A New Era in Small-Scale Hydropower

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The interior of a small turbine.
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With a high enough head, a small scale hydropwer system can generate electricity from a little stream like this.
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The chart gives you a good idea of how much output in watts you may expect per different gpm (gallons per minute), for varing feet of head. Multiply the number of watts by 24-watt-hours to get the total number of watt-hours generated in one day. Divide this by system voltage to get your amp-hour per day output.
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The turbine unit with attached feeder pipes.
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The powerhouse that services the Coulter ranch houses the turbine, (left) batteries (center, in wooden box),  and the power-center and DC to AC inverter (right)
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A typical hydroelectric layout. 1. Site of dam or weir to divert water. 2. Stock tank or pond 3. Penstock. 4. Powerhouse with electric lines running to home. 5. Rock-lined tailrace.

Two years ago, Norm and Sue Benzinger, owners of the Coulter
Lake Guest Ranch, a wilderness retreat in th Rockies, had a
problem: They were seeing too much of the propane delivery

The ranch’s propane bill had topped $10,000 in
1992–much of it consumed by a generator. Hoping to
slash his energy costs, Norm contacted Ken Olson, a
renewable energy expert who directs Solar Energy
International in nearby Carbondale, Colorado.

“He said he had a stream falling down the hillside,”
recalls Olson. “Turned out it was a great water power

Working together, Olson and Benzinger installed a
hydroelectric turbine. Now the generator, which used to
drone for hours a day, has fallen silent. A water power
system that cost $6,000 will save $2,500 in its first

Over the last 10 years, small-scale hydropower technology
has taken a quantum leap thanks to the invention of the
microturbine. Inside a metal case that is smaller than a
bread box, a miniature water wheel, not much bigger than a
cinnamon roll, is coupled to a pickup truck generator. When
the wheel is spun by a jet of pressurized water,
electricity is created. The design is simple yet
sophisticated, a triumph of appropriate technology.

Progress has also been fueled by the dramatic evolution of
solid-state inverters and load controllers–the brains
in the Benzingers’ system. A decade ago, inverters, which
transform direct current (DC) to alternating current (AC),
and con trollers, which govern electrical production, were
dumb, unreliable, and inefficient beasts. Tamed with
computer chips, they now perform the same tasks in a much
more intelligent, reliable, and energy-efficient manner.

Together, these advances have revolutionized the world of
homeowner hydro. Because a microturbine requires only a few
quarts or gallons of water per second, it’s now possible
for even a slender stream to provide all the electricity a
house or modest farm requires.

Although this technology sometimes makes sense for people
whose homes are already connected to the utility, it’s most
economical for those living, or contemplating, life “off
the grid”–a group that includes homesteaders as well
as farmers and ranchers who irrigate or own water
impoundments. With utilities charging $10,000 or more to
extend power lines a mile, an understanding of hydro basics
can prove valuable indeed.

Water into Gold

Hydropower is one of the oldest forms of alchemy, a way to
convert falling water into wealth. Historically, that
wealth has been measured in many coins: milled flour, sawed
wood, and pumped water. Today, the currency of choice is
most often the kilowatt-hour.

By almost every measure, water power is the world’s best
energy resource. What’s cleaner? Cheaper? Even among
renewables, hydro is a head above. Falling water is more
reliable than the wind, and it works at night, too, unlike
the sun. Per dollar invested, a hydro system will typically
produce three to 10 times more energy than a photovoltaic
(PV) or wind power system.

Hydro’s disadvantage? It discriminates against the many in
favor of the few. The wind and sun are democratic: everyone
gets some. Water does not spread its blessings; it
concentrates them. You either have water or you don’t. And
most don’t.

For this reason, hydropower has always been viewed as a
finite resource. We humans can mine more coal or build more
PV panels, but it’s not in our power to make rivers or
invent streams. Today, however, thanks to the inspired
tinkering of a handful of ingenious engineers, the
landscape has changed. No new rivers have been created, but
the horizon has moved nonetheless, the scope for alchemy
extended. Good hydro sites remain rare. But they’re less
rare than ever before. Now even a brook or creek can be
spun into gold.

A Typical System

In the vocabulary of hydro experts, the word typical is
typically missing. “Every site is different,” they insist.

“Every installation, unique:” Talking to them, you get the
impression they’d sooner cut off a finger than com pose a
rule of thumb.

That said, the system at the Coulter Lake Guest Ranch is,
in many respects, typical. A short distance uphill from the
lodge is a screened concrete box, the intake,
which channels water into a pipe or penstock.
After falling downhill, the penstock terminates in a small
shed or, to give it its fancy name, powerhouse.
Inside are the turbine, generator, batteries, inverter, and
load controller. After passing through the turbine, the
water flows out of the powerhouse through another pipe and
into a rock-lined ditch or tailrace.

What is most remarkable about the setup is its water
source–a spring-fed ditch three feet wide and six
inches deep. Just half this piddling quantity feeds the
turbine, enough to produce 400 watts continuously, plenty
to power the Benzingers’ lodge or a home.

To anyone familiar with electricity, that statement may
sound absurd. After all, 400 watts is only enough power for
four 100-watt lights–and a refrigerator momentarily
draws 1,500 watts when its motor starts. But 400 watts,
over 24 hours, is 9,600 watt-hours. And, believe it or not,
that will amply fuel a modern version of what Zorba the
Greek once jokingly referred to as the “complete
catastrophe”: husband, wife, kids, fridge, freezer, washing
machine, dishwasher, microwave, computer, VCR, stereo,
Dustbuster, Crockpot, plus a garage full of power tools.
Note that these are standard, 110-volt tools and
appliances–Makita, Kenmore, Maytag, whatever. You’re
not outfitting your house from an RV catalog.

There is, of course, a hitch. In most residential systems,
you can’t use an electric stove, electric hot water heater,
or electric clothes dryer. They guzzle too much juice. No
baseboard heat, either. For cooking, drying, and space
heating, a hydro household will rely on sun, wood, and

But wait. If a system only provides 400 watts at one time,
what supplies the surges of power needed to start that
refrigerator motor? For that matter, where does the power
come from when 10 lights, stereo, washer, computer, and TV
are all running in the evening?

Batteries. An inverter draws juice stored in a battery bank
to start motors and meet evening and morning peak needs.
The batteries recharge when the lights go off, or the next
day when the kids are at school.

Thus, if you are willing to heat your food, home, and water
with some combination of propane, wood, and sun, then a
300- to 500-watt system will provide all the electricity
you need and then some. Nor is 300 watts the lower limit,
particularly if you use energy-efficient lights and
appliances. A 50-watt turbine, the Lil Otto manufactured by
Bob-O Schulze, can power a weekend cabin, while 100-200
watts is adequate for an energy-conscious household. Don
Harris, who built the Benzingers’ machine, runs two houses
and his shop (lathe, mill, etc.) on 150 watts of

What About the Cost?

If the owner of a PV system needs more power, they buy
another module or two. In hydro, though, what you have is
what you have. Moreover, the correlation between how much
money a hydro system costs and how much power it generates
is not linear. Sometimes it’s inverse. A marginal site may
cost more to develop, yet generate less power, than a prize
winner. It all depends on stream size, penstock length, and
other variables.

That said, a 400-watt system would typically cost $4,000 to
$6,000, broken out like this: turbine, $700-1,000;
batteries, $800-1,600; solidstate inverter and load
controller, $1,200-2,000; transmission line and other
electrical equipment, $500- 1,000. To this, add the price
of penstock pipe (in some systems, the largest single cost)
and of the intake, powerhouse, and labor.

Once you’ve bought a system, “fuel” is free. Since hydro
systems are very reliable, annual maintenance costs should
be $100 or less. But plan on replacing the batteries every
decade or so.

Smaller systems are less expensive. A weekend cabin setup
might run $800 to $1,500. And if you already own a wind
power or PV system, adding a hydro turbine to help charge
your batteries can cost as little as $400.

So far we’ve been talking about DC or “battery-based”
systems, where alternating current is supplied by an
inverter. But if you are blessed with water–say, 10
times more than you need for a DC system–you may be
able to dispense with the inverter and generate AC

AC Systems

Nine years ago, David Scott, a teacher who lives six miles
off the grid near Gypsum, Colorado, got tired of trudging
through the snow each morning to start a propane generator.
Back then, his family was using 6,000 gallons of propane
each winter to provide heat, hot water, and electricity to
the three buildings on their property. Energy costs were
eating them alive.

One summer Scott installed a hydro system. It wasn’t cheap.
Expenses–not including his time or use of a friend’s
backhoe–were $14,000, half of it for 4,000 feet of 8″
pipe. By the end of August, though, Scott was the proud
owner of a 35,000-watt (35-kilowatt or 35-kW), hydro system
that, in his words, “sounds like a Boeing 747 when you turn
it on:” (It ought to: Water enters his turbine at 98 mph.)

This system generates a staggering amount of electricity,
whose retail value is about $21,000 a year. Since there’s
no utility to sell it to, Scott uses it to light and heat
his house, a guest house, and a 1,600-ft2 apartment. The
surplus goes through a transformer and then to a neighbor,
who uses it to heat and power his house.

Although Scott’s AC system is much larger than most, it
illustrates the possibilities. Over an eight-year span,
it’s been shut down four times for routine maintenance. And
with a useful life of 50 years or more, it’s already paid
for itself many times over.

“Just in Colorado, there are probably dozens of places that
could be doing this,” says Scott. “Few people realize how
fairly simple it is.”

Although AC systems cost $7,000 to $20,000 and up, they
provide much more electricity than a battery-based system
at a cheaper per unit cost, often including a surplus that
can heat a hot tub, radiant floor, greenhouse, or what have
you. But one principal advantage of an AC system–no
batteries–is also a principal constraint. An AC
system must be big enough to start a refrigerator motor,
with power left over to meet evening and morning peaks. For
this reason, most AC systems are 3 kW or bigger, with 5 to
8 being optimal. Below 2 kW, you’ll have to go with DC and
an inverter.

There is rarely any need to agonize over the AC versus DC
choice, because generally speaking it doesn’t exist. At
nine of 10 sites, AC isn’t an option. The reason has to do
with head and flow.

Hydro Physics

“What’s your head and flow?”

Call Powerhouse Paul to talk hydro and that’s the first
question he’ll ask. These variables dictate
everything–how much power can be produced, what type
of turbine is best, what size penstock pipe is required,
and so forth.

Head (or “drop” or “fall”) is the vertical distance between
the intake at top and turbine at bottom. Flow is the
quantity of water passing through the turbine.

Hydropower texts are replete with arcane equations, but the
relationship between head and flow is not complicated. To
determine your site’s power potential, multiply the two.
For example, a site with 10 units of flow and one unit of
head will produce 10 units of energy, as will a site with
one unit of flow and 10 units of head.

In the equation, head and flow are equally valuable. On the
ground, though, head trumps. Yes, power can be generated at
heads as low as three feet, but this re quires tremendous
quantities of water, large turbines, expensive diversion
structures, and expert planning. For backyard applications,
you’ll want at least 15 feet of head, and preferably 50
feet or more. On the other hand, you don’t need much flow.
Microhydro isn’t really “garden hose” technology, but in
terms of water required, it’s close.

Recall that 400 watts will power a house. To generate that
we’d need approximately: 100 gallons a minute falling 50
feet. Or 50 gallons a minute falling 100 feet. Or 25
gallons falling 200 feet. Or 16 gallons–a mere
quart each second!–falling 310 feet.

The implication is clear. A rill, tiny brook, step-across
creek, mountain spring, irrigation ditch–with enough
head behind it, a trickle of water from any of these can
produce a torrent of power.

As head drops below 50 feet, power production diminishes
and the economics of small hydro systems become
increasingly tenuous. Nonetheless, if you’ve got a small
pond a mere 25 feet above from which you can divert 100
gallons a minute, you can still generate 200 watts. Combine
that with efficient lightbulbs and appliances, and you’ve
got energy independence.

Surveying a Site

Okay, you’ve got a possible hydropower site. How do you
assess its potential?

Two people can survey most sites in a day or less. You’ll
need a notebook, pencil, stopwatch, tape measure, bucket,
shovel, and plastic tarp. Wear tennis shoes. Your feet will
get wet.

Head first. Although a topographic map or handheld
altimeter will provide a rough idea, more precise
measurement requires some sort of level. In open terrain,
use a builder’s level or transit, four-foot carpenter’s
level, or cigar-shaped sight level.

If you know what a transit is, you probably know how to use
one. To use a carpenter’s level or sight level, cut a staff
of known height a few inches shorter than you are tall.
Start at the proposed turbine location. Put the level on
the staff and center its bubble. Then sight along it as
your assistant climbs the hill. When his or her feet are
level with your eye, have them stop. Bring the level up to
that point and continue in this fashion uphill. At the
intake, total your results.

In brushy terrain, use a water level–a 50-foot length
of tubing attached to a plastic container–that can be
snaked around trees, rocks, and other obstacles. Water
levels are accurate and easy to use. They can be bought for
$30 or cobbled up for $10.

A third method–perhaps simplest of all–exploits
the fact that every foot of head equals 0.43 pounds per
square inch (psi) of water pressure. Screw two or more
hoses together, carry them to the intake and fill with
water. Attach a pressure gauge to one end and carry it
downhill. Note the pressure. Bring the other end to that
spot (keep the hose full!) and repeat. At the bottom,
divide your psi readings by.43. That’s your head. Keep
track of hose lengths, too, and you’ll know how long your
penstock needs to be.

Head is fixed. It won’t change in a lifetime. Streamflow is
trickier. It’s always in flux. Are you measuring during
snowmelt? In the dry season? After a big rain?

Since any single measurement of flow is probably
unrepresentative, it’s best to measure flow repeatedly over
the course of a year. What you want to establish is the
reliable yield. Try also to establish a winter flow, since
that’s the season you’ll probably use most electricity.
This will help you determine how close hydro will come to
meeting your energy needs.

There are many ways to measure flow. For a shallow stream,
three or four feet wide, the bucket-and-stopwatch method is
simplest. Build a temporary dam with stones, dirt, and
plastic tarp, leaving an outlet to one side. Next,
improvise a trough (a piece of culvert or metal roofing
works well) to channel the entire stream into a container
of known volume. Time how long it takes to fill. If a
five-gallon bucket fills in 15 seconds, the flow is 20
gallons per minute.

As stream size increases, measuring flow becomes more
difficult. Unless you contemplate an AC system, it also
becomes somewhat less important. Remember, if you’ve got 50
feet or more head, two gallons a second is all you really

The best way to measure stream flow in large streams is to
dam them with a wooden weir, with a rectangular opening of
known size in its center. (Sometimes easier said than
done.) Next, measure the difference in height between the
bottom of that opening and the top of the pond that forms a
few feet upstream. Plug this measurement into a “flow rate
weir table” (found in a hydropower textbook) to get your

Strive to be accurate as you measure head and flow, but
don’t worry if you’re off by a few inches or ounces. Close
enough is good enough.

Regulations and Red Tape

After measuring head and flow, and estimating your power
output, you decide to build. The first step is to obtain
the necessary permits. Here, generalizations really are
useless. In some states, small hydro systems aren’t
regulated. In others, they get lumped in with domestic
water systems, which rarely encounter permitting problems.
(If you are developing a new homesite, design your penstock
to provide both water and power.) Finally, there are
states, California for example, where the red tape is more

In truth, many people fail to get a permit, either as an
act of civil disobedience or because they fear bureaucrats
who strain at gnats while swallowing camels or because they
just don’t want to bother. But this can be risky.

Remember, water regulations are designed to protect you as
well as the resource. It’s worth jumping through a few
hoops to guarantee your water rights.

With this is in mind, the best approach is to find out what
the law is, then decide how to proceed. In most
cases, it’s easy to comply. Begin by calling your state
energy office or water resources department.

So much for humanity’s laws. How about Nature’s?

In contrast to huge dams whose reservoirs invariably wreak
immense havoc, home-owner hydrosystems impound no water and
have few environmental impacts. Nonetheless, taking too
much water out of a stream, even if its only for a few
hundred yards, can raise its temperature enough to kill
fish and other aquatic life. Diverting the entire flow is a
hanging offense–or should be. In California, during dry
years, Don Harris will close his intake for months at a
time. (He uses photovoltaics for backup power. PVs dovetail
nicely with hydro: If it’s not raining, the sun is usually

If you have any questions about the impact of your system
on salmon, salamanders, or frogs, Harris suggests that you
explore them with the biology department of the nearest
university or the local fish and game department.

Remember, we all live downstream.

Do It Yourself?

In most cases, the answer is yes. Indeed, you may have
simply to keep costs within reason.

With the help of reference books from the library and guide
sheets from turbine manufacturers, any reasonably adept and
persistent person can design and install a hydro system. Be
forewarned, though: It will cost more and take longer than
you expect. Since there is a learning curve involved,
expect some head-scratching. Here’s a primer to get you

The most trouble-prone point of a hydro system is the
intake. A poorly designed diversion structure is a constant
migraine. If you want to get it right the first time, study
the site in detail. Ask yourself. What happens in a
drought? A flood? And remember that uncontrolled
diversions, however brief, may cause mudslides and horrific

In many cases, a small rock or log dam is built to create a
pool a few feet deep. This traps silt and provides a place
for the intake pipe, usually located in a concrete or
plywood box. Often it’s easier and wiser to divert water
away from the stream to a 55-gallon drum, stock tank, or
tiny pond and begin the penstock there. In any case, the
intake must be screened to prevent leaves and gravel from
being sucked down the pipe. To avoid endless trips up the
hill, design the screen to be self-cleaning.

The penstock should be as short, straight, and steep as
terrain permits. Avoid undulations and abrupt changes of
direction. Most penstocks are polyvinyl chloride (PVC) or
polyethylene pipe.

PVC is generally cheaper. Unfortunately, sunlight degrades
it, and it will shatter if it freezes. A plugged penstock
at minus 30 is the worst nightmare imaginable. In a perfect
world, every penstock would be buried to protect it from
falling trees, freezing, bears, and other mischief. But
many aren’t. If you intend to leave PVC on the surface,
paint it before installing it. In a cold climate, be sure
to insulate it with fiberglass wrap or a thick layer of

Although polyethylene pipe can be more difficult to install
than PVC and, in large diameters, more expensive, it is
also much more frost-tolerant. Where winters are frigid and
the penstock won’t be buried, it is the choice. Be
forewarned though: Unrolling a coil of poly is like
wrestling a 100-foot python.

Sizing the penstock involves a tradeoff. The smaller the
pipe, the cheaper its cost. But friction (and thus power)
losses increase as pipe diameter decreases. So, the longer
the penstock, the larger the pipe needs to be. Most
household systems have 2″-4″ penstocks, although AC systems
often require 6″, 8″, or larger.

A powerhouse doesn’t have to be large or expensive. A
concrete floor is nice, not essential. Plan the equipment
layout so that maintenance will be convenient. And be sure
to install a pressure gauge and shutoff valve upstream of
the turbine. This gauge is your troubleshooting tool.
(Pressure higher than normal? A turbine nozzle is plugged.
Pressure too low? The problem is uphill, probably at the
intake.) Powerhouses are generally sited on the stream
bank, which makes them vulnerable in a flood. Make sure
yours is out of the floodplain!

A complete discussion of the many kinds of hydro turbines
is beyond the scope of this article. Although each type has
its niche, there is a great deal of overlap. Most
home-owners use either a Pelton or Turgo. (These are
designs, not brand names.) At heads over 50 feet, both work
well. Since a Turgo can handle more water, it’s often the
choice for lower heads. If you are very handy with a
welding torch and want to build your own turbine, build a
cross-flow–a squirrel cage-like contraption efficient
across a wide range of head and flows.

Transmission lines can be run overhead, but underground is
neater and safer. They need to be properly sized for
current and distance. It’s not uncommon for the powerhouse
to be a few hundred feet away from where the electricity is
being used. Beyond this, however, you’ll need to step the
voltage up. In extreme cases, power can be pushed a mile or

Experts recommend that you seek an electrician’s services
when it comes to wiring. DC, AC, inverters, controllers,
batteries–leave this to a pro. Insist that the
installation meets the National Electric Code. Your life
depends on it.

By now it should be clear that installing a hydro system
isn’t a weekend project. It’s a long, sweaty job that might
take a few weeks or even a summer. At the end, however, you
can look forward to a moment of bliss: turning on the
penstock valve for the very first time.  

For Further Information

Turbines for DC systems are manufactured by
Harris Hydroelectric Systems and Energy Systems & Design.

Turbines for AC systems are manufactured by Canyon Industries and Dependable Turbines.

Books Many valued reference books are out of
print but can be found in a library. Look for
Harnessing Water Power for Home Energy, by Dermot
McGuigan, published in 1978 by Garden Way Publishing
Company, and Energy Primer, published in 1974 by
the Portola Institute.

Two books in print, Micro-Hydropower Sourcebook
(Allen Inversin, NRECA Foundation) and
Micro-Hydro Power (by Peter Fraenkel, Intermediate
Technology Publications) are design and installation manuals for
development workers overseas. Both are exhaustive and
leavened with real world difficulties and

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