Nick Palmer advocated long-lasting machines. I pointed out that with
some devices, a longer life would increase the use of resources,
pollution and other problems.
Design engineers often aim for a working life of around 20 years,
close to one human generation. I suppose this is force of habit, or
perhaps an arbitrary number. But it is handy to have everyone
planning for approximately the same duration. See:
http://guidedtour.windpower.org/en/tour/econ/oandm.htm
QUOTES:
Operation and Maintenance Costs for Wind Turbines
Modern wind turbines are designed to work for some 120 000 hours of
operation throughout their design lifetime of 20 years. That is far
more than an automobile engine which will generally last for some 4
000 to 6 000 hours.
Operation and Maintenance Costs
Experience shows that maintenance cost are generally very low while
the turbines are brand new, but they increase somewhat as the turbine
ages. . . .
Turbine Reinvestment (Refurbishment, Major Overhauls)
Some wind turbine components are more subject to tear and wear than
others. This is particularly true for rotor blades and gearboxes.
Wind turbine owners who see that their turbine is close the end of
their technical design lifetime may find it advantageous to increase
the lifetime of the turbine by doing a major overhaul of the turbine,
e.g. by replacing the rotor blades.
The price of a new set of rotor blades, a gearbox, or a generator is
usually in the order of magnitude of 15-20 per cent of the price of
the turbine.
Project Lifetime, Design Lifetime
The components of Danish wind turbines are designed to last 20 years.
It would, of course, be possible to design certain components to last
much longer, but it would really be a waste, if other major
components were to fail earlier.
The 20 year design lifetime is a useful economic compromise which is
used to guide engineers who develop components for the turbines.
Their calculations have to prove that their components have a very
small probability of failure before 20 years have elapsed.
The actual lifetime of a wind turbine depends both on the quality of
the turbine and the local climatic conditions, e.g. the amount of
turbulence at the site, as explained in the page on turbine design
and fatigue loads.
Offshore turbines may e.g. last longer, due to low turbulence at sea.
This may in turn lower costs . . .
END QUOTE
Note that the towers are engineered to last 100 years, and I expect
they will last longer.
There are some high tech machines such as Boeing 747s which last
longer than 20 years, but a large fraction of the machine, including
the engines, have to be changed out more often. Railroad locomotives,
nuclear power plants, and hydroelectric dams and generators are among
the longest lasting equipment.
There is usually a trade-off between power density and longevity, and
between lightweight engines and longevity. The 4 engines on a 747
engine put out a terrific amount of power, 65 MW, and they weigh ~16
tons total. A diesel locomotive weighs 122 tons, a lot of it in the
motors. It outputs about 2.5 MW I think (3,200 horsepower from the
diesel which drives the electric generators; a hybrid):
http://hypertextbook.com/facts/2001/RadmilaIlyayeva.shtml
I cannot find exact numbers, but anyway, I know that the railroad
equipment lasts many more hours and is in service for more years than
aircraft engines. I used to have a 1950 edition of the Britannica
with some specifics about that. There is something to be said for
pre-internet compilations.
- Jed
