One reason more reaction turbines are not in use is the lack of available machines in
small sizes. There are many potential sites with 2 to, 10 feet of head and high flow
that are not served by the market. An excellent article describing very low-head
propeller machines appeared in Home Power Issue #23.
Generators
Most battery-based systems use an automotive alternator. If selected carefully, and
rewound when appropriate, the alternator can achieve very good performance. A
rheostat can be installed in the field circuit to maximize the output. Rewound
alternators can be used even in the 100-200 Volt range.
For higher voltages (100-400 Volts), an induction motor with the appropriate
capacitance for excitation can be used as a generator. This will operate in a small
battery charging system as well as in larger AC direct systems of several kilowatts. An
article describing induction generation appeared in Home Power Issue #3.
Another type of generator used with micro hydro systems is the DC motor. Usually
permanent magnet types are preferable. However, these have serious maintenance
problems because the entire output passes through their carbon commutators and
brushes.
Batteries
Lead-acid deep-cycle batteries are usually used in hydro systems. Deep-cycle
batteries are designed to withstand repeated charge and discharge cycles typical in
RE systems. In contrast, automotive (starting) batteries can tolerate only a fraction of
these discharge cycles. A micro hydro system requires only one to two days storage.
In contrast, PV or wind systems may require many days' storage capacity because the
sun or wind may be unavailable for extended periods.
Because the batteries in a hydro system rarely remain in a discharged state, they
have a much longer life than those in other RE systems. Ideally, lead-acid batteries
should not be discharged more than about half of their capacity. Alkaline batteries,
such as nickel-iron and nickel-cadmium, can withstand complete discharge with no ill
effects.
Controllers
Hydro systems with lead-acid batteries require protection from overcharge and
over-discharge. Overcharge controllers redirect the power to an auxiliary or shunt load
when the battery voltage reaches a certain level. This protects the generator from
overspeed and overvoltage conditions. Overdischarge control involves disconnecting
the load from the batteries when voltage falls below a certain level. Many inverters
have this low-voltage shutoff capability.
An ammeter in the hydro output circuit measures the current. A voltmeter reading
battery voltage roughly indicates the state of charge. More sophisticated instruments
are available, including amp-hour meters, which indicate charge level more accurately.
Conclusions
Despite the careful design needed to produce the best performance, a micro hydro
system isn't complicated. The system is not difficult to operate and maintain. Its
lifespan is measured in decades. Micro hydro power is almost always more
cost-effective than any other form of renewable power.
Who should buy a micro hydro system? In North America, micro hydro is cost-effective
for any off-grid site that has a suitable water resource, and even for some that are
on-grid. Homeowners without utility power have three options: purchasing a
renewable energy system, extending the utility transmission line, or buying a gasoline
or diesel generator.
Transmission line extension can be expensive because its cost depends on distance
and terrain. Even the initial cost of a hydro system may be lower. A gasoline generator
may be cheaper to purchase but is expensive to operate and maintain.
The life-cycle cost of the hydro system (3-25 ¢/kWh) is much lower than that of a
generator (60-95 p/kWh). Once the hydro system is paid for, there's no monthly
electricity bill and minimal maintenance costs. Since utility rates tend to rise, the value
of the power increases, making your investment "inflation-proof."
©1994 Paul Cunningham and Barbara Atkinson.
< Micro Hydro Part I
small sizes. There are many potential sites with 2 to, 10 feet of head and high flow
that are not served by the market. An excellent article describing very low-head
propeller machines appeared in Home Power Issue #23.
Generators
Most battery-based systems use an automotive alternator. If selected carefully, and
rewound when appropriate, the alternator can achieve very good performance. A
rheostat can be installed in the field circuit to maximize the output. Rewound
alternators can be used even in the 100-200 Volt range.
For higher voltages (100-400 Volts), an induction motor with the appropriate
capacitance for excitation can be used as a generator. This will operate in a small
battery charging system as well as in larger AC direct systems of several kilowatts. An
article describing induction generation appeared in Home Power Issue #3.
Another type of generator used with micro hydro systems is the DC motor. Usually
permanent magnet types are preferable. However, these have serious maintenance
problems because the entire output passes through their carbon commutators and
brushes.
Batteries
Lead-acid deep-cycle batteries are usually used in hydro systems. Deep-cycle
batteries are designed to withstand repeated charge and discharge cycles typical in
RE systems. In contrast, automotive (starting) batteries can tolerate only a fraction of
these discharge cycles. A micro hydro system requires only one to two days storage.
In contrast, PV or wind systems may require many days' storage capacity because the
sun or wind may be unavailable for extended periods.
Because the batteries in a hydro system rarely remain in a discharged state, they
have a much longer life than those in other RE systems. Ideally, lead-acid batteries
should not be discharged more than about half of their capacity. Alkaline batteries,
such as nickel-iron and nickel-cadmium, can withstand complete discharge with no ill
effects.
Controllers
Hydro systems with lead-acid batteries require protection from overcharge and
over-discharge. Overcharge controllers redirect the power to an auxiliary or shunt load
when the battery voltage reaches a certain level. This protects the generator from
overspeed and overvoltage conditions. Overdischarge control involves disconnecting
the load from the batteries when voltage falls below a certain level. Many inverters
have this low-voltage shutoff capability.
An ammeter in the hydro output circuit measures the current. A voltmeter reading
battery voltage roughly indicates the state of charge. More sophisticated instruments
are available, including amp-hour meters, which indicate charge level more accurately.
Conclusions
Despite the careful design needed to produce the best performance, a micro hydro
system isn't complicated. The system is not difficult to operate and maintain. Its
lifespan is measured in decades. Micro hydro power is almost always more
cost-effective than any other form of renewable power.
Who should buy a micro hydro system? In North America, micro hydro is cost-effective
for any off-grid site that has a suitable water resource, and even for some that are
on-grid. Homeowners without utility power have three options: purchasing a
renewable energy system, extending the utility transmission line, or buying a gasoline
or diesel generator.
Transmission line extension can be expensive because its cost depends on distance
and terrain. Even the initial cost of a hydro system may be lower. A gasoline generator
may be cheaper to purchase but is expensive to operate and maintain.
The life-cycle cost of the hydro system (3-25 ¢/kWh) is much lower than that of a
generator (60-95 p/kWh). Once the hydro system is paid for, there's no monthly
electricity bill and minimal maintenance costs. Since utility rates tend to rise, the value
of the power increases, making your investment "inflation-proof."
©1994 Paul Cunningham and Barbara Atkinson.
< Micro Hydro Part I
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
| |
 |
Alternative-Heating-Info.com
Micro Hydro Systems Components (continued)
Centrifugal pumps are
sometimes used as practical
substitutes for reaction
turbines with good results.
They can have high efficiency
and are readily available (both
new and used) at prices much
lower than actual reaction
turbines.
However, it may be difficult to
select the correct pump
because data on its
performance as a turbine are
usually not available or are not
straightforward.
sometimes used as practical
substitutes for reaction
turbines with good results.
They can have high efficiency
and are readily available (both
new and used) at prices much
lower than actual reaction
turbines.
However, it may be difficult to
select the correct pump
because data on its
performance as a turbine are
usually not available or are not
straightforward.