Backup generator

[woody1]

We've just been without electric for 36 hours. And we're the lucky ones; some poor buggers will be without until early next week.

We've got a woodburner as backup heating, which we also use to heat water and do rudimentary cooking. I run an LED light from the car's battery to give us some light. But our main problem is we're on private water; no electric = no water.

We had 3 power outages last year due to storms. None as long as this one but the trend with climate change is clear; more frequent and more severe.

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I don't know much about generators. I'm guessing something fairly modest would power:

• Oil central heating (burner ignition and circulating pump)
• Fridge/freezer
• Couple of LED lights
• TV
• Microwave

The main issue is the private water. The borehole pump is a 1kW (4A) induction motor but the start-up current will be far, far higher.

The other question is how long can you run generators for? We'd need something that can be run more or less continuously for many hours at a time.

Thanks.

[malvolio]

You need to work out the minimum amperage you need to replace the mains power first. I suspect your pump is out of reach of the usual small gennies and a big one is likely uneconomic. You might be better off with a pair of small ones, one for the house and one for the pump if you can get the needed grunt.

Back in the farming days in the wilds of west Wales we had 240v gennies in the outhouse running off an old tractor or a lister diesel running at one bang per second, with a matching waver in the lights and the tv picture as the voltage fluctuated. Modern electrics would prefer a smoother solution

Motorhomes have the same basic problem when off grid The usual workaround is solar panel (100 amp minimum 200-300 is common) and batteries plus low consumption appliances such as a 12 volt TV. A lot of people then add an invertor to get 240v. However unless you have a serious level of solar and battery, that would only run a matter of hours. Remember, overall power is calculated in watts as (wattage = volts x amps). If one goes up the other goes down.

[hobnob]

I agree with malvolio that step 1 is to quantify your requirements. There are devices that you can plug into a socket to monitor how much electricity you're using, but hopefully you could also get specifications from the product manuals.

One alternative to a generator is home storage batteries. These technically count as an EPS (Emergency Power Supply) rather than a UPS (Uninterruptible Power Supply), because of the transfer time (i.e. how many milliseconds it takes for the power to kick in). However, they should be fine for a fridge/freezer etc. Again, it would be a case of sizing the system.

I was looking at generators recently, so I'll do a quick summary for you. As I understand it, you can't refuel them while they're running. So, how long it will run for mainly depends on how big the fuel tank is.

You'll need some way to connect your devices to the generator. There will be a commando socket on the side of the generator where you can plug in a cable (similar to an EV charging point or a hook-up at a campsite). In theory, you could have a power strip which plugs into the commando socket, then has a row of 3-pin sockets; you could then run extension leads through the window to plug your fridge etc. into the power strip.

A better approach is to have an inlet on the side of your house, i.e. another commando socket. The inlet gets wired into a power transfer switch (along with the normal mains supply). This could be a manual transfer switch (MTS) or an automatic transfer switch (ATS). Basically, the switch will choose between 2 inputs (generator or mains) and then give a single output to a consumer unit. You then use all your devices as normal.

NB The generator can also be manual or automatic. Realistically, if you have to go outside to manually start the generator then you might as well have a manual transfer switch. Likewise, if you don't have a generator permanently installed, then you might as well have a manual transfer switch (cheaper) for the times when you connect a mobile generator.

You could go a step further by splitting your consumer unit into essential and non-essential circuits. The non-essential board would just have mains power, while the essential board would be connected to the transfer switch. I've worked in places where the power sockets have different colours for the on/off switches to show which circuit they're on, e.g. red switches for essential power and white switches for non-essential. However, it will be a judgement call about what counts as essential (e.g. your TV). Don't forget about your internet router, smoke alarms, burglar alarm, etc. (Even if you're not worried about someone breaking in, it would be annoying for the alarm burglar alarm to go off because it thinks an intruder has cut the power.)

The generator needs ventilation, because it produces carbon monoxide (it’s basically an internal combustion engine, like a car/van). So, it has to be run outside, not inside a building (e.g. a garage).

I think the generator has to be at least 1.5 m from a building. (More specifically, from any openings in a building, e.g. doors and windows.) That might mean that a driveway isn’t practical, but maybe it could go at the bottom of a garden. Don’t put the exhaust pipe too close to a wooden fence, otherwise it could start a fire!

[Dorkeaux]

Some good advice from the other posters.

I have a modest regulated electric start generator feeding a commando socket outside the house to a row of six standard mains sockets inside the house.

You need to consider grounding. You can float like I do, but in retrospect it would have been less risky for me to drive an external grounding spike for the generator.


Microwaves can draw a lot of power, I'd consider dropping that from your calculation, but do what you must of course.

Another thing, I run my generator on LPG or patio gas, not petrol.
LIquid fuel goes off, gas does not.
Also, if the power outage is widespread the local petrol pumps won't work either. The locker with patio gas will, though.

Try Toolstation if your needs are modest.

[woody1]

Thanks. As an aside, two of our neighbours have big solar setups. These didn't help. I'm guessing that at this time of the year, the battery banks might not get fully charged. They also have ground source heat pump hot water/under floor heating which I imagine would drain the batteries PDQ.

In terms of connecting to the house circuits, our meter box has an isolating switch to disconnect us entirely from the mains supply. I was therefore thinking of just having a plug/socket to hook the generator to the inlet side of the consumer unit. Just need to remember to NEVER have the generator connected when the isolating switch is ON.

What would be really useful is an electric car with a 240VAC outlet. Fully charged batteries in one of them would keep stuff running a fair while.

[WTFH]

OFCH uses a bit more electricity than you might expect.
As for the car, the tech is called V2H or V2G (Home or Grid) and it’s not about having a 230VAC output on the car, but bi-directional charging, i.e. the car can power the house through the charger.
It’s becoming popular in Europe, but the UK electric companies are claiming it is bad - because it will impact their profits.

[hobnob]

Thanks. As an aside, two of our neighbours have big solar setups. These didn't help. I'm guessing that at this time of the year, the battery banks might not get fully charged.

Solar panels and home storage batteries are independent, i.e. you can have just panels, just batteries, or both together. You can charge the batteries from mains power (either as the sole source or to "top up" the solar power). Depending on your tariff, it might make sense to charge them overnight and then drain them during the day.

In terms of connecting to the house circuits, our meter box has an isolating switch to disconnect us entirely from the mains supply. I was therefore thinking of just having a plug/socket to hook the generator to the inlet side of the consumer unit. Just need to remember to NEVER have the generator connected when the isolating switch is ON.

I've seen people talking about an interlock system as an alternative to a transfer switch:
electrical - What are the Pros & Cons of a generator transfer switch vs an interlock? - Home Improvement Stack Exchange
The basic idea is that you have mains power and generator power both connected to the consumer unit, then the interlock means that it's physically impossible to use them both at once (because you won't be able to flip one of the circuit breakers). However, this might just be a USA thing, i.e. I don't know whether it's compatible with BS 7671 for the UK.

You're talking about going a step further, and doing it on the honour system. E.g. having a piece of paper stuck to the wall next to the consumer unit which says "Remember to use the isolator in the meter cabinet!" I don't think that would be legal or safe.

See:
Frequently Asked Questions to Bellwood Rewinds
"How Do I Connect a Generator To My Home?
A few precautions must be observed when you are connecting a generator to your house. It is of vital importance that the generator is isolated from the mains supply. This helps to ensure that the generator is not attempting to power up the whole neighbourhood, but also makes sure that it does not electrocute a utility worker trying to restore the mains supply. To properly achieve this, a double-pole, break-before-make changeover switch must be installed by a qualified electrician. This switch must be fitted between the electricity meter and the building consumer unit. The switch connects the building to either the mains supply or to a lead which can be plugged into the generator itself."

I believe that the changeover switch is the transfer switch (ATS/MTS) that I mentioned before, i.e. it's separate from the isolator switch that just sits between the meter and the consumer unit.

At this point, I think you really need to discuss your plans with a qualified electrician rather than trying to DIY it.

What would be really useful is an electric car with a 240VAC outlet. Fully charged batteries in one of them would keep stuff running a fair while.

There are a few options for this, but they aren't widespread yet.

V2H (Vehicle to House) would be ideal, but it would require a bidirectional charger, and I believe that those are proprietary (e.g. if you buy a Ford charger then it would only work with Ford cars).

V2L (Vehicle to Load) is simpler, because you'd have a DC/AC inverter built into the car, i.e. the EV would be acting as a generator. That means that you could either plug devices into it directly (like a hook-up at a campsite) or connect it to an inlet and transfer switch. So, if you get your house ready for a generator, you could then replace the generator with a V2L EV later (no re-wiring involved).

[woody1]

At this point, I think you really need to discuss your plans with a qualified electrician rather than trying to DIY it.

Agreed.

We could probably live without electricity in the house for a few days if we could just keep the water going. From what I've read, start-up current could be between 3 to 7 times the running current, so we might need a generator as big as 10kW. The pump only runs for about 20 seconds to recharge the expansion vessel, and then the water pressure lasts for quite a while before the pump cycles again. Overall, it doesn't consume much electricity, so it seems a bit overkill having a massive generator to power it.

Maybe a big battery and inverter might do the job?

[malvolio]

Agreed.

We could probably live without electricity in the house for a few days if we could just keep the water going. From what I've read, start-up current could be between 3 to 7 times the running current, so we might need a generator as big as 10kW. The pump only runs for about 20 seconds to recharge the expansion vessel, and then the water pressure lasts for quite a while before the pump cycles again. Overall, it doesn't consume much electricity, so it seems a bit overkill having a massive generator to power it.

Maybe a big battery and inverter might do the job?

Could be the best option. Add a solar panel to keep the battery charged - they work as long as there is light, it doesn't have to be bright sunshine and you only need a trickle charge (on a smaller scale, my panel keeps the motorhome leisure batteries charged through a van cover in the winter...). That would take the pump away from the mains altogether.

[WTFH]

There are a few options for this, but they aren't widespread yet.

V2H (Vehicle to House) would be ideal, but it would require a bidirectional charger, and I believe that those are proprietary (e.g. if you buy a Ford charger then it would only work with Ford cars).

V2L (Vehicle to Load) is simpler, because you'd have a DC/AC inverter built into the car, i.e. the EV would be acting as a generator. That means that you could either plug devices into it directly (like a hook-up at a campsite) or connect it to an inlet and transfer switch. So, if you get your house ready for a generator, you could then replace the generator with a V2L EV later (no re-wiring involved).

Scroll down here for a list of cars (as of May 2025) and further down for chargers:
https://www.carwow.co.uk/editorial/g...ional-charging

Since Woody has talked about Audis in the past, it's worth noting that the VAG MEB platform used in the Cupra, Skoda and VWs on that list is the same as is used on the Audi e-tron Q4 & Q5, so in theory they could work bi-directionally - note that it's only the "85" models that support it (i.e. 77kWh battery), and the software (at least in the Skodas) is set to allow a max of 4000 hours V2H - I'm not sure if this is due to battery performance or to appease energy supply companies.