“Before and after” electricity bills – see the real difference solar panels can make

Don’t let your eyes glaze over with all these numbers – it’s quite simple to read.

“General usage” (1) refers to electricity that the homeowner needed to buy from the grid. $613.90 worth, to be precise.

“Supply charge” (2) is the daily charge from AGL for simply having his house connected to the grid.  This cost him $0.83 per day, and $74.70 total for the billing period.

“Credits – standard Feed-In Tariff” (3) shows the amount of solar energy he exported to the grid, the amount he’s paid as a feed-in tariff ($0.20 per kWh) along with the money he made from this (which was added as a credit to his electricity bill) – $380.16.

Now – what we want to work out from this bill snapshot is – how much of the total solar energy generation was this homeowner self-consuming, and how much electricity was he exporting to the grid?

This is where it gets slightly more involved. If the homeowner had consumption monitoring, it would have been really easy to generate a report with this information.

But sit back – I’ll do the work for you.

First – we know he has a 10.8 kW system. I know his exact location from his electricity bill – so I’ve input that into a solar energy calculator called PVWatts to estimate what his system should have given him in the billing period.

Then – I get this nifty result:

The billing period is between April and July. Adding the “AC energy” numbers together from the image above for those months – I get 2,616 kWh expected generation.

Let’s go back and compare that to the figures on his bill. It showed solar electricity exports of 1,900 kWh (4 on the image above) – that’s solar energy exported to the grid for a feed-in tariff.

Now – when a solar power system generates electricity, and you don’t have a battery, a decision is made by your home in real time:

1) If something in the home needs energy, the solar system will supply the energy to whatever needs it.

If not enough solar energy is being generated to cover this demand – the grid will top up the rest.

2) If more solar power is being produced than is needed in the home – the rest of the energy is exported to the grid.

So, if the homeowner generated around 2,616 kWh for the billing period, and exported 1,900 kWh to the grid – that means the remaining 700 kWh of electricity was self-consumed in the home.

In other words, he exported 73% of his solar electricity generation, with 27% self-consumed in the home.

That kind of self-consumption percentage suggests to me the homeowner doesn’t have people during the home on weekdays – in other words, they’re a ‘9-to-5’er.

Those numbers above also tell me that his electricity bill would have been $646 higher if he didn’t have solar panels installed. That’s a big chunk of change!

We’re starting to build a common theme here – larger solar power systems = big electricity bill reductions. Again – this is why I recommend installing as much solar as you can.

In this instance, we have a Queensland homeowner install a 9.3 kW system, switch to a retailer that offered a good feed-in tariff, and get a $678 quarterly bill reduction as a result.

Again – this is for an autumn/winter bill. This means $678 is the least this person will save per quarter. 

Popping the numbers from their electricity bill into my calculator gives the following prediction:

As you can see – My solar calculator predicted his bill would be $55 for the autumn/winter period. Bang on what his electricity bill actually was – $55.

They should also be expecting a nice credit on their bill in the summer/spring quarters.

To contrast with the two previous (winter-time) electricity bills, here’s a late summer/early autumn bill from a New South Wales homeowner.

They had a 6.6 kW solar system installed – which is smaller than the previous two examples – but this is a much more typical size for a system nowadays, especially for single-phase homes that are generally limited to 5 kW inverter capacity.

Even with this “smaller” system – they managed to take their summer electricity bills from $427 to a $134 credit. Not too shabby!

Let’s take a peek at what my calculator predicted their bills to be for the rest of the year:

What a result! If their energy usage habits stay consistent, they may never actually need to pay an electricity bill again!

Another example of a summer electricity bill reduction with a “smaller” 6.6 kW system.

While summer is the period in which you’ll save the most with solar panels, it’s also the period that tends to be the most expensive for households as they blast the air-conditioning all day long.

Let’s plug their numbers into my calculator and see what kind of bills they can expect for other seasons…

In this instance, their electricity bill will creep up to $240 in winter – but as the calculator shows, it would be double that without solar panels!

I’m hoping the previous four examples of homeowners seeing awesome savings from solar power with no batteries would be enough to convince the battery fanatics that batteries, economically, just aren’t necessary if you want low bills.

To really drive the point home – I’ll use this electricity bill an example.

This home installed a 6.6 kW solar system with a 10kWh Sonnen battery. You can see above that their summer bills went down by a whopping $1,171.

A lot of the savings comes from their very high self-consumption ratio, meaning their house used a lot of energy during the daytime that their solar system offset.

But – digging into their data – I saw they were only cycling their battery 1.1 times per day, on average. Let’s do some simple maths to show how much the battery contributed to that $1,171 saving:

Cycling a 10kWh battery 1.1 times will get you 11kWh of energy per day. This home is paying 25c per kWh for grid electricity.

So – 11 kWh of battery energy used per day means that they haven’t had to buy 11 kWh from the grid. 11 X 25c = $2.75.

This means the battery saved them $2.75 per day, right?

Wrong! This is because when you have excess solar energy and store it in your battery, you’re choosing not to sell it to the grid for a feed-in tariff.

Meaning – you need to subtract the feed-in tariff from the cost of grid electricity to get the true savings from a battery.

So, the real saving is 25c (grid electricity cost) minus 12.5c (feed in tariff) multiplied by 11 (kWh) = $1.40. This is what the Sonnen battery actually saved this household per day – $1.40. Or – $123 for a 90-day period.

With a bill saving of $1,171, the Sonnen’s saving of $123 is only a measly 11% of this electricity bill. All the rest of the savings were from solar power!

My calculator shows the breakdown visually:

A 10kWh Sonnen battery will cost you approximately $16,000 fully installed. So with a saving of $123 a quarter – or $492 per year – you’re looking at a simple payback of over 20 years for the battery system!