Written by Brian Betz
Much has been documented about the use of micro-hydro turbines for residential off-grid applications. However, I have not read much regarding the use of these turbines in cold weather. Given the shorter daylight hours of winter, micro-hydro production in the winter-time is ideal for off-grid systems. If the penstock (pipeline) is buried below grade there may not be much to worry about in terms of the cold. Even 12” of dirt around a pipe moving 20gpm to 140gpm will prevent it from freezing in most cases. And a moderately insulated “hydro-shed” will prevent the water lines from penstock to turbine from freezing. I have spent the last 2 ½ years running a micro-hydro turbine in a semi-cold climate without a buried pipeline. I have learned many things about how water freezes and “what not to do” in a system like this. Much of this knowledge has been gained the hard way.
A micro-hydro system with a buried pipeline in cold weather has two main concerns. One is the intake freezing or plugging. The second is the penstock lines to turbine, freezing solid in the hydro shed. You may want to read about the phenomena of Frazzle Ice. Frazzle Ice can plug an intake and stop the water from flowing. Frazzle Ice can occur in mountain streams, particularly in area where there are waterfalls. The more common concern may be freezing in the hydro-shed. However, if the penstock is buried the water should be warm enough that it won’t freeze before entering the turbine. Some additional insulation like a blanket, rigid foam, tarp or a combination of all three may be needed during exceptionally cold weather.
If the penstock is exposed there is huge risk of a damaged or destroyed pipeline in the event of a loss of flow. Lines feeding the turbine may start to freeze causing the flow to stop and the entire pipeline to be frozen and destroyed. In my own case, I have seen freezing in a relatively insulated hydro shed on the lines feeding the turbine. The water in the exposed penstock (4” PVC in my case) was not freezing. But because the flow has been reduced in the lines feeding the turbine, ice starts to form quickly in the penstock. If the turbine produces a large amount of electricity it may produce its’ own heat. This can provide valuable heat to the hydro-shed as well. Unfortunately, in my case the turbine is making less than 250 watts and does not make enough heat to help offset the extreme cold. Extra insulation over the turbine is necessary to prevent the lines in my system from freezing. When there is a good amount of snow on the ground it helps insulate the pipeline and the hydro shed I have successfully run the turbine well below 0F with 2’ of snow on the ground. However, I have also had it all freeze at 15F when there was no snow on the ground proving how well even snow can insulate the lines.
It is safe to say that micro-hydro isn’t as easy if the penstock cannot be buried. But in my own case it was well worth the hassle to install a system for our home. When the micro-hydro is running we have no need for our backup generator. My modest 225 watts from the turbine turns into 5400 watt hours over the course of the day. In cloudy north Idaho this means the battery bank stays full when the sun is completely absent for weeks on end. It also allows me to have a small battery bank 450Ah @24 volts. My batteries are almost always between 94%-100% which extends the life of my small battery bank to hopefully 7-12 years. I have had to drain my system three times this year to prevent a major freeze up but again it is worth it for the output that I have achieved.
I am still learning what I can and can’t do with my system. Here are some helpful hints I have picked up the last few years.
- It is always easier to drain the penstock if you think the system could start to freeze up rather than risk the problems associated with a freeze up. It is absolutely imperative that the penstock go downhill or level the entire length of the penstock. If the penstock goes uphill at any point water will sit and freeze. I have lost a lot of sleep wondering if the system will freeze. But as I mentioned before, depending on snowfall amounts, the temperature where I have problems can vary greatly.
- I have been able to use rubber couplers with pipe clamps in a few key areas to facilitate draining the penstock. While I don’t recommend their use, they can be very helpful. Especially if you have any uphill sections. These drain couplers are not meant to hold pressure, but can hold up to 10 psi. If you use these couplers you must make sure the pipe is prevented from being “pushed” out of the coupler. It is imperative your penstock is securely anchored in your hydro room and it should be anchored at several points along the penstock route. You don’t want the penstock sliding downhill.
- The wire should be placed in conduit and buried. Any splices should be absolutely water tight. I recommend a butt end connector with shrinkable plastic. A well pump splice kit is perfect.
- If possible, place the penstock in the water. The water will greatly help it from freezing. I have seen my penstock locked in ice with the water still moving inside. I create “mini dams” with rocks in my creek to back up the water to create “pools” so the pipe can be somewhat submerged. There are no fish in my creek.
- Some sort of pipe insulation can help. I have used 4” corrugated drain pipe split and placed over the 4” PVC pipe to add a layer of insulation. How much it helps is hard to know. “Bubble wrap” type insulation is another option, but it is somewhat expensive and not easily held in place.
- It is always best to keep the sun off the pipe. The sun will decay most types of plastic.
Just because you cannot bury a penstock doesn’t mean you can’t do micro-hydro in a cold climate. However, if you can bury most or even part of the line it will help greatly. If your temperatures in winter are similar to those here in North Idaho, 20F+, micro-hydro can give you a lot of much needed power at the time of year you need it most. I absolutely love my Hydro-Induction turbine and would happily and confidently recommend a system like mine to anyone living off-grid.
Brian Betz is a tech at Backwoods. Many of you who are interested in microhydro may have talked to him. He LOVES to talk about the benefits of producing your own power with water! He and his family live completely off-grid here in north Idaho.