Electricity requirements

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basil_brush
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Electricity requirements

Post: #200882 basil_brush
Wed Jun 23, 2010 7:02 pm

It's been a while since I posted here but I have a conundrum. My friend and I are hoping to buy six acres of cheap low lying land in Somerset (yes, we checked the flood risks) and build a straw bale house. But I am really stuggling to estimate our electricity generating requirements, and to make matters worse we are on a very tight budget.

We hope to get a second-hand aga off ebay or such for heating and hot water, so that's not included. So the things which must be powered are washing machine, dishwasher (though if necessary I could wash dishes by hand as part of my chores in lieu of paying rent to my friend, lol), some LED lights (or perhaps fluorescent bulbs, though we are not keen on those because the kids often break them and let the mercury vapour out), fridge, chest freezer and 2-3 computers (this varies a lot, the tiny Acer Revo is only about 70 watts, whereas the normal sized desktops tend to be 200-600 watts [at least that's the power supply rating, it doesn't mean they are actually drawing that much continuously]).

Obviously we can reduce capacity by not having everything on at the same time, but preferably there needs to be as much flexiblity as we can afford - apparently our budget is only about a meager 2000 pounds for a generation setup, hence why we're searching for the cheapest option.

I'm also worried about the effect of inductive loads, such as motors, as I know they cause a surge on starting - I know inverters have a surge rating (typically double their continuous rating) but what about petrol/diesel generators or other alternators, how are they affected? Has anyone had any problems with surge overloads?

I am interested to hear both a) what other people think would be the cheapest option, and b) what other people's generating devices and capacity are and what they can power with it.

I'm trying to consider all possible options. Wind, solar, petrol/diesel, biogas and tapping heat from aga etc. My friend has been rather keen on wind turbines - in my research I've even seen some people buying magnets and making their own coils, attaching them to DIY vertical turbines, which seems a really cool project - but I worry about how much we would actually get out of wind turbines in Somerset, and of course there's the big cost of deep cycle batteries (I've read that overall Nickel Iron ones are a good choice but they are very hard to find these days). I definitely want to experiment with wind eventually but we have so much else to deal with in our first 1-2 years that a solution with good reliability is important.

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MKG
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Re: Electricity requirements

Post: #200886 MKG
Wed Jun 23, 2010 7:33 pm

Hmmm. You're not, I think, looking at surge rating correctly. An inverter's surge rating has nothing to do with its "start-up" requirements - it just means that it is protected against input variations up to that value. All generators (whatever their input) take more energy to start than to run normally - but in the case of a petrol/diesel generator, that means that it's the hydrocarbon fuel consumption which goes up temporarily. Inductive loads such as motors certainly do create a starting surge - but the surge depends upon the work that the motor is being asked to do - a highly-loaded motor will create a much greater surge than one which is asked to do merely turnover work.

I'm not trying to put you off, but it does appear that you would benefit a little from improving your understanding of electrics (please forgive me if that sounds presumptious). If your lifestyle depends upon your decisions, make sure you know what you're talking about. Electrickery isn't rocket science - there are very simple equations which cover all circumstances, and they're well worth learning.

Mike
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basil_brush
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Re: Electricity requirements

Post: #200893 basil_brush
Wed Jun 23, 2010 8:17 pm

Yes, I was aware that the inverter surge rating is the max transient load it can handle, apologies if I didn't express myself clearly enough. :)

Thanks for your note about motor surge being dependent on physical load. I presume then that a drill or vacuum cleaner will have a much lower surge than say a fully loaded washing machine.

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Re: Electricity requirements

Post: #200904 KathyLauren
Wed Jun 23, 2010 10:43 pm

Generators and surge loads get complicated. When a surge from a motor starting (for instance) hits the generator, it will not be able to handle it immediately. Because you have suddenly increased its load, it will slow down. The governor will very quickly (but not instantaneously) adjust the throttle to compensate, but it is a mechanical system and will take a second to respond. The revs have to drop before the governor knows it needs to make an adjustment.

This is not a problem for a light bulb, but very bad news for a computer. When the generator revs drop, the frequency of the current drops too, along with the voltage. Electronic devices don't handle frequency changes gracefully. The good news is that a laptop can handle the frequency and voltage drop where a desktop can't, because the laptop runs off its battery. (All the plug on a laptop is doing is keeping the battery topped up.)

The generator should be sized to handle the surge, not just the steady load. Otherwise, the governor will run out of throttle before it has compensated for the surge. Assume that any motor draws double its running load when starting.

For assessing your loads, you might want to borrow an ammeter from an electrician. If you actually measure what current each appliance draws, you will be able to anticipate your needs.

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Re: Electricity requirements

Post: #200936 Odsox
Thu Jun 24, 2010 8:56 am

Regarding wind turbines, you should not rely on one to supply you all year round, so you definitely need some other source of generation.
I have a one kilowatt turbine which has been running now since early January, so I missed most of the windy winter weather, but when the wind is above "a bit breezy" or above 6 m/s, it will supply the whole house. But then you have days on end with no wind and even during the winter the wind usually drops off at night.
If you have a bank of batteries you can of course smooth out the wind/calm cycles but one thing to be aware of is that the charge controller and especially the inverter all consume your precious stored power, even when not working, so look carefully at the specifications when working out battery amp hours versus drawing requirements.
I have 3 ex UPS inverters and the worse one draws just over an amp all the time, even when not supplying power, but "proper" new inverters (arm and a leg job) some only consume about 300 mA, which is still a figure to take into account. You will of course need a pure sine inverter and not a modified sine, or your motors won't last long.
Hope that helps.
Tony

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Re: Electricity requirements

Post: #200939 basil_brush
Thu Jun 24, 2010 9:28 am

I already suspected it, but I'm really coming to the conclusion that the only way to get power without hassle and constant worry is to get a 6-8 kw generator and then try adding solar and wind later to reduce fuel costs.

Can anyone advise on the choice of diesel or petrol generators? I notice that for small 1-2 kw ones the petrol ones seem to be somewhat more economic, but for higher outputs the diesels seem to be more economic. I'm making an educated guess that red diesel is around 80 pence a litre (prices are rarely advertised and it seems you need to start calling people to get a price).

I notice that some diesel generators have Automatic Voltage Regulation and some sellers claimed that this is required for sensitive devices such as computers (maybe it's not true, I don't know). So do we need to be very careful in our choice of generator? (I realise from KeithBC's reply that laptops are ok, but being able to run a desktop one too would be an advantage.)

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Re: Electricity requirements

Post: #200943 Odsox
Thu Jun 24, 2010 9:43 am

If you intend to add wind or solar later it sort of implies that you will be getting batteries/inverter, in which case it might be an idea to look into running the house on batteries from the outset and using a petrol or diesel generator to charge the batteries when necessary. That way there are no worries about regulation or frequency as the inverter will take care of it, simpler although it's probably a slightly less efficient way .
Just a thought.
Tony

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Re: Electricity requirements

Post: #200946 basil_brush
Thu Jun 24, 2010 10:43 am

I think we prefer to delay the cost of buying batteries for a year or two if possible, as it's probably nearly 1000 pounds for the batteries alone (I saw a 400 Ah solar deep cycle lead-acid battery on ebay for about 250 pounds and I suppose we would need at least three of those), but you have a good point. Thanks. :icon_smile:

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Re: Electricity requirements

Post: #200962 Big Al
Thu Jun 24, 2010 12:23 pm

http://midsummerenergy.co.uk/solar_panel_information/solar_panel_calculator.html
this site has a solar calculator where you can put all your info in and it helps work out your needs.

You mention that you can always reduce your comnsumption etc, just what we done over the last 3 and a bit years. Then it was over 10,000 KWH per year electrikery now it is around 3308 and that is with a 1993 F rated fridge and freezer and an electric oven and hob so it can be done.

You mentioned getting a second hand aga of a site, be careful as these beasts take a lot of hard wear and tear so be sure to check them out. I looked at a reconditioned one once, I liked it but the price tag was still over £3k for a refurbed 15 year old 4 door one.

Good luck anyway
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basil_brush
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Re: Electricity requirements

Post: #200986 basil_brush
Thu Jun 24, 2010 3:02 pm

Thanks for the solar calculator, it's very useful in helping to work out the amp hour rating of the batteries. It's the damn washing machine that really pushes things up!

By the way, I love your signature Big Al, very amusing. :iconbiggrin:

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Re: Electricity requirements

Post: #201003 pumpy
Thu Jun 24, 2010 9:50 pm

basil_brush wrote:I already suspected it, but I'm really coming to the conclusion that the only way to get power without hassle and constant worry is to get a 6-8 kw generator and then try adding solar and wind later to reduce fuel costs.

Can anyone advise on the choice of diesel or petrol generators? I notice that for small 1-2 kw ones the petrol ones seem to be somewhat more economic, but for higher outputs the diesels seem to be more economic. I'm making an educated guess that red diesel is around 80 pence a litre (prices are rarely advertised and it seems you need to start calling people to get a price).

I notice that some diesel generators have Automatic Voltage Regulation and some sellers claimed that this is required for sensitive devices such as computers (maybe it's not true, I don't know). So do we need to be very careful in our choice of generator? (I realise from KeithBC's reply that laptops are ok, but being able to run a desktop one too would be an advantage.)

You probably won't find a petrol gennie above 4kva output....... always go for a diesel. All larger gensets have an integral AVR, . General rule of thumb...... 415v- 3 phase, kva X 1.5 = capacity in amperes. 415v, 3 phase gennie converted to 240v single phase(domestic supply),kva x 2.4 = capacity amps, dedicated 240v gennie=kva
x 4.5 maximum amps. Incidentally, the start current of a electric motor can be up to 6x the rated current. :icon_smile:
it's either one or the other, or neither of the two.

basil_brush
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Re: Electricity requirements

Post: #201019 basil_brush
Fri Jun 25, 2010 6:06 am

Thanks Pumpy! That was very useful, all I need now is a clamp ammeter. :iconbiggrin:

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Re: Electricity requirements

Post: #201907 dave45
Sun Jul 04, 2010 9:57 am

Odsox wrote:I have 3 ex UPS inverters and the worse one draws just over an amp all the time, even when not supplying power, but "proper" new inverters (arm and a leg job) some only consume about 300 mA...


You can do better than that... my Studer AJ500 only consumes 0.3W in standby (tickover) mode

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Re: Electricity requirements

Post: #201910 Odsox
Sun Jul 04, 2010 10:28 am

Thanks for that Dave, but therein lies the problem.
For a 48v Studer with low tick over wattage I would have to pay well over a grand sterling.
I think I will live with my present setup for a while longer and see if that sort of expense is justifiable.
Tony

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