Near Canberra - What size off-grid solar system?

Hey all,

We are looking at getting another round of quotes for an off-grid system near Canberra (our build got delayed and our existing quote has gone up significantly).

Before I talk to more providers I wanted to get a better understanding of the kinds of specs we will actually need. This is our usage sheet:

Two questions:

  1. What size inverter/panels/batteries would make sense
  2. If we wanted to avoid a generator, how many days redundancy would we need (3 days?), and how would that change 1.

Hi Tom,

I’m an off-grid system designer in Vic and the load table is quite accurate considering your winter heating loads. The daily consumption of 25 to 30kWh is quite high for a residential off-grid system. A few quick calcs suggest the following:

  • Min Inverter-charger size 7.5kW
  • Min solar array size 15kW (optimum 20kW)
  • Min AC coupled solar inverter 10kW
  • Min battery bank 55kWh
  • Backup generator min size 10kVA

This is a very large and expensive system due to the large battery bank required which itself would cost around $40k alone. You really can’t survive a winter without a backup generator as you can easily have 4 to 5 very overcast days in succession. It may be possible with an alternative heating source but not if you are relying solely on the split system, you will need a gen-set.

What is the energy rating of the building? Have you maximised north-facing glass to increase passive heating. Double glazing etc.
The cost is directly proportional to the winter consumption (kWh) as this determines the battery and solar array size. Your heating loads may actually be considerably lower than estimated if the house is very well insulated and is maximised for passive heating.

Hope this helps,
Jason

Hey Jason,

Thanks so much for the reply.

Yeah I think trying to estimate the airconditioning, hot water and induction usage has been by far the hardest thing :joy: especially because we have been living in an old, not well insulated west facing house the last few years.

The new build will be very well insulated, north facing with a lot of glazing (all double glazed), concrete floors and it’s only 161m2 floor space with 2 adults living there full time:

It might be that this is more realistic in terms of the hot water, aircon and induction, which changes things pretty drastically:

You might find the real consumption is even lower than you expect since your new house is very well insulated, double-glassing etc. My 2 bedroom all-electric home uses 12 to 15kWh /day in mid-winter.

Oversizing the solar array is quite common these days and panels are relatively cheap so you should still stick with a larger 12kW+ solar array. However, the modern lithium battery banks used for off-grid solar systems such as Powerplus Energy are very modular and you could easily start out with a smaller battery capacity (around 35kWh) and see how it performs through winter. If it’s adequate then no worries, otherwise it’s very easy to increase the capacity so long as you have space available?

Where was the off-grid system going to be installed? Inside a shed?

Good to hear, I have asked out builder if there is any more information we can use to try and figure out how much we will need to use the air con so will see how that goes :slightly_smiling_face:

Space should be ok, we will have a carport that has a dedicated store area at the end which is 2m x 5.5m which we plan to house the system in.

Thanks for all the help, aiming to get 2-3 quotes as soon as I can so will post them up once I have them :pray:

Hi Tom,

I suggest you look at purchasing an 8 Panel Dual Axis-solar Tracker (DAT).
If fitted with say 8x 445W (3.56kW) Solar Panels 8 panels will generate 36kWh energy in 10 hours of Sunlight.
If fitted with say 8x 500W (4.0kW) Solar Panels 8 panels will generate 40kWh energy in 10 hours of Sunlight.

That will cost approx. $11k
30kWh (3x 10kWh) LiFePO4 will set you back $12k
OR …30kWh (2x 15kWh) Graphene Super Capacitor (SC) modules will set you back $30k
12kW Off-Grid Inverter with built in MPPT & AGS function $3.3k
6kW Silenced Gen-set (62dB) $2k (Commonly Only used during extended Bad Weather)
All up approx. TOTAL $28.3k

That is just the Supply cost of the Equipment, the Installation of a DAT unit is commonly Ground mounted, and is Not that difficult, as commonly installed by Farmers, as they usually have the equipment to dig a hole for a foundation Pole and a Trench back to where the Inverter & Batteries are installed/mounted.

Professionals charge approx. $150mt to Trench & Lay Conduit, that you just need a length of 4mm3 or 6mm3 Solar Cable back to the Inverter.

That system will supply Free Energy for the next 30years, excluding any equipment failures/damage etc.

Off-Grid is King ! :cowboy_hat_face:

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