Fast-flowing water has great power. The energy (kW/m2) increases as the cube of the velocity
(V3) in meters per second (m/s).
Faster currents have much more power.
Energy Density of Flowing Water: kW/m2
= 0.5 x V3
Conversion factors: One m/s is equal to 2 knots or 2.2 mph, or 3.3 feet per second (fps).
Energy in 1 square meter of flowing water at 1 m/s = 0.4 kW;
at 2 m/s = 4 kW; at 3 m/s = 13 kW; at 4 m/s = 32 kW
In an open channel, a good turbine in the stream
has efficiency of about 40% "water to wire". So a 2 m/s flow of 1 m2
can generate about 1.6 kW at the power cable output. If it is constant
power, and the value of power is $0.10 / kW, the turbine output is worth $1400/year. In many countries, islands and remote communities
with higher energy costs it is worth $4000 - $5000 a year. This is from a
turbine of 1 m2 size, or about the size of
a large armchair.
To estimate the power of free-flowing water at
your site:
- Estimate the cross-sectional Area (A) in square meters.
- Estimate the current Velocity (V) in meters per second (1
m/s = 3.3 ft/s = 2 knots)
Then, Total Stream Power (TSP) in kW/hr
= A x 0.5 x V3
Generation Power = TSP x
30% (for a general estimate of the power available)
This is a very simple estimate. The maximum that could be extracted from an open stream
depends on the site. Not more than 15%-30% of the power can be extracted
without significantly affecting the whole stream for some distance in the flow.
If it is a canal and most of the flow can go through the turbine, the efficiency
can reach 60%. Actual power is affected
by the total stream size, turbulence and other factors. The stream is
always fastest about 10% of the depth below the surface and in the center of the
channel. It slows significantly near the bottom. Streams almost
always have seasonal velocity changes, so you need to know the annual
variations. The value of electricity produced from a Hydrokinetics turbine
depends on the stream, the device, the operating conditions and the local value
of electricity including renewable energy incentives that may be available.
We will be happy to help you to determine your opportunities.
Contact us.
