WIND POWER (revised 2013)
Traditional use of wind to pump water on farms – part of rural electrification
was that wind mill pumps were removed to promote electrical use.
In theory 13 times more wind power than all current worldwide electrical
production, but getting it to where it is needed is the issue
Wind produced via solar energy – hot air rises, cool air falls – day and night
breezes of the ocean or mountain. Wind currents act like ocean currents
and are predictable – prevailing winds
Small scale – remote locations, sometimes combined with solar, or a small
generator, can be off-grid or grid-tied systems, grid tied means it is
connected to the larger electrical system.
Large scale wind farms - costs of wind generation has dropped dramatically
– if environmental costs are factored in, wind is cheapest alternative energy
Large installations can be started slowly and built up unit by unit.
Competition from cheap natural gas has changed this equation.
Design types horizontal axis – most common
Vertical axis type
Three blade most common, but two and even single blade units are made
Large units require substantial cooling of the generator bearings
In large systems when the wind varies the rotation of the generator must be
constant since it has to parallel with other generators to produce the correct
voltage and frequency. Uses an adjustable gearbox = an auto transmission
in reverse to keep the generator operating at a constant speed and voltage.
Site location is critical – even a small difference in placement can make a
large difference
Wind systems are 25-40% efficient and improving
Large systems use pitch control of the blades to optimize wind use, like a
sailing ship or a helicopter
Big farms require very little maintenance due to advanced engineering,
automation, and remote monitoring.
Problems with public perception of aesthetics or scenic views, cats kills 279
million birds, wind farms 50,000
small wind ( lower, smaller blades)= fewer kills
Small scale systems up to 20 kilowatts
First make the house efficient
only makes power when wind is blowing so batteries or grid tied systems
are needed for other times
Small wind tower at least 30 feet high and 200 feet from houses trees etc.
the higher the better due to ground level wind turbulence.
Wind generators are noisy – and can through ice in the winter
Economics
Bigger is more costly, but produces more, taller is better, the labor is not
much more for bigger units, maintenance is not much more = bigger is
better. Large scale costs are “reasonable” and they can be located in farm
land helping rural economies.
Environmentally favorable, little CO2 etc.
Use much less water than a nuclear or coal plant; 500 gallons per MWh
verses 1 gallon per MWh for a wind farm.
Small wind
Is small wind feasible?
Is there enough wind
Are towers allowed, zoning laws and covenants
If you have remote access with poor access to grid
At least $150 a month in electric bills (2007)
Can afford long term investments
Enough space (at least 1 acre) rural area
it might be economically feasible
noise (55 Db)
First – reduce energy use
insulation and weatherization
upgrade heating and cooling
double pained windows
energy efficient lights
phantom loads
energy efficient appliances (refrigerator uses up to 25% of electrical usage)
Small, energy efficient appliances
Micro turbines – 20 to 100 kW
10 kW turbine to pump water = wind electric water pumping system is more
flexible
typical home requries10,000 kWh per year
needs over-speed protection and start and stop velocity controls
Rotor, generator/alternator, tower, tail
most horizontal – up wind (face the wind)
Siting
wind is a fluid and encounters friction and turbulence like any fluid
ground drag – wind slower at the surface
most resistance 60 above flat ground and 60 above tallest trees
much turbulence around buildings
turbulence can cause turbines to hunt (rotate) excessively damaging the
turbine
wind data maps for general location then a site specific plan is developed
tower height, the higher the better and sweep (diameter) of the blades
should be 30 feet above any obstacle within 300 ft of houses trees hill etc.
To increase a 60 foot 10-kW generator up to 100 ft = 10% cost increase but
29% more power winds higher and truer the higher you go
towers stand alone or guyed
if the tower is not a tip down type then maintenance done by climbing
do not mount on houses
needs batteries, inverter, connecting wires
2007 80ft tower 3-10 kW $15 to 50 K
Self install??????????
concrete
raise tower
wiring
install batteries
maintenance – annual, mechanical and electrical connections, tension guy
wires, inspect and repair blades, bearings (replace at 10 years) overall 20
year life span
output =local conditions, rotor sweep, air density (thinner air at higher
altitudes)
siting is critical – general wind flow, but local conditions like hills trees,
buildings (up wind) local turbulence
grid tie systems will need to meet grid specifications for safety (disconnect
when power is out on the grid), synchronized (voltage, frequency power
quality) some utilities require liability insurance
less wind in summer – use solar or generator to back up
off grid at least average annual 9mph wind, grid not nearby, live free or die
approach, want clean power
Maintenance
semi annual – spring and fall
calm days
lockout blades
disconnect from grid
climbing gear do you like heights? moving heights
listen for unusual sounds
turbine – blades, tail, internal components, open or disassemble (?)
lose connections, retorque, tension guy wires, rust, cracks
lightning control systems
over speed connection mechanism
climbing safety, harness, tools
battery maintenance
Generators
a generator produces DC, an alternator produces AC
rotor contains permanent magnets (some expensive model sue
electromagnets)
stator (windings where the electricity is induced)
direct drive, the rotor connected to the blades
more expensive units will use a gearbox between the blades and rotor
blades made of composites, fiberglass foam etc.
tail keeps blades facing the wind
governors and over speed controls most use furling = turn the blades out of
the wind to slow them down – the tail moves to position the turbine at an
angle to the wind
expensive turbines can change the blade pitch
shut down system completely stops rotation – mechanical brakes or electric
brakes (dynamic brake)