We have already referred briefly to the tests with the Benthuizen windmill. Some details may be given of them here. The tests were taken to find out in how far wind-power in a mill might be combined with an electric drive, and further whether the change-over from one kind of drive to the other would be possible in a simple manner during day-to-day operation. The technical appointments of the Benthuizen windmill were highly suitable for these tests; the only thing needed was the inclusion of an overrunning clutch.
'Tandem' operation was found to be actually feasible: in periods of absence of wind the water-raising apparatus (in this case a rotary pump) was driven by the electric motor and in periods when the wind was favourable the sails drove the water-raising apparatus and supplied any surplus of wind power in the form of electricity to the public electricity network.
The tests continued from 1948 to 1951 and furnished valuable information. Anyone who wishes to learn more about these tests is recommended to read the report delivered by the Committee and published by the Dutch Windmill Society in cooperation with the Organization T.N.O. in 1951. The result was that the mill in day-to-day operation appeared capable of generating a quantity of energy in the order of magnitude of 50,000 kWh a year.
During the tests several new aspects presented themselves, which made it desirable to call into existence a separate institute which was to study everything connected with the generation of electricity in greater detail and to put it to practical tests.
Thus in 1951 the Stichting Elektriciteitsopwekking door Windmolens (Foundation for the Generation of Electricity by Windmills) was established, which undertook to carry out different investigations and to examine the possibilities of more automatic operation. The latter includes automatic winding of the mill and adjustment of the sails. If any new inventions should be made, they might also be used to improve windmills in general.
Since its establishment this Foundation has equipped two windmills for the generation of electricity: the corn mill De Hoop (Hope) at Wervershoof (North Holland), which started trial operations in 1955, and the corn mill De Kraai (the Crow) at Achttienhoven, province of Utrecht, which started in 1958. Both mills are equipped with shutter sails and sky scrapers in the streamlined tips, so that they are reefed automatically and the mill can be stopped smoothly.
Special safety devices have been provided to prevent the mill from racing in case of a gale or of a failure of the electric supply.
There remains the great difficulty in the economic sense that the generated electricity that is supplied to the public network has only a small commercial value.
The devices that make possible electric winding and reefing are interesting, just as is the safety device in case of gales. These devices would seem to give great satisfaction and their application will be able to lighten the miller's duties considerably, so that he will have more spare time for other occupations.
The third windmill to be equipped for the generation of electricity is the mill De Traanroeier at Oudeschild, Texel.
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