McKinney J.D., Warnick C.C. Microhydropower Handbook Volume 1
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Head =
2h = 2
!h
10 f
t
I
P = 0.c
i
Twice the head
and half the flow
Flow = Q*
Q=
10 cfs
---T2-
. .
I. ,.
.,
_..
I
Head = h
h = 10 ft
Half the head
and twice the flow
Flow = 2Q
2Q =
20 cfs
P = 8.4 kW
INEL 2 2320
Figure 2-5.
Effect of doubling either head or flow.
2-15
.-
_
_
Figure 2-6.
Stream without a dam.
.
Figure 2-7. Waterfall.
2-16
m
Figure 2-8. Dam.
Figure 2-9. Canal drop.
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._.. -.-- .
Slide gate
valve
.
Vacuum
Power
INEL 2 1275
Figure 2-10.
Run-of-the-stream development.
’ Powerhouse
INEL.2 2322
.
Figure 2-11. Run-of-the-stream dev?lopment.
2-18
1’.
i
,,r! -.
/
.:
appropriate nomenclature.
In
a run-of-the-stream development, an intake
structure diverts water from a stream to a penstock. The structure
consists of:
r
I
e
/
ir
l
e
0
.
l
Stream Diversion Works--The diversion works divert water from
the stream into the intake system.
Settling Basin--The settling basin is located near the diversion
works and is used to settle out suspended material before the
water enters the power canal..
Power Canal--The power canal carries water from the diversion
works and settling basin to the forebay. A canal is useful where
the water can be carried at approximately the same elevation to a
point from which the penstock can be made as steep, straight, and
short as possible.
Forebay--The forebay is a settling basin designed to settle out
suspended material before the water enters the penstock.
Some
type of forebay is required in all run-of-the-stream developments.
Penstock
Intake
Structure--The penstock intake structure provides
the transition from the forebay to the penstock.
It also provides
the framework for the trashracks and intake gates.
The penstock carries the water from the forebay to the turbine.
Ideally, the penstock should be as steep,
straight, and short as possible.
The powerhouse contains the turbine-generator, controls, and associated
equipment,
and the tailrace returns the water to the stream.
The design head can be adjusted depending on the available flow and
power requirements (Subsection 3.4.1). Therefore, the location of the
intake structure is a function of how much head is needed. At natural
sources that capitalize on the change in elevation of a waterfall, the head
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1
._
.
-_
.
-
_.
-_
is set by the elevation of the waterfall, and the design procedures should
be the same as for manmade sources where the head is established by the
characteristics of the site.
Natural sources may have aesthetic value, which should be considered.
‘-'For example,
if all the water flow from a waterfall or a stream is to be
used for power production,
the waterfall or a portion of the stream will be
.
.dried up.
If only a portion of the flow is used, aesthetic and other
environmental effects are minimized.
Natural sources are subject to annual stream variation. For Category 2
developers, power generating potential will vary with the flow.
2.6.2 Manmade Sources
Existing manmade sources can generally be modified to install a micro-
hydropower system without much of an environmental impact. The construction
of a dam for the sole purpose of developing microhydropower systems is gen-
erally economically prohibitive.
However, if a dam is being built for other
purposes, a microhydropower system may be a logical and economica:l addition
'\
ta the project. Small dams typically have a relatively small change in
elevation (head), 35 feet or less. With a small head, the-flow has .to be
larger to produce a given amount of power, and larger flow means bigger
turbines--and thus more expense than for installations operating with a
larger head to produce the same amount of power. Figure 2-12 shows a possi-
ble installation at an old mill site.
Figure 2-13 shows a siphon penstock
that could be used on an existing dam at which there is no way to draw the
water out of the reservoir.
.I
.’
In certain parts of the country,
manmade structures suctvas canal drops
provide excellent opportunities for hydropower production. Flow can be
t
seasonal, but it is generally constant during the months of operation.
For
canals where the flow is seasonal,
care should be taken to ensure that
enough energy can be produced annually to justify the expense.
Figure 2-14
shows such an installation,
.
.
2-20
I
..---
Q.
-
-.
. .
Open- -
flume-
c.-
---.
.I
Figure 2-12.
Installation at an old mill site.
INEL 2 1270
2-21
.-
-
_
. _
/I’
IN&L 2 1261
l
Figure 2-13.
Siphon penstock at an existing dam.
2-22
f
Slide aates
Minimum of ten pipe
Speed
increaser. f
diameters between
turbine and Y
connection
Generator\ k<
.
/
Figure 2-14. Installation at a canal.
2-23
INEL 2 12711
Wastewater discharge from industrial or domestic treatment plants may
have sufficjent head and flow to be useful for hydropower. Those associated
with such institutions may want to develop such a source.
Private develop-
ers may be able to develop such a source,
but the first hurdle is obtaining
permission.
Sources of this nature usually offer a steady flow, which helps
to optimize turbine selection and minimize equipment cost.
Figure 2-15
'shows such an installation.
2.7 Typical Example Sites
._.
Two site examples are presented in Appendix B. One involves developing
a,n existing dam,
and the other makes use of a natural, run-of-the-stream
source.
The specifications for these examples are given below. The devel-
oper is encouraged to determine which example most closely represents the
site to be developed and to follow the details of the example as a guide
for proceeding through the handbook.
2.7.1 Manmade Source
An existing dam is located on a small stream in the rolling hills of
New Hamp,shire.
The developer's site includes an old, retired gristmill.
The mill and dam produce a 12-l/2-foot drop in the stream elevation.
Up;tream from the dam,
the pool has filled in with gravel and silt, leaving
.it only 3 feet deep.
The elevation of the pool is fairly constant, wi
.
,I-fhe.crest of the dam acting as the spillway.
In a 20-foot wide gorge
the'dam, the depth of the stream's normal flow varies from 26 inches
,..
..April to 8'inches in late August.
Occasional spring rains will raise
;. .
"stream to 3-l/2 feet.
Twice in the last fifteen years the stream has
. ' '_ .
flooded above the 5-foot gorge and inundated a lower pasture. During
th
below
n
the
those
floods, the stream was approximately 40 feet and 60 feet wide, respectively,
and the depth of water in the pasture averaged 3 inches and 8 inches
The developer's residence and 75-head dairy operation are located near
the old mill. The residence includes a washer, dryer, refrigerator,
freezer, electric stove, hot water heater, and electric heat. The electric
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