Home Power Systems: Micro Hydro, by L.K.O.

Monday, Feb 18, 2013

Note: This article is part of a series of feature articles about alternative / sustainable / renewable energy solutions for self-sufficiency. A prior related article in SurvivalBlog that complements this one is Home Inverter Comparison: Off Grid and Grid Tied. Upcoming articles in this Home Power Systems series include: Photovoltaics, Batteries, Wind generators, Solar Water Distillers, Solar Ovens, Solar Water Heating and Energy Efficiency/Conservation.)

Overview of Micro Hydro: One Component of a Home Power System One primary source of locally generated electricity - in the right location - is hydroelectric power generated by a small system of integrated components harnessing the power of falling water, generally called 'small hydro', 'micro hydro', or 'pico hydro' for the smallest of systems. The realtor mantra of "location, location, location" is particularly true for micro hydro systems, perhaps more than for any other local power source, including solar and wind energy systems. If you don't have sufficient flow (volume of water per minute) and head (vertical drop between the water source and the location of the turbine), you can stop exploring micro hydro as a possible energy source right there. However, if you do have just the right location, micro hydro can be one of the most cost effective, efficient, simple and reliable sources of off-grid (or grid-tied) power.

The beauty of a micro hydro system is the simplicity of stored potential energy (gravity) being converted into kinetic energy (moving water) further converted into electrical energy through the generator within the turbine, with basically one moving part (aside from the water. :-) Since the process of converting moving water to electricity doesn't cause any significant atmospheric emissions, greenhouse gases or pollutants (aside from the manufacture and installation of the components, which is arguably a consideration for any energy system), micro hydro, when properly sited and correctly installed and maintained, enjoys - unlike its much larger 'environmental footprint' sibling, large scale hydro - a justifiably deserved status as a relatively clean, renewable, and sustainable power solution.

Micro hydro systems usually cost relatively little to maintain and operate, if they are properly designed and installed. Since heating and electrical demand are typically higher in winter months, even a system with a power output that tapers off slightly in summer can be a good demand-correlated design, as long as summer cooling needs are minimal or provided by non-electrical means. If you have the added advantage of sufficient year-round flow, your micro hydro system can, in many cases, either reduce or even eliminate the need for battery storage and/or other more elaborate and expensive backup systems, which makes it even more attractive, economical, simple and reliable.

Often the sites that have that amount of flow don't have majestic mountain top panoramic vistas, but that might be an acceptable trade off for many, considering the energy-independence such a site can provide. The micro hydro classification generally goes up to systems making 100kW of electricity or less. Larger installations within this range can power larger homes (with less painstaking economizing of energy loads during planning phases) or even small or neighborhood communities if energy distribution (and other multi-load issues) are carefully thought through and properly designed. In multi-property and/or multi-family micro hydro installations, easements, formal legal agreements, safety, power line losses and other related issues should be taken even more fully into consideration.

Micro Hydro Go/No-Go Feasibility Probably the biggest single viability factor in any micro hydro installation is the product - not to worry, it's simple math - of the head (vertical distance between the water intake and turbine/generator) and the flow (typically measured in gallons per minute) of any proposed system. Here's a simple formula for a ballpark idea of your stream's capacity: Multiply the head (in feet) by the flow (in gallons per minute or gpm), and divide by 12. Power (Watts) = head (feet) * flow (gpm) / 12 This yields an approximation of the potential wattage of a fairly efficient micro hydro system. As an example, with 60 gpm and 80 feet of head, your system should generate something in the range of 400 watts (80*60/12). Over a 24 hour period, assuming steady flow, the generated power would be 9,600 Watt-hours or 9.6 kWh (24 hours/day x 400 Watts). Since this formula involves the product of two factors, a site can still be viable - to a certain extent - if the result of the multiplication is still adequate.

For example, if the flow is only 15 gpm, but the head is 320 feet, the site has about the same 400 Watts of potential power as the 60 gpm, 80 feet of head example. This rough formula starts to fail (the potential power decreases) in the fringe examples of very high head and very low flow, due to friction losses in typically long pipe (penstock) runs needed for sites like these, and minimum flows needed to keep turbines turning. The simple formula also becomes too optimistic at the other end of the spectrum, in massive flow but negligible head situations less than 2 or 3 feet. Read "Myth 5" in the article Micro Hydro Myths & Misconceptions if you're still convinced that you can harness the river flowing past or through your property with a negligible elevation drop.

Measuring Head and Flow Now that you know the formula, how can you obtain adequately accurate measurements for the head and flow parameters? We'll start with flow measurement. For low flow situations, a 5 gallon bucket and a stopwatch or timer can do the trick. Here's a video showing a common kitchen pot and a watch to measure flow. For higher flow situations, a weighted-float method - scroll down this page to read details - can provide an estimate of flow. Now onward to head measurement. If you have a super tall 'Yosemite Falls scale' vertical drop, you could use the altimeter app on your smart phone for a very rough estimate of the head since some of the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) digital elevation model apps are accurate to +/- 10m or perhaps two readings from a 7.5 minute USGS topographic map (since some have contour lines as small as 10 feet. More likely, for any head measurements of around 200' or less, it's far more accurate to measure the head in other ways. Check out this detailed article: Hydropower Head Measurements that offers 3 different methods to accurately measure the vertical drop between inlet and turbine. These include: 1) Using a surveyor's transit or level and pole, 2) Using a Hose and Pressure gauge, and 3) using a Precision Zip-Level Pro 2000ª. Here's a video showing PVC pipe to measure head.

Regulatory Considerations for Micro Hydro Other 'make or break' considerations for micro hydro systems include regulatory and legal issues around the use of the water. Some jurisdictions don't allow individual or neighborhood hydroelectric systems, even if theoretically every drop is returned to the stream from which the energy-generating water would be temporarily diverted. Some of these considerations include proposed projects requiring dams (that might cause flooding), affecting threatened and endangered species, location within an area classified as a National Wild and Scenic River, Wilderness Area, or National Park, and/or other factors affecting fish or wildlife. This Federal Energy Regulatory Commission page goes into detail about these locations where micro hydro should not be considered.

This page lists additional concerns that warrant investigation before investing in any micro hydro development.

Generally, micro hydro systems are 'run of river' systems which means that the diverted water ends up back in the same stream or river that it was taken from after powering the turbine. If this takes place entirely on your property, this makes it much simpler and minimizes any legal, regulatory, insurance or other administrative issues that might need to be dealt with. When in doubt, the due diligence of a few hours of online research, talking with local micro hydro experts, neighbors (particularly adjacent property owners and/or others that might be affected by diverted water in any conceivable way), appropriate local and state authorities, and other knowledgeable parties can be time well spent, and save further wasted time, expense and effort. Here's a directory of micro hydro consultants world-wide that might be helpful.

Limitations of Micro Hydro Systems Site characteristics define the main limitations of micro hydro systems. Besides the obvious problem of not enough flow (or head), seasonal fluctuations can be a major concern. If there is adequate solar exposure, in some cases this can mitigate having enough pressure only in the rainy/high runoff months and still make a viable overall renewable energy (RE) system. In much the same way, a wind and solar combination can even out shortcomings in one technology by complementing with another that makes up for winter or summer energy deficiencies; when the sun is generating lots of photovoltaic energy, often a wind generator or micro hydro turbine is not, and vice-versa. Overall, if there's enough seasonal overlap - and battery storage - a system can still be viable. A wind and micro hydro only combination might be more difficult, again depending on the location, if, for example, there's plenty of wind and stream flow in winter months, but neither has much capacity in the summertime. If solar and wind aren't feasible complements for a seasonal system - which is often the case down in canyons where hydro power is more plentiful, a conventional fossil-fueled generator backup might still be a viable solution, as long is the generator is only needed on a very short-term or emergency backup basis.

Another frequent disadvantage (compared to wind and solar energy systems) is the typical distance from the turbine to the house (and/or location of loads such as shops and garages). The optimal locations for both extracting water and returning it to the watercourse on any given property are often much more constraining than the relative easy of siting the location of a wind generator or photovoltaic array as close to the load destinations as possible.

Micro Hydro Construction Assuming you've made it this far, and done your homework on flow, head, etc., dealt with all the regulatory, bureaucratic, legal, and other considerations above and still are interested, now you can design your micro hydro system.

Unlike some solar or wind powered installations that can be a bit more turnkey or even approaching appliance-like status, thanks to advances in technology over the past few decades, micro hydro systems tend to be more custom with unique elements and individual considerations for each site. The path that water follows when flowing through a micro hydro system is sometimes called 'civil works' and there's often a bit of civil engineering, hydrology and fluid dynamics involved; fortunately, micro hydroelectric systems have matured to where system design is fairly straightforward. It's still a good idea to hire an expert or at least get someone knowledgeable with micro hydro experience to review your detailed plans before you begin or spend any significant amount on the project.

In general, there are many common components, starting with the intake point where water is diverted, sometimes a canal leading to a forebay, a penstock (closed piping within which pressure builds for subsequent turbine use), the turbine (including the generator) wiring and other electrical components (which may include batteries and other regulation) that interface the generator with intended loads, and finally a tailrace channel that returns water that emerges from the turbine back into the stream or river. We'll look at each of these components and consider selection and design factors for each. This page has a diagram showing typical components.

Water Diversion and Intake Filtering Water used by the micro hydro turbine is diverted at the intake point. All systems should have some mechanism to exclude silt (e.g. a settlement basin and some type of filtering), both floating and submerged debris, fish and other aquatic life, ice and anything else that could impede the flow or clog the system. A progressive filtration approach with larger bars or screens that leads to finer filters may be helpful. The intake components often have some sort of mechanical valve or gate to shut off the supply for maintenance and inspection. Here's an article that describes a variety of intake systems with typical price ranges. Some systems benefit from a canal and forebay to divert an adequate portion of the flow to minimize turbulence and ensure steady pressure to the penstock, which is the next point in the water's travel. These canals and forebays can be made with concrete, asphalt, gunite/shotcrete or similar materials.

Penstock Considerations The enclosed piping that carries water to the turbine is called a penstock. If the distance between the intake or forebay and the turbine is long and/or convoluted, the cost of the penstock can become a major cost factor. For longer runs, larger diameter pipe may be needed to avoid losing much of the initial water pressure to pipe friction. Each bend in the piping also introduces additional losses due to turbulence of the water inside the pipe fitting; obviously a perfectly straight penstock run isn't usually practical, but care should be made to approach this ideal, minimize unnecessary bends and keep internal pipe surfaces smooth to optimize flow. A seasoned micro hydro installer can assist with pipe sizing and layout. Here's a formula and online calculator (using the Hazen-Williams Equation) for estimating friction head loss in water pipes. Also, since materials used in penstock piping expand and contract with temperature swings, make sure to factor this into your design.ÊTo be thorough in your penstock design, this article covers many other important details, as well as pipe sizing guidelines.

Turbine Selection The choice of turbine (and a generator carefully matched that optimizes mechanical to electrical power transfer efficiency, as well as transmission line considerations) depends greatly on the amount of head and flow. Since this usually requires site-specific design, we'll just cover some of the primary types here and where they are generally used. Most turbines also have a valve (or valves) that can slowly and safely be engaged (since there's often tremendous pressure at the bottom of the penstock) for turbine and generator maintenance.

Pelton wheel turbines have a ring of small buckets arranged around a wheel, each one catching the flow of one (or several) jets of water. In some systems with seasonal pressure variations, the number of active jets can be changed to optimize efficiency and performance. Pelton turbines work well with lower flows as long as there is sufficient head pressure. If you're familiar with electrical circuitry, this would be analogous to higher voltage, lower current systems (although we're talking about a water pressure and current here).

Francis turbines- with their spiral casing being fed by the penstock - direct water through vanes attached to a rotor, and benefit from both radial and axial flow. This type of turbine is better suited to higher flow, lower head situations.

Cross-flow turbines also known as Banki-Michell, or Ossberger turbines, use a series of fixed, curved blades mounted between the perimeters of two disks, forming a cylinder. Water flows into one side of the cylinder and out the other side, which drives the blades. Cross-flow turbines are optimal for even lower heads and larger flows. Their simpler, self-cleaning design, and hence lower manufacturing and operating cost, can be helpful.

Propeller turbines, of which the Kaplan turbine is an example, are also optimal for very low heads with big flows. Blades can be either fixed (like a boat's propeller), or adjustable, as in the Kaplan turbine, which optimizes efficiency with varying flows. There are other types of turbines and variations, and numerous vendors. Regardless of the type of turbine being considered, always consult with the vendor and/or an experienced micro hydro installer to make sure the components match both the hydraulic and electrical characteristics of your system. As an example of typical power output for a variety of head and flow values, here's a chart for one vendor's turbine (Harris Hydro Pelton Wheel).

Tailrace Before jumping from hydraulic power to electrical power, let's follow the water's return from the turbine back to the stream, usually called a tailrace. Since we don't care about maintaining pressure at this point, now that the water has done the work we wanted it to do, it can flow back to the stream or river of origin through any convenient and appropriate mechanism. Often a tailrace consists of an open, lined canal, channel or flume to minimize the cost of piping. The effects of erosion, debris and freezing temperatures should be factored in to ensure that this end-of-the-route part of the system remains as low-maintenance as the other components.

Generators Generators can be either Direct Current (DC) which generally power an inverter, or Alternating Current (AC) which typically have lower transmission losses for longer runs, and can also be part of on-grid (synchronous) as well as off-grid systems. In most cases, generators are paired with specific turbines to maximize efficiency, cost-effectiveness, safety and other considerations. Your installer or RE consultant can advise which turbine/generator pairings will optimize your particular setup.

Wiring Just as water pressure decreases due to smaller pipe diameter constriction, electrical pressure (voltage) also decreases as wire diameters go down. For similar reasons, wire gauge should be sized and optimized to match the needed run between the turbine and load(s) and/or inverter(s) and/or batteries. Low gauge (higher diameter) wire gets more expensive quickly, so longer runs benefit from higher voltages, but then safety and regulatory issues come into play (particularly with DC voltages above 48 Volts). (As an aside, cross-country utility power transmission lines use extremely high voltages to minimize power losses, since power losses are proportional to (I^2)*R [current squared times resistance], so sending power long distances at high voltages and low currents decreases the power loss that goes up exponentially as the current goes up.) Here's an American Wire Gauge (AWG) chart to help with wire sizing and another to choose appropriate wire size for any renewable energy project (not just micro hydro).

Electrical Components There are numerous variations in electrical system architecture for micro hydro sites, just as the hydraulic components vary widely. Four main classifications include the permutations of systems with and without batteries, and with and without grid connection. For this reason, it's best to work with the intended load(s) and variations on a case-by-case basis. A micro hydro professional (augmented with other online and offline resources) can be of tremendous help here. That being said, a few generalizations can be made. As suggested above, systems with steady, consistent year-round flow can often minimize or even eliminate storage (e.g. battery) and/or backup (e.g. generator or wind/solar complementary sources). The most reliable systems will have some sort of battery storage, charge controllers, and unless a home or shop or outbuilding is designed for Direct Current (DC) wiring, lighting and appliances, an inverter. Here are numerous professional Renewable Energy (RE) consultants as well as online resources.

Other Micro Hydro Advantages and Uses Along with the obvious benefits of self-reliance and energy independence that micro hydro systems provide, don't forget to explore any tax credits or incentives for local, state or federal renewable / sustainable power! These vary over time and vary with the specific technology, but when in effect, can sometimes defray a significant portion of an alternative/remote power system. While this article addresses primarily water power converted to electrical power, let's not forget the historical precedent that goes back many more centuries; water to mechanical power. Here's an example of a commercial water-powered grain mill in southern Oregon which is a fun and educational stop if you happen to be nearby.

Additional References
Wikipedia article on Micro Hydro Home Power Magazine (a wealth of useful info on all aspects of Renewable Energy) Energy Planet on Micro Hydro PesWiki: River Energy Federal Energy Regulatory Commission: Micro Hydro Neweras Develop. Limited: Micro Hydro  

Vendor Contact Info
Here are a few micro hydro manufacturers; there are many more online. Home Power Magazine: Micro Hydro Equipment and Products Energy Source Guides: US Micro Hydro Turbines MicroHydroPower.net: Manufacturers Directory  

About The Author: L.K.O. is SurvivalBlog's Central Rockies Regional Editor


Copyright 2005-2012 James Wesley, Rawles - SurvivalBlog.com All Rights Reserved