FIELD AND BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to a system for, and a method of, washing solar collectors.  
           [0002]    Solar collectors are commonly used for heating water or air in buildings. There are two types of solar heating, passive and active. Passive heating relies on architectural design to heat buildings. The site, structure, and materials of a building can all be utilized to maximize the heating effect of the sunlight falling on it, thereby lowering or even eliminating the fuel requirement. A well-insulated building with a large glass window facing south, for instance, can effectively trap heat on sunny days and reduce reliance on gas or oil or electricity. Entering sunlight warms the air and the solid surfaces in those rooms exposed to it, and this warmth is carried to other rooms in the building by natural convection. Interior finishes such as brick or tile are often incorporated into buildings to absorb the sunlight and reradiate the heat at night.  
           [0003]    In active heating, mechanical means are used to store, collect, and distribute solar energy in buildings in order to provide hot water or space heating. The sunlight falling on a collector panel of a building is converted to heat, which is transferred to a carrier fluid (usually a liquid, less commonly air) that is then pumped to a conversion, storage, and distribution system. In liquid-based systems, water (or less commonly glycol) is made to flow through tubes that are in contact with a flat-plate collector. The flow may be achieved by pumping, or by natural currents caused by the decreasing specific gravity of water with increasing temperature. The collector is a blackened metal plate that absorbs sunlight and is insulated on the front with layers of glass and air; the glass allows visible light to fall on the plate but traps the resulting heat, which is then transferred to the carrier fluid. Alternatively, the fluid may be pumped through an evacuated glass tube or a volume of space onto which a large volume of sunlight has been focused (and hence concentrated) by reflecting mirrors.  
           [0004]    After picking up heat from the collector, the carrier fluid is pumped down to an insulated storage tank, where it can be used immediately or stored for later use. The system can supply a home with hot water drawn from the storage tank, or, with the warmed water flowing through tubes in floors, walls and ceilings, the system can provide space heating. The storage tank allows water heated during sunny periods to be used at night or during cloudy days. If the carrier fluid contains antifreeze to keep it from freezing during cold weather, a heat exchanger is used to transfer the heat of the carrier fluid to water that can be used for domestic purposes. Residential heating systems using flat-plate collectors typically heat carrier fluids to temperatures between 65° C. and 90° C.  
           [0005]    The advantages of solar power are manifest: free, unlimited, non-polluting source of energy. However, active solar-energy systems such as those described above tend to be capital intensive with respect to heating systems utilizing conventional (usually fossil) fuels. In addition, the performance of solar-energy systems is heavily dependent on climatic conditions. As a result, solar-energy systems usually require a supplementary, conventional heating unit, which further increases the capital costs associated with such systems. Thus, in order to compete effectively with heating systems that utilize conventional (usually fossil) fuels, solar-energy systems must be sufficiently efficient to overcome such inherent drawbacks.  
           [0006]    One major cause of inefficiency in solar-energy units is the clouding of the solar panels with dust and sediment. The most important mode of heat transfer to the pipes is radiative heat transfer from the sun. Even a small amount of dust and the like, dispersed on the surface of the solar panel, can drastically reduce the energy radiated from the sun directly to the pipes in the solar panel. Moreover, in many climates in which solar energy has particular potential, there is substantially no rain over the entire hot season (as much as 6-8 months, or practically never in extreme arid climates), such that dirty solar collectors are not cleaned by rain. Even in many rainy areas, the rainwater itself leaves a residue on the solar collector surface, such that collector performance does not approach the maximal level.  
           [0007]    Finally, it must be emphasized that solar panels are generally mounted on a roof, preferably a sloped roof, making access for routine cleaning impractical, difficult, and often dangerous.  
           [0008]    It must be emphasized that no prior art for washing solar collection panels exist in the field, except the inconvenient, rather dangerous method of manual washing by a flexible hose.  
           [0009]    There is therefore a recognized need for, and it would be highly advantageous to have, a system for, and a method of, cleaning such solar panels, in which the cleaning is performed automatically, and in a simple and efficient manner.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention is a system for, and a method of automatic washing of solar collection panels from dust, sediment, and the like, which tend to accumulate over time. The solar collector washing system comprises: (a) a solar collector having a solar collecting surface, the collector disposed in an angled position; (b) a water pipe mounted substantially above the solar collecting surface, the water pipe having a plurality of holes distributed along a length of the pipe for distribution of water onto the solar collecting surface, and (c) a control mechanism, operatively connected to the pipe, for releasing the water supply.  
           [0011]    According to another aspect of the present invention there is provided a method of washing a solar collector comprising the steps of: (a) providing a system including: a water pipe substantially mounted substantially above a solar collecting surface, the water pipe having a plurality of holes distributed along a length of the pipe for distributing water on the solar collecting surface, the pipe connected to a water supply; a control mechanism for releasing a supply of water, and (b) releasing the supply of water onto a solar collecting surface via the pipe.  
           [0012]    According to further features in the described preferred embodiments, the control mechanism is designed and configured to operate according to a predetermined criterion.  
           [0013]    According to still further features in the described preferred embodiments, the control mechanism is an electrically activated control valve.  
           [0014]    According to still further features in the described preferred embodiments, the control mechanism is an electrically-controlled valve responsive to a microprocessing unit (MPU).  
           [0015]    According to still further features in the described preferred embodiments, the control mechanism is a hydro-mechanical unit.  
           [0016]    According to still further features in the described preferred embodiments, the hydro-mechanical unit includes: (a) a water tank having an inlet and an outlet; (b) a pivoted T-shaped element having a floating arm connected to the water tank by a pivot; and (c) a stopper arm making up a base of the T-shaped element and connected to the floating arm, the stopper arm having a detachably attached seal for blocking the outlet when the tank is in a filling state.  
           [0017]    According to still further features in the described preferred embodiments, the predetermined criterion includes a time-duration.  
           [0018]    According to still further features in the described preferred embodiments, the predetermined criterion is a time-interval.  
           [0019]    According to still further features in the described preferred embodiments, the predetermined criterion is a date.  
           [0020]    According to still further features in the described preferred embodiments, the solar collector washing system further comprises: (d) a timer for setting the predetermined criterion.  
           [0021]    According to still further features in the described preferred embodiments, the timer is a mechanical timing unit.  
           [0022]    According to still further features in the described preferred embodiments, the timer is an electrical timing unit.  
           [0023]    According to still further features in the described preferred embodiments, the timer is associated with a microprocessing unit (MPU).  
           [0024]    According to still further features in the described preferred embodiments, at least one of the holes is a nozzle.  
           [0025]    According to still further features in the described preferred embodiments, the inlet includes a drip-emitter.  
           [0026]    According to still further features in the described preferred embodiments, the drip-emitter is designed and configured to emit a substantially constant flow.  
           [0027]    According to still further features in the described preferred embodiments, the solar collector washing system further comprises a wiping unit including a wiper, the wiper contacting the solar collecting surface.  
           [0028]    According to still further features in the described preferred embodiments, the wiping unit is activated by the MPU.  
           [0029]    According to still further features in the described preferred embodiments, the method further comprises: (c) filling a water tank to a predetermined level to provide the supply.  
           [0030]    According to still further features in the described preferred embodiments, when the predetermined water level is attained, a floating arm in the tank is lifted, opening thereby an outlet in the tank through which the releasing the supply of water is effected. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0031]    The invention is herein described, by way of example only, with reference to the accompanying drawings. With specific reference now to the drawings in detail, it is stressed that the particulars shown are by way of example and for purposes of illustrative discussion of the preferred embodiments of the present invention only, and are presented in the cause of providing what is believed to be the most useful and readily understood description of the principles and conceptual aspects of the invention. In this regard, no attempt is made to show structural details of the invention in more detail than is necessary for a fundamental understanding of the invention, the description taken with the drawings making apparent to those skilled in the art how the several forms of the invention may be embodied in practice.  
         [0032]    In the drawings:  
         [0033]    [0033]FIG. 1 a  shows a system for washing solar collectors, according to the present invention, having an electric valve and an MPU;  
         [0034]    [0034]FIG. 1 b  is a schematic illustration of a water washing line according to the present invention, mounted above a solar collector;  
         [0035]    [0035]FIG. 2 illustrates a system for washing solar collectors having a hydro-mechanical control mechanism. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0036]    The present invention is a system for and a method of automatically cleaning of solar collection panels from dust, sediment, and the like, which tend to accumulate over time.  
         [0037]    The principles and operation of the system and method according to the present invention may be better understood with reference to the drawings and the accompanying description.  
         [0038]    Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of the components set forth in the following description or illustrated in the drawing. The invention is capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting.  
         [0039]    As used herein in the specification and in the claims section that follows, the term MPU refers to a microprocessor unit.  
         [0040]    Referring now to the drawings, FIG. 1 shows a system for washing solar collectors. The system includes a water washing line  50 , mounted above the uppermost edge of a solar collector  25 . Water washing line  50  is sufficiently long to wash the entire width of solar collector  25 . Holes  60 , disposed along the length of water washing line  50 , provide outlets for the water to flow on to surface  28  of solar collector  25 .  
         [0041]    One major cause of inefficiency in solar-energy units is the clouding of solar panels with dust, debris, sediment or deposits. Even a small amount of dust and the like, dispersed on the solar collection surface  28 , can drastically reduce the energy radiated from the sun directly to the pipes in the solar panel. Efficient washing is vital for proper functioning of the solar collector. In the system for, and the method of washing the solar collector  25  of this invention, water flowing down on the surface  28  of the angled collector  25  washes down the dust, debris and sediments accumulated on the surface  28  and also dissolves any soluble deposits, thus improving the energy efficiency of the solar collector.  
         [0042]    Various shapes are suitable for holes  60 , including round, oval, and rectangular geometries. The holes may also be slit shaped. According to a preferred embodiment, holes  60  are fitted with nozzles, for improved washing of solar collector surface  25 .  
         [0043]    Water washing line  50  is fed by water flowing from the main water system  85  through a feed line  10 , a manual valve  20 , installed for maintenance purposes, and an electrically activated valve  30 , which is normally closed. The feed line  10  can be connected to washing line  50  at an intermediate position. This requires washing line  50  to have two sealed ends  65 . Alternatively (not shown), feed line  10  can be connected to washing line  50  at one end of washing line  50 , with the distal end being sealed. Washing water is released by a control mechanism that opens electrically activated valve  30  according to a predetermined criterion, as will be described in further detail below.  
         [0044]    According to a further embodiment the holes  60  are nozzles that improve the distribution of the water on the collection surface  28 , thus improving the washing efficiency.  
         [0045]    In a preferred embodiment, electrically actuated valve  30  Is directly activated by a timer (mechanical or electric), or through a microprocessing unit (MPU)  40 , as well as other devices known to those skilled in the art, according to at least one predetermined criterion (e.g., time interval, date, etc.). The duration of the washing step can also be controlled using the above-mentioned devices according to a specified parameter (by sustaining valve  30  in an open position for a given amount of time or until achieving a given cumulative flow) and according to standard practice in the art. Electrically actuated valve  30  and MPU  40  are preferably designed to be operated by means of DC batteries or by a suitable AC/DC electric converter.  
         [0046]    In a preferred embodiment, the washing system further includes a wiping unit. The wiping unit includes a wiper  175 , a motor  165 , and an arm  170  connecting wiper  175  to motor  165 . Preferably, motor  165  operates at 24 V, and is operatively connected to MPU  40 , such that the wiping unit is activated solely during the duration of each washing period.  
         [0047]    [0047]FIG. 1 b  is a schematic illustration of water washing line  50  according to the present invention, mounted above a solar collector  25 . Solar collector  25  is mounted such that solar collection surface  28  is disposed at an angle, as is generally practiced in the art to absorb as much solar radiation as possible. This disposition at an angle is utilized by the present invention to enhance the washing effect along the downward slope  78  of solar collection surface  28 .  
         [0048]    According to another aspect of the present invention, provided in FIG. 2, water-washing line  50  is fed by a hydro-mechanical system  200 , which obviates the need for electrical components. Hydro-mechanical system  200  includes a water tank  100  with a capacity of at least one washing, typically 5-30 liters, according to the size of solar collector  25 , and the environmental conditions, washing frequency, etc.  
         [0049]    A pivoted, T-shaped element  150  having a floating arm  120  is connected to water tank  100  at a first end of the T by a pivot  80  that enables floating arm  120  to float according to the water level in water tank  100 . A stopper arm  140  making up the base of the T is connected to floating arm  120  by means of a pivot  70 . The movement of stopper arm  140  is substantially limited by a hollow, cylindrical guide  130  to a vertical up and down motion through guide  130 . In a down position, a seal  145  positioned at the base of stopper arm  140  closes an opening  105  at the bottom of water tank  100 . When water tank  100  has been filled to a requisite fill level, floating arm  120  is lifted by the water, thereby lifting stopper arm  140  and seal  145 , such that opening  105  at the bottom of water tank  100  is exposed. Consequently, water in water tank  100  drains into water washing line  50 , and flows through holes  60  disposed along the length of water washing line  50  and on to the surface of solar collector  25 , as described above.  
         [0050]    A water feed line  10  receiving water from the main water system  85  leads to water tank  100 . Preferably, water feed line  10  is equipped with manual maintenance valve  20 .A small opening  110  towards the end of water  20  feed line  10  allows water to slowly drip into water tank  100 , such that the fill time (which in this case determines the time interval between washings) for water tank  100  is slow, typically within the range of 2-30 days, depending on the application.  
         [0051]    Small opening  110  is preferably a standard, low-flow rate drip emitter. More preferably, small-opening  110  is a drip emitter having a flow rate that is substantially insensitive to water line pressure. An example of such a drip emitter is provided in U.S. Pat. No. 4,653,695 to Eckstein, which is incorporated by reference for all purposes as if fully set forth herein.  
         [0052]    As used herein and in the claims section that follows, the term “predetermined criterion” refers to a parameter, set in advance, that provides the basis for activating a valve (e.g., electrically actuated valve  30  and/or another releasing device, such that wash water for the solar collection surface is released. Without wishing to be limited by specific examples, a typical predetermined criterion is absolute time (i.e., date, date/hour/minute, etc.) or time interval (e.g., every 3 weeks). In the above-described hydro-mechanical system,one predetermined criterion is the fill time of water tank  100 , which is generally determined by the fill level inside water tank  100  and the flowrate from small opening  110  into water tank  100 .  
         [0053]    Although the invention has been described in conjunction with specific embodiments thereof, it is evident that many alternatives, modifications and variations will be apparent to those skilled in the art. Accordingly, it is intended to embrace all such alternatives, modifications and variations that fall within the spirit and broad scope of the appended claims.
The present invention is a system for, and a method of automatic washing of solar collection panels from dust, sediment, and the like, which tend to accumulate over time. The solar collector washing system comprises: (a) a solar collector having a solar collecting surface, the collector disposed in an angled position; (b) a water pipe mounted substantially above the solar collecting surface, the water pipe having a plurality of holes distributed along a length of the pipe for distribution of water onto the solar collecting surface, and (c) a control mechanism, operatively connected to said pipe, for releasing the water supply.