 products now competing in the market and more coming.

There’s also some delightful commercial initiatives showing up in the Australian market with new energy companies and products.

Enova Energy, for instance is committing to paying higher prices for buying back solar power.

A new company, Allgrid Energy, claims it will go to market selling battery and inverter systems for less than $10,000.

And with the Adelaide City council offering $5000 rebates for battery systems there’s also leadership being shown in the public sector.

Here are the details of comparative costs between different size solar arrays.

The Sustainable House solar system costs and production analysis

 1996March 2015August 2015
Cost of panels (including inverter cost and installation fees)$26,000

18 panels x 120W


6 panels x 327W


6 panels x 260W

Cost of batteries and storage system$17,800

Alpha ESS storage system and batteries with 8kWh storage(1.5 days supply with no sun)


Battery with 2kWh storage (total of 10kwh storage; 2 days supply with no sun)

Additional credits$300/year

Selling energy back to the grid


One-time renewable energy credits


One-time renewable energy credits

Additional costs$550

To disconnect from grid

Total cost per kW of power production$11,820/kW solar power$4,600/kW solar power$2,430/kW solar power
Total cost per kWh of energy storage$2,225/kWh energy storage$1,500/kWh energy storage

Note: cost of panels in August 2015 were significantly lower than in March 2015 because the size of panels were lower but also because of falling prices in the market.

Expected panel production

Since the Sustainable House began producing solar power, there have been three major installations or upgrades. Below is a summary of the three installations and the total system capacity after each one:

DateInstallations and removalsTotal capacity
19968 x 120W panels installed16kW total
March 2015
  • 6 x 327W panels installed
  • 6 x 120W panels removed
40kW total capacity
August 2015
  • o 6 x 260W panels installed
  • 9 x 120W panels removed
52kW total capacity

We can estimate the average daily production by month for each system and then compare those values to what the different monitoring systems report.

1996 system: 2.1kW capacity
March 2015 system: 3.40 kW capacity
March 2015 system: detailed expected production
August 2015 system: 3.52kW capacity

Analysing the panel production before and after: the August 2015 solar system upgrade

The solar production analysis compares the panel production data reported by the available systems on 2 July 2015 to 6 July 2015 with the values reported on 12 August 2015 to 17 August 2015.

The upgrade to the solar system (six additional panels and 2kWh in additional storage) occurred on 5 August 2015.

Note: Before the system upgrade, Tigo values only reflect the solar production from the six 327W panels. After the system upgrade, Tigo values reflect the solar production from the six 327W panels and the six 260W panels.

  • The Alpha values reflect the solar production of the entire panel system both before and after the system upgrade.
  • As shown in the diagram on page 1, Tigo reports production at the panels while Alpha reports the power received at the system after wiring losses have occurred.
Pre-system upgrade (2.68kW)
Post-system upgrade (3.52kW)


Pre-system upgrade

  • Given our expected production values for July, the Alpha system is reporting daily production to be 1kWh less that we expected: 6.6kWh/day reported versus 7.6kWh/day expected production.
  • Given our expected production values for the new panels in July, the Tigo system is reporting daily production of 0.5kWh less than we expected: 3.9kWh/day reported versus 4.4kWh/day expected production.

Post-system upgrade

  • Given our expected production values for August, the Alpha system is reporting daily production to be 2.4kWh/day less that we expected: 7.2kWh/day reported versus 9.6kWh/day expected production.
  • Given our expected production values for the new panels in August, the Tigo system is reporting daily production of 1.5kWh less than we expected: 8.1kWh/day reported versus 9.6kWh/day expected production.

The expected values we’re using to compare to the reported production values are just estimates, and it’s not surprising that the actual production values are a bit lower than the expected estimates.

However, what does raise concern is the fact that the Alpha system is showing lower production values than Tigo. A likely explanation for this can be seen because the Alpha system is reporting production values after cable losses and Tigo is reporting production values at the panels.

If this is the case, it would seem that the system is losing roughly 1kWh per day due to inefficiencies in wiring transfers and conversion between DC and AC.

Further analysis needs to be conducted to confirm that this discrepancy is indeed due to wiring losses and determine if and how these losses can be reduced.

Analysing energy consumption before and after the August 2015 upgrade

This section is a technical analysis undertaken in conjunction with environmental engineer Marianna Verlage.

Like the analysis for solar panel production, the consumption data compares the usage reported by the available systems on 2 July 2015 to 15 July 2015 with the values reported on 12 August 2015 to 17 August 2015.

There is a discrepancy of about 1kWh/day between Alpha and the other reporting systems for energy consumption. However, unlike the differences observed in the solar production section, this discrepancy points more toward a possible calibration issue with Alpha as opposed to differences in where the energy is measured.

It is important to first acknowledge that the Efergy and Wattwatchers systems are reporting consumption values taken at the meter box which should represent the energy used by the house. The Alpha system however, is between the meter box and solar panels (see solar system diagram) and is not only reporting the energy used by the house but is also measuring the energy consumed by the storage system.

When only this information is taken into account, it would suggest that Alpha’s larger consumption values by roughly 1kWh/day represent the energy required to run the storage system. However, the Alpha system claims a <2 W consumption and an inverter efficiency of 97 per cent (for every kWh DC going in we should get 0.97 kWh AC coming out), so if these numbers are correct these shouldn’t be the sources of our losses. The battery efficiency is another possible source of power losses, and we will be looking into their efficiency further.

The reason we believe the Alpha system may not be calibrated or may have some software issues is because of the base load it reports.

The Alpha system shows an average base load for the house to be 0.25kW (it is important to note that to be conservative, we took the single lowest value reported by Alpha during the 12am-6am timeframe for each day, so the actual baseload Alpha reports is even higher than this). If we extrapolate just the base load out for the entire day, this results in a daily usage of 6kWh, which is higher than the total daily usage that Alpha reports.

Because of this uncertainty about the accuracy of the Alpha system, we cannot confidently conclude what the house’s average daily consumption is including the power used by the storage system. However, we can be fairly confident (given the values reported by both Efergy and Wattwatchers) that the energy consumption inside the house is between 4-5kWh per day with a base load of 0.85kW to 0.9kW. More research and analysis should be done to resolve the discrepancies with the Alpha system.

How much is your off-grid system worth to you – and to this starving bear?

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  1. There is one unfortunate consideration for those looking at going/constructing off grid at the moment. The majority of banks will not offer a mortgage for properties not connected to the electricity grid. At least for on-sales in the relatively short term this means that the number of potential buyers for off grid properties is much smaller. Hopefully this will change over the next few years?

    1. Hi, Sarah, that’s a very interesting bit of news. I have not heard that. Could you let me know where that information is or the list of banks? I’m very keen to know more about this if you can take a moment to let me know, please? My email is on my website if you wish to email me directly. Usually the financing equation has at its heart the capacity of the borrower to repay the loan. With lower outgoings for electricity the capacity to repay the loan is increased, not reduced. And some banks sell finance aimed at house purchasers or owner for properties with items that produce lower outgoings such as rain tanks, insulation, solar panels and batteries. Thank you, Michael

    2. Hi Sarah – some of our local credit unions offer reduced mortgage rates for NABERS rated homes – check out Summerland Credit Union and watch for Southern Cross Credit Union’s Green Loan launch shortly.

  2. After your “bulk Buy” scheme unfortunately failed to materialise, I went shopping, and have just signed up with Soltek for an additional 3kW system using Yingli Panda panels and a Growatt inverter (which, with my current system will give me just on 5kW after the 60c/kWh finishes next year, at a cost of $5140. It seems a good deal to me, what do you know of the company and hardware?

    1. Hi, Bon,
      You’re determination is inspiring to me. And sharing the information about the products as you have helps all of us who want to know the products and materials available to choose from. The quality of solar panels is somewhat independently assessed and they are rated into “tiers” one, two, etc. Your question about the quality of the products you’ve chosen is key to me and others so what I’ll do is a little follow up story or blog about the products you’ve chosen and others and aim to get it out in the next few weeks.

      I’m particularly impressed that you haven’t waited for the rock star product, Tesla, to arrive sometime later next year. Two reasons prompted me to go now and may have motivated you, too: Earth can’t wait that long, and independent technical reports on Tesla for solar are unclear and don’t cover the range of inverters that may or may not be compatible with it nor the additional cost of those other products – so why wait when all we have is a lot of PR?

      Watch this space, please. Thanks for sharing this, much appreciated, Michael

  3. Michael, your book ‘sustainable house’ put my husband and I on a mission towards sustainability. We’re now building an offgrid passivehaus in Gundaroo and we believe we won’t need heating or cooling. I’m adapting accounting standards so that firms can include their ecological capital on their books and we run a social enterprise called My Farm Shop to learn about how to market and supply sustainable, ethical meat to Canberrans. Your book and your subsequent work has continued to inspire us and keep us well-informed. Thank you very, very much.

    1. Sue, yours is a great story; people like you and your project inspire and I’m grateful you told it here on TFE. I’d love to blog, etc your project and work for others to know about so don’t hesitate to contact me via my website. Your accounting work will move mountains, I’m sure. Keep going, thank you, Michael