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Thread: Micro Hydro As Alternative Power

  1. #1

    Default Micro Hydro As Alternative Power

    When I first came to Nicaragua over five years ago there was a lot of rural property in the north for sale. One farm in particular was remote and off the grid but had the potential for a small hydro operation, and possibly year around. I did a lot of research into the functionality of a small hydro plant, but wound up buying something else.

    With the success of my dam, and in a relatively dry year as well, I'm re-visiting the possibility of generating hydro during the winter -when the power is needed most. I've experimented with a relativelly large solar setup at my place in Condega, 4KW of panels, 16 golf cart batteries, an MTTP controller, and a large (6KW - 11KW) inverter. I've learned a lot.

    When the sun shines, solar is great. During the rainy season, output falls dramatically. Very dramatically. I've had a grid tie in Condega too, so was able to supplement from Disnorte.

    Some of the things I've learned:

    There are a lot of built in losses in a solar system. You generate the power, and store it in batteries. As the batteries are charged, you lose approximately 15%. YOu take a similar hit when the power leaves the batteries. Inverters vary tremendously in efficiency, but generally fall into a 85 - 95% efficiency band. But, the larger the inverter, the more the inverter takes for "housekeeping". Mine draws about 250 watts /hour to keep itself energized and cool. That's a lot, and adds up over 24 hours. As long as you have surplus power, it's not important, but when the solar output falls, you're paying Disnorte to keep the inverter on, and dduring the hours of 10PM to 5AM, way more power than you are consuming.

    The place I have in Condega is big, and the inverter was sized so I wouldn't have to worry about simultaneous use of the various appliances. The washer and dryer can be running, I can be taking a shower using my widowmaker, and Nuria can be toasting bread for breakfast. The inverter is still loafing, with plenty of capacity to spare. But, I pay dearly for this convenience.

    At night we have those tiny Christmas lights you see strung around trees, strung around the courtyard. It makes for a great ambiance, and generally in the afternoon- evenings I have plenty of power after a sunny day. Not during the rainy season. If I'm not there, Ariana often leaves them on all night.

    The last couple of months I decided to find out just how much it would cost me to use Disnorte exclusively. I was planning on moving the solar plant to the farm anyway, as soon as I had sufficient roof to support the panels. It was quite a surprise. I've attached the October Disnorte bill showing usage and cost. Oddly, the number is almost identical to what our electrical cost in Tucson is, but we use three + times as much. A lot of that is AC.

    Back to hydro: One of the beauties of hydro is, as long as you have the water, it's 24/7. Properly designed (mostly keeping the water in the penstock clean and free of debris), it's just a matter of greasing some bearing every three months. I started out looking at larger units, but soon realized, unlike solar, smaller can be better. A 700watt hydro generator, running 24 hours, would generate almost three times what I am currently using at the place in Condega. I used 8.5 KWH /day in October; the 700 watt hydro unit would generate 21 KWH /day. The surplus could be diverted to a large electric water heater -which I already have.

    I would have to buffer the larger demands with a battery bank and an inverter, but I already have that. I would use a simple charge controller for the hydro output, and when the controller clicked off, the output would go directly to an electric water heater. The water heater will not care what voltage it sees, as long as it's below the nominal 220, and the heating elements are equally happy with AC or DC.

    The same inefficiencies would apply. Into the batteries, out, and through the inverter. No free lunch here either. The link has some detail that tells the story.

    I would only need a 3" penstock, and less than a 100 foot fall, which I have. I think I could use sanitario for the pipe, keeping the cost down as the pressure would be less than 50 lbs/ sq ". The pipe and the hydro unit could be tucked into the barranca that used to drain the area now blocked by the dam. There is some trade-off between flow and head, but during the rainy season I doubt that flow will be a problem. Even when water is tight, I could use the hydro to make up for a shortfall in the solar, then turn it off.

    So, I have an inquiry emailed to the Chinese manufacturer. I should be easily able to put everything in place for next year's rain.
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  2. #2
    Viejo del Foro Daddy-YO's Avatar
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    Default Re: Micro Hydro As Alternative Power

    Thanks for sharing your experiences & thinking on this 'charged' topic. Lots of interesting detail.

    Something I don't understand: with hydro-power can't you convert it directly to alternating current? And isn't the waterhead itself an energy storage system, such that you only run it when you need the AC.

    Photovoltaics produce DC, so if you could find appliances that ran on DC, you could save the conversion losses, but you still need the storage batteries for when it's dark.
    I never met a Semite I didn't like.

  3. #3

    Default Re: Micro Hydro As Alternative Power

    Quote Originally Posted by Daddy-YO View Post
    Thanks for sharing your experiences & thinking on this 'charged' topic. Lots of interesting detail.

    Something I don't understand: with hydro-power can't you convert it directly to alternating current? And isn't the waterhead itself an energy storage system, such that you only run it when you need the AC.

    Photovoltaics produce DC, so if you could find appliances that ran on DC, you could save the conversion losses, but you still need the storage batteries for when it's dark.
    Yes, you can pull the power off directly as AC. If you have enough water, this would be the way to go. But, it gets to be a surprisingly large amount of water as the power generated goes up.

    There are some items that avoid the conversion process, which is wasteful. For example, Fyl had a 24 VDC refrigerator. The difference in cost because of the small numbers, specialized market, is big, and selection is limited. He cobbled together some LED lights, by soldering individual LEDs together. It was pretty ugly, but he had a sweet and submissive wife. Mine has more of a "don't want to live like a refugee" attitude.

    You can draw directly from a hydro unit, I had a friend who had something like that at 7000 feet on the eastern side of the Sierra Nevada. But, he had the water, a big creek running through his place, and an elevation drop. I don't.

    The newer hydro units use a combination of electronic regulation to maintain frequency and voltage within limts, and also automatically dump excess power. My friend's system was very mechanical, carefully calibrated relays would close as the voltage rose a couple of volts, and divert the power to what in effect were heating elements. He used radiant heating in the winter, so this worked well for him. In the summer, the heat was just wasted to air. A large electric water heater works well to absorb the excess. He had no batteries, so could not use the microwave while he was using some other large draw appliance, etc. But, it kept his place warm in the winter, which otherwise would have cost a fortune in propane, or a lot of work and aggravation in wood. I heated with wood for a year, and believe me, THAT gets very old fast. The romance lasts about a week.

    If you generate DC, you are just charging batteries, and the charge controller handles what can be a very wide range of voltage. Frequency doesn't enter the picture, as you are dealing with DC. It really simplifies things If you are running the power any distance, from the generation point to the pont of usage, there are more considerations because of the loss of power in the transmission wire, especially at lower voltages. The unit I was looking at generated 380 VAC which would avoid that loss, I would drop the voltage at the batteries using a transformer (more loss), and rectify it, (again, more loss, but small). This would then be fed to the batteries, and the excess diverted to some other load.

    This makes sense for me as I already have the other components in the system.

    You can read books until you're blind, but living with these systems really teaches you the limitations. I was blindsided by the power used by my inverter just to live, some 6 KWH /day. Once we get the system re-installed on the farm we will turn off the big inverter (when Alexi goes to bed), and use a much smaller one to provde enough for some lights and alarms. That will save almost 2 KWH, and help avoid another consideration for solar plant users: avoiding battery discharge. The life of the batteries is directly dependent on the extent they are discharged, and the frequency. Batteries in "float" service, like at nuclear power plants, have very long lives, in excess of 30 years.

    You gain an appreciation for the "grid".

    Getting Ariana to turn off the coffee maker in the morning, and computer when she's finished, and lights at night, would help considerably too, but that's probably a losing battle . . .
    Last edited by KeyWestPirate; 10-19-2014 at 05:25 PM.

  4. #4

    Default Re: Micro Hydro As Alternative Power

    I'm not to good with electricity, still need to learn more. Found a vid that might fit your scenario.

  5. #5

    Default Re: Micro Hydro As Alternative Power

    The video demonstrates the trade-off between volume or flow and head. He has a very small head, so has to provide a very large volume of water from his pond to get the 500 watts. At my place in the Sea of Cortez we had a 12 - 16 foot tidal range. If I had had a natural basin that I could have enclosed I could have used something like the system in the video. Then again, the sun shines flawlessly there, and that was my first solar experience. When it starts raining in Nicaragua, solar output plummets.

    In comparison, the unit from China that I linked to will provide 750 W with a flow of 1.3 gal/sec (still a lot of water) and a 65 foot head. There's also friction in the pipe. I have about 100 feet of drop, and was going to buy the next larger size of pipe specified, 4 inch instead of three.

    I also have a steep barranca that flows heaviily when it rains. This might be more suitable (with a small dam) than the lake. I have until next year to figure it all out

    The video also demonstrates the difference between attempting to use the power directly from the unit, as compared to storing it in batteries.

    500 watt continuous (what he is approximately getting) is 12 KWH /day, or more than I use in Condega from the grid. But, 500 at any given moment is not much.

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