There’s a new myth floating around: if your energy retailer gives you a free 3-hour energy window in the middle of the day, you don’t need solar panels. Just get a big battery, charge it for free during the magic window, and run your house on battery power 21 hours per day.
Or the slightly more restrained version:
“I’ve already got a modest solar system, but if it ever falls short, I’ll just top up the battery during the free window – no need for more solar panels”
Sounds clever.
In practice? Not really.
Let’s start with the appeal. The logic is tempting: skip the cost of solar panels. Just buy a battery. You can fill it up with free electricity from the grid. Maybe even charge your EV too. Feels like you’re gaming the system.
But the system’s gaming you.
Not As Easy As It Sounds
To make this work, you need:
- A big battery in terms of capacity (kWh) to get through the other 21 hours.
- A powerful battery inverter (kW) to charge fast enough in the 3-hour window.
- Enough grid connection headroom to do it all without tripping your main breaker.
Let me explain that last one. Say you’ve got a 10kW charger running for 3 hours. That pulls 43 amps on a single-phase connection. If your main breaker is 63A, you’ve got 20A left over to run everything else in the house. That’s not much. Add a kettle, a clothes dryer, and you’re in trip city.1
Even if you’re on a beefy 100A supply, charging your EV at 7kW takes 32A. Add that to the 43A and you’re at 75% of your capacity without any regular appliances running. Suddenly your free electricity hour has turned into an episode of The Weakest Link.
But worse than the tech challenges is you’ve surrendered your autonomy. You’re trusting your retailer to keep the window open.
Forever.
You’re betting they won’t quietly change the plan or jack up prices outside the window. And if they do? Tough luck. Your system is now built around that window.
A breakdown of residential electricity price components. If you rely on your retailer, sooner or later they’ll make sure you pay to cover the costs.
Solar Is A Ticket To Independence
Energy independence was the whole point of going solar. You owned your panels. You made your own power. You used the grid like a backup. Batteries became part of that same story. A way to rely on the grid even less.
This free window idea flips that on its head. Now, you rely on them – on the retailer – the very entity solar was supposed to liberate you from.
And let’s be real. No retailer is giving you free power out of kindness. If they’re losing money 3 hours a day, they’ll make it back somewhere. Maybe it’s the shoulder rate. Maybe it’s the daily supply charge. Maybe it’s the tiny (or non-existent) FiT.
Electricity prices in South Australia last week. The brief dips below the line are the only points at which prices went negative (apart from the sabbath – amen).
There’s No Such Thing As a Free Lunch
And when negative wholesale prices are rare (like most of winter in SA), your retailer’s not getting paid to take that electricity either. They’re paying transmission, distribution, environmental and metering costs. Those don’t go negative. So guess who ends up subsidising your “free” power?
Yeah. You do. Just somewhere else on the bill.
I love a good deal as much as anyone. And if you’ve got a battery already, sure – top it up for free when you can. But ditching panels altogether? Or not expanding your solar because you’re banking on three free hours a day? That’s shortsighted.
Aussies used to install panels to take back control. To future-proof their bills. Let’s not forget that. Let’s not go backwards.
Let’s make solar panels great again.
Phase Shift is a weekly opinion column by SolarQuotes founder Finn Peacock. Subscribe to SolarQuotes’ free newsletter to get it emailed to your inbox each week along with our other home electrification coverage.
Footnotes
- If you do get a beefy battery installed, please make sure your installer configures it so it can do real-time dynamic load management, and don’t even think of buying a battery without this feature. It constantly monitors your household load and dials back your charging power when necessary to avoid tripping your main breaker. ↩
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Thanks, Finn.
Let’s not forget where that negative pricing comes from, either. It somes from households’ PV systems. We have a chance to break out of our British every-man-for-himself culture and into the (globally!) more common community-minded way of thinking.
Have (recently) installed as much solar PV as will fit.
Unfortunately it’s not sufficient for covering our winter demand (unavoidable shading), so we import (free) energy to make up the difference.
Who knows for how long such tariffs will exist but for now it works.
What solar PV does do is lock in energy supply at a known low cost, be it 4-8c/kWh over it’s life. Which is much more than FIT, so use it or lose it.
But the paradigm has changed.
The solar PV (14.7 kW) part of our equation was far more expensive than the battery (32 kWh).
And precisely because of the change in tariff mix (daytime cheap, night time expensive, zero FIT), solar PV alone is no longer the “no-brainer” option it once was.
63 A single phase is still a decent capacity and dynamic load balancing manages that nicely. Definitely ensure large loads have that capability (e.g. home storage, EVSE), or at least a means to easily adjust limits.
Are people really willing to forego the federal battery rebate (T&C: you need new or existing solar) for this? That rebate would outweigh years of potential savings.
Anyhow, from a society point of view, it sounds like a net positive. Another battery charging during the day and discharging during the night. The net downside is for the individual, and that’s their choice.