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Why batteries alone aren’t enough
Why batteries alone aren’t enough and why power cuts aren’t the real problem
There’s been a big increase in people installing home batteries over the last few years. Most of the focus is on using more solar, having backup power during a power cut, or being ready for EVs and heat pumps. All of that makes sense.
What doesn’t get talked about nearly enough is something that causes far more damage far more often and most people never realise it’s happening.
Voltage issues.
When people think about grid problems, they think about blackouts. Lights off, everything stops. Those events are inconvenient, but they’re rarely what damages equipment.
The real problems tend to happen before a power cut, when power comes back on, or during everyday grid instability that never causes a full outage. Voltage spikes, low voltage, rapid swings and poor reconnection after a fault often go completely unnoticed. Nothing trips, nothing alarms, but your equipment still feels it.
Modern homes are full of sensitive electronics. Inverters, batteries, EV chargers, heat pumps and smart appliances are all designed to operate within a specific voltage range. When voltage drifts outside that range, even briefly, components are stressed. Not enough to fail immediately, but enough to shorten their lifespan.
That’s why people see inverters failing without warning, EV chargers needing new control boards, heat pumps throwing random faults or batteries reducing output or locking out. The damage usually shows up weeks or months later, which makes it feel like bad luck.
A clean power cut is actually simple, everything shuts down safely.
Voltage instability is worse because equipment stays powered while operating outside safe limits. Components heat up, degrade over time and eventually fail. From the homeowner’s point of view it looks random, but it usually isn’t.
This is where there’s a big misunderstanding around batteries. A battery on its own does not isolate your home when the grid becomes unstable. It doesn’t control how power is restored and it doesn’t protect appliances from voltage problems. Without proper power cut protection and isolation, the battery and everything connected to it is still exposed to the same issues coming from the grid. In some cases, the battery takes the hit first.
The system that protects a home during a power cut should also be managing what happens during voltage events. It should disconnect cleanly when the grid misbehaves and only reconnect once things are stable again. When this is done properly, the whole house is protected, not just the lights.
This isn’t about luxury or over engineering. Most electrical damage isn’t dramatic. A single voltage spike can destroy an inverter control board, damage EV charger electronics or reduce battery lifespan. None of that is cheap to fix.
As homes become more like small power stations, protection needs to keep up.
Backup power and power quality are no longer separate conversations. They are the same problem.
If you’re installing or upgrading solar and batteries, don’t just ask whether it will work in a power cut. Ask what’s protecting your equipment the rest of the time. That’s where the real value is.
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17 Replies
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I think that there are lot of pieces here. But the prime issue is if there is a power cut in the region. In the past it happened once every 10-20 years, these days, even if briefly, it happens quite regularly – anything up to several times a year, some a 20 minute outage, some much longer. Now, protecting equipment is one thing, but in terms of power outage, any solar setup where it can go into offgrid mode to utilise the battery and solar without dependency from the grid is a good thing. On very hot days in the summar, people with large batteries can go literally weeks with the right conditions where the solar fills up the battery to cover the evening hours. Then there is the EV backup. If people have an EV, they can use that as another tool to provide a charge in the house. The problem really depends on where you live. Some places require power just to flush the toilet, but most places don’t. And pragmatic backups like torches and candles etc are always a good thing and whether to go if you need to just get out of the house due to a lack of power especially when its cold and gas it lost too etc. So backup hotels etc. But the fact that the National Grid is posting on Facebook implies the risk is high enough such that everyone should be ready. As we’re coming out of winter I don’t think it’s weather related, but should there be wars in Europe either through Russian/Ukraine escalation or US attacking of Greenland and the battle extends into Europe, no doubt rightly or wrongly, utilities will suffer one way or another.
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Surely that is the point of using surge protection sockets for sensitive kit such as PC’s, TV’s etc?
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Surge sockets handle spikes at a single outlet. They don’t manage supply quality for the whole property. That’s the gap most homes with batteries still have.
And this is why it is important that people understand the difference between transient spikes and sustained voltage issues.
Surge protectors help with transient spikes. What this is about is sustained voltage fluctuations and poor supply quality, over or under-voltage that lasts seconds to hours, and repeated swings outside the ideal range. That’s not something surge protectors deal with, and it’s what damages modern electronics over time.
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my question also. I am not aware of how this affects invertors and gateways, you would “hope” they have inbuilt surge/voltage protection?
I guess I am not aware of how this affects invertors and gateways, you would “hope” they have inbuilt surge/voltage protection? I know (having run a place on generators in the past) that some kit around the house is fine with “dirty current” and can handle spikes and instable voltage (fridge freezers etc), whereas as kit that is more sensitive to this (PC’s and most electronics with a circuit board) require clean current (pure sine in the case of generator supply) and/or surge protection.
All my computer stuff and audio is surge protected. My experience of white goods is they last 15 years or more without it. About the only possibly sensitive things not protected are my inverters. (Well, maybe my LED light bulbs as well.)
If surges are really such a big issue, it would make sense for inverters to have surge protection built in. I get there may be areas of the country where the problem is much greater than others. Is there any publicly available information about that?
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This is why the regulations now require a Surge Protection Device at the consumer unit (close to the mains incomer anyway, so can be in it’s own sub board).
SPDs are essentially packages Voltage Dependent Resistors that are manufactured to present a near short circuit when the voltage exceeds 280 (ish) volts.
Not perfect, nothing in electricity is, but a real protection and only a few quid a unit.
Most EV, solar & heat pump installers fit a new sub board when they install their kit and most will include a SPD. By the nature of the system, a SPD fitted in a secondary CU for solar will also provide protection for the whole house.
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As someone that has experienced catastrophic damage to many devices throughout my home caused by a lightening strike, I am a firm believer in surge protection and now fit consumer grade versions on just about everything. Not just mains powered devices but phone lines, aerials and network cables too.
I think that it is now a requirement that new homes be fitted with a surge protection devices (SPD).
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We had a problem a while back, it was a power cut the battery seemed to kick in for a while, but eventually lights were dimming, TV not working etc I checked the supply and it was only about 120v, so I switched everything off, the power came back on a few hours later, recently the board replaced our pole transformer with a nice Toshiba 25kw unit, this replaced the old 11kw unit I’m not sure if this will help to smooth surges or not 10kv supply to our isolated farmhouse
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A lot of quotes I’ve got do not offer Island mode in a power cut. In South Africa people installed inverters and auto changeovers for this very reason.
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Power cuts are rare in the UK. Island mode inserts a layer of equipment between you and a very reliable grid. That equipment can fail – meaning having island mode can make your supply less reliable than without it.
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This is really interesting, thankyou.
Last week I had several warning texts about a power outage, as far as I’m aware none happened as the clocks stayed set so I didn’t worry.
But shortly afterwards our van didn’t charge overnight and one of the components turned out to be burned out.
Having read your post I’m wondering if there was a connection
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it’s highly likely. The grid are considering altering grid voltages to bring them in line with European ranges.
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I wouldn’t have thought of it at all, we asked our electrician and he said to get the more expensive ( whatever it was that failed)
I said I’d rather have the most expensive of all electrical stuff as it’s always cheaper than a house fire!
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Excuse my ignorance but everything I have read showed me my system would switch off if there was a power cut, regardless of what I had. Does my battery stay on then?
We don’t get many and I know that’s not the point of this post. You’ve given me something to ask my Electrician but could someone help with this please?
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Some people have the extra kit that disconnects the house from the mains and allows it to run ok batteries. Things like powerwalls, the GivEnergy All-in-one, various “gateway” add ons.
Depending on the nature of the fault, that “disconnecting from the mains” might not be fast enough to prevent damage.
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I knew about EPS but not the switch over mechanism.
I’ve not really researched it as I have an off grid system that would support us if the grid tied system were to be disconnected.
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I had noticed the EV charger was lighting up red one night saying over voltage. So I looked at my data from a Tuya smart monitor and it was almost continuously around 252-257v range. If it wasn’t for the EV charger not lighting up red, I would have never known.
Called SSEN who then said they were doing some big projects locally but will send somone out to check anyway. Turns out three transformers along the line I was on all needed replacing. Now it’s relatively stable, if a tad high at 250 to 252v.
It would be nice to have some sort of UPS style kit for the whole home conditioning the poor quality supply.
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I had a type 1 SPD fitted where my supply comes in. Property is rural and fed by overhead lines. And also a type 2 SPD fitted on my distribution board in the house. I had no idea before I had these fitted that there were different SPD types.
I appreciate from the OP that these wont address sustained variations. Very helpful post @adrian-west
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