What size solar system do I need?
What size solar system do I need?
How much will solar save me on electricity?
How many solar panels will fit on my roof?
Australians can now find reliable, tailored answers to these questions and more with the launch of SunSPOT Version 3, the Australian PV Institute’s best-in-class solar and battery calculator.
With support from the Australian Government, SunSPOT has undergone transformative redevelopment making it easier to use, more accurate and available everywhere.
Project Leader Dr Anna Bruce says, “SunSPOT has been built by engineers at UNSW’s world leading School of Photovoltaic and Renewable Energy Engineering specifically to help people understand what solar can do for them – not to help retailers sell solar.”
“It’s the only independent tool with this level of customisation available to the general public.”
“All other solar calculators seek to capture personal information and generate sales leads.”
“Now, with nationwide delivery and improvements to its usability and accuracy, SunSPOT is able to help the vast majority of Australians confidently navigate the complex solar market.”
Meet the Brown family, who are investigating solar with SunSPOT
Our fictitious family of four live in the Inner West Council area of Sydney and want to find out how solar can help them financially.
The Browns have two children and, having looked at a recent electricity bill, they know they use 15kWh (“kilowatt-hours”) of electricity per day on average. The Browns have a maximum budget of $10,000 for the solar and would like it to pay for itself in savings from the electricity bills in about five years.
What size system do the Browns need?
After putting in the address and answering some simple questions about their electricity usage, SunSPOT presents the Browns with a suggested system size that will give the best return on investment (based on their current electricity use) – 6kW (six kilowatts)
It provides estimates of cost and savings for this size system.
What is a kilowatt?
What is the difference between a kilowatt (kW) and a kilowatt hour (kWh)?
The Brown’s SunSPOT estimate
The system cost guide is within their $10,000 budget. The payback period is longer than they’d hoped.
How many solar panels will fit on the roof?
The Browns want to know how much space a 6kW system will take up on their sunny roof area, and if there’s room to add more panels.
They want to put in air conditioning, too, and swap the gas hot water to an electric heat pump hot water system. With their electricity use set to go up, going for a bigger system is sensible.
Where should the panels go on the roof?
The Browns live in an area where the local council has subscribed to SunSPOT so they are using the premium version of SunSPOT.
The key difference between the premium and standard version is seen in the image below. The red- and orange-coloured dots show the best place for solar panels. There are no dots in the standard version, and users must make their own assessment of the sunniest place for the solar panels to go, and the amount of shading on the roof.
In the premium version of SunSPOT, the best areas for solar panels on a roof are indicated by red and orange dots.
Premium SunSPOT calculates the solar radiation on each 0.25m2 roof area and can identify the best place to position the solar panels. It uses spatial mapping LiDAR data and Bureau of Meteorology weather data to do this.
You can find out more about the data used in SunSPOT’s calculations.
Using SunSPOT, the Browns map realistically scaled solar panels on the areas with red dots on the roof. SunSPOT suggests they position 17 panels for the 6kW system but there’s room for more, so they add another 5.
The Browns are able to see how many solar panels will fit on their roof using SunSPOT.
It amounts to 22 panels and a 7.7kW sized system. They apply this new size to their estimate and get updated results which they can now compare to the 6kW size system.
The time to payback is longer, but their annual electricity bill estimate is about $130 cheaper.
Will solar save the Browns more money when they increase their electricity use?
The Browns want to know if the savings increase when they get air conditioning and swap the hot water and stove top to electricity. They’ll be spending less on gas and using more electricity. Under Energy usage SunSPOT lets them add more details about their planned energy usage. They remove the gas appliances and add the air conditioning to see what the impact is.
After saving the changes the Browns then recalculate the estimate.
The payback time reduces by around six months. (Note that this doesn’t include the financial costs and benefits of switching from gas to electric appliances.)
What if they get a battery?
The Browns think about how much electricity they use at night and wonder if a battery would increase the savings. They add an 8kW battery to the estimate and recalculate.
SunSPOT calculates the savings with an 8kWh battery installed.
The results don’t look as convincing as they’d hoped. While the annual electricity bill is a gratifying $29, the time to pay the battery and solar back is over 10 years which exceeds the warrantied life of most batteries.
With SunSPOT’s estimates and the knowledge they can come back to the tool anytime to try another system size, tariffs or scenarios, the Browns feel ready to talk to solar companies and get some quotes.
How to get the most accurate results from SunSPOT?
For more accurate estimates, users can add details about electricity use in the house, and the tariffs in their electricity plan. And for the most accurate results, users with a smart meter can upload 12 months of smart meter data.
Find out more here:
How to get your meter data
Understanding your bill