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8/12/2019 Electrical-Engineering-portal.com-Wind Power Applications Grid Connected or Not
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Wind p ower app lications, Grid co nnected or no t? (on photo: The wind turbines, each with a rated p ower output of 3.2megawatts (MW) and a hub height of 143 metres, are intended for the Poysdorf-Wilfersdorf III wind farm in the north-east of
Aus tri a.)
by Edvard
Wind power applications, Grid connected or not?
Thereareperhapsfour distinct
categories o f wind power which sho uld be discussed.
These are:
By small, we mean a size appropriate f or an individual to o wn, up to a f ew tens of kilowatt s. Large refers toutility scale.
Small, Non-Grid Connected
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Home wind turbines - des igned for ease o f use, they are smoo th and quiet.
Small wind turbine - Grid connected (Horizo ntal-axisturbine d esig ned and installed in San Francisco)
If one wants electricity in a locat ion notserviced by a utility, one o f the options isa wind turbine, with bat teries t o level outsupply and demand. This might be a your home, a remot e antenna and transmitter site, o r a Third-World village.
The costs will be high, on the order of
$0.50/kWh , but if the to tal energy usageis small, this might be acceptable.
The alternatives, photovoltaics,microhydro, and diesel generators, are no tcheap either, so a careful economic st udyneeds to be done f or each situation.
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Small, Grid Connected
The small, grid connected turbine is usually not economically feasible . The cost of wind-generatedelectricity is less because the utility is used f or s to ragerather than a batt ery bank, but is s till not competitive.
In order f or t he small, grid connected turbine to have anyhope o f f inancial breakeven, the turbine owner needs t oget so mething close to t he retail price f or t he wind-generated electricity.
One way this is done is for t he owner to have anarrangement with the utility called net metering. With thissyst em, the meter runs backward when the turbine isgenerating more t han the owner is consuming at t hemoment.
The owner pays a monthly charge for t he wires to hishome, but it is conceivable that t he utility will sometimeswrite a check to t he owner at t he end of the month, rather than the o ther way around.
The utilities do not like this arrangement. They want t o buy at wholesale and sell at ret ail.
They f eel it is unf air to be used as a st orage system without remuneration.
For mos t o f the twentieth century, utilities simply ref used to connect the grid to wind turbines. The utility hadthe right t o generate electricity in a given service territo ry, and they would not to lerate co mpetition. Then a lawwas passed that ut ilities had to hoo k up wind turbines and pay them the avoided cos t f or energy.
Unless the s tat e mandated net metering, the utility t ypically required the installation o f a second meter, onemeasuring energy consumption by the home and the o ther energy production by t he turbine.
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Large, non-grid connecte d wind turbines installed on mountain
The owner would pay the regular retail rate, and the ut ility would pay their est imate o f avoided cos t, usually thef uel cost of some base load generator.
The owner might pay $0.08 to $0.15 per kWh , and receive $0.02 per kWh f or t he wind-generatedelectricity. This was f ar f rom enough to eco-nomically just ify a wind turbine, and had the ef f ect of killing thesmall wind turbine business.
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Large, Non-Grid Connected
These
machines would be installed on islands, high mountains o r native villages in the f ar nort h where it isvirtually impossible to connect to a large grid. Such places are typically supplied by diesel generators , and havea substantial cost just f or t he imported f uel.
One or more wind turbines would be installed in parallel with the diesel generators , and act as f uel saverswhen the wind was blowing.
This concept has been s tudied caref ully and appears to be quite feasible technically . One would expect themarket to develop af ter a f ew turbines have been shown to work for an extended period inhostile environments.
It would be helpf ul if the diesel maintenance companies would also carry a line of wind turbines so the peoplein remote locations would not need to teach another group of maintenance people about the realities of life atplaces f ar away f rom the nearest hardware sto re.
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Large, Grid Connected
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In Schlalach-Mühlenfließ, a small town in the German region of Brandenburg, 16 gigantic wind turbines stretch into the air.Every tower has huge, ro tating b lades and a height of clo se to 180 meters.
Wemightask if theutilitiesshouldbeforced
to buywind-
generated electricity f rom thes e small machines at a premium price which ref lects t heir environmental value.
Many have argued this over the years.
A bet ter question might be whether t he small or t he large turbines will result in a lower net cost to so ciety.
Given that we want t he environmental benef its o f wind generation, should we get the electricity f rom the windwith many thousands of individually owned small turbines, o r sho uld we use a much smaller number of utility-scale machines?
If we could make the argument that a dollar spent on wind turbines is a dollar not spent o n hospitals, schoo ls,and the like, then it f ollows that wind turbines should be as ef f icient as poss ible. Econo mies of scale andcosts of operat ion and maintenance are such that the s mall, grid connected t urbine will always need to receivesubst antially more per kilowatt hour than the utility-scale turbines in order to break even.
There is o bvious ly a niche market for turbines that are not connected to the grid, but small, grid connectedturbines will probably not develop a thriving market. Mos t of the action will be f rom the ut ility-scale machines.
Sizes o f these turbines have been increasing rapidly. Turbines with rat ings near 1 MW are now common, withprotot ypes of 2 MW and more being test ed. This is s till small compared to the needs o f a utility, so clust ers o f
turbines are placed to gether to f orm wind power plants with to tal ratings o f 10 to 100 MW .
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Resource: Electric Power Generation: Non-Conventional Methods – Saifur Rahman Virginia Tech