Back-up generator

[Stones]

I'm thinking of installing a back up generator in our new build, perhaps utilising the generator I will probably end up buying to supply power on site (rather than pay for a temporary supply/paying to move the meter at a later date).

From what I've read it seems pretty straightforward. I would need to install a 100A mains / generator changeover switch that would allow me to isolate the house from the grid when using the generator. These seem to be readily available and available from about £60 upwards. 

I don't really see the need for an auto changeover system (given the significant difference in outlay that this would entail) as in reality it would perhaps only be in use a couple of times per year. All I'm interested in is having enough power to run some essential systems / appliances - lighting, fridge, small heater or ASHP, MVHR, UFH pump.

There are however a few things to consider:

Conventional or inverter generator
Size of generator (1000W / 2000W etc) 
Fuel type
Should I wire the house such that there are 2 CU's, one with the essential systems, the other with circuits not required in the short term or just switch off hob, cooker, showers etc when the genny is running
If I install Solar PV how would this work - something else to switch / leave off if the genny is running 

[ProDave]

I have installed these mains / generator switches, they do exactly what you expect them to do.  Watch your earthing, you cannot rely on the DNO PME earth during a power cut, the lines may be down, so drive in an earth rod as well.

Perhaps just use a normal split load dual rcd board and put essential stuff on one side and less essential on the other, but watch the rcd current ratings.

I am not sure how solar pv would work with a generator. If it thinks the frequency is right then the inverter ought to start up, but it could get "interesting" if the solar pv generation was more than you were using and it started "exporting" power to the generator.

The alternative is get your supply onto the site now, and do as many of us have done and have your meter installed in a permanent meter box in a fence or wall on the site boundary. No need to pay to have it moved later.  Then sign up to a no standing charge tariff like the one ebico offers so with the tiny usage during build, you will get tiny electricity bills. In fact I have not actually paid anything in nearly 2 years.

[Jeremy Harris]

I've looked into this a while ago, as we are prone to power cuts here and the new build is 100% electric.  All the advice I had at the time was to buy a petrol inverter generator and convert it to LPG, so that you don't get any problems from fuel going stale or gumming things up.

I've not got around to it yet (it'll probably take another power cut to spur me into action!).

[ToughButterCup]

Being fairly close to Heysham nuclear power station is no barrier to power cuts for us. We have four or five a year. I am weighing up the pros and cons of doing a similar exercise as you, Jason.

I bumped into the problem referred to by Dave above; and have yet to solve it. My son suggests I consider LiPo battery-powered kit for lighting needs, and I tend to agree. A LiPo battery harnessed to LEDs produces a useful amount of light (The Bosch range as an example).

This problem makes you think about the meaning of the word  essential. Food is essential, but isn't a trip to a local restaurant the simplest answer for many? (I accept that's not always possible) What about MVHR? Is that essential during  the modal  power cut duration? (and how long is that?) How much is a small gas stove?

The trouble for me is that I'm not all that inconvenienced by the odd power cut: we don't live in the Republic of the Congo

But I love the idea of being independent of the power supplier

[Jeremy Harris]

Here cuts happen several times a year and most are only an hour or two and not really an issue.  We have had much longer duration cuts though, two years ago we lost power for two days in winter.  Not a problem for our current house, as I have a small inverter that will run the gas combi boiler (the inverter connects to the car, so I just run the car whenever we want to boiler to run), so we have hot water and some heating, and we have a gas cooker and an open gas coal-effect fire, so the only real loss is lights, and I have a collection of home-made LEDs that are connected to LiPo battery packs and work well.

MVHR isn't an issue if the power goes off, you can always crack a window open to get some ventilation. The main problem with the new house is that all the cooking is electric, so we'll probably have to get a small camping stove.  The other problem for longer power cuts is the water pump, we can go for a day or so without the pump running, but we'd have no hot water (the Sunamp needs power and the PV stops working when there's a power cut) and we'd need at least a 2kW generator to run the water pump for maybe ten to twenty  minutes or so a day.

[Crofter]

Our last significant power cut was last winter- 37hrs. The novelty of playing piano by candlelight and sitting around the woodburner was starting to wear thin.

I assume that for houses with MVHR, you would just crack open a window or two?

I have just bought a dinky little petrol generator from Lidl which would at least give us some lighting. Have yet to test it on anything bigger like the freezer- it's surprisingly hard to find information on the wattage of these things.

[ProDave]

Fridges and freezers are awkward things. Although the running current is low, they have a very high start up surge that can stall a small generator. Inverter generators may fair better.  But do you really need to keep a freezer running? certainly not during a 1 hour power cut.  2 winters ago after a storm our power was off for 2 days. Thank goodness for the wood burner. Yes the freezer thawed, but was all the food wasted? No. Once thawed it's still good to keep in a fridge for a few days, so that was the next few days food sorted, and what we couldn't eat in that time was cooked, and then re frozen as ready meals.  Anyone who just bins the contents of the freezer if it thaws is simply not trying hard enough.

We will have a gas LPG hob again and the only inconvenience is having to use a match to light the gas when the power is off, and the kettle on the stove takes longer to boil than an electrtic kettle.

So it comes back to lighting, and we have two gas camping lights that do the job.

[Crofter]

The Lidl gennie is an inverter one, max output of 1200w, 1000w continuous. I don't know if it will come anywhere close to being able to run a fridge or freezer, I take it I won't damage anything by trying, though?

 

We probably have more in our freezers than most people, as we are three hours from Inverness and tend to stock up. Hence a full size freezer in the kitchen plus a second chest freezer in the shed.

[reddal]

I bought a 5kW diesel generator a few years ago for similar reasons. However I never got it wired into a switchover box as I discovered we have a 3 phase consumer unit - and couldn't work out how to feed that from the single phase generator. The circuits in the house are spread between the 3 phases - nothing uses all three. I could power one of the phases from the generator - but this would mean choosing 1/3 of the curcuits and the way its been wired up wouldn't be ideal.

I've used the generator a few times around the property - and once during a power cut with a big extension cable trailing into the house.

Thinking about it I havent powered it up in over year. Damn I bet these things need some kind of maintenance to stop them dying when not used for long periods. I need to sort that...

- reddal

[Crofter]

It's probably just fine. I imagine the engine is similar to a marine diesel, i.e. simple and robust. By far the most likely source of problems will be fuel. Old diesel can collect condensation from the air, and can get 'diesel bug' which produces horrible black sludge. So check the filter and the fuel. If it's white diesel, stick it in your car and buy fresh stuff for the gennie.

[Stones]

Rob, I saw those genny's in Lidl as well.  There are still a few left - and feedback when you fire it up would be appreciated.

I think the general consensus that lighting is the biggest must have in a power cut is probably right.  Cooking is easy, we can just buy a small gas camping stove.  Heating shouldn't really be an issue given what we are building, although with an inverter heat pump (and a low starting current) I don't see any reason why we couldn't run the HP off a genny.  I am planning to use a SunampPV for my DHW,  and given it is designed to work with variable charging from excess PV, don't see why it wouldn't charge from a genny.  I'll have to run that one past them.  

Seems to me that for the relatively low cost of a installing a changeover switch, I'd be silly not to. At least I would then have the option.  The ability to sit out a winter power cut in comfort is very attractive...

 

[Crofter]

I've literally just fired up the Lidl genny for a ten minute test run. Compared to similar little 4 stroke gennies it seems to run very smoothly and isn't too noisy- then again I'm comparing it against various borrowed secondhand examples which were well past their prime, I've not had the luxury of a brand new one before.

 

I'm away to test it with my dinky Halfrauds pressure washer just now, which is going to be borderline as it will probably be drawing too much power...

[Crofter]

And I can happily report that it does run my (1400w) pressure washer. A wee bit underpowered but the gennie adjusts to the load quickly. It will do what I need it to do anyway.