WO2020127206A1

WO2020127206A1 - Windturbine dehumidifier system comprising secondary wind power source

Info

Publication number: WO2020127206A1
Application number: PCT/EP2019/085564
Authority: WO
Inventors: Thomas Rønnow Olesen; Rasmus Toftegaard
Original assignee: Cotes A/S
Priority date: 2018-12-21
Filing date: 2019-12-17
Publication date: 2020-06-25
Also published as: DK201800097U3; TW202035861A

Abstract

Herein is detailed a dehumidifier system (2) for an offshore wind turbine (30) comprising a removable wind generator (1), which can be releasable attached to the offshore wind turbine (30), and a dehumidifier (3) operatively connected (5,51) to the removable wind generator (1) for electrical power transmission from the removable wind generator (1) to the dehumidifier (3) such that during operation of the removable wind generator (1) the dehumidifier (3) is powered; characterized in that the removable wind generator (1) generates not more than 5 kW electrical power at 4 m/s wind speed.

Description

WINDTURBINE DEHUMIDIFIER SYSTEM COMPRISING SECONDARY WIND

POWER SOURCE

TECHNICAL FIELD

Within the field of offshore wind turbine dehumidifiers, a wind turbine dehumidifier is proposed comprising at least one fantail or mini-wind turbine as secondary power sources for a wind turbine dehumidifier, the at least one fantail or a mini-wind turbine mounted on the foundation, tower or nacelle of the offshore wind turbine during use of the dehumidifier .

BACKGROUND

Modern power generating wind turbines have achieved a unique position in Denmark in the effort to reduce the nation's CO₂ footprint and to mitigate climate change. Denmark is particularly suited to reap the benefits of a comprehensive renewable energy investment from wind turbines due to the geographical location where frequent wind-bearing low pressures pass over sea and land. In particular, the low- lying seabed within Denmark's offshore territory has created a significant investment in the development of offshore wind turbines .

However, offshore wind turbines place special and increased requirements for dehumidification and eventual desalination of the indoor air in the foundation, tower and nacelle of the offshore wind turbine to avoid corrosion, condensation and mold formation. This dehumidification process contributes to the wind turbine's operating energy consumption, which operating energy consumption of modern wind turbines, and especially offshore wind turbines, can be quite considerable. In particular, this operating energy consumption must be maintained even if the wind turbine's own power production shuts down for whatever reason in order to avoid consequential damage to electronics and other equipment installed in the wind turbine's foundation, tower and/or nacelle.

A particular problem of the shutdown and discontinuation of the electricity supply for the operation of offshore wind turbines is the very rapid molding that takes place in the interior of offshore wind turbines due to the high humidity of the sea air, which molding requires continuous dehumidification to counteract. Here high operation costs have been cited for cleaning off the interior of the offshore wind turbine against molds, condensation and/or salt-induced corrosion formation originating from production stops, costs that nevertheless are necessary to secure the mill and operating personnel against these same conditions.

Therefore, solutions are needed to solve the problem of providing secondary power sources for wind turbines, and especially offshore wind turbines that can ensure operational flow, even when the wind turbine experiences a downtime.

A further, but very significant, problem arises in the very design phase of the offshore wind turbine, where no operational power supply has been established yet. Here, even very modest delays in establishing operating power supply can result in the emergence of mold in the interior of the offshore wind turbine; just as salt-induced corrosion cannot be slowed down or reduced without adequate means for lowering the air humidity in the sea air. Therefore, in both situations, secondary power supplies are needed to ensure operational power to the wind turbines during downtime and production shutdowns. Typically, these secondary power supplies will be short-term batteries, or land- or ocean-based gasoline or diesel-powered power generators for longer-term consumption.

However, in particular during the construction phase of offshore wind turbines, it is not possible to use onshore power to operate equipment in the offshore wind turbine, and it is therefore necessary to use offshore power generators, typically diesel generators, which are costly and rapidly depleted due to the extreme operating environment, in addition to contributing negatively to the efforts to decrease carbon dioxide in the atmosphere.

Therefore, to address some of the challenges posed by a lack of operating power during construction or during operation shutdown of offshore wind turbines, the present inventors propose the present dehumidifier, which dehumidifier comprises means for operatively connecting the dehumidifier to at least one smaller, secondary wind turbine mounted on either the foundation, tower and/or nacelle of a primary wind turbine as described herein to producing a dehumidifier for a wind turbine comprising an internal power source, characterized in that the internal power source is a wind turbine mounted on an outside surface of a wind turbine having a production capacity of not more than 5 kW electrical power at 4 m/ s wind speed.

It has long been known to mount small, secondary windmills, so-called fantails (see Fig. 1), or bar windmills, on a tower or nacelle of a primary windmill (20), thereby gaining access to utilizing a smaller, but more flexible, source for converting wind energy to mechanical energy. The original fantail (1) having been patented in England in 1745 by Edmund Lee. Fig. 1 depicts a self-tapping smock mill (20) comprising a fantail (1) on the cap, which winds up an automatic turret, which, unlike a tail to be operated manually from the ground, ensures that the cap is always rotating according to the wind direction, so the mill (20) is curled up in the wind. The fantail (1) is mounted on two rose bushes opposite the wing side. When the wind strikes the fantail (1) from the side, it turns, thereby triggering small cogs and shafts associated with a tooth ring on the mill (20), thereby turning the entire mill cap. When the fantail (1) shelters and stops, the windmill (20) is curled up in the wind.

The present invention utilizes the advantageous situation that, during absence of operating power for a production wind turbine, small wind turbines, e.g. for domestic use, can still produce enough power to ensure the operation of, for example, the necessary dehumidification of the production wind turbine's interior, i.e. foundation, tower and nacelle. The particular advantage of utilizing weak winds to produce operating current over solar cells is partly independence from sunshine, which can be scarce in northern Europe, thereby reducing the need for backup batteries, but also due to reduced maintenance, which is particularly significant for offshore solar cells due to salt pollution of the solar surface and due the risk that the solar cells can blow down in severe weather due to their large surface area.

SUMMARY OF THE INVENTION

According to the invention there is herein detailed a dehumidifier system (2) for an offshore wind turbine (30) comprising a removable wind generator (1), which can be releasable attached to the offshore wind turbine (30), and a dehumidifier (3) operatively connected (5,51) to the removable wind generator (1) for electrical power transmission from the removable wind generator (1) to the dehumidifier (3) such that during operation of the removable wind generator (1) the dehumidifier (3) is powered; characterized in that the removable wind generator (1) generates not more than 5 kW electrical power at 4 m/ s wind speed .

In one embodiment, a dehumidifier system (2) for an offshore wind turbine (30) according to the invention is disclosed comprising a removable wind generator (1) and a dehumidifier (3), wherein the dehumidifier (3) is a drying wheel dehumidifier comprising a drying wheel (31) .

In one embodiment, a dehumidifier system (2) is described for an offshore wind turbine (30) according to the invention comprising a removable wind generator (1) and a dehumidifier (3), wherein the dehumidifier (3) is a drying wheel dehumidifier comprising a drying wheel (31), which dehumidifier (3) further comprises a burner whereby heated regeneration air for regenerating the drying wheel (31) is obtained by combustion of a fuel, preferably a fuel oil such as diesel.

In one embodiment, a dehumidifier system (2) for an offshore wind turbine (30) according to the invention comprising a removable wind generator (1) and a dehumidifier (3), and further comprising a reserve power supply (4) comprising at least one reserve battery (41) and an inverter (42); wherein the wind generator (1) is operatively connected (5,51,52) to the dehumidifier (3) and the reserve power supply (4) for power transmission from the wind generator (1), and the reserve power supply (4) is operatively connected (53) to the dehumidifier (3) for power transmission from the reserve power supply such that during operation of the wind generator (1), the dehumidifier (3) and the reserve power supply (4) are charged, and when the wind generator (1) is not in operation, the dehumidifier may be powered by the reserve power supply (4) .

In one embodiment, a dehumidifier system (2) for an offshore wind turbine (30) according to the invention is disclosed comprising a removable wind generator (1) and a dehumidifier (3), wherein the dehumidifier (3) and the reserve power supply (4) are assembled into a removable dehumidifier unit (6) .

In one embodiment, a dehumidifier system (2) for an offshore wind turbine (30) according to the invention is disclosed comprising a removable wind generator (1) and a dehumidifier (3), wherein the removable wind generator (1) generates less than 3 kW at 4 m/s wind speed.

In one embodiment, a dehumidifier system (2) for an offshore wind turbine (30) according to the invention is disclosed comprising a removable wind generator (1) and a dehumidifier (3), wherein the removable wind generator (1) comprises fasteners (91,92) for attachment to an outer surface of the wind turbine's foundation (8) or tower (9), preferably at least one bracket belt (91) or at least one support (92) .

In one embodiment, a dehumidifier system (2) for an offshore wind turbine (30) according to the invention is disclosed comprising a removable wind generator (1) and a dehumidifier (3), wherein the removable wind generator (1) comprises folding means (101) for folding the removable wind generator (1) up and/or down.

In one embodiment, a dehumidifier system (2) for an offshore wind turbine (30) according to the invention is disclosed comprising a removable wind generator (1) and a dehumidifier (3), wherein said folding means (101) of the removable wind generator (1) are operatively connected for power transmission from a comprised reserve power supply (4), whereby said folding means can be activated for folding up and/or down of the removable wind generator (1) without use of an external power supply.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 Smock windmill with fantail and swing.

Fig. 2 Dehumidifier system according to the invention. Fig . 3 Mounted dehumidifier system.

Fig. 4 Mounted removable wind generator on foundation. Fig . 5 Mounted removable wind generator on tower.

Fig . 6 Mounted removable wind generator on nacelle.

Fig. 7 Tables 1 to 3.

DETAILED DESCRIPTION

According to the invention, there is disclosed herein a dehumidifier system (2) for an offshore wind turbine (30) comprising a removable wind generator (1), which can be releasable attached to the offshore wind turbine (30), and a dehumidifier (3) operatively connected (5,51) to the removable wind generator (1) for electrical power transmission from the removable wind generator (1) to the dehumidifier (3) such that during operation of the removable wind generator (1) the dehumidifier (3) is powered; characterized in that the removable wind generator (1) generates not more than 5 kW electrical power at 4 m/ s wind speed .

It is preferred that the dehumidifier (3) is a drying wheel dehumidifier comprising a drying wheel (31) .

For operatively connecting (5,51) the removable wind generator (1) with the dehumidifier (3), cables for electrical power transmission according to the skilled person's general knowledge are most suitable.

The conditions at sea, both during the construction of offshore wind turbines and during their downtime, makes it extremely problematic to establish emergency power to avoid moisture-induced damage. The present invention solves this problem by assembling a removable wind generator (1) and a dehumidifier (3) to a dehumidifier system (2), and attaching the removable wind generator (1) to an offshore wind turbine (30), such that power can be quickly established to the dehumidifier (3) locally and without dependence on the establishment of operating current from central power generators such as e.g. land-based power generators or offshore central power generators run on fuels oils such as diesel .

The present disclosure distinguishes between wind turbines and wind generators for ease of understanding of the invention according to the present disclosure. Wind (power) turbines and wind (power) generators, obviously, both serve the purpose of transforming kinetic energy comprised in the wind into electrical energy to be transmitted via power cables to suitable sites of use. However, in the context of the present disclosure, wind turbines are considered distinct from wind generators based on size. A wind turbine in the context of the present disclosure must always be transported and assembled from parts at the site of power production, whereas wind generators in the context are considered smaller in size such that a wind generator may be transported as a single unit to a site of power production, but may still be assembled from parts on site if desired. Hence, a wind generator can be mounted on a wind turbine, but a wind turbine cannot be mounted on a wind generator.

Accordingly, in one embodiment of the invention there is disclosed the dehumidifier system (2) wherein the offshore wind turbine (30) generates at least 0.5 MW, 1 MW, 1.5 MW, 2 MW, 2.5 MW, but preferably 3 MW, 3.5 MW, or at least 4 MW of electrical power when producing electrical power.

In one embodiment of the invention, the dehumidifier system (2) further comprises a secondary connection for primary operating power from a primary power source such as a wind turbine and a switching relay arranged to allow switching between primary operating power and power transmission from the removable wind generator (1) comprised in the dehumidifier system, in the event of a failure of the primary operating power.

In on embodiment of the invention, the dehumidifier system (2) further comprises connecting means for operatively connecting to a primary electrical power source, such as said offshore wind turbine (30), for electrical power transmission from said primary electrical power source to said dehumidifier system (2), and a switching relay arranged to allow reversible switching from electrical power transmission from said primary electrical power source to electrical power transmission from said removable wind generator (1) comprised in said dehumidifier system (2), in the event of a failure of said primary electrical power source .

It is intended that the removable wind generator (1) should not generate more power than 5 kW electrical power at 4 m/ s wind speed. A useful removable wind generator that meets such conditions could be, for example, SD3 or SD3EX from SD Windpower (https : //sd-windenergy . com/small-wind-turbines/ sd3-3kw- wind-turbine/ ) . This maximum limit is chosen in that most current production wind turbines are not operational at wind speeds lower than 4 m/s, so the removable wind generator (1) must be operational when the production wind turbine on which it is mounted stops down due to lack of wind, while at the same time keeping the removable wind generator small enough for the intended purpose.

In preferred embodiments, the removable wind generator (1) produces 3 kW electrical power at 4 m/ s wind speed, preferably 1 kW electrical power at 4 m/ s wind speed. Also smaller removable wind generators (1) can be used, such as removable wind generators producing e.g. 0.3 kW, 0.4 kW, 0.5 kW, 0.6 kW, 0.7 kW, 0.8 kW or 0.9 kW electrical power at 4 m/ s wind speed, preferably 0.4 kW, 0.5 kW or 0.6 kW electrical power at 4 m/ s wind speed, but then it is often advantageous to connect more than one wind generator (1) operationally to the dehumidifier (3) . The removable wind generator (1) shown in the figures is representative and further removable wind generators other than a 3-blade rotor with a horizontal rotor shaft can also be used. In certain embodiments, one or more removable wind generator (s) with vertical rotor shaft (s) may be advantageous . In a particular and preferred embodiment there is detailed a dehumidifier system (2) for an offshore wind turbine (30) comprising a removable wind generator (1) and a dehumidifier (3), wherein the dehumidifier (3) is a drying wheel dehumidifier comprising a drying wheel (31) .

Drying wheel dehumidifiers are particular well suited for offshore wind turbine (30) purposes as their mode of operation allows for construction of dehumidifiers with a minimal footprint compared to the transported water. For proper operation, drying wheel dehumidifiers rely on appropriate conducts and flow paths for interior and exterior air, appropriate heating means for heating regeneration air, air-moving means (e.g. pumps and/or fans), etc. In the context of the present invention, it is considered that the skilled person is knowledgeable in the construction of drying wheel dehumidifiers and knows to manufacture an operating drying wheel dehumidifier.

In a particular embodiment of the dehumidifier (3) comprising a drying wheel dehumidifier comprising a drying wheel (31), the dehumidifier (3) further comprises heating means in the form of a burner, whereby heated regeneration air for regenerating the drying wheel (31) can be obtained by combustion of a fuel, preferably a fuel oil such as diesel.

In general, heating means for heating regeneration air in offshore wind turbines are electrical heating means. However, (the present dehumidifier system (2) being intended for backup purposes) a burner may replace or be combined with electrical heating means. This reduces the operating power current requirement for the dehumidifier (3) from approx. 1 kW for dehumidifying an offshore wind turbine (30) to between 150-200 W, which can be achieved with a portable wind generator, such as a household portable wind generator.

Fig. 2 shows the dehumidifier system (2) according to the invention in its most general embodiment of being installed on a wind turbine. It is particularly preferred that the wind turbine on which the dehumidifier system (2) is to be installed is an offshore wind turbine (30), and while the dehumidifier system (2) can service also land based wind turbines, the need is less significant as land based back-up power can be supplied more easily during construction and/or downtime of the land based wind turbine.

In an embodiment of the invention there is detailed a dehumidifier system (2) for an offshore wind turbine (30) comprising a removable wind generator (1) and a dehumidifier (3), the dehumidifier system (2) further comprising a reserve power supply (4) comprising at least one reserve battery (41); wherein the wind generator (1) is operatively connected (5,51,52) to the dehumidifier (3) and the reserve power supply (4) for power transmission from the wind generator (1); and the reserve power supply (4) is operatively connected (53) to the dehumidifier (3) to power transmission from the reserve power supply (4), such that during operation of the wind generator (1), the dehumidifier (3) is powered and the reserve power supply (4) is charged, and when the wind generator (1) is not powered, the dehumidifier may powered by the reserve power supply (4) .

It is preferred, that the dehumidifier (3) and, if included, the reserve power supply (4) are assembled as a removable dehumidifier unit (6) such that the wind generator (1) and the removable dehumidifier unit (6) of the dehumidifier system (2) can be positioned independently of one another in relation to a wind turbine's, in particular an offshore wind turbine's (30), interior and exterior as defined by the wind turbine wall (7) (cf . Fig. 3) . In an embodiment thereof, the dehumidifier (3) and the reserve power supply (4) are assembled with the removable dehumidifier unit (6) comprising means for operatively connecting (51,52) the dehumidifier (3) and the reserve power supply (4) to the removable wind generator ( 1 ) .

In the above embodiments of the reserve power supply (4), the reserve power supply (4) may comprises a switching relay arranged to allow switching between operating power transmission from the wind turbine, when the wind turbine is producing, and secondary power transmission from the removable wind generator (1) . Also, and in some embodiments, the switching relay is arranged to allow switching between sources of secondary power transmission, e.g. between solar cells installed on the wind turbine and the removable wind generator (1) . Thereby the backup capacity of the reserve power supply is further augmented.

As concerns the mounting location and the installation of the removable wind generator (1), there are a number of safety aspects that require consideration. E.g., it must be ensured that operating personnel manning the wind turbine cannot be harmed by the removable wind generator (1) at the location where it is installed. E.g., one of the challenges for the operating personnel is to be able to access an offshore wind turbine (30) and its work platform (81) by boat, and necessarily from several sides depending on the wind direction. Therefore, if the removable wind generator (1) is temporarily mounted on the work platform (81) of the offshore wind turbine (30), which is the easiest, cf. below, it may be advantageous to employ the abovementioned burner solution and one or more small household-type wind generators, rather than a larger wind generator. Alternatively, the removable wind generator (1) should be mounted at an appropriate height on the offshore wind turbine's tower (9) or on the nacelle (10) so that the removable wind generator (1) does not pose a danger to the operating personnel.

A further problem with the installation of the removable wind generator (1) is due to turbulence formation around the tower and nacelle. Depending on the direction of the wind, there is a risk of turbulence, whereby the offshore wind turbine's tower (9) could affect the wind movement to the detriment of the removable wind generator's electricity generation and durability .

The examples on Figs. 4 and 5 are shown to illustrate how the removable wind generator (1) can be mounted either (Fig. 4) on the foundation (8) or work platform (81) of the offshore wind turbine (30) , or (Fig. 5) on its tower (9) .

For the smallest of the intended removable wind generators (1), 1 kW or less, it is simple to mount the wind generator on the work platform (81) on the foundation (8) which provides access to the interior of the tower (9) and docking facilities for supply and crew ships. Possible mounting points are indicated by arrow (M) , both directly on the work platform itself (81) but also on the railing of the platform (82) . The latter is best suited for the smallest wind turbines that only need to remain mounted for short time mounting, while mounting directly on the work platform (81) is more stable and can handle larger wind generators (1) and stronger winds. For the larger wind generators, it is desirable to place them away from the work areas near the sea surface, and mounting of the wind generator (1) should thus be done either on the tower (9) by welding directly on the tower, bolting or by using one or more fastening means (91,92), such as one or more bracket belts (91) (Fig. 5) or supports (92) . The advantage of using one or more bracket belts (91) is that the wind generator (1) can be moved more easily along the belts if it turns out that the wind conditions and turbulence around the turbine tower make an initial mounting location inappropriate. Alternatively, one may choose to use a support (92) for the wind generator (1) which can be attached to tower (9) or foundation (8) and create a longer distance between the wind generator and the wind turbine, thereby reducing turbulence.

Thus, in one embodiment of the dehumidifier system (2) according to the invention, the removable wind generator (1) comprises fastening means (91,92) for fastening to an outside surface of the wind turbine's foundation (8), tower (9), or nacelle (10), preferably one or more bracket belts (91) and/or one or more supports (92) .

However, it is particularly preferred to mount the removable wind generator (1) on the offshore wind turbine's nacelle (10), especially on the nacelle's working platform, when this has become possible (Fig. 6) . When mounting on the nacelle (10), both the safety of the operating crew is avoided, as well as the turbulence and the wind shade created by the tower (9) of the offshore wind turbine (30) .

In a particularly preferred embodiment (Fig. 6B) of the dehumidifier system (2) according to the invention, the removable wind generator (1) comprises folding means for folding up and down (101) the removable wind generator (1) . In this way, the wind generator (1) can be folded in to a sheltered position in harsh weather conditions when desired, and folded out to a production position when the dehumidifier (3) has a need for power from the removable wind generator (1) .

In a particularly preferred embodiment thereof, the removable wind generator is a collapsible and removable wind generator (1) . As a collapsible and removable wind generator (1), it may be advantageous to use a vertical wind generator (1) with a vertical rotor shaft, thereby reducing the space requirement on the nacelle's work platform in the wind generator's (1) collapsed state. Alternatively, and likewise preferable, a 3-blade rotor with horizontal shaft and collapsible wings can be used as the collapsible and removable wind generator (1) .

In one embodiment, it is contemplated that said folding means for folding up and down (101) the removable wind generator (1) are operatively connected for power transmission from the reserve power supply (4) when this is included in the dehumidifier system (2), whereby said folding means for folding up and down (101) the removable wind generator (1) can be activated for folding up and down the removable wind generator (1), e.g., when the wind turbine is shut down due to wind speeds below the wind turbine's minimum operating wind speed.

Further, there is disclosed according to the present invention a method for providing electrical power to a dehumidifier (3) for an offshore wind turbine (30), the method comprising attaching a removable wind generator (1), which does not generate more than 5 kW electrical power at 4 m/ s wind speed, to an offshore wind turbine (30) and connecting the dehumidifier (3) operatively (5,51) to the removable wind generator (1) using cables for electrical power transmission.

In an embodiment of the method for providing electrical power to a dehumidifier (3) for an offshore wind turbine (30), the dehumidifier (3) and the removable wind generator (1) are operatively connected (5,51) to form a dehumidifier system (2) according to any of the herein presented aspects and embodiments .

Further, there is disclosed according to the present invention the use of a removable wind generator (1) attached to an offshore wind turbine (30), which removable wind generator (1) does not generate more than 5 kW electrical power at 4 m/ s wind speed, for electrical power generation by the removable wind generator (1) to an item requiring electrical power, during a period of time when the offshore wind turbine (30) does not produce electrical power.

In an embodiment thereof, there is detailed the use of a removable wind generator (1), wherein the item is a dehumidifier (3) or a dehumidifier unit (6) comprising a dehumidifier and a reserve power supply (4) according to any of the embodiments thereof detailed herein.

EXAMPLES

For illustration of the invention, a simulation was performed of the efficacy of a dehumidifier (3) with and without a reserve power supply (4) comprising from 1 to 3 batteries of 100 Ah each. The dehumidifier (3) was normalized to a capacity of 100% operative dehumidification of a target wind turbine to below 65% RH (below which levels of relative humidity (RH) , molds cannot form or grow) when operating at full power supply, i.e. when the target wind turbine supplies power. The dehumidifier (3) was a drying wheel dehumidifier with electrical heating of the regeneration air for the drying wheel. The weather conditions were Danish coastal waters average, e.g. such as they apply e.g. to the Horns Rev 3 Offshore Wind Farm.

In the simulation a comparison was performed between two sources of secondary power transmission to the reserve power supply to the dehumidifier (3) provided respectively by 0 to 3 solar cells (SC) of 500W, and 0 to 3 removable wind generators (WG) of 400W. The results are reported as on time of dehumidifier where needed in [%h], and time meeting target of relative humidity below 65% RH in [%h] . Results for time meeting target above 85%h are within current specifications for time meeting target of relative humidity below 65% RH. Above this time meeting target value, mold formation cannot occur within the time the volume to be dehumidified is exposed to humidity levels above the required target. The results are reported in the attached tables, c.f. Tables 1 to 3 in Fig . 7.

As can be seen from the tables, more than 100 Ah supplementary battery capacity augmented by more than 1.5 kW solar cell capacity is needed for operating a drying wheel dehumidifier if <65%h relative humidity is to be met effectively at sufficiently long time periods (above 80%h, c.f. Table 1) . There is little gain from adding additional batteries for augmentation (c.f. Tables 2 and 3) .

Contrary to this, with 0.4 kW wind power generation (c.f. Table 1) only 100 Ah supplementary battery capacity is needed for operating a drying wheel dehumidifier if 85%h relative humidity is to be met (@ 66%h on time) . And, with 0.8 kW wind power, the simulation showed that battery augmentation could be dispensed with for dehumidifying purposes under the given conditions. Combining 0.5 kW solar cells with 0.4 kW wind power was (almost) equally good as 0.8 kW wind power.

The simulations therefore clearly show that under the prevalent weather conditions in Danish coastal waters secondary power supply from wind energy was preferable over solar energy.

CLOSING COMMENTS The term "comprising" as used in the claims does not exclude other elements or steps. The term "a" or "an" as used in the claims does not exclude a plurality. A reference sign used in a claim shall not be construed as limiting the scope. Although the present invention has been described in detail for purpose of illustration, it is understood that such detail is solely for that purpose, and variations can be made therein by those skilled in the art without departing from the scope of the invention.

Claims

1. A dehumidifier system (2) for an offshore wind turbine

(30) comprising a removable wind generator (1), which can be releasable attached to said offshore wind turbine (30), and a dehumidifier (3) operatively connected (5,51) to the removable wind generator (1) for electrical power transmission from the removable wind generator (1) to the dehumidifier (3) such that during operation of the removable wind generator (1) the dehumidifier (3) is powered; characterized in that the removable wind generator (1) generates not more than 5 kW electrical power at 4 m/s wind speed.

2. A dehumidifier system (2) for an offshore wind turbine

(30) according to claim 1 comprising a removable wind generator (1) and a dehumidifier (3), wherein the dehumidifier (3) is a drying wheel dehumidifier comprising a drying wheel (31) .

3. A dehumidifier system (2) for an offshore wind turbine

(30) according to claim 2 comprising a removable wind generator (1) and a dehumidifier (3), wherein the dehumidifier (3) is a drying wheel dehumidifier comprising a drying wheel (31), the dehumidifier (3) further comprising a burner, whereby heated regeneration air for regenerating the drying wheel (31) is obtained by combustion of a fuel oil, preferably diesel.

4. A dehumidifier system (2) for an offshore wind turbine

(30) according to any of the claims 1 to 3 comprising a removable wind generator (1) and a dehumidifier (3), the dehumidifier system (2) further comprising a reserve power supply (4) comprising at least one reserve battery (41); wherein the wind generator (1) is operatively connected (5,51,52) to the dehumidifier (3) and the reserve power supply (4) for power transmission from the wind generator (1); and the reserve power supply (4) is operatively connected (53) to the dehumidifier (3) to power transmission from the reserve power supply, such that during operation of the wind generator (1), the dehumidifier (3) is powered and the reserve power supply (4) is charged, and when the wind generator (1) is not powered, the dehumidifier may be powered by the reserve power supply (4) .

5. A dehumidifier system (2) for an offshore wind turbine

(30) according to claim 4 comprising a removable wind generator (1) and a dehumidifier (3), wherein the dehumidifier (3) and the reserve power supply (4) are assembled into a removable dehumidifier unit (6) comprising means for operatively connecting (51,52) the dehumidifier (3) and the reserve power supply (4) to the removable wind generator (1) .

6. A dehumidifier system (2) for an offshore wind turbine

(30) according to any of claims 1 to 5 comprising a removable wind generator (1) and a dehumidifier (3), wherein the removable wind generator (1) generates not more than 3 kW at 4 m/s wind speed.

7. A dehumidifier system (2) for an offshore wind turbine

(30) according to any of claims 1 to 6 comprising a removable wind generator (1) and a dehumidifier (3), wherein the removable wind generator (1) comprises fastening means (91,92) for attachment to an exterior of an offshore wind turbine's foundation (8), tower (9) or nacelle (10).

8. A dehumidifier system (2) for an offshore wind turbine

(30) according to claim 7 comprising a removable wind generator (1) and a dehumidifier (3), wherein the fastening means (91,92) can be a bracket belt (91) and/or a support ( 92 ) .

9. A dehumidifier system (2) for an offshore wind turbine

(30) according to any of claims 1 to 8 comprising a removable wind generator (1) and a dehumidifier (3), wherein the removable wind generator (1) comprises folding means for folding up and down (101) the removable wind generator ( 1 ) .

10. A dehumidifier system (2) for an offshore wind turbine

(30) according to claim 9 comprising a removable wind generator (1) and a dehumidifier (3), wherein said folding means for folding up and down (101) the removable wind generator (1) are operatively connected for power transmission to a reserve power supply (4) comprised in the dehumidifier system (2), whereby said folding means for folding up and down (101) can be actuated for folding up and down the removable wind generator (1) without external power supply.

11. A dehumidifier system (2) according to any of the preceding claims 1 to 10, further comprising connecting means for operatively connecting to a primary electrical power source, such as said offshore wind turbine (30), for electrical power transmission from said primary electrical power source to said dehumidifier system (2), and a switching relay arranged to allow reversible switching from electrical power transmission from said primary electrical power source to electrical power transmission from said removable wind generator (1) comprised in said dehumidifier system (2), in the event of a failure of said primary electrical power source.

12. A method for providing electrical power to a dehumidifier

(3) for an offshore wind turbine (30), the method comprising attaching a removable wind generator (1), which does not generate more than 5 kW electrical power at 4 m/ s wind speed, to an offshore wind turbine (30) and connecting the dehumidifier (3) operatively (5,51) to the removable wind generator (1) using cables for electrical power transmission.

13. A method for providing electrical power to a dehumidifier

(3) for an offshore wind turbine (30) according to claim 12, wherein the dehumidifier (3) and the removable wind generator (1) are operatively connected (5,51) to form a dehumidifier system (2) according to any of the claims 1 to 11.

14. Use of a removable wind generator (1) attached to an offshore wind turbine (30), which removable wind generator (1) does not generate more than 5 kW electrical power at 4 m/ s wind speed, for electrical power generation by the removable wind generator (1) to an item requiring electrical power, during a period of time when the offshore wind turbine (30) does not produce electrical power.

15. A use of a removable wind generator (1) according to claim 14, wherein said item is a dehumidifier (3) or a dehumidifier unit (6) comprising a dehumidifier and a reserve power supply (4) according to any of the claims 1 to 11.