Micro-hydro electric power systems use many of the same system components as PV solar systems, therefore, combination systems are practical to consider if a small stream or other source of water under pressure, such as an artesian well, is available.
Water from a small stream, farm pond, springs, even artesian wells, etc. is diverted into a pipe and runs down hill to the turbine site. At the lower end of the pipe line, nozzles are installed to increase pressure and sprayed at a small pelton, turgo or other type runner wheel turbine which turns an alternator or generator. One type of turbine is one that produces DC which can directly charge a battery bank (which can be shared with a solar array). Charging batteries with water power allows you to size the system for your average load and run off the batteries during your times of peak load. This makes it possible to make use of a smaller stream than would otherwise be possible.
Another type of system can be battery-less and directly back-feeds the utility grid. Such a system directly reduces your electric utility bill. Net metering in New York State allows your hydro-power system to not only power your lights and appliances (loads), but it can spin the meter backwards and earn you credits at the same retail rate the power company charges you. This system with the addition of batteries could provide backup power during utility outages.
With the advent of UL listed and approved grid tie inverters, it is now possible to directly utility grid tie a micro-hydro site at relatively low cost and eliminate batteries. With Net Metering, your NY power company credits you at retail for your back fed energy, however it doesn't pay to over-produce. The advantage of this is maximum financial benefit. The disadvantage of this scheme is that when utility power is lost, the system must shut down to prevent back feeding a dead utility grid and you have no power from your system.
A dump load and a relay must be included in the system, so when there is a utility outage hydro power is diverted to the dump load. Hydro Turbines must never be allowed to “free-wheel” and always have a load on them or they will burn out! If you want power from the system during a Utility outage, you can have batteries as well as grid tie. This way, the batteries will power your home when utility power is not available. The beauty of a battery-less system, however, is you have no heavy toxic batteries to deal with and your system is much more reliable than systems with aging batteries.
Typically, a stream with either 50 feet or more of vertical drop across your site and 30 gallons per minute (gpm) or more, or a wide deep stream with high flow 100 gpm or more and a vertical drop of 12 feet or more are practical to consider for making electricity. With even greater flow rates, lower head levels can be utilized with turbines specifically designed for low head sites. Low head sites may utilize a sluice way, instead of a pipe line. A minimum head of 6 feet is required. The closer the turbine location to the building needing the power the better.
Great Brook Solar evaluated a site for a customer with 8 feet of head and 3,400 gallons per minute flow. He can drive two 1,600-watt turbines with 3/4 of this flow. There are 3,413 BTU of heat available for every 1,000 watts of power. This means that he only has 10,900 BTU per hour available for heating his home from this 20-foot-wide stream. Most homes require something in excess of 50,000 BTU/ Hr in the coldest weather. However, the coldest part of the winter is at most 10% of the heating season. 10,900 BTU-hr could significantly reduce heating bills during more mild parts of the heating season. So, don’t throw away your furnace.
The philosophy is to charge batteries with direct current (DC) and convert it to typical household AC with inverters. Check the Outback Power site for more info on inverters. AC turbines exist, but they need a stream big enough to produce power to meet your peak loads. With a battery bank and inverters sized to your peak load to charge continuously with a small DC turbine we can get by with a much smaller stream and pipe.
Micro-scale hydroelectric systems are surprisingly simple. Much of the system can be installed by a do-it-yourself-er handy with tools, however, most of the electrical connections should be done by a professional familiar with the national electric code, low-voltage, high-amperage DC wiring and common AC wiring practices (in particular any connections to the utility grid should be done by a licensed electrician). Please realize that micro-hydro turbines are NOT maintenance-free. They require almost daily ,or at least weekly, maintenance to keep penstock (pipe line or sluice way) intakes free of debris. They are not suitable for part-time homes. Debris in the water can, and will, chew away at your runner. Maintenance costs can add up. If you need a maintenance-free system, then consider solar PV power.
Your micro hydro power system may not require a large dam. All that is needed is a small dam big enough to divert water from a stream into a pipe and keep air and debris out. We divert the water as high as possible on the hill into a schedule 40 PVC pipe or a polyethylene pipe and run it down hill to the turbine location as low on the hill and as close to the load as possible. In areas of prolonged winter freezing, the pipe must be buried and/or insulated. Often laying the pipe in the stream completely submerged is sufficient to prevent freezing in milder climates. Low head sites may be an exception. Generally dams are required for low head sites.
The head (pressure) of the stream and the flow rate must be measured to determine how much power is available.
How to Determine A Flow Rate: A small stream flow rate can be measured by temporarily diverting the water into a 5-gallon pail and timing how long it takes to fill. This should be done several times to get an average time. If time is in seconds the flow rate = 300 divided by the number of seconds to fill the pail. Another method helpful with larger streams is to measure and mark off a 20-foot section of stream free of debris and rocks, (better yet, a section of culvert pipe where the stream crosses a road), measure the average depth and width in feet. Toss in a floating object such as a stick of wood or a dry reed and time in seconds how long it takes to float down stream the 20 feet. Do this about ten times and take the average time. The flow rate = [(stream width ft. x avg. depth ft. x 20 ft) x 60 sec./ min] / the avg. number of seconds for floating objects to travel 20 feet. This is the flow rate in cubic feet per minute. To convert to gallons per minute, multiply by 7.48 gal./ cubic foot.
How to Determine The Head: The pressure or head is the vertical-height difference between the top of the pipe and the bottom. This can be measured with a transit. Or with a builders level at the highest point on the stream site on a tall object of known height at the bottom of the proposed pipe. This can be done in small steps and added by sighting on an object of known height such as a 10-foot-long 2×4. Another method is to measure the static pressure directly by diverting water at the top of the stream into a garden hose. Place the other end of the hose at the proposed bottom of the pipe, the turbine location, and place a pressure gauge on the downhill end. The measured pressure is the static head in psi (pounds per square inch). Be sure you allow the water to run through the hose to expel it of air before installing the pressure gauge. Air in the line will give you false readings.
To get an idea of the power potential of your site, multiply the Head (feet) x the Flow (gpm) and divide by 5.3 then multiply the result by 0.35 . The result is the approximate instantaneous wattage taking average efficiency losses into account. Pipe diameter and length also greatly affect this output. The longer and/or smaller the pipe, the less the output. So, keep your pipe run as short as possible and as big as you can afford (within limits). A 4-inch pipe is minimum! If you have more than 50 feet of head, use a pipe type capable of holding the pressure without rupturing IE schedule 40 or schedule 80 PVC, Polyethylene SDR-11 or even steel pipe. Cheap drain pipe won’t do! In most cases, a 6 inch diameter pipe is far superior to a 4-inch one. All of the electrical components of the system are the same as with wind or solar electric systems. The only difference is the hydro electric turbine and generator unit.
A good place to start is with your current electric bill. What is your kilowatt hour usage per month? We need to know your average daily kwhr usage. This is your electric bill KWHR divided by the number of days the bill covered. Do this for a winter bill and a summer bill because your seasonal usage is probably different. Then divide the result by 24 hours to see what your average hourly KW usage is.
When you consult with Great Brook Solar, you will need to provide the following information:
1. The head (elevation height difference between the proposed pipe inlet and outlet) or the measured pressure
2. The Flow rate of the water in gallons per minute, or liters per minute
3. The proposed pipe length along the ground from top to turbine location at the bottom
4. The distance between the turbine location and the house or building where the power is to be used.
5. Do you already have a dam on the site?
Don’t Risk Installing a Micro Hydro Power System Yourself! Consult with Great Brook Solar First.