The minimum state of charge that a battery maintains can be adjusted to suit your priorities – whether that’s maximizing energy trading profits, protecting against blackouts, or reducing degradation. You can even adjust it temporarily in response to unusual conditions – as I discovered during an electricity price spike earlier this week.
A price increase that drained my battery
I had a Sungrow SBR home battery (pictured above) installed a few months ago and came to Amber to see what life was like on the roller coaster at the wholesale price.
The ride was fairly uneventful until last Sunday evening, when wholesale electricity prices shot up in part due to a severe wind drought – an event that led Pauline Hanson to falsely claim that we South Australians were paying $5 just to boil a kettle (even though almost all non-Amber households were protected from price spikes by flat retail pricing).
Amber’s AI-driven energy management system, still in the process of learning my home’s consumption patterns, was a little happy to take advantage of the very attractive prices and increased the export of the energy stored in our battery at a profit.
I was pretty happy with that – until I realized that our battery only had just over 25% capacity before one cold evening. Suddenly it looked like I would have to buy back the energy I had just sold, even though prices were still horrendously high.
The June 21st price increase as reflected in the Amber app.
Time for a fireside chat
My partner raised a skeptical eyebrow when I intercepted her as she was about to turn on the ducted heater, and I suggested out of nowhere that it was a great evening to get our little-used fireplace going.
She didn’t want to buy it, and I reluctantly had to admit that after spending thousands on our new energy storage system, we’d both be better off adding an extra jumper instead of channeling reverse.
But then another thought occurred to me: Why don’t we instead lower our battery’s minimum reserve so that it uses more of the stored energy than usual to get us through the evening with the heating on without driving up our electricity bill by drawing from the grid?
The minimum reserve level of a battery
A home battery generally has a programmable minimum reserve level that the system will not fall below, allowing homeowners to keep the lights on and the refrigerator running in the event of a power outage.
Typically this value is between 10% and 30% of your battery capacity. It is advisable to save at least 2 kWh. However, which percentage you choose should depend on the size of your system, your priorities, and your system’s backup capabilities.
The higher you go, the longer the payback period is, as some of your battery capacity remains unused most of the time. But the lifespan of your battery is also extended because the battery is under less strain.
However, if you choose a lower reserve, you will use the battery more often and benefit from better financial returns – you will use less electricity from the grid and export more at a profit.
The chemistry of modern batteries reliably works much harder than, say, traditional lead-acid batteries, but you’re also putting more strain on the battery and risking degradation, especially if you regularly drive at less than 20%.
If the charge level drops very low in exceptionally cold weather, this will also damage the battery, although this is more likely to be the case in freezing conditions, which are not common in Australia.
During a power outage, you are obviously more vulnerable to running out of power. This may pose a greater risk if you are located in a peripheral area of the power grid where power outages are more common.
Manufacturers often specify the recommended state of charge for the battery as well as the maximum depth of discharge (DoD), which in turn can affect warranties. So think about this before you start messing with the reserve level.
Sungrow has set a lower limit for the battery so you can never use the last 5%, while other manufacturers allow 0% but force a mains charge immediately to restore a safe level.
How do you change the reserve level of a battery?
The answer depends heavily on the brand of your battery, but a good installer will ask you about your preferred level during installation and will do this for you – and maybe even show you how to adjust it yourself.
In my case, in typical Sungrow style, I had to navigate a somewhat complicated adventure through options with obscure names hidden in menus and submenus of the brand’s iSolarCloud app (to be fair, many other brands subject users to similarly byzantine journeys).
The menu path was in my app:
- Click on the small hexagon icon on the right of the home screen and select that ‘Device’ Option;
- Choose “Energy storage system” (the inverter);
- Swipe right through multiple menus to get there ‘Settings’then select ‘General Settings’;
- Search and select ‘Backup mode’ and activate it;
- This will make the ‘Reserved battery SOC for off-grid (%)’ box appears (as shown below);
- Enter the percentage preferred for the reserve level (the ‘readback value’ under this number it is displayed what value it is currently set to);
- Then strike ‘Apply settings’ And ‘confirm’.
It’s all about as intuitive as trying to find a needle in a haystack during a hurricane, but once you know the steps it’s easy.
Since I’m on Amber, I had to use the Amber app to make further selections ‘Devices’, “SmartShift Settings”and then enter the new reserve ratio percentage in the appropriate field so Amber’s AI can know where I set it (it won’t sell to the grid below 25% anyway unless you instruct Amber to do so).
Amber actually has a pretty good overview of how to optimize the reserve level at other brands, from Sigenergy to Fox ESS to Anker.
You may only do this once
In most cases, when you first insert the battery, this feature is usually set and then forgotten. However, it does provide options if you are faced with unusual circumstances. Since the battery is under greater strain than usual in the winter and energy prices are rising, we had the opportunity to stay warm all night long without having to draw a lot of money from the grid.
So I adjusted our settings from the 20% we normally use to 10% and restored the old setting once everything was back to normal.
There are risks and opportunities here – times of high energy prices reflect an overloaded grid, meaning the risk of a power outage is greater than usual.
But since energy prices were so exorbitant that I was inclined not to use much electricity anyway, I figured we could do that too.
There are other circumstances in which you may want to temporarily change your reserve requirement – perhaps bad weather is forecast and you want to set it higher to cover an impending power outage, or a letter in your mailbox specifically warns in advance of a planned power outage.
In our case, temporarily reducing our reserve requirement allowed us to use our heating without running out of a big bill during a price spike – and our chimney still hasn’t been accessed.
For more information on home energy systems, check out our solar battery guide.
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