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Running electricity long distances (or alternatives)

  1. Jun 26, 2008 #1
    Hi guys. I'm new to these forums, but have been wanting a place to ask questions like this for awhile. You all seem like a nice bunch (unlike the computer science communities I'm typically a part of) so I'd like to start off with a topic that's been bugging me for awhile.

    My father has a rather large piece of land with a nice creek that runs through it, and we enjoy spending most of our time in it. I don't have exact distances, but let's say it's about 1000 feet away from his house. For the past several years we've talked about getting electricity down there somehow. My first thought was to put in a water wheel attached to a generator to just produce the electricity we need. There is a section of the creek that is solid stone, and over time erosion has created a nice 1 foot wide channel where all of the water runs through with enough force to sweep your feet out from under you if you're not careful.

    I've found several people talking about doing the same things, but the best was about a guy who took a log that fell across his creek..he cut a channel into the log, and used a modified squirrel cage fan with generator to produce enough electricity to do what he needed. Well, I've been unable to find a squirrel cage fan, and my brain hasn't managed to come up with any alternative for this water wheel, so for now I've put that aside to come back to later.

    What I'd like to know now, is what it's going to take to get electricity from my father's house to the creek. The uses of this are going to vary, but in a couple of weeks we're going to have a live band out there. That will probably mean we'll need to be driving speakers and amps, as well as several lights (either a string of 100 watt bulbs or some flood lamps.) I know enough about electricity to understand that extension cords are out of the question for something like this simply because the distance is too great for the cords to maintain the proper voltage (There's also the problem of making sure the breaker we use can handle the load). I feel like it might be worthwhile to use some sort of transformer to step the voltage down and the current up (I think that's how it works) to emulate what happens on actual power lines that run cross-country. Then once at the creek it could be converted back. I don't know how to build a system like this, nor do I really know what I'd be looking for if I tried to buy/order it. Help? :)


    Also, in regards to the waterwheel/turbine/hydroelectric issue, I'd like to discuss that in greater detail. Primarily I'd like to learn how to convert the dc power generated from that into ac as efficiently as possible (unless there are ac generators available.) I'd also be interested in finding a way to use the system above to maybe transfer some of that generated energy back to my dad's house so that he wouldn't be as reliant on the electric company. I've heard of folks using complicated circuitry to feed electricity back into the grid, and having the electric company send them checks if they fed more back than they used. That's a wet dream of course, but we're just talking right? :)

    Speaking of dc to ac conversion...we toyed with the idea of just charging up a couple of car batteries and connecting those to a dc to ac converter to power a few 100 watt light bulbs for simple lighting. Maybe even throwing a solar cell on those batteries to keep them charged during the day so we could use them at night. I've also heard of the 12v lights that you can use instead of normal AC bulbs. How difficult would it be to setup something like that?

    Yes, I realize this was a lot, but truthfully I've been thinking about this for years. I've just not had the know-how, time, or money to get any of it done. I'm finally starting to have the money and time, so I would like some help with the know-how. Plus I'm always open to new ideas. I very much like the idea of living off the grid so to speak. This would be a big jump in that direction.

    Thanks for reading all that rambling and I look forward to any constructive criticism :)
     
  2. jcsd
  3. Jun 26, 2008 #2

    berkeman

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    Welcome to the PF. It truly is a great resource.

    Couple of comments. First, you should calculate how much power is available from tapping into the creek. That will give you a reality check on whether you can power bands at parties, or even if you can power a couple light bulbs. You can get a quick idea of the power available by figuring out how much water falls how many feet in a second, and using the weight of the water to calculate the potential energy change per second. Then swag a 50% efficiency for however you convert the delta-PE to electrical power (yes, an AC generator).

    Second, if you could get enough power to be useful, you would use an AC generator, and then use a step-up transformer to drive the lines to your house (to minimize the I*R losses in the wire). Then at the house you would use a step-down transformer, and probably an inverter to stabilize the power at 110Vrms (US).

    Finally, the overall concept that you're asking about is "cogeneration". Here is a wikipedia.org page about it:

    http://en.wikipedia.org/wiki/Cogeneration
     
  4. Jun 26, 2008 #3

    stewartcs

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    The voltage drop in the cable is dependent on the load and the resistance in the cable. A standard cooper solid core 10 AWG cable has about 1.07 ohms per 1000 ft. So based on your 1000 ft cable, if your load is hypothetically maxed out for that size wire then the voltage drop is Vdrop = I x R, which equals 30 x (1.07 x 2) = 64.2 volts. That's a pretty big drop. Use a step-up transformer to reduce it to an acceptable level. If you double the voltage with a transformer, you'll cut the current in half.

    For example: Let's say that I want to distribute 1 million volt-amps. I could use 1000 volts and 1000 amps. However, the I x R drop in the wire would be horrendous. So instead, I use a step-up transformer to pump the voltage up to 500,000 volts, and send 2 amps. I still send 1 million volt-amps, but now a 2 ohm resistance drops only 4 volts in the cable. A 4 volt loss in 500,000 volts is minuscule.

    Hope that helps.

    CS
     
  5. Jun 26, 2008 #4

    dlgoff

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    All of the above is good stuff. But I like to get down and dirty. How about just renting or buying a generator?

    Oh. And welcome to PF. You'll find all the resources you need here.
     
  6. Jun 28, 2008 #5

    Ouabache

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    Welcome Waverly360 to PF !!

    Regarding how you might generate electricity from your stream, I found some useful articles searching the web under small hydro power.
    This page also points out references to "small scale DIY hydroplants". Therefore another good search on the net is "small scale hydropower". One reference points to Home Power Magazine, with a useful article by Cunningham and Woofenden titled "Microhydro Electricity Basics".

    To get something up an running soon for your live band, I would also look into what dlgoff has suggested, renting or buying a portable generator. To figure out how large a generator (capacity), make a rough estimate of your load, list all the equipment (with current, power ratings) that your band would need and add on another 20%. That will help you select the size of generator required. The generators may be rated for horsepower, amps, or watts. (For example I see a 45A, 5.5KW portable generator can be rented for $80/day and a 100A, 12KW generator rental for $125/day).
     
  7. Jun 29, 2008 #6
    You really must stop "powering a few 100 watt bulbs". Only about 2.5% of the 100 watts makes it into useful light. The rest just warms up the air, (and the earth). A 17 watt low energy bulb delivers the same light.

    The losses in electric lines are proportional to the square of the current. Double the current, and you quadruple the losses. Triple the current, and its nine times the losses. This is why audio PA lines are transformer boosted to 100V, and there are step-down transformers in the speakers. Exactly the same reason why electricity is sent across the country at many thousands of volts, and stepped down again at the sub-station, and then again at the pole-pig transformer near the house.

    Here in the UK - we use 240V, so it would not be too much of a problem to use 10mm^2 domestic flat cable to power a live band 200 to 300 metres away, provided they kept it down to a couple of kilowatts. In USA with only 115 volts, its not so easy. You could, in theory, use transformers to get the voltage up, and step it down again at the point of use. It is a very bad idea to try and use just one step-up just to restore the drop in the line because that is load dependent. Switch off a few lights, and the voltage will rise to silly places and bust the equipment!

    If you are rural, and need energy independence, look at http://www.otherpower.com/

    Keep in mind that unless electric energy is stored, it gets used up within a few microseconds of being generated, wherever it comes from! Wind power is only useful by itself if you have enough to do the job at the time, or you can have it synchronized to the incoming grid power so you use it while being augmented by some from the grid. This way, you get to save the bill at the rate the supplier charges you. The deal in the UK sucks because for energy run back to the grid, the supply companies first accuse us of fraud, then only rebate 1/10th of its value. In Germany, you get to discount the bill beyond the amount you save, which is why Germany roofs are so covered with photovoltaics that the grid supply is becoming unstable! The very flexible electronics packs that can accept almost anything and generate synchronised AC power that does not return any to the grid until it is in excess of the load are now very available. They can usually can be set to never deliver back to the grid. as an option.

    If you have steady running water, and enough height drop that a hydro turbine (OK - water wheel) is feasible, then you can also synchronize to grid, and become largely self-sufficient without inconvenient power fails when it stops. For wind generators to work, they need to be high enough to feel 5-8mph minimum. In a decent (say 12mph) breeze, a 2.8metre turbine might give you 500watts. They don't work when the wind stops. Batteries are expensive, and their manufacture has a carbon and pollution footprint of its own. You need also to know that when the wind is 80mph, you won't have a spinning death thing get loose!

    I also live rural, with lots of power outages. So far, my greatest successes have been in simply not using the energy in the first place. I will probably use PV's combined with solar augmented water heating, on grounds of low maintenance and lack of moving parts. :smile:
     
    Last edited: Jun 29, 2008
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