Rooftop solar panels

How to get the most out of your solar PV system part 2: What’s your electricity usage pattern?

by James Martin II on 7 June, 2016

in Installation advice,Solar system sizes

For anyone who has a solar PV system for your home/business or is thinking about getting one, understanding electricity usage patterns throughout the day is integral for guaranteeing a good return on investment. Previously we published an in-depth article about getting the most out of a solar PV system, with a focus appropriate system sizing & conscientious power usage.

(Part 1 of this series looks at solar PV system size selection considerations.)

Since that time, Warwick Johnston of solar consultancy SunWiz has published an excellent, data-centric article that investigates the topic of electricity usage patterns in even more detail. On top of making the important point that Australia’s distributed solar PV systems easily ‘pay their way’ on the electricity grid – countering arguments to the contrary by the current government and Australia’s electricity infrastructure establishment – the article also serves as something of a sales guide for solar installers, as well as a user’s manual for solar system owners.

Read the full article →

James Martin II

James Martin II

Communications Manager at Solar Choice
James has been Solar Choice's primary writer & researcher since 2010. He lives in Newcastle in a house with a weird solar system.
James Martin II

{ 6 comments }

Diego 28 April, 2016 at 11:40 am

Take away the 500W base load in these graphs, and these households will half their annual electricity usage (or bill – a little bit more complicated because of fixed daily charges of up to 1$).

500W energy used around the clock (the base line or lowest line around 0.5 left scale in the graphs), equals 12 kWh of electricity usage per day (0.5kW x 24 hours = 12 kWh). That is more than half of 20 kWh usage per day of these household as described in this article.

So get rid of all standby (including hardwired stuff like aircons and remote fans – turn them off at the breaker panel), microwave with a nice clock on it and entertainment electronics, turn off internet modems and wireless access points overnight)
Get rid of old unused and inefficient appliances (that old energy hog fridge and the old beer fridge in the basement everyone)
And get rid of inefficient lighting (halogen downlights) and replace with LED’s.
Install an energy efficient pool pump. This saves 2/3.
Choose to install insulation instead of buying that bigger 7kW aircon. A 3.5kW energy efficient model will suffice (5 stars or more).

How do I know how big my base load still is, you ask? Tell an electrician to install a whole house energy meter like one of these http://reductionrevolution.com.au/collections/wireless-energy-monitors

At that point – 8 kWh electricity usage per day, the 5 kWp solar system will also be able to produce enough electricity for not so sunny days and for an electric car.

8 kWh per day is not possible you say? Well we use 8 kWh per day for a two person household with a two year old, and we have aircons and a 50.000 litre pool, with an energy efficient pool pump of course.

Solar Choice Staff 7 June, 2016 at 4:39 pm

These are great points, Diego. Thanks for commenting.

John 2 February, 2016 at 9:08 pm

Would it be possible to annotate these graphs in terms of how the peaks and troughs relate to the % compared to overall kWh for the day? I’m guesstimating based on the relative sizes of the shapes in the graph, but if you have this data somewhere, a vertical axis would be really handy.

Solar Choice Staff 3 February, 2016 at 10:01 am

Hi John,

We’ve left out the numbers here on purpose – the aim in this article was primarily to allow readers to visualise what their electricity usage might look like based on the number of people (and their age) in their home. We have worked approximations of these usage patterns into a battery storage system sizing estimator tool that we’ve put together, but they’re only rough estimates. You can download the original data which SunWiz used to compose these charts on the AusGrid website.

For what they’re worth, I’ve included some output graphs from our estimator below. All of the charts are for 20kWh of electricity consumption with a 5kW solar system – they only thing that changes is the consumption pattern. You’ll see that there is data for two days – the solar output data that you see is the annual average for Sydney, repeated twice. (Please ignore the numbers that appear on the right axis in some charts – those are for battery state of charge and don’t apply in this situation. The numbers on the left axis are the ones you want to pay attention to.)

Hope this helps!

Double peak:
Double peak pattern

Evening peak:
Evening peak

High day, evening peak:
High day evening peak

Day focus:
Day focus

Evening focus:
Evening focus

Mike Ives 7 February, 2015 at 1:51 pm

Excellent site thanks. One question please. Am I right in thinking the household demand gets precedence for the PV generated electricity and any surplus then goes to the grid or

all PV generated electricity goes straight to the grid and a credit is given for any surplus between what is exported exported to the grid and what is imported to the household?
We live in Tasmania if that makes any difference to the answer.
Many thanks

Solar Choice Staff 19 February, 2015 at 3:06 pm

Hi Mike,

Thanks for the comment. These days, the vast majority of solar energy systems are ‘net metered’, which basically means that your meter flows in two directions. So you correctly described what happens in your first guess – basically, the power from your solar panels will go directly into your home and flow into any devices that are in operation. Whatever is not used is then sent into the grid and you get a credit.

It’s very rare these days for anyone to have a ‘gross metering’ setup – which is the second situation you described. This is because it makes no sense economically: why would you export your solar power to the grid for 8¢/kWh when you could use it yourself and save up to 25-30¢/kWh? It’s best to use as much of the solar power you generate as you possibly can. (This is what is driving so many Australians to consider energy storage systems.)

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