How To Predict Your Electricity Bills With Solar Panels Installed 

Last updated: May 2020


For those of you that haven’t got solar yet, how do you know what your bills will be if you do get solar? 

Well, my solar and battery calculator will answer that question. Here’s how it works. 

Let’s say I live up near Brisbane – postcode 4008. I’m looking at buying a nice big 9kW system. It’s north facing 22 degrees from horizontal, no battery yet thank you very much. 

Size of solar power system and orientation

The cost of the system, that’ll be about $9,000. I’ll pay 24 cents per kilowatt hour for my electricity from the grid. What’s my current bill? Well, let’s say $700 a quarter, $2,800 per year, and a feed in tariff of 18 cents.

Cost of system, electricity and feed in tariff

Let’s calculate the savings.

The Solar Savings Results

Solar savings results

Now, the first thing to realize about the results is they will vary depending on what your self-consumption ratio is. Now, your self-consumption ratio is how much of the solar energy you generate and use in your home and how much you export to the grid. A good number to start with is 30% self consumed, 70% exports. And if I use that number, the calculator tells me I’m going to save almost $3,000 in the first year. That’s pretty good. That gives me a payback of just over three years for the $9,000 that I’ve spent. 

But here’s the really exciting bit – for me anyway. Your next four bills, if you remember before we got solar, our bills were around $700 per quarter. They vary slightly by season, but what are the bills going to be like after solar?

Seasonal solar power savings

Well, in summer we’re looking at a $33 credit. Autumn, we’re looking at a $54 bill, Winter $53, and Spring – the best season of the lot, $143 credit. And that’s the best season because up in Brisbane we get heaps of sunshine in spring, but we don’t use too much electricity to cool the house. 

Testing The Calculator

Those are impressive savings, but are they too good to be true? Well to test the calculator, we asked people to send in their before solar bills and their after solar bills. And here’s the before and after bill from a user called Shane who funnily enough lives in postcode 4008 near Brisbane. 

Electricity bills before and after solar power

Before he got solar, his bill was $733. After Shane got a nine kilowatt system his autumn bill was $55 . How does that compare with the calculator? Well, here’s his autumn bill. We estimated a $699 bill before solar and, a $54 bill after. So pretty accurate. Now I’m not guaranteeing your calculator results could be within $1 of your actual results, but if your inputs are realistic, the results will be pretty close.

Adding A Battery

So those savings are with solar only. But what if Shane added a battery? Well, let’s edit the inputs of the calculator and give Shane a battery to see how much that would save him. So we’ll keep everything else the same, but we’ll give Shane a Tesla Powerwall 2 battery that’s going to cost them an extra just over $15,000 (at the time of writing – May 2020); bringing the cost of the entire system with solar and batteries to just over $24,000. Everything else stays the same. 

Solar panels with battery added

So the results are in, we will change the self-consumption ratio back to 30% without batteries, so we can compare it with the previous results. The first full year savings, solar and batteries, $3,164 and that comprises of 2,868 from the solar but only $296 from the $15,000 battery. 

So the simple payback of the whole system looks okay at seven years, but that’s made up of a three year, two month payback for the solar and a whopping 32 year payback for the batteries. 

Now, the economics of batteries will improve rapidly as we go forward, but right now in 2020 not everyone’s buying batteries because they want to save money. Some people just love the technology. That’s why I bought one. Some people want to support the battery industry and some people want to backup their home, and if that’s you, go for it.

To find out how much installing a solar power system could save you on your electricity bills try our solar and battery calculator.

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