Field of Technology

The present disclosure relates appliances in general to the use of intermittent energy source for powering appliances, and in particular to the use of off grid, solar driven appliances such as pumps.

Background

Water production on remote wells for plants' irrigation, livestock and other applications have long been problematic for low production rates of solar pumping systems on deep wells and failure rates along with the maintenance costs and access challenges of windmill water production. Many within the industry have resorted to point of use generators, which require repeated trips to the remote well site to fuel and start the generator to pump the required water to satisfy water consumption needs. Solar power has been found as an effective answer to this challenge, but with solar powered water pumping systems, flow rates on deep water wells are typically very low when compared to the flow rates of a standard deep well pump supported by AC electrical power. Solar energy production is dependent on exposure to sunlight. Water production capabilities will be decreased or can cease in long times of decreased or no sunlight. A typical system for using energy derived from the solar source for deep well water pumps includes a pump, a motor, a motor driver, a controller, a transmission, and a solar panel array, optionally with grid connection (e.g. for backup purposes).

Most of the available systems utilize centrifugal type of pumps, where one or more sets of impellers rotate at a certain RPM (generally in the range of 2000-3000 RPM) in order to pump water efficiently. However, the optimal efficiency curve of a centrifugal pump is further limited by several factors such as well depth, impeller diameter and impeller pitch, which in return reguire the use of different number of impellers for each depth range, as well as special impeller design for each diameter and flow rate. Consequently, centrifugal pump efficiency is considered to be in the range of 50-65%.

A further complication associated with these systems is the fact that "off grid" solar powered systems suffer from changes at the level of retrievable solar energy, changes that are caused due to changes in the time of the day and the date of the year (i.e. changes of the relative sun angle) , as well as due to other factors such as: cloudiness, dust, etc. Furthermore, since centrifugal pumps maintain their maximum efficiency over a narrow range of RPM (e.g. to pump water), that constraint presents a problem at time of low irradiation periods where very small amount of water is pumped to no water at all. This in turn causes a typical efficiency loss of 15- 25%.

In order to enable a centrifugal system to operate under the various constraints described above, one common solution is to manufacture and store several pump sizes to enable providing an efficient system that is able to operate under specific pre-defined operating conditions. However, any predetermined centrifugal pump configuration sacrifices the operational efficiency under varying operating conditions, depending on how far are the actual operating conditions from the designed operating conditions .

Windmill water production is also a common solution to water production issues on remote water well sites. Typically, windmills are very wasteful when producing water. Unless turned off by an operator, windmills pump water as long as wind is present. Once the storage vessel is full, excess water generally spills out onto the ground wasting the water and the operating efforts of the windmill. Windmills also tend to be expensive and difficult to maintain, often involving risky and hazardous conditions to the technician performing maintenance .

Use of a diesel electric generator, can overall present a very expensive approach to water production. A generator typically requires an operator making a trip to the site with a container of fuel, fueling the generator, and then starting it along with the deep well pump in the well. Obviously, the operator would not wait the several hours that it takes the generator to consume the fuel, but would leave the site understanding that when the generator has consumed all of the fuel, it will stop running. Allowing the generator to run out of fuel under an electrical load in this manner is extremely hazardous to both the generator and the deep well pump, often shortening the operating life of each of these devices. This practice further can lead to expensive repairs or early replacements of either the generator or the well pump.

Summary of the Disclosure

It is an object of the present disclosure to provide an improved system for retrieving water from a well (e.g. for irrigation, livestock) using renewable energy, such as solar energy, as the sole source for energy.

It is still another object of the invention to provide a pumping system for retrieving water from a well, adapted for use in deep wells (e.g. in the range of 50 to 200 m deep) having a relatively reduced diameter (e.g. about 150 mm diameter) in order to fit narrow wells.

It is yet another object of the invention to provide a deep well pumping system that requires very little maintenance .

It is another object of the invention to provide a pumping system for retrieving water from a well, comprising a temporary energy storage means that improves the energy efficiency of the system.

Other objects of the invention will become apparent as the description of the invention proceeds.

According to a first embodiment of the disclosure there is provided a system for retrieving water from a water well, comprising:

a collector operative to collect renewable energy (e.g. solar, wind, etc.) and convert it into electrical energy;

a positive displacement pump comprising a servo motor that is energized by said electrical power, adapted to be submersed in a well and to retrieve water therefrom;

an electronic controller adapted to match the electrical energy being retrieved from the renewable source with the power being consumed by the positive displacement pump, preferably, while maintaining the highest possible efficiency rate under various operating conditions ;

an egress means adapted to convey water retrieved from the well.

Unlike the pumps that are typically implemented in prior art systems for pumping water from wells that rely on the use of centrifugal pumps, the inventors of the present invention were surprisingly able to achieve a considerably better performance by using the positive displacement pump described herein.

According to another embodiment, the system further comprising a water storage means for holding water retrieved from the well.

In accordance with another embodiment, the servo motor is a rotary motor.

By yet another embodiment, the pump comprises a rotary servo motor directly coupled to a ball screw nut flange.

According to another embodiment, the pump is a twin rod pump that is detachably connected to the ball screw nut flange.

According to still another embodiment, the collector is a solar collector having at least one solar collecting unit directed to intercept sun irradiation and to convert solar energy captured thereby to electrical energy.

In accordance with another embodiment, the positive displacement pump is a double acting piston pump.

By yet another embodiment, the positive displacement pump is a single acting piston pump.

According to still another embodiment, the single acting positive displacement piston pump further comprises electric storage adapted to store surplus of electrical energy for use while operating the pump during a time period that is essentially equal to a time period required for the pump to complete its movement once, while being refilled with water (e.g. in the downwardly direction) .

In accordance with another embodiment, the stored electrical energy is consumed while the pump moves while pumping the water (e.g. in the upwardly direction).

According to another embodiment, the electric storage is a capacitor (e.g. about 0.5 Farad at 65 volt). Brief Description of the Drawings

For a more complete understanding of the present invention, reference is now made to the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 demonstrates an example of a pump that comprises a rotary servo frameless motor directly coupled to a ball screw, for use in accordance with an embodiment of the present invention;

FIG. 2 demonstrates an example of a pump that is a twin rod pump, detachably connected to the ball screw nut flange .

FIG. 3 demonstrates an example of a 3D view of a tubular linear motor used in accordance with an embodiment of the present invention;

FIG. 4 illustrates a tubular linear motor, directly coupled to a single acting cylinder pump; and

FIG. 5 illustrates a tubular linear motor, directly coupled to a reciprocating cylinder pump.

Detailed Description of the Disclosure

In the following description, for the purposes of explanation, numerous specific details are set forth in order to provide a better understanding of the present invention by way of examples. It should be apparent, however, that the present invention may be practiced without these specific details.

In order to increase the total efficiency and efficiency range of the pump used according to the present invention, a positive displacement piston pump is selected (preferably but not necessarily a double acting pump is used. This type of pump typically comprises a cylinder and a piston/plunger that travels back and forth within the cylinder. The pump is equipped with two check valves that open and close in a synchronized cycle thereby allowing the pumping action. The typical efficiency of such a positive displacement piston pump is 90-95%.

In the case of single acting reciprocating piston pump, water is pumped only in one of the stroke directions. Using single acting reciprocating piston simplifies the structure of the pump and reduces the dynamic hydraulic losses of its water passages. It requires a longer or faster stroke than in double acting reciprocating pump.

Unlike the single acting reciprocating piston pumps, double acting reciprocating piston pumps pump water during both up and down strokes. The advantages are shorter pump design and more steady flow.

There are many electro-mechanical motor-transmission combinations that may be used for driving a water ump. The driving (motor) types may include: wind mills, water mills, AC/DC electrical rotating motors foot and hand cranks. The transmission types for such motors may include gear drives of various types, chain drives, belt drives and any combination thereof.

Fig. 1 exemplifies a an assembly (5) comprising a frameless rotary motor associated with a double acting reciprocating cylinder pump (10) according to one embodiment of the present disclosure. The frameless motor comprises a magnet (rotor) assembly (20) , a coil (stator) assembly (30), a hall assembly (40) and power cables (50) . The motor typically does not have a shaft nor bearings, so that the rotary servo motor is directly coupled to a ball screw (60), thereby operating the pump's piston (70) via a mechanical transmission.

FIG. 2 illustrates a twin rods arrangement 100 of a pump detachably connected to the ball screw nut flange, having twin rods 110, and ball screw nuts 120. This arrangement, has the advantage of reducing the overall length of the pump being used.

According to another embodiment of the present disclosure, the pump comprises a linear motor. A linear motor as exemplified in Fig. 3, is a DC servo motor that comprises a high force, permanent magnet rod or bar made of north (320) and south, high power permanent magnets (310) surrounded by a stator primary (330) which includes a set of coils (340) next to or surrounding the rod or bar, leaving a small air gap (350) there-between . By commutating the current passing through the coils, an electromagnetic field is generated, which in turn forces the rod or bar to move in one or other direction along the central axis of the motor. FIG. 3 demonstrates an example of a 3D view of a linear (tubular) motor.

According to another embodiment of the present disclosure, a linear motor is directly connected to the piston pump rod without any transmission there-between. One of the major advantages of this embodiment, is, that it completely eliminates the need for transmission, thereby eliminates transmission losses of about 20-30%.

Figs. 4 and 5 exemplify such possible arrangements, where FIG. 4 illustrates a tubular linear motor, directly coupled to a double acting cylinder pump, whereas FIG. 5 illustrates a tubular linear motor, directly coupled to a reciprocating cylinder pump. The arrangement shown in this FIG. 5 comprises an inlet check valve (510), an outlet check valve (520), a liquid upper chamber (530), a liquid piston (540), a magnet rod (550), coils (560), a liquid lower chamber (570) and a piston (580) .

The use of a single acting piston pump requires that during the pumping (up) stroke, the system would use a certain current while during the pump refill (down) stroke, the system would use a substantially less current, about one quarter of the current required for the pumping action. Typically, solar panel pumping systems do not include (battery) storage due to price and maintenance limitations. Thus, using a single acting cylinder pump without a storage means (e.g. battery) would lead to about 30-40% of energy loss.

According to another embodiment of the present disclosure, the system further comprises a capacitor (e.g. a relatively large capacitor of about 0.5 Farad at 65 volt) , that is used for a cyclic, temporary energy storage during the pump refill stroke and utilizes the stored energy during the pumping stroke of the respective cycle. The use of the capacitor in such a manner will save about 30-40% of the energy that would have otherwise been lost. In addition, it also increases the available current for the pumping stroke without adding solar panels by using current derived from converting solar energy into current, together with the current retrieved from the capacitor in which the current that was not consumed in the preceding down (refill) stroke, has been stored. As will be appreciated by those skilled in the art, the parameters exemplified above, such as those that relate to size, voltage, cycle frequency of the capacitor, etc. are provided as an example only, and any other applicable values for these parameters may be used while implementing the present invention, all without departing from the scope of the invention.

The system provided by the present invention comprises a controller adapted to match the electrical energy being retrieved from the renewable source with the power being consumed by the positive displacement pump while maintaining the highest possible efficiency rates, which is implemented according to an embodiment of the invention by using a servo control loop (a maximum power loop) . The system may further comprise a processor configured to provide a feedback that will be used to track the instantaneous maximum power point tracking (MPPT) by sensing the voltage drop between the boost and the motor drive. This loop is based on the solar panel characteristics, so that the voltage drops substantially when the power drawn by the system is higher than the instantaneously available power. One of the advantages of using the solution provided by the present invention is the ability to monitor and control both the boost and the drive as part of a single integral power loop rather than controlling the boost and the drive individually.

In the following table, Table 1, a comparison is provided between certain parameters that characterize different types of systems, which may be used for utilizing solar radiation as an energy source for pumping water.

Table 1 : Typical pumping systems parameters

In this disclosure, the term "comprising" is intended to have an open-ended meaning so that when a first element is stated as comprising a second element, the first element may also include one or more other elements that are not necessarily identified or described herein, or recited in the claims.

The present invention has been described using detailed descriptions of embodiments thereof that are provided by way of example and are not intended to limit the scope of the invention in any way. The described embodiments comprise different features, not all of which are required in all embodiments of the invention. Some embodiments of the present invention utilize only some of the features or possible combinations of the features. Variations of embodiments of the present invention that are described and embodiments of the present invention comprising different combinations of features noted in the described embodiments will occur to persons of the art. The scope of the invention is limited only by the following claims.