Patent Publication Number: US-2023133424-A1

Title: Method for performing working using osmosis

Description:
CROSS-REFERENCE TO RELATED APPLICATION(S) 
     This application is a Section 371 National Stage Application of International Application No. PCT/EP2021/056807, filed Mar. 17, 2021 and published as WO 2021/185900 A1 on Sep. 23, 2021, in English, and further claims priority to European Application Ser. No. 20164659.3 filed Mar. 20, 2020. 
    
    
     BACKGROUND 
     The invention relates to a method for performing work using osmosis and to an osmotic motor. 
     In recent years the demand for clean energy production has grown exponentially. Many different renewable energy sources, such as solar energy and wind energy are being implemented to gradually shift economic dependence away from non-renewable energy sources. Another type of renewable energy source, namely, energy production from osmotic gradients, has thus far been under-utilized as a part of the energy transition. 
     The concept of osmotic motors or osmotic energy production has been known and even implemented in various configurations. A strategic location for osmotic energy production is the connection point between a river and a body of salt water, i.e. a river mouth. Such locations provide an abundant and continuously replenished supply of both fresh water and salt water. Thus, natural mixing of salt water and fresh water at river mouths takes place continuously. However, this osmotic mixing process cannot yet be controlled in such a way that a sufficiently reliable and strong supply of energy arises therefrom. 
     In contrast with other clean energy sources, such as sun and wind, osmotic mixing of salt and fresh water takes place continuously and is largely independent of weather conditions. Thus, osmotic energy production provides the benefit of a steady stream of reliable energy that can complement other clean energy technologies. 
     However, certain limitations of known methods have provided a challenge for increasing the efficiency of osmotic energy production and have thus far lead to under-utilization of this advantageous technology. 
     For example, US 2018/0085708 A1, US 2014/0007564 A1, KR 101239440 B1 and WO 2011/064252 A1 suggest specific concepts of osmotic energy production. These concepts are based on pressure retarded osmosis, i.e. on maintaining specific, elevated pressure conditions. However, these concepts may be disadvantageous in terms of net energy production. 
     Disclosed embodiments of the present invention to provide a method for performing work using osmosis and to provide an osmotic motor which address current limitations of this technology. 
     SUMMARY 
     According to a first aspect, the invention relates to a method for performing work using osmosis comprising the steps of 
     i) providing a motor comprising a supply chamber, a pressure chamber comprising at least one inlet and at least one outlet, and a membrane permeable to fluid, preferably water, and at least partially impermeable to salt ions, the membrane enabling fluid communication between the supply chamber and the pressure chamber;
 
ii) providing low salt concentration fluid, preferably low salt concentration water, in the supply chamber;
 
iii) closing the at least one outlet of the pressure chamber;
 
iv) flowing high salt concentration fluid, preferably high salt concentration water, into the pressure chamber;
 
v) allowing the pressure within the pressure chamber to increase as fluid crosses the membrane into the pressure chamber;
 
vi) using the increased pressure within the pressure chamber to perform work;
 
vii) opening the at least one outlet of the pressure chamber and allowing the fluid to drain from the pressure chamber and the pressure in the pressure chamber to decrease;
 
viii) repeating steps iii to vii.
 
     Preferably, the at least one outlet is sealed in step iii). 
     Preferably, the steps iv), v), vi) are performed sequentially and preferably in this order. 
     Preferably, the motor further comprises a turbine. Thus, step vi may further comprise flowing fluid out from the pressure chamber due to increased pressure and allowing the fluid to operate the turbine to perform work. A turbine provides a direct way to convert the pressured flow into electricity such as in hydroelectric power systems. The pressure chamber may have a fixed volume for this purpose. 
     Alternatively, the pressure chamber may comprise a variable volume, preferably wherein the pressure chamber further comprises a piston. In such a configuration the expansion and contraction of the pressure chamber, through, for example, movement of the piston, may be used to perform work. 
     Preferably the at least one outlet comprises a valve, wherein the method further comprises the steps of opening the valve to relieve at least a portion of the pressure within the pressure chamber, wherein the flow of fluid emitted from the valve is used to perform work. Flow through the valve preferably is intermittent. In other words, the fluid may be intermittently emitted from the pressure chamber to perform work. 
     In other words, a flow of fluid emitted from the pressure chamber in order to perform work (e.g., for generating electric energy in a generator) may be intermittent. 
     More preferably the valve is a non-return valve. A valve, and especially an overpressure and/or non-return valve, may assist in preventing backflow into the pressure chamber. The valve may be configured to open once a predetermined pressure is reached, in particular once a predetermined pressure is reached within the pressure chamber. The valve may be fully mechanical for this purpose. Alternatively, one or more pressure sensors may be provided in order to measure whether the predetermined pressure is reached, upon which the valve may be opened (e.g., by an electrical control unit). 
     The motor may comprise at least one accumulator, in particular at least one hydraulic accumulator. Such hydraulic accumulator may be helpful, for example, when the fluid is intermittently emitted from the pressure chamber to perform work. In particular, such accumulator may allow to maintain the pressure supplied to the turbine within a desired range, despite the intermittent fluid supply from the pressure chamber. The accumulator may be interposed between the pressure chamber and the turbine. 
     The method may further comprise the step of building up and maintaining a certain level of pressure in the outflow resulting from the pressure chamber by means of the accumulator. In other words, the accumulator may receive the outflow from the pressure chamber, build up pressure, and maintain a certain level of pressure in the outflow from the accumulator, which is then used to perform work (e.g., via the turbine). Accordingly, the accumulator may be configured to build up and maintain a certain level of pressure. 
     The at least one outlet may be provided by at least one outflow port of the pressure chamber. 
     The at least one outlet of the pressure chamber may include at least one first outlet and at least one second outlet. The at least one first outlet may be formed as at least one first outflow port of the pressure chamber and the at least one second outlet may be formed as at least one second outflow port of the pressure chamber. Alternatively, the at least one first outlet and the at least one second outlet may be connected to the pressure chamber via a common outflow port, if desired. For example, the at least one first outlet and the at least one second outlet could also be provided by a fluid valve having at least one inlet and at least two outlets (e.g., a dual outlet valve or a three-way valve). In any case, the at least one second outlet may also be referred to as a “secondary outlet” or “secondary outlet port” hereinafter. 
     When at least one first outlet and at least one second outlet is provided, the increased pressure within the pressure chamber that is used to perform work may be released through the at least one second outlet (e.g., the at least one secondary outlet port). Step vi) may thus include utilizing a high pressure flow through the at least one second outlet to perform the work. Accordingly, the method for performing work using osmosis may comprise a step of opening the at least one second outlet to emit high pressure flow through the at least one second outlet to perform the work. The second outlet may be closed and/or sealed during step v). 
     When the at least one first outlet and at least one second outlet is provided, the at least one first outlet may allow to drain fluid from the pressure chamber, for example to drain fluid that is not intended to be used for performing work. In other words, fluid draining from the pressure chamber via the at least one first outlet may bypass work harvesting and power generation. Accordingly, the method for performing work using osmosis may comprise a step of opening the at least one first outlet, thereby draining fluid from the pressure chamber. The first outlet may be closed and/or sealed during step v). The first outlet may be closed and/or sealed during step vi). 
     The at least one first outlet and the at least one second outlet may each be provided with a respective closeable and/or sealable valve (e.g., an overpressure and/or non-return valve). 
     The at least one first outlet and the at least one second outlet may each be provided with a respective closeable and/or sealable valve (e.g., overpressure and/or non-return valve, or an electrically actuated valve), as described above. Closing and/or sealing the respective outlet may thus comprise closing the respective valve. 
     Preferably, the steps iii to viii are repeated at least 2 times per hour, more preferably at least 10 times per hour, more preferably at least 20 times per hour, and even more preferably at least 60 times per hour. This allows providing an adequate intermittent flow through such valve and/or an adequate intermittent movement of such piston to perform work. 
     Preferably, the at least one inlet is at least one inflow port. 
     Preferably the motor further comprises an osmotic barrier configured to reversibly block the exchange of fluid between the supply chamber and the pressure chamber. The method may further comprise the steps of positioning the osmotic barrier over the membrane such that the fluid flow between the supply chamber and the pressure chamber is prevented, and removing the osmotic barrier after using the increased pressure to perform work. An osmotic barrier may help to separate the replenishment of the high salt concentration fluid within the pressure chamber and the buildup of pressure within the pressure chamber. 
     It is preferred that during filling of the pressure chamber by fluid crossing the membrane (step v) a maximum pressure achieved within the pressure chamber is at least 0.3 MPa relative to atmospheric pressure (also referred to as “gauge”), more preferably at least 1.3 MPa (gauge), and even more preferably at least 3 MPa (gauge) or at least 4 MPa (gauge). This pressure may be lower than a maximum theoretical osmotic pressure as the amount of water flowing through the membrane is proportional to the maximum theoretical osmotic pressure minus pressure in the pressure chamber. It is preferred that the pressure in the pressure chamber during energy generation is at least 10% lower, more preferred at least 25% lower, most preferred at least 50% lower than the maximum theoretical osmotic pressure of the system. 
     It is also preferred that flowing of low salt concentration fluid into the supply chamber is performed while the pressure chamber is either empty or at a pressure lower than 1 MPa (gauge), more preferably lower than 100 kPa (gauge), more preferably lower than 1.0 kPa (gauge), or even at atmospheric pressure. 
     It is preferred that during the flowing of high salt concentration fluid into the pressure chamber in step iv the pressure in the pressure chamber is lower than 1 MPa (gauge), lower than 100 kPa (gauge), or even lower than 1.0 kPa (gauge), or even at atmospheric pressure. 
     Alternating between a low pressure for chamber filling and a higher pressure for performing work may help in achieving higher efficiency of the osmotic motor system. It may require none or less work to introduce the high salt concentration fluid into the pressure chamber and/or improve the flow of fluid through the membrane at the beginning of step v, since flow through the membrane tends to be higher when the pressure difference between the chambers is small. Particularly, the motor may alternate between a lower pressure for chamber filling and a higher pressure during which fluid crosses the membrane, either in the pressure chamber or the supply chamber or in both chambers. The pressure chamber may alternate between the lower pressure for chamber filling and the higher pressure during which fluid crosses the membrane at least 2 times per hour, more preferably at least 10 times per hour, more preferably at least 20 times per hour and even more preferably at least 60 times per hour. The higher pressure in the pressure chamber preferably results from the fluid that enters the pressure chamber by crossing the membrane. 
     Preferably the method further comprises the step of sealing the inlet (e.g., the inflow port) of the pressure chamber after flowing high salt concentration fluid into the pressure chamber. Sealing the inlet (e.g., the inflow port) may promote a reliable and reproducible buildup of pressure within the pressure chamber. 
     Preferably the low salt concentration fluid has a salt concentration below 5 parts per thousand, more preferably below 1 part per thousand, and even more preferably below 0.5 parts per thousand. Similarly, it is preferred that the high salt concentration fluid has a salt concentration above 5 parts per thousand, more preferably above 20 parts per thousand, and even more preferably above 30 parts per thousand. In relation to one another it is preferred that the high salt concentration fluid has a salt concentration at least 100 times higher than the low salt concentration fluid, more preferably at least 500 times higher and even more preferably at least 1000 times higher. A high osmotic gradient between the low salt concentration side and the high salt concentration side of the membrane enables more work to be performed. 
     An inclination and/or height difference may be employed for creating a current and/or pressure that flows the low salt concentration fluid into the supply chamber and/or the high salt concentration fluid into the pressure chamber. Such current or pressure preferably is created without the use of electrical energy (e.g., without the use of pumps) and/or without the use of mechanical energy (e.g., without the use of mechanical energy created by the motor). For example, a naturally occurring current or pressure is employed for flowing the low salt concentration fluid into the supply chamber and/or the high salt concentration fluid into the pressure chamber. For example, it is preferred that the low salt concentration fluid flows into the supply chamber by gravity and/or that the high salt concentration fluid flows into the pressure chamber by gravity. Similarly, it is preferred that the fluid is drained from the pressure chamber by gravity. Using a gradient or pressure to flow fluid through the osmotic motor system reduces the amount of energy input required and consequently enhances the overall efficiency of the method. 
     Preferably the high salt concentration fluid is sea water, wastewater or brine, wherein the brine preferably results from a desalination process, such as reverse osmosis, an evaporation process or a condensation process. Preferably the low salt concentration fluid is fresh water from a river. Such fluid sources are readily found worldwide and promote the usability of the osmotic motor system. 
     Preferably the pressure in the pressure chamber decreases as the fluid from the pressure chamber is drained. Preferably the pressure in the pressure chamber decreases as work is performed. 
     The supply chamber may remain filled through two, five, ten, twenty or more repetitions of steps iii to vii. In order to compensate for fluid crossing into the pressure chamber, low salt concentration fluid may be added to the supply chamber as required. 
     Preferably, pressure built up within the pressure chamber during step v takes place in less than 15 minutes, more preferably in less than 10 minutes, end even more preferably in 5 minutes or less. 
     When repeating steps iii to vii, the replenishment of the pressure chamber with new high salt concentration fluid in steps vii and iii takes place in less than 3 minutes, preferably less than 2 minutes, more preferably less than 1 minute or less than 0.5 minutes. 
     According to a second aspect the invention relates to a motor comprising: 
     a supply chamber configured to receive a supply of low salt concentration fluid, preferably low salt concentration water;
 
a pressure chamber configured to receive a supply of high salt concentration fluid, preferably high salt concentration water, the pressure chamber further comprising at least one inlet and at least one closeable outlet;
 
a membrane permeable to fluid molecules and at least partially impermeable to salt ions, the membrane enabling fluid communication between the supply chamber and the pressure chamber, wherein the pressure chamber is configured to alternate between a closed configuration, wherein the at least one closable outlet is closed and pressure builds within the pressure chamber, and an open configuration, in which the at least one closable outlet is open and pressure within the pressure chamber reduces.
 
     The motor may be used in the above-mentioned method. The features of the motor may translate to features of the method and vice-versa. 
     The at least one outlet may be at least one outflow port. The at least one outlet may be sealable. In particular, the at least one outflow port may be sealable. 
     The at least one inlet may be at least one inflow port. 
     The motor may be configured for performing work. Particularly, the motor may be configured for using the increased pressure that is generated within the pressure chamber to perform work. 
     Preferably the motor further comprises a generator and/or turbine in fluid connection with the pressure chamber. In this case, the pressure chamber may have a fixed volume. 
     In another configuration, it is preferred that the pressure chamber has a variable volume. Preferably such pressure chamber further comprises an expansion portion configured to allow the pressure chamber to reversibly increase in volume. More preferably the expansion portion of the pressure chamber is a piston. 
     Preferably the motor further comprises an osmotic barrier configured to reversibly block the exchange of fluid between the supply chamber and the pressure chamber through the membrane. 
     An osmotic barrier allows for the build of pressure in the pressure chamber to be controlled and possibly to only take place during certain phases of the motor work cycle. 
     Preferably the pressure chamber further comprises a valve configured to release fluid from the pressure chamber. More preferably the valve is an overpressure and/or a non-return valve, as discussed above. 
     It is preferred that the osmotic membrane provides a stabilized salt rejection of at least 95%, more preferably at least 98%, and even more preferably at least 99% when subjected to a test salt concentration of 32.000 mg/L NaCl at 25° C. with an applied pressure of 5.5 MPa, and with 10% recovery. The efficacy of the membrane is related to the speed of pressure build up within the pressure chamber and the overall total pressure within the pressure chamber that can be achieved. Higher salt rejection leads to faster speeds and overall higher achievable pressures. 
     Preferably the supply chamber further comprises at least one inlet (e.g., at least one inlet port) and at least one outlet (e.g., at least one outlet port), preferably wherein the inlet (e.g., the inlet port) and/or the outlet (e.g., the outlet port) is sealable. Sealable ports on the supply chamber promote a motor system wherein the supply chamber is filled in a stepwise and/or intermittent manner. 
     Preferably the motor is configured to provide at least 100 Watts of energy, more preferably at least 1 Kilowatts, and even more preferably at least 1 Megawatt of energy. 
     Preferably in the closed configuration of the pressure chamber a maximum pressure achieved within the pressure chamber is at least 1 MPa, more preferably at least 2 MPa, and even more preferably at least 2.3 MPa. Higher maximum pressures enable a greater amount of work to be performed by the motor. 
     Preferably in the open configuration of the pressure chamber a minimum pressure achieved within the pressure chamber is at most 1 MPa, more preferably at most 100 kPa, and even more preferably at most 1.0 kPa. Low pressure during filling of the chamber allows for quicker filling and replenishment of high salt concentration fluid. 
     The invention may also relate to a system comprising the above-described motor and a generator for producing electric energy. Such generator may comprise a turbine. The motor may be configured to carry out the above-described method. 
     According to the invention, the motor, or a system comprising such motor, may also comprise a plurality of pressure chambers. All pressure chambers may be connected, via one, a plurality of or a corresponding number of osmotic membranes, to a single (i.e. the same) supply chamber. Alternatively, the plurality of pressure chambers may be connected via one osmotic membrane, a plurality of or a corresponding number of osmotic membrane elements, to a plurality of supply chambers. e.g. a corresponding number of supply chambers. A plurality of pressure chambers has the advantage that during the time in which no energy is produced in one pressure chamber, another pressure chamber may produce energy. Furthermore, the amount of energy produced during a cycle is decreasing as fresh water is diluting the salt water in a pressure chamber. In case a cycle takes a few minutes, the plurality of pressure chambers enables an operation mode in which every few seconds a new cycle starts. 
     The one or the plurality of pressure chambers may be connected to one or a plurality of turbines/generators. Accordingly, the above-described motor/system may also comprise a plurality of turbines and/or generators. A plurality of turbines and/or generators enables a greater adaptability of the system to a varying demand for current. For example, the number of turbines/generators that produce current may be varied according to the demand for current. 
     Accordingly, the method described above may be adapted to the motor with a plurality of pressure chambers. For example, the method steps described herein may be applied to any of the plurality of pressure chambers, alone or in parallel with other pressure chambers of the plurality of pressure chambers. If the method steps are applied to several pressure chambers, the method steps applied to one pressure chamber may be shifted in time as compared to one or several or all other pressure chambers. 
     It is also contemplated that several motors run in parallel. 
     The present summary is provided only by way of example and not limitation. Other aspects of the present invention will be appreciated in view of the entirety of the present disclosure, including the entire text, claims and accompanying figures. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be explained in more detail in the following text with reference to preferred exemplary embodiments which are illustrated in the appended drawings, in which: 
         FIG.  1   a    schematically depicts a pressure chamber in a low pressure configuration; 
         FIG.  1   b    schematically depicts the pressure chamber being filled with high salt concentration fluid in the low pressure configuration; 
         FIG.  1   c    schematically depicts the pressure chamber in a high pressure configuration, where due to osmotic transport of fluid across the membrane pressure within the pressure chamber builds and the pressure is used to perform work by driving a turbine; 
         FIG.  1   d    schematically depicts the pressure chamber in a low pressure configuration as fluid is drained from the pressure chamber: 
         FIGS.  2   a    schematically illustrates an alternative configuration of the motor in which the pressure chamber comprises a piston, an inlet of the pressure chamber being in an open configuration as high salt concentration water is flowed in; 
         FIG.  2   b    schematically illustrates the pressure chamber of  FIG.  2   a    being in a closed configuration wherein pressure buildup due to osmotic transport of fluid across the membrane drives the piston to move; 
         FIG.  3    schematically illustrates another configuration of the motor, wherein the motor further comprises an osmotic barrier and wherein the supply chamber comprises inlet and outlet valves: 
         FIG.  4    provides an example configuration of the osmotic motor. 
     
    
    
     While the above-identified figures set forth one or more embodiments of the present invention, other embodiments are also contemplated, as noted in the discussion. In all cases, this disclosure presents the invention by way of representation and not limitation. It should be understood that numerous other modifications and embodiments can be devised by those skilled in the art, which fall within the scope and spirit of the principles of the invention. The figures may not be drawn to scale, and applications and embodiments of the present invention may include features, steps, and/or components not specifically shown in the drawings. 
     DETAILED DESCRIPTION 
     In the following discussion of the inventive method and motors the terms “fresh water” and “salt water” will be used merely out of convenience. Nevertheless, the principles of osmotic pressure, osmotic gradient, and the functioning of an osmotic motor are not dependent on the specific use of fresh water and salt water. These terms are to be understood as being short-hand for a liquid containing a low solute concentration (fresh water) and a liquid containing a high solute concentration (salt water). The liquid in use may be any liquid and the solute in use may be any substance dissolvable in the liquid given the constraint that a suitable membrane can be implemented which is capable of separating the liquid from the solute. In fact, the exact concentration of solutes in fresh water and salt water can vary between locations and the solutes implied in fresh water and salt water include numerous components that will later be discussed in more detail. 
       FIG.  1    conceptually illustrates the steps of extracting work using an osmotic gradient according to the present invention. In  FIG.  1   a   , a simplified example of an osmotic motor is outlined. The motor  100  includes a supply chamber  110 , a pressure chamber  120  having at least one inlet  130  (exemplified here as an inflow port) and at least one outlet, and an osmotic membrane  150 . The outlet may comprise at least one first outlet  140  (exemplified here as an outflow port  140 ) and, optionally, at least one second outlet  144  (exemplified here as a secondary outlet port  144 ). 
     The supply chamber  110  is configured to receive a liquid supply having a low solute concentration, such as fresh water. The extent of the supply chamber  110  is not entirely depicted within  FIG.  1   a    and can be adapted in size and shape to suit the needs of the motor. 
     Adjacent the supply chamber  110  is the pressure chamber  120 , which is configured to receive a liquid supply having a high solute concentration, such as salt water. The pressure chamber  120  as depicted in this example has a defined volume, this volume being related to the amount of work the can be performed, i.e. the amount of energy that can be extracted from the motor. 
     On one side of the pressure chamber  120  is positioned the inlet  130 . The inlet  130  allows for the inflow of salt water into the pressure chamber  120 . The pressure chamber  120  further comprises the at least one first outlet  140 , which allows the fluid to later drain out of the pressure chamber  120 . The first outlet  140  preferably is positioned below the inlet  130 , for example on another side of the pressure chamber  120  than the inlet  130 , more preferably on the opposite side of the pressure chamber  120  than the inlet  130 . The first outlet  140  may further comprise a valve  143 , which may be operated to either hold the fluid within the pressure chamber  120  and thereby help to build up pressure and/or to drain the pressure chamber  120  and reduce pressure. As such, the valve  143  may also be referred to as a first pressure chamber outlet valve. 
     Preferably, a valve  133  is provided to close the inlet  130  (e.g., the inlet port). As such, the valve  133  may also be referred as a pressure chamber inlet valve. 
     In between the supply chamber  110  and the pressure chamber  120  the osmotic membrane  150  is positioned, which is permeable to the liquid in the supply chamber  110  and at least somewhat impermeable to the solute within the pressure chamber  120 . The membrane  150  should form a connection between the supply chamber  110  and the pressure chamber  120  through which the liquid can cross. It is preferred that no other channels without such membrane exist to communicate fluid between the supply chamber  110  and the pressure chamber  120  in order to allow osmosis to occur at the membrane. 
     As an initial step, fresh water is provided into the supply chamber  110  as shown in  FIG.  1   a   . This step may be performed either as a distinct filling step or, alternatively, fresh water may be continuously supplied or flowed through the supply chamber  110 . If the fresh water is supplied in a separate step, it is preferred that at least the inlet  130  of the pressure chamber  120  is closed and/or sealed, e.g. by closing the pressure chamber inlet valve  133 . Preferably, the outlet  140  is closed and/or sealed as well. e.g. by closing the first pressure chamber outlet valve  143 . 
     As the work will be used that is generated during filling, it is preferred to first fill the pressure chamber  120 , close the pressure chamber inlet valve  133 , and then fill the supply chamber  110 . Since it is not necessary to drain the supply chamber  110  in every cycle, it is also possible to fill the pressure chamber  120  while the supply chamber  110  remains at least partially filled (e.g., at least 50% filled) or entirely filled. 
     A shown in  FIG.  1   b   , the outlet  140  of the pressure chamber  120  is closed and/or sealed and the inlet  130  is opened such that salt water flows into the pressure chamber  120 . In the illustrations provided the density of cross-hatching is intended to illustrate the concentration of solute within the liquid (not to scale). Thus, it is clear that the liquid in the pressure chamber  120  at this point has a higher solute concentration than the liquid in the supply chamber  110 . 
     Over time the transition is made between  FIG.  1   b    and  FIG.  1   c   , in which water from the supply chamber  110  is allowed to cross the membrane  150  into the pressure chamber  120 , thereby reducing the solute concentration within the pressure chamber  120 . Simultaneously, as more water crosses the membrane  150 , the pressure within the pressure chamber  120  begins to climb. It is advantageous to have both the inlet  130  (e.g., the inflow port) and the outlet  140  (e.g., the outflow port) closed at this stage. The raised pressure within the pressure chamber  120  can then be used to perform work. Merely as an example, the at least one second outlet  144  (exemplified here by the secondary outlet port  144 ) is shown in  FIGS.  1   a  to  1   d   , through which the liquid is allowed to exit the pressure chamber  120 . One way to extract work from the high pressure within the motor is to utilize the high pressure flow through the at least one second outlet  144  (e.g., in secondary outlet port  144 ) to turn a turbine  160  as shown in  FIG.  1   c    by the black arrow. Alternative methods for extracting work from the motor will also be discussed. 
     In  FIG.  1   d    the outlet  140  (e.g., outflow port  140 ) has been opened allowing the fluid in the pressure chamber  120  to drain out. It may also be advantageous to seal the inlet  130  (e.g, inflow port  130 ) at this point to prevent unwanted build-up of liquid within the pressure chamber  120 . Once the pressure within the pressure chamber  120  has reached an acceptably low level and the pressure chamber  120  is substantially empty, the outlet  140  (e.g., outflow port  140 ) can again be sealed and the process then begins again as in  FIG.  1     a.    
     Preferably, the build-up of pressure within the pressure chamber  120  is distinctly separate from the filling of the pressure chamber  120  with salt water. This is highly beneficial as the filling of the pressure chamber then does not take place against the pressure of a fluid in the pressure chamber  120 . Generally, osmotic motors operate using constant fill and constant pressure to perform work continuously, such as by continuously turning a turbine. The present configuration of a two-step fill and pressure build-up process, however, allows for higher efficiency in work output. 
     In other words, it is preferred to fill the pressure chamber  120  (see  FIG.  1   b   ) while the pressure therein is lower than the pressure achieved during pressure build-up (see  FIG.  1   c   ). Preferably, the pressure chamber  120  is at least partially emptied for this purpose. For example, filling of the pressure chamber  120  may be performed (e.g., begin) when the pressure chamber  120  contains at least 30% less volume of high salt concentration fluid than during pressure build-up, at least 50% less volume of high salt concentration fluid than during pressure build-up, or at least 75% less volume of high salt concentration fluid than during pressure build-up. The pressure chamber  120  may be also be substantially empty of high salt concentration fluid (see  FIG.  1   a   ). 
     For example, during filling of the pressure chamber  120  (see  FIG.  1   b   ) after it has been at least partially emptied (see  FIG.  1   d   ), the pressure may be as low as 1 MPa or less, 100 kPa or less, or even 1.0 kPa or less. Meanwhile, a maximum pressure achieved within the pressure chamber  120  during pressure build-up by fluid crossing the membrane (see  FIG.  1   c   ) may be at least 0.3 MPa, at least 1.3 MPa, at least 3 MPa. or even at least 4 MPa. 
     The cycle of filling and emptying the pressure chamber  120  shown throughout  FIGS.  1   a  to  1   d    may be performed at least 2 times per hour, more preferably at least 10 times per hour, more preferably at least 20 times per hour, and even more preferably at least 60 times per hour during generation of power by the motor  100 . The at least one inlet  130  may be configured such that the pressure chamber  120  may be sufficiently replenished with new high salt concentration fluid quickly, e.g., within less than 3 minutes, less than 2 minutes, less than 1 minute, or even less than 0.5 minutes after it has been at least partially emptied (e.g., at least 30%, at least 50%, or at least 75% when compared to the volume of high salt concentration fluid during pressure build-up) or completely emptied. 
     As further shown in  FIGS.  1   a  to  1   d   , the at least one second outlet  144  may comprise a valve  145 . This valve  145  may also be referred to as a second pressure chamber outlet valve. The second pressure chamber outlet valve  145  valve may be opened to emit and/or drain fluid from the pressure chamber  120  once sufficient pressure has been built up. The flow emitted from the pressure chamber  120  through the second pressure chamber outlet valve  145  may then be used to perform work (e.g., via the turbine  160 ), see  FIG.  1   c   . The second pressure chamber outlet valve  145  may be intermittently opened and closed, for example at least once during each filling and emptying cycle of the pressure chamber  120 . In some examples, an intermittent opening/closing may comprise opening and closing the valve  145  more than once during each cycle, e.g. up to 10 or even 100 times. 
     The second pressure chamber outlet valve  145  may be configured to automatically open once a predetermined pressure in the pressure chamber  120  is reached. The valve may be fully mechanical for this purpose. Alternatively or additionally, one or more pressure sensors (not shown) may be provided within the pressure chamber  120  in order to measure whether the predetermined pressure is reached, upon which the valve may be opened (e.g., by an electrical control unit). The second pressure chamber outlet valve  145  may further be configured as a non-return valve in order to prevent backflow into the pressure chamber  120 . e.g., from the turbine  160  and/or from an accumulator. Such accumulator is discussed with reference to  FIG.  4    in more detail below, but the skilled reader will appreciate that it may also be employed in connection with the arrangement shown in  FIGS.  1   a  to  1   d    and  3 . 
     As shown in  FIGS.  1   a  to  1   d   , the second pressure chamber outlet valve  145  may be closed during filling of the pressure chamber  120  (see  FIG.  1   b   ) and/or during the emptying of the pressure chamber  120  (see  FIG.  1   d   ). 
     While  FIGS.  1   a  to  1   d    show the at least one first outlet  140  and the at least one second outlet  144  of the pressure chamber  120  being provided at two different locations, it will be appreciated that both the first and the second outlet could be provided via a common duct (e.g., via a common outflow port). Such configuration is shown in an exemplary manner in  FIG.  3   , but may also be used in connection with the arrangement shown in  FIGS.  1   a  to  1   d    and  3 . 
       FIG.  2    illustrates an alternative example of the method and motor. The motor  200  comprises a supply chamber  210 , a pressure chamber  220 , and a membrane  250  for separating fluid in the supply chamber  210  from fluid in the pressure chamber  220  but enabling exchange of at least one solute therebetween. The pressure chamber  220  is provided with an inlet  230  (exemplified here as an inflow port  230 ) and an outlet  240  (exemplified here as an inflow port  240 ). 
     In  FIG.  2   a   , high salt concentration fluid (e.g., salt water) is flowed into the pressure chamber  220  through the inlet  230  (e.g., through the inflow port). The outlet  240  (e.g., the outflow port) is closed and/or sealed. The supply chamber  210  as illustrated surrounds the pressure chamber  220  and is separated from the pressure chamber  220  by the osmotic membrane  250 . However, the supply chamber  210  may alternatively be placed merely adjacent to the pressure chamber  220 . 
     In this configuration the motor also comprises a piston  270  positioned within the pressure chamber  220  and being slidable therewithin. In the configuration of the motor  200  shown in  FIG.  2   a   , the piston  270  is proximate to the inlet  230  as only a small volume of salt water is provided within the pressure chamber  220 . 
     As shown in  FIG.  2   b   , fresh water is flowed into the supply chamber  210  while the inlet  230  (e.g. inflow port) and the outlet  240  (e.g. outflow port) are reduced in flow capacity or completely sealed. Due to the osmotic gradient across the membrane  250 , water flows from the supply chamber  210  into the pressure chamber  220  by traversing the osmotic membrane  250 . As more water enters the pressure chamber  220 , the pressure within the pressure chamber  220  rises. In contrast to the method shown in  FIG.  1   , the pressure chamber  220  has a variable volume in that the piston  270  may be moved by the liquid in the pressure chamber  220  in order to increase the volume within the pressure chamber  220 . 
     In subsequent steps, which are analogous to those depicted in  FIG.  1   , the fluid within the pressure chamber  220  can subsequently be drained through the outlet  240  (e.g. outflow port) and the piston  270  can be returned to its initial position. The piston  270  may be moved in this circumstance either by being pulled along by a sudden drop in pressure within the pressure chamber  220 , by being biased toward the initial configuration (e.g., by a spring and/or gravity), or through the momentum of a rotating element in connection with the piston  270  which drives the piston  270  forward again. The repeated motion of the piston  270  can therefore be used to perform work. 
     In this configuration the separation of pressure chamber  220  filling and the pressure build-up phases of the motor is performed, for example, by draining the supply chamber  210  before or while the pressure chamber  220  is filled. Thus, filling of the pressure chamber  220  is not performed against an existing pressure. The supply chamber  210  may be provided with one or more inlets and/or one or more outlets for filling and emptying the supply chamber  210  (not shown). The one or more supply chamber inlets and/or the one or more supply chamber outlets may each be provided with a respective valve (not shown). 
     As mentioned for the embodiment of  FIGS.  1   a  to  1   d    above, it is preferred to fill the pressure chamber  220  (see  FIG.  2   a   ) while the pressure therein is lower than the pressure achieved during pressure build-up (see  FIG.  2   b   ). Preferably, the pressure chamber  220  is at least partially emptied for this purpose. For example, filling of the pressure chamber  220  may be performed (e.g., begin) when the pressure chamber  220  contains at least 30% less volume of high salt concentration fluid than during pressure build-up, at least 50% less volume of high salt concentration fluid than during pressure build-up, or at least 75% less volume of high salt concentration fluid than during pressure build-up. The pressure chamber  220  may be also be substantially empty of high salt concentration fluid. 
     For example, during filling of the pressure chamber  220  (see  FIG.  2   a   ) after it has been at least partially emptied, the pressure may be as low as 1 MPa or less, 100 kPa or less, or even 1.0 kPa or less. Meanwhile, a maximum pressure achieved within the pressure chamber  120  during pressure build-up by fluid crossing the membrane (see  FIG.  2   b   ) may be at least 0.3 MPa, at least 1.3 MPa, at least 3 MPa, or even at least 4 MPa. 
     As further mentioned above, the cycle of filling and emptying the pressure chamber  220  may be performed at least 2 times per hour, more preferably at least 10 times per hour, more preferably at least 20 times per hour, and even more preferably at least 60 times per hour during operation of the motor  200  (e.g., during generation of power). The at least one inlet  230  may be configured such that the pressure chamber  220  may be sufficiently replenished with new high salt concentration fluid quickly. e.g., within less than 3 minutes, less than 2 minutes, less than 1 minute, or even less than 0.5 minutes after it has been at least partially emptied (e.g., at least 30%, at least 50%, or at least 75% when compared to the volume of high salt concentration fluid during pressure build-up) or completely emptied. 
     Turning back to  FIGS.  2   a  and  2   b   , it is shown that the inlet  230  may be provided with a pressure chamber inlet valve  231 . The pressure chamber inlet valve  231  may be opened for filling the pressure chamber  230  (see  FIG.  2   a   ). The pressure chamber inlet valve  231  may be closed and/or sealed during pressure build up (see  FIG.  2   b   ). As such, the pressure chamber inlet valve  231  may be intermittently opened and closed during generation of power by the motor  200 , e.g. at least 2 times per hour, more preferably at least 10 times per hour, more preferably at least 20 times per hour, and even more preferably at least 60 times per hour. 
     The outlet  240  may be provided with a pressure chamber outlet valve  241 . The pressure chamber outlet valve  241  may be closed and/or sealed during filling of the pressure chamber  230  (see  FIG.  2   a   ). The pressure chamber outlet valve  241  may be closed and/or sealed during pressure build up in the pressure chamber  230  (see  FIG.  2   b   ). The pressure chamber outlet valve  241  may be opened during emptying of the pressure chamber  220  (not shown). As such, the pressure chamber outlet valve  241  may be intermittently opened and closed during generation of power by the motor  200 , e.g. at least 2 times per hour, more preferably at least 10 times per hour, more preferably at least 20 times per hour, and even more preferably at least 60 times per hour. The pressure chamber outlet valve  241  may be closed when the pressure chamber inlet valve  231  is opened, in particular during filling of the pressure chamber  220 . 
       FIG.  3    illustrates another example configuration of a motor  300  with a supply chamber  310 , a pressure chamber  320 , and a membrane  350 . The pressure chamber  320  is provided with an inlet  330  (exemplified here as an inflow port  330 ) and an outlet  344  (exemplified here as an outlet port  344 ). 
     As shown in  FIG.  3   , the supply chamber  310  may further be provided with an inlet  360  (exemplified as an inflow port  360 ) and an outlet  370  (exemplified as an outflow port  370 ). As has been previously mentioned, the supply chamber  310  may operate in either a constant flow capacity, wherein a supply of low salt concentration fluid is continuously flowed into the supply chamber  310 , or in step-wise manner, wherein low salt concentration fluid is flowed in, stored for the pressure build-up phase of the pressure chamber, and then replenished for another cycle. It will be appreciated that this concept is equally applicable to the embodiments previously described. Therefore, also the supply chambers  110  and  220  may be provided with such an inlet and/or such an outlet. 
     In the configuration shown in  FIG.  3   , the motor  300  also comprises an osmotic barrier  380 , which is reversibly positionable between the supply chamber  310  and the pressure chamber  320 . The osmotic barrier  380  may be positioned on either side of the membrane  350  or even within portions of the membrane  350 . Importantly, the osmotic barrier  380  halts or substantially reduces the flow of liquid from the supply chamber  310  to the pressure chamber  320 . In this sense, an osmotic barrier  380  may be particularly advantageous when a constant flow of low salt concentration fluid is provided in the supply chamber  310 , as this would prevent undesired transmission of fluids across the membrane  350  during non-pressure build up steps of the motor  300 . However, such osmotic barrier  380  may be provided in any of the motors discussed herein, also those described with reference to  FIGS.  1 ,  2  and  4   . 
     As also depicted in  FIG.  3   , the outlet port  344  may be combined with and/or include an overpressure and/or non-return valve  345 . The overpressure and/or non-return valve  345  has a set pressure value upon which it opens and allows fluid to pass through to perform work. In this example a turbine  360  is depicted but any analogous system may be used for performing work. Any such system for performing work may also be combined with an accumulator, as described hereinafter. 
     As shown in  FIG.  3    the outlet  344  may provide a first outlet  346  towards turbine  360  and a second outlet  347 , which may be provided as an additional exit. The second outlet  347  may be formed by or provided with a valve  348  or any equivalent. The second outlet  347  allows to drain fluid from the pressure chamber  320  that is not intended to be used for performing work. In other words, fluid draining from the pressure chamber  320  via the second outlet  347  bypasses work harvesting and power generation (e.g., bypasses the turbine  360 ). 
     Furthermore depicted in  FIG.  3    is the outlet  370  (exemplified here by outflow port  370 ) which allows to drain the fresh water. As the fresh water may contain a low concentration of salt and just the water part is diffusing through the membrane the salt concentration is rising in the fresh water during operation and therefore it might be necessary to reduce the salt content of the fresh water in the supply chamber  310  by draining the water from time to time. 
       FIG.  4    demonstrates a further example of an osmotic motor  400 . Therein an osmotic membrane element and the fresh water supply chamber may be formed as one unit, which is indicated with reference numeral  410  in  FIG.  4   . Examples of such commercially available units are FilmTec™ SW30 membranes from DuPont de Nemours, Inc, in combination with an appropriate holder. 
     The pressure chamber  450 , also known as the salt water reservoir, holds the higher salt concentration water. Osmosis then takes place across each osmotic membrane element which is located in between the respective supply chamber and the pressure chamber  450 . The fresh water is supplied at  401 . The salt water is supplied at  402 . The salt water may be supplied into a salt water reservoir  420  for instant replenishment of the salt water in the pressure chamber  450 . The salt water reservoir  420  may be located above the pressure chamber  450 . 
     As further shown in  FIG.  4   , any of the motors described herein may further include an accumulator  470  which is placed in the flow path between the pressure chamber  450  and the generator  460  (e.g., a turbine). The accumulator  470  serves to build up and maintain a certain level of pressure in the outflow from the pressure chamber  420  (i.e., in the flow supplied to the generator  460 ). In some cases the accumulator  470  may aid in providing adequate flow pressure to the generator  460  such that it may continue performing work even in between pressure build-up phases within the pressure chamber  450 . 
     The accumulator  470  is, in particular, at least one hydraulic accumulator. The accumulator  470  is interposed between the pressure chamber  450  and the turbine and/or generator  460 . 
     Another potentially useful configuration of any of the motors discussed herein is to provide the liquid outlet such that liquid leaving the pressure chamber  120 ,  220 ,  320 ,  450  is aided in the flow direction by gravity. In this way, not only the phase of performing work, but additionally the draining of the pressure chamber  120 ,  220 ,  320 ,  450  may be performed with greater energy efficiency. 
     In addition to having a single pressure chamber  120 ,  220 ,  320 ,  450 , as with the examples described above, the motor/system may also comprise a plurality of pressure chambers  120 ,  220 ,  320 ,  450 , which may be operatively connected to the one or more supply chambers via the one osmotic membrane or several or a corresponding number of osmotic membrane elements. 
     For example, the plurality of pressure chambers enables an operation mode in which every few seconds a new cycle starts. 
     It is also an aspect of the present invention that the system comprises a plurality of turbines and/or generators  460 . For example, the number of turbines/generators  460  that produce current, may be varied according to the demand for current. 
     The method described above may be adapted to the motor with a plurality of pressure chambers  120 ,  220 ,  320 ,  450 . For example, the method steps described herein may be applied to any of the plurality of pressure chambers  120 ,  220 ,  320 ,  450 , alone or in parallel with other pressure chambers  120 ,  220 ,  320 ,  450  of the plurality of pressure chambers  120 ,  220 ,  320 ,  450 . If the method steps are applied to several pressure chambers  120 ,  220 ,  320 ,  450 , the method steps applied to one pressure chamber  120 ,  220 ,  320 ,  450  may be shifted in time as compared to one or several or all other pressure chambers  120 ,  220 ,  320 ,  450 . 
     While a wide range of osmotic membranes are commercially available, the selection of the membrane may influence the efficiency and cost of providing the inventive osmotic motor. Generally, it is advantageous to provide an osmotic membrane which provides a stabilized salt rejection of at least 95%. For greater efficiency, a stabilized salt rejection of at least 98%, or even more preferably at least 99% is preferred. The values for stabilized salt rejection are measured when the osmotic membrane is subjected to a test salt concentration of 32,000 mg/L NaCl at 25° C. with an applied pressure of 5.5 MPa, and with 10% recovery. However, it is acknowledged that with increasing quality of the osmotic membrane, greater costs may be incurred, thus it is foreseen that the ultimate selection of the osmotic membrane is based on the specific requirements of the osmotic motor. 
     Another important aspect of providing energy utilizing one of the osmotic motors as described are the relative pressures utilized during different phases of operation. In the closed configuration, wherein pressure is built up within the pressure chamber  450 , the pressure chamber  450  may be configured to operate with a pressure achieved being at least 1 MPa (gauge), preferably at least 2 MPa (gauge), more preferably at least 2.3 MPa (gauge). This pressure may be referred to as the maximum pressure achieved by the system. Greater maximum pressure within the pressure chamber  450  allows for a larger extraction of work from the system. 
     In contrast, in the open configuration, wherein pressure within the pressure chamber  450  is reduced and the pressure chamber  450  may be drained may achieve a pressure within the pressure chamber being at most 1 MPa (gauge), preferably at most 100 kPa (gauge), more preferably at most 1.0 kPa (gauge). This pressure may be referred to as the minimum pressure achieved by the system. It is also envisioned that in the open configuration of operation the pressure within the pressure chamber  450  may be substantially equal to local atmospheric pressure. 
     The osmotic motors described above are envisioned to provide at least 100 Watts of energy, preferably at least 1 Kilowatt, and more preferably at least 1 Megawatt. Due to the ease of setup and ample availability of fresh water/salt water mixing locations, multiple osmotic motor systems may be positioned together and operated either in parallel or alternating, such that continuous energy generation is performed. 
     While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and non-restrictive; the invention is thus not limited to the disclosed embodiments. Variations to the disclosed embodiments can be understood and effected by those skilled in the art and practicing the described invention, from a study of the drawings, the disclosure, and the appended claims. In the aspects and claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality and may mean “at least one”. 
     As far as reference is made to a “closing” or “sealing” of an inlet or outlet herein, a fluid tight closing is generally preferred. It should be noted, however, that a (partial) closing providing a sufficient restriction of flow through the respective inlet or outlet may be sufficient for achieving the effects described therein in some cases. Therefore, also a partial sealing or closing may be encompassed. 
     The following are preferred aspects of the invention: 
     1. A method for performing work using osmosis comprising the steps of
         i) providing a motor comprising a supply chamber, a pressure chamber comprising at least one inlet (e.g., an inflow port) and at least one outlet (e.g., an outflow port), and a membrane permeable to fluid, preferably water, and at least partially impermeable to salt ions, the membrane enabling fluid communication between the supply chamber and the pressure chamber;   ii) providing low salt concentration fluid, preferably low salt concentration water, in the supply chamber;   iii) closing and/or sealing the outlet of the pressure chamber,   iv) flowing high salt concentration fluid, preferably high salt concentration water, into the pressure chamber,   v) allowing the pressure within the pressure chamber to increase as fluid crosses the membrane into the pressure chamber;   vi) using the increased pressure within the pressure chamber to perform work;   vii) opening the outlet of the pressure chamber and allowing the fluid to drain from the pressure chamber and the pressure in the pressure chamber to decrease;   viii) repeating steps iii-vii.       

     2. The method according to aspect 1, wherein the pressure chamber has a fixed volume and wherein the motor further comprises a turbine, wherein step vi comprises fluid flowing out from the pressure chamber due to increased pressure and operating the turbine to perform work. 
     3. The method according to aspect 1, wherein the pressure chamber has a variable volume. 
     4. The method according to aspect 3, wherein the pressure chamber further comprises a piston, wherein movement of the piston due to increased pressure within the pressure chamber performs work. 
     5. The method according to any one of the previous aspects, wherein the outlet further comprises a valve, wherein the method further comprises the step of
         opening the valve to relieve at least a portion of the pressure within the pressure chamber, wherein flow of fluid emitted from the valve is used to perform work.       

     6. The method according to aspect 14, wherein the valve is an overpressure and/or a non-return valve. 
     7. The method according to any one of the previous aspects, wherein the motor further comprises an osmotic barrier configured to reversibly block the exchange of fluid between the supply chamber and the pressure chamber and the method further comprising the steps of
         positioning the osmotic barrier over the membrane such that fluid flow between the supply chamber the pressure chamber is prevented; and   removing the osmotic barrier after using the increased pressure to perform work.       

     8. The method according to any one of the previous aspects, wherein during filling of the pressure chamber a maximum pressure achieved within the pressure chamber is at least 3 MPa, preferably at least 5 MPa, and more preferably at least 7 MPa. 
     9. The method according to any one of the previous aspects, wherein flowing low salt concentration fluid into the supply chamber is performed while the pressure chamber is either empty or at a pressure lower than 1 MPa, preferably lower than 100 kPa, more preferably lower than 1.0 kPa. 
     10. The method according to any one of the previous aspects, further comprising the step of
         sealing the inlet of the pressure chamber after flowing high salt concentration fluid into the pressure chamber.       

     11. The method according to any one of the previous aspects, wherein the low salt concentration fluid has a salt concentration below 5 parts per thousand, preferably below 1 part per thousand, more preferably below 0.5 parts per thousand. 
     12. The method according to any one of the previous aspects, wherein the high salt concentration fluid has a salt concentration above 5 parts per thousand, preferably above 20 parts per thousand, more preferably above 30 parts per thousand. 
     13. The method according to any one of the previous aspects, wherein the high salt concentration fluid has a salt concentration at least 100×higher than the low salt concentration fluid, preferably at least 500×higher, and more preferably at least 1000×higher. 
     14. The method according to any one of the previous aspects, wherein a naturally occurring current or pressure is employed for flowing the low salt concentration fluid into the supply chamber and/or the high salt concentration fluid into the pressure chamber. 
     15. The method according to any one of the previous aspects, wherein the low salt concentration fluid flows into the supply chamber by gravity and/or wherein the high salt concentration fluid flows into the pressure chamber by gravity. 
     16. The method according to any one of the previous aspects, wherein the fluid is drained from the pressure chamber by gravity. 
     17. The method according to any one of the previous aspects, wherein the high salt concentration fluid is seawater, preferably wherein the motor is installed at the estuary of a river. 
     18. The method according to any one of the previous aspects, wherein the high salt concentration fluid is wastewater or brine, wherein the brine preferably results from a desalination process, such as reverse osmosis, or a condensation process. 
     19. The method according to any one of the previous aspects, wherein the low salt concentration fluid is seawater. 
     20. The method according to any one of the previous aspects, wherein the pressure in the pressure chamber decreases as the fluid from the pressure chamber is drained. 
     21. The method according to any one of the previous aspects, wherein the pressure in the pressure chamber decreases as work is performed. 
     22. A motor comprising:
         a supply chamber configured to receive a supply of low salt concentration fluid, preferably low salt concentration water.   a pressure chamber configured to receive a supply of high salt concentration fluid, preferably high salt concentration water, the pressure chamber further comprising an inlet (e.g., an inflow port) and a sealable and/or closeable outlet (e.g., an outflow port);   a membrane permeable to fluid molecules and at least partially impermeable to salt ions, the membrane enabling fluid communication between the supply chamber and the pressure chamber,   wherein the pressure chamber is configured to alternate between a closed configuration, wherein the outlet is sealed and pressure builds within the pressure chamber, and an open configuration, in which the outlet is open and pressure within the pressure chamber reduces.       

     23. The motor of aspect 22, wherein the pressure chamber has a fixed volume and wherein the motor further comprises a turbine in fluid connection with the pressure chamber. 
     24. The motor of aspect 22, wherein the pressure chamber has a variable volume, preferably wherein the pressure chamber further comprises an expansion portion configured to allow the pressure chamber to reversibly increase in volume. 
     25. The motor of aspect 24, wherein the expansion portion is a piston. 
     26. The motor of any one of aspects 22 to 25, further comprising an osmotic barrier configured to reversibly block the exchange of fluid between the supply chamber and the pressure chamber through the membrane. 
     27. The motor of any one of aspects 22 to 26, wherein the pressure chamber further comprises a valve configured to release fluid from the pressure chamber, preferably wherein the valve is an overpressure valve. 
     28. The motor of any one of aspects 22 to 27, wherein the membrane provides a stabilized salt rejection of at least 95%, more preferably at least 98%, and even more preferably at least 99% when subjected to a test salt concentration of 32,000 mg/L NaCl at 25° C. with an applied pressure of 5.5 MPa, and with 10% recovery. 
     29. The motor of any one of aspects 22 to 28, wherein the supply chamber further comprises an inlet (e.g., an inlet port) and an outlet (e.g., an outlet port), preferably wherein the inlet and/or the outlet is closeable and/or sealable. 
     30. The motor of any one of aspects 22 to 29, wherein the motor is configured to provide at least 0.1 Watts of energy, preferably at least 0.5 Watts, and more preferably at least 1 Watt. 
     31. The motor of any one of aspects 22 to 30, wherein in the closed configuration a maximum pressure achieved within the pressure chamber being at least 1 MPa, preferably at least 2 MPa, more preferably at least 2.3 MPa. 
     32. The motor of any one of aspects 22 to 31, wherein in the open configuration a minimum pressure achieved within the pressure chamber being at most 1 MPa, preferably at most 100 kPa, more preferably at most 1.0 kPa.