How much power does a household need?

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How much power does a household need?

Postby windgat on Thu Nov 29, 2007 10:41 am

This is not an simple question. Firstly, one can look at the current electricity bill and from that work out the kW hours per month. Usually the majority of this is for heating. Electric stoves, space heaters and the hot water cylinder are big power users. So power use can be dramatically reduced by using gas heating, and direct solar water heating. To run a 'normal' household without any economising on power would require a large turbine. In an urban or suburban environment, it is more practical to look at supplementing grid power with wind and possibly solar.

So a kettle usually consumes about 2 kW, so at first glance a 1kW wind generator can not run a kettle. However, this is false reasoning. A kettle is on for a very short time, and the generator would charge batteries, and the appliance would run off the battery (possibly via an inverter to turn the battery DC current into the AC current that most domestic appliances require), so the full answer to this requires knowing how many minutes a day the kettle (for example) is used, and how much wind is available over time. Also, if you have grid power, during times of high usage/low wind the mains power can be used to top up the batteries via a standard battery charger.

The best way to estimate power production is by the diameter of the turbine and the local wind speeds (see the data on the web page 'Western Cape Wind speeds' on this site). Note that the rated 'watts' of the generator itself is not a good measure, and many commercial producers fudge the figures in all kind of disingenuous ways to make the product look good. If you refer me to a web page showing specifications of a generator, I would be happy to critically analyse it for you.

The approach I have taken is to start slowly by using the wind power for an alternative set of lights, installed in addition to the standard lighting. This means you do not rely 100% on the wind for power, and also that you have lights during a power failure. Lights are available which can run off DC directly (CFL and LED - see the web page 'Electrics' on this site). Almost all electronic equipment uses DC current internally, and some are easy to run directly of batteries, like laptop computers, and others need and inverter (to make AC current), although usually the AC is just used to generate DC again internally, which of course loses some power each time a conversion is made.

A great solution is a grid tied (or grid sync'ed) inverter, which merges the available wind power with the incoming grid power. Unfortunately these are currently still quite expensive due to low demand.
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Re: How much power does a household need?

Postby Power4nico on Sat Jul 19, 2008 2:15 pm

As "windgat" has explained this is quite an excercise. However, for a quick calculation (for the suburban area's) is to take an average of your monthly electricity account, and see what your KwH / month usage is. Bring this down to a daily amount, and you have ultimately "How much power does a household need", and that is for your house (not mine or anyone else's). From this point you can decide which items are consuming the most power (usually the geyser, aircons and Heaters), and see if you can do something to reduce their consumption.
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Re: How much power does a household need?

Postby windgat on Sat Jul 19, 2008 5:17 pm

'Need' is also a tricky word. The calculation you describe is a good one for determining what a household uses... but what it actually needs is a slightly different issue.
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Re: How much power does a household need?

Postby esawyja on Tue Oct 28, 2008 10:49 am

Hi all,
So I got my magnets and wire from windgat!!! hiiiaaayyy....,,, soon I will have it up and running, I hope! I had a look at my eishkom account and according to them, I'm using on avarage about 1,5KWh per month, that was the worst one, the best one was April at just under 1KWh, so what does that mean in terms of my daily consumption and what would I need in terms of windpower?
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Re: How much power does a household need?

Postby windgat on Wed Oct 29, 2008 1:25 pm

1.5kWh a month = 1500Wh a month = 50wh a day. Which would mean all you use is the equivalent of one 60W bulb which you leave on for 50 minutes a day. That doesn't seem right somehow...
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Re: How much power does a household need?

Postby esawyja on Wed Oct 29, 2008 3:06 pm

Yea, that is what I thought as well, but the statement is a bit confusing, they have a graph on the bottom, with all the months and mine is between 1000 and 2000 and the unit is in kWh... but on top, this month it says "TOTAL ENERY CONSUMED FOR BILLING PERIOD (kWh) = 1,218.00" ... Energy charge 1,218 kWh @ R0.3952 /kWh = R481.35
... am I missing something, like a couple of zeros
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Re: How much power does a household need?

Postby windgat on Wed Oct 29, 2008 4:57 pm

A low use western style house uses about 30kWh a day. That's about 1000kWh a month. So looks like you are using 1200kWh a month.

For arguments sake lets say you get 500W from your turbine 12 hours a day. Thats 180kWh a month. So you still need about 1000kWh from somewhere to be Eishkom independent! Also, 500W for 12 hours is perhaps optimistic for inland areas.

The easiest kWh to get is the one you save. Using gas for cooking and heating is a very good start. A solar water heater is a huge saving, perhaps 40-60% of a typical total bill. If you use LED lights that can also save a lot. One approach is to use the wind energy to charge batteries, which you use to run all your lighting - mainly LED (direct from the battery) with perhaps some 12V CFL. This avoids the need for an inverter, and means no lights out if Es-skom load sheds you. Its also easy to wire a small UPS to use the batteries so that in emergencies you can use your computer (or other AC appliance).
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Re: How much power does a household need?

Postby turning green on Sun May 10, 2009 9:07 pm

The American Wind Energy Ass. has just held the biggest exhibition ever in Chicago and there the most popular domestic turbines were between 3 kw and 5 kw and the most popular was 3.42 kw. I looked up what the diameters were to be able to generate these powers and it was as I expected - about 5m dia (2.5m radius) for 3kw and 6m dia (3m radius) for the 5 kw. Typically the height of the masts are 12 m and the costs for the 3kw about R60 000 (rands) and the 5kw about R80 000 (rands).

Two observations. First that's what they consider necessary to run a household and secondly these things are BIG. I've ignored the costs. The size is impressive and will that be suitable to be erected in a built-up area ??

Personal opinion. Is it necessary to aim for complete independance in towns and cities ?? Rural maybe but I think back-up is the way to go for towns and cities - we're unlikely ever to have no utilities.
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Re: How much power does a household need?

Postby Greystoke on Mon May 11, 2009 7:15 am

My objective is to lower cost AND to be less vulnerable to power cuts. I'm already cooking on gas (which is a GREAT improvement in the cooking :D ) and I'm building solar panels for my two geysers (one is in the granny flat). The kitchen and bathroom taps are on tankless heaters.
The next is either a photovoltaic panel or . . . a windcharger to power an emergency light/electronic circuit.
Regards
Cor
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Re: How much power does a household need?

Postby turning green on Mon May 11, 2009 8:08 am

Greystoke - share your objectives. Solar geyser done and dusted. 2.5 kw generator primed and ready. Got gas. Busy with wind turbine. After that I'm going to tackle food production - got sweet potatoes already. Thinking in direction of water tanks, shade cloth areas and worm breeding !!!!

All that's missing is the calamity !!!!!!!!!
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Re: How much power does a household need?

Postby Greystoke on Mon May 11, 2009 1:31 pm

I actually forgot the food production . .

I'm in to hydroponics. The advantage of that is the efficient use of water AND nutrients, as nothing goes to waste.
At the moment I'm concentrating mostly on herbs, but I've got a working production line of Swiss Chard, and next Spring I'm starting up a tomato set-up, and then cauliflower and broccoli.

Now, what else did I leave out?

Should I move into a cave? Image

BTW: @ windgat
Your "Hyperactive member", has gone a bit lame. Got a stroke last year, and I'm still not fully recovered (walking around with a stick). So, a lot of plans I had have gone into the bottom drawer. But, you never know . . maybe I can drive again by Xmas. :)
Regards
Cor
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