I posted a week ago to inquire what capacity generator I might need to power things like central heating, freezer, large american fridge freezer. The consensus seems to be, go for a 2 kw one, Honda if possible.
I also note that things like inverters can do some of the jobs that a generator can. Would one be relevant in my case?
Thanks for your help in advance.
Mike
I'm not sure why people recommended Honda, they are hideously expensive for the specification. I'd recommend that you have a look at Kipor generators which are well built, electronically stabilised and very quiet for the capacity. Given the price differential you coudl probably run to a 4 or 6KVA Kipor for the price of a 2KVA Honda.
In brief, no. I use an 800W inverter in a remote barn to provide lighting only. I've tried to use it for some other applications and it has burned out a Switched Mode PSU and has difficulty driving difficult loads. This is because the AC output is modified square wave. Good enough for lighting and not for much else. A proper sine wave inverter will cost as much as a generator and you still have to buy sufficient batteries to supply current and to maintain them between blackouts. I you really want to have a 2KVA standby from an inverter I suspect you will be looking at 10x110AH batteries, a 250W solar panel to charge them with appropriate charging circuit and a 2KVA inverter or a 2VA inverter/charger. Personally I wouldn't expect to see much change from £3000.
You would need an unrealistic sized battery to carry the same energy as a tank of petrol, and you can't easily top it up when it runs low and you still don't have your mains supply back on. (The more expensive generators actually use an inverter as the final stage to generate a good quality output, but that's fed from the generator, not batteries.)
I've got a 17Ah battery and an inverter. In theory that would keep my heating alone running for something like 90 minutes if the inverter is 100% efficient (it's probably not far off, as it doesn't get hot).
Indeed it could,
A bank of lead acid batteries and an inverter is perfectly capable of running a whole house for many hours..days even, if you spend the money on batteries.
Essentially is a very big UPS....;-)
Not sure how big those go, or how many batteries you can hook up to them. I'd be definitely interested tho.
Could charge on off peak and run the house off it during the day.. ;-)
Almost certainly not. The cost of inverters powerful enough, with a suitable overhead, to run even modest devices will be great. I have found that switch on surges mean that at least 50% additional power handling is needed, depending on the sort of load. And of course you will need to spend a lot on batteries to store the necessary energy if the idea is to have more than a few minutes running time, and then find somewhere to put them. 1kWh = 3.6 MJ. 1amp hour at 12V is 1 x 3600 x 12, which is 43 kJ (remember ItV from physics?). Thus if my calcs are correct you need 83 Ah, which might need to be doubled to allow for inverter inefficiency. That's two meaty batteries for just one electricity unit.
Peter Scott
? Not really.
Depends on what you call unrealistic.
You can get a kilowatt hour of battery for about 150 quid..
30 of them would give you enough to power a house for a day, including things like the odd heater, shower and electric kettle, and be about the same size as a fridge. About the same (output) energy as a car tankful of fuel.
Jump leads and your car?
85%-95% is fairly normal on a HF inverter.
Well,. it all depends..
Here is a data point..3500Watts, 5KVA, around £1500...
I would think around £6000 might easily get you a 24hr+ electricity supply, at normal sorts of loads.
With off peak being about 8 times cheaper than on peak, its an interesting calculation..
If your quarterly bill is more than around £150, its probably worthwhile..
THEN use a genny set to charge the batteries.. ;-)
If you read down the spec, at full load of 5kW this only provides just under 10 mins of power. For 24 hours, at say 1 kW load, you would need about 30 of these beasts. As the tech data says these are for giving enough time for safe shut-down. Even if you use external batteries the question of storing enough energy still remains. On a slightly different issue, I am a great advocate of photovoltaics, but storing enough electrical energy for overnight remains the major problem.
Peter Scott
I find my invertor is about 80% efficient. It draws 10A @ nominal 12V for every 100W of 240Volts it pushes out into a resistive load, so no power factor stuff is taken into account.
Less - I've seen 110 Ah 'leisure' batteries advertised at GBP65 recently.
There again one litre of petrol gives you about 10 kWht (thermal) or, say, 3 kWhe (electrical) and costs just over one pound.
I've never needed it in anger, but my tests showed a standard large car battery (IIRC 75A/hr) ran mine for 12 hours and still had enough charge to start the car. Of course it depends on how often the pump runs and things like motorised valves operate - mine was a pretty basic system with no boiler electronics.
It makes no sense at all to use batteries for some of these applications. Far better (and cheaper) to use a portable calor gas etc ring for kettle boiling - and the same for local heating. An inverter only really makes sense to run central heating. Even a freezer is better off run from a small genny.
Oh. it depends on what you want.
I would simply LOVE a system that when its cold and wet and the trees take out a power line, did not require me to have to fiddle around starting up motors and rewiring the house..to get the TV and the lights back on. Cooking we can do on te aga...and having te oil boiler work would be fine..
AND if it almost paid for itself by using off peak electricity overnight to charge batteries I ran off during the day, it would be magic.
I was just curious to do the sums on a completely 'battery powered' house.
It is NOT as expensive as I thought..if you can cope with only about 24 hours continuous battery usage.
Obviously if its a mini hurricane and loads of lines are down (as happened the other year), one expects delays, and goes very economical on the batteries.
A remote start generator and a changeover switch can make it painless. Some generators can be configured with an automatic changeover switch and automatic starting.
The last time I looked at sucha s system is was about £800 for a 6KVA generator with remote/auto start and £80 for the changeover switch. That's a lot cheaper than an inverter/battery system.
Anyone know what the efficiency is likely to be of going mains-->battery charger-->battery-->inverter-->mains?
In other words, how many kWhs need to go into the charger to get 1kWh out of the inverter?
As long as the overall efficiency is better than about 50%, you *could* be better off by buying all your electricity at the off-peak rate and storing it in batteries - but you'd have a hell of a capital investment (and probably maintenance/replacement costs) to contend with.
When you find a good 'un for that sort of money let us know please;!...
Might be cheaper to buy a small valley in a depressed area and build a pumped storage scheme.
Owain
This one's only 5KVA but autostart and a bit cheaper.
IIRC it's around 75%.
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