Financial feasibility is usually the governing factor. How much is the power worth? Note that transmitting small amounts of energy, such as an energy-efficient household would use, can be pretty inexpensive over long distances. Every site is unique, and careful balancing of factors is required. Ultimately, the maximum feasible distance is directly related to the depth of your checkbook and what is “worth it” to you.
A microhydro system will generate continuously, if it has a constant water supply. This alone is a significant advantage over either wind or solar power because a battery bank may not be required, and a smaller battery bank will suffice if one is needed. Also, microhydro is generally less expensive per kilowatt-hour than either wind or solar electricity. It’s working all day, every day. If you had a site where all three systems had equal potential near to the point of use, microhydro would probably be the least expensive choice per delivered watt-hour.
The hydrological cycle follows the human consumption cycle very well where summer cooling is not used. In winter, when a stream usually has more flow, households tend to use more energy; in summer, households use less energy and generally have less water. Solar electricity provides the opposite result, giving the highest yield in the summer, when you typically need less. Hydropower is there when you need it. When the sun goes down and the wind stops blowing, your hydro turbine will continue generating electricity.
Q: What are the limitations of hydro-electric systems compared to other RE systems?
The main limitations of hydro-electric systems are the limitations of the water supply. No water equals no power. Few people have access to a good microhydro site—there are far fewer potential sites than solar and wind sites. And few people who live near good sites are aware of the potential of microhydro. Hydro is for one home in 1,000 at best, so the technology has only a light dusting of installations. These will generally be in rural environments near or in the mountains.
Even though hydropower is comparatively inexpensive and consistent, it requires special conditions that may be hard to come by. First, you need head, which usually means a location close to mountains. Second, it takes the land area to collect the water and develop the head. Third, it requires physical spaces for an intake, penstock, and power house. Fourth, the permitting process can be difficult, because you will be physically altering the watershed, even if only a little.
A little simple math will answer this question. First, measure your head and flow and apply a formula to determine how much you can generate. Then get price quotes for the intake, penstock, and powerhouse equipment. Add it all up and divide by the lifetime energy you expect to produce, and you will have your cost per kilowatt-hour.
While every site has so many unique elements that generalizing is pretty risky, with an appropriate water supply, a microhydro system is usually many times less expensive than a PV system. Maintaining a microhydro system also can be quite inexpensive. There is just the one moving part, and bearing replacement is required only every few years. The intake can be the only point of regular maintenance, and the system shouldn’t cost anything but labor to maintain. On the other hand, PV arrays that are mounted on fixed racks have no moving parts, or intakes, to maintain.
PV and microhydro systems aren’t always treated equally with various incentives (rebates, tax credits, and net metering may only be available for PV systems), so that may also be a consideration. Financial viability is ultimately a personal assessment of the value of the energy produced for the system owner.