Hello,
I am also new to micro-hydro power generation. However I am not new to electronics and power generation in general. So I will try to answer your questions regarding the general electrical aspects of the system. 1. A rectifier is a device (made from diodes) that converts the positive and negative currents of AC to all positive. The rectifier does not create DC it creates AC such that all parts of the signal are above zero. It basically inverts the negative portion of the signal and allows the positive portion to pass through as is. This assumes that you are using a full wave rectifier. You can also use a simpler rectifier called a half wave rectifier that blocks the negative portion of the signal and allows the positive portion to pass through. This however is far less efficient because it discards half of the signal. At this point we still have AC and need to use a capacitor to smooth the signal to produce DC. 2. The only difference between a Generator and an Alternator is that a Generator produces DC current and the Alternator produces AC current. Which is what Alter in Alternator stands for, alternating. As in Alternating Current (AC). They both produce AC initially, but a Generator has a rectifier built into it. It has occurred to me that since your system charges batteries from a Generator (which more than likely produces AC in spite of the name) it would be easier for you to connect an AC hydro generator to your system. Provided it produces something close to 60Hz. One thing you should be very careful about is to isolate the hydro generator and the fossil fuel generator. One or both could literally explode if they are connected to the same circuit but do not have the same rotation in the wiring. Converting from DC to AC at the generator would not only increase the transmission efficiency because the signal is now AC but it will likely be in the 120 or 240 volt level thus reducing the current and thus reducing the line loss. From reading the specifications modified sine wave inverters are more efficient than the pure sine wave inverters. However the modified sine wave inverter producing far more harmonic distortion in the signal and thus can heat up motors, transformers and even the transmission lines. So I'm not sure what the net efficiency would be for a system using a modified sine wave inverter versus a pure sine wave inverter. It seems to me that the easiest way for you to transmit AC would be using an AC hydro generator. Because you have not yet purchased a hydro generator you have many options from which to choose. From my own research (I am also looking to install a hydro generator) AC systems are more expensive than DC based systems. You could get a hydro generator that produces a high DC voltage (say 120VDC). This would reduce the loss over that of a 48VDC system. In the end I don't know what the price/performance ratio of either system would be. A 48VDC system is far less lethal than a 120VDC system, so care should be observed when using the higher voltages. Because you will be consuming around 50kWh per week, it seems that a 1kW generator would be sufficient. Which translates into around 8 amps of current for a 120VDC system. It might be easier to install a large conductor and go DC. Once the conductor is laid you can alway increase power output and not replace the conductor provided it is of sufficient size. For me the biggest pain would be the installation of the transmission line. I sent this to the entire group so that others can comment on things that I may have gotten wrong. Michael McCarrick Daniel Kim wrote: >Okay... just went through all of the email thread -- I really really >appreciate all of you (some of you quite passionately) posting to help me out.. > >Now, I am getting a little bit more sense of what is necessary here.. and >what kind of parameters / limitations I need to consider... > >Well, as mentioned before, here's a list of parameters that I have to work >with: > >1) completely off-grid system >2) a big main battery bank (48V @ 1700AH) hooked up to 15KW LP generator for >peak usage backup >3) a rack of Trace (or Xentrax) inverter/charger is hooked up between the LP >generator and the battery bank. It can handle up to 120amps. >4) main battery bank will eventually be hooked up to 3 cabins (one of them >being a 2500 square feet residence!). >5) weekend usage only, but we can assume that it's almost every weekend. >Assume that during the weekend, we'll be using something like 40-50KWH. >6) creek is 800-1000ft away from the battery bank, 120ft head w/ 60-70GPM flow >7) we're willing to spend up to $6,000 on the hydro system, if it can fully >charge the batteries (which would be able to store about 40KWH of usable power >- at 50% discharge limit) during the weekdays. > >I think having these parameters will actually help narrow down the choices a >bit... Basically, we're hoping that with the hydro charging the batteries >throughout the week when no one is there, we won't need to use the LP >generator (especially with the skyrocketing price of propane these days) as >much. > >So, it is not an option for me to run directly off of the AC hydrogenerator... >it has to charge up the battery bank (b/c of the high usage during the >weekend). And because of the high storage of the battery bank, we would like >to get as much power out of the stream as possible (i.e., minimize power loss). > >Now, many of you guys are talking about rectifiers and transformers and >alternators and induction motors, etc... I'm sorry, but I have a hard time >understanding that.. (please have patience, I'm a newbie!) So far, I've >basically figured out what an inverter/charger does... I understand AC & DC, >and I understand the basic way that voltage and amperage works. But I don't >know what a rectifier does... does it convert AC to DC?? But wouldn't my >inverter/charger do that for me? What's an alternator? > >Anyway, for that reason, I am having a bit of a hard time understanding what >is actually being suggested by many of your postings. Hopefully, with the >parameters that I listed above set, it will narrow down the range of >possibilities... It seems like some of you were being very creative with what >I could do! That's great, and I really appreciate that.. but the reality is >that my range of possibilities isn't that wide... so with my parameters, >perhaps all those ideas with rectifiers and alternators would not be >applicable?? Not sure. > > >Now, moving onto the things that I DO understand... >I see that some of the postings have suggested that I just get a DC >hydrogenerator and just get thick #2 wires to transmit the power up to the >battery bank 800-1000ft away. That's an idea that I at least understand. I >also understand that DC current is safer than AC. But I also understand that >DC current doesn't travel as well as AC -- even with a #2 wire, wouldn't the >power loss be pretty significant? Even at something like 48V, wouldn't the >loss be significant? And the added cost of a #2 wire is also something that >I'm concerned about, as it will add about $700 more to the wiring, right? But >I'm open to suggestions. If DC generators are cheaper than AC generators and >the power loss over #2 wires is not that much, maybe I can buy into that... >Any thoughts on this? > >Another posting suggested that I get a DC hydrogenerator powering a small >battery bank, and then use an inverter to convert it to AC and make it >travel... that's something that I also understand... And I DO have a small >battery bank (just a 1KWH storage system)... so that idea sounds intriguing. >Basically, I would put the small battery bank and the extra cheap inverter >down at the stream next to the DC hydrogenerator, and let the hydrogenerator >charge the batteries, and let the inverter convert the battery voltage to AC >and push it for 1000 ft, right? Now, I'm just wondering what advantage this >particular system would have over me just getting an AC hydrogenerator to >begin with (since it looks like this system is basically "simulating" an AC >hydrogenerator). Wouldn't it be simpler to just buy an AC hydrogenerator? Or >maybe there's some nice advantage to having this DC->batteries->inverter->AC >system that I'm not seeing? > >Anyway, this is sort of where I'm at here.. Hopefully that gives you a better >idea of my knowledge level and my situation. When there's all these >parameters & limitations, sometimes the job becomes easier - and hopefully >this is one of those situations where the limitations that I have @ my site >actually makes the job easier. > >Thank you again for all your postings, it has been tremendously helpful.. >although at times I didn't really understand what all those terms meant... >Please have patience with me, I'm learning as fast as I can. > >Thank you again, I really appreciate it. > >--Daniel > > > > > > >--------------------------------- >Do you Yahoo!? > Meet the all-new My Yahoo! – Try it today! > >[Non-text portions of this message have been removed] > > > > > > > >Does your company feature in the microhydro business directory at >http://microhydropower.net/directory ? If not, please register free of charge >and be exposed to the microhydro community world wide! > >NOTE: The advertisements in this email are added by Yahoogroups who provides >us with free email group services. 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