How much solar power do I need?

Sizing your solar panel to suit your electricity needs can be a daunting task, but with our solar PV system guide you can find out how to calculate your home’s energy use, the system capacity you will need and other considerations such as the pros and cons of batteries.

Have a question on installing solar panels? Ask us in the comments below.


Sigh. I do wish that Choice would stop releasing tests of products that I’ve just purchased. I have just commissioned our hybrid solar system - 18 x 270W north facing panels, 5kW inverter & an 11.5kWh battery. This seems to be providing just about all of the power that our low use home needs at the moment (2 people, led lighting elec stove & oven, fridge, freezer & usual entertainment system & computers) though I need to change the settings on the heat pump HW system so that it doesn’t do its heating in the middle of the night when the ambient temperature is low & the battery at its minimum. Installed by Evergen who sized it all based upon our normal usage indicated by power bills & details of our home. I like the fact that it uses CSIRO developed intelligent software to learn our patterns of use & optimise the system’s operation.

Btw we decided to go solar after ACTew AGL advised us that our contract with them had finished, that they no longer bundled with other products, and that we needed to sign a new contract before they would allow us to see its terms & conditions - ‘just sign first, and we’ll send you the contract. If you don’t like it you have x days to let us know & cancel’. I contacted them three times & they said the same thing each time, so it wasn’t any sort of mistake. No thanks, that strikes me as being unconscionable behaviour, if not illegal. The PV system has cost a good chunk of our savings, but its a relief to be independent of ACTew’s clutches.


… from the article: "In southern regions such as Hobart it could be as low as 3.5kWh per day, while the same 1kW of panels in Darwin could generate 5kWh." … or somewhere in between the same 1 Kw of panels might give you 6 kWh per day - I ‘feed back’ a shade under 20 kWh per day with a total generation of about 30 kWh per day from 5 kW of panels, with feed in tariff equalling usage tariff … has to be some advantage living in the sand :wink:

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Some of the cons of lithium batteries is after a number of cycles, the storage capacity of the battery reduces. For example, when new, the Tesla Powerwall 6.4 kilowatt-hour battery is rated for a warranted storage of 5.44 kilowatt-hours. But after the first 2 years that drops to 4.6 kilowatt-hours. And 3 years later it drops down to only 3.8 kilowatt-hours of warranted storage.

Zinc Bromide batteries on the other hand will retain the rated storage for the battery life, but as significantly more expensive for the same storage capacity than lithium batteries.

If setting up an off the grid system, the deterioration of battery capacity over time/number of cycles needs to be considered as it will affect the initial storage capacity and PV generation required to maintain supply over the nominated battery life.

Battery size/storage volume and location may also be another consideration.


Thanks @draughtrider. I take it you’re located somewhere in the Northern Territory? Great place to go solar, with all that sunshine and a generous feed-in tariff too!


datashet, you still have your savings - you’ve simply moved them from “cash at bank” or whatever, to “solar power equipment”, increasing the capital value of your main asset - your home. What you can now look forward to is replenishment of your bank account, from the savings in electricity costs.

I’m planning to take this further. I intend to install a bank of solar panels, a back-up battery system and an emergency generator, and if it works as planned, take the house off grid, so that I don’t even have to pay for the existence of the connection to the power grid.

And I fully intend to plan it to provide for an electric car. Despite the hostile publicity launched at electric cars by the big oil companies, electric cars ARE coming. And I intend to have one. So my savings will be a great deal more than my present electricity power bill.


How practical is it to go off grid? Are we are asking the wrong question?

My recent requests for quotes (we use around 8kWh a day) left me with a 15yr pay back ignoring the fact the batteries would not last that long and not factoring in a backup source EG generator.

It may be better to consider what makes up the costs in our bills and to look for ways to improve.
Would it be simpler to look locally at community based power schemes?

Using only the existing local infrastructure we could all share power from our solar systems or a local solar farm.
Back up would not be limited to home batteries which may be more effective in a centralised system for peak demand and emergency back up.
Other forms of energy storage including pumped hydro or generation (wind) really work best at scale, and will not fit in the average backyard anyway.
It’s also a great way to take the load off the statewide grid. The grid would see a lighter load for power trading between areas that are short on solar etc on any given day.
It might also be a great way to transition out of the grid as more local schemes come on, all the older generators.

Why not take the whole local community off grid?

Going off grid as an individual risks a change to Government Policy forcing all land owners to pay for the availability of power at their property whether you connect or not. Foreign companies have invested in Australian utilities purchased from our governments with forecast growth in demand and a captive market. A near perfect guarantee of capital growth and increasing profits from greater demand.

While power prices are rising many modern homes now use less power. LED lighting, higher efficiency inverter air cons, lower power flat screens, better household insulation reducing cooling or heating loads etc. It appears that as we each use less it is costing us much more because the investors in the grid and generation need to maintain profits. The last consumer on grid will need deep pockets.


Very interesting thoughts @mark_m. I know there are at least some places in Australia solving energy problems on a localised community level, but I don’t think it’s super common. You make some good points about the expected growth and the possible regulatory or government intervention that could become factors in the future, depending on what consumers end up doing.

Tagging our @Energy-Campaigner group in case anyone would like to add their thoughts.


This is often raised, but I think that it would be impossible to implement now that the electricity networks have been sold off. Mandating you pay a private company for a service you dont use? … I can’t see that flying. In any case, if you refuse to pay because you aren’t using it, they can hardly disconnect you!

I’ve been off-grid since 1991, and whilst the power line passes about 350m from my house, I have no intention of connecting to the grid, whatever crazy plan a government might try to implement.


As our illustrious government often follows the lead from elsewhere don’t bet it cannot happen!

The Off-Grid Laws of Every State in America: What States Allow Off Grid Living? and

for illustration.


Hopefully those will remain ‘only in America’ stories :wink:


Well the Dutch once taxed the windmills. In some countries windows were taxed on the number in a house (so I guess how much sunlight they let in) in one place not repealed until 1920s (France). If a Government think they can do it you bet they will try.


… couldn’t happen here …


Any thing is possible.

Logic is not necessary.

It would exhaust all of us coming up with the many contrary examples and hypotheticals. I offer one that is not imaginary.

Just ask any farmer in NSW (re water allocations and licenses to harvest overland flows) why he has to pay the Government to be permitted to collect the rainfall that drops on his land and then pay for each Meg he uses?

Because the government of the day can.

This suggests strongly it is not beyond government to regulate and or tax even the collection of solar energy (or any other bright idea we have), windmills and windows not considered.

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