WO2013108210A1

WO2013108210A1 - Overcoming power loss in photovoltaic arrays having differential generating capacity by substring energy harvesting paths

Info

Publication number: WO2013108210A1
Application number: PCT/IB2013/050443
Authority: WO
Inventors: Doron Shmilovitz
Original assignee: Ramot At Tel-Aviv University Ltd.
Priority date: 2012-01-19
Filing date: 2013-01-17
Publication date: 2013-07-25

Abstract

A method and device for generating power with a photo-voltaic array may include collecting power generated by a string of the photoelectric generators (PEG's) and harvesting, with a substring harvesting path, power generated in a proper substring of the string. Optionally the harvested power may be adjusted separately from the collected power. The device may optionally include a maximum power point tracker. The method may optionally include detecting a location in the array having excess generating capacity. Optionally the substring may be chosen to include the location having excess generating capacity. The substring harvesting path may optionally include a DC to DC converter.

Description

OVERCOMING POWER LOSS IN PHOTOVOLTAIC ARRAYS HAVING DIFFERENTIAL GENERATING CAPACITY BY SUBSTRING ENERGY

HARVESTING PATHS RELATED APPLICATION/S

This application claims priority from US Provisional application 61/588,262 filed 19 January 2012.

The contents of all of the above applications are incorporated by reference as if fully set forth herein.

FIELD AND BACKGROUND OF THE INVENTION

The present invention, in some embodiments thereof, relates to a method and system to improve power output of photovoltaic arrays and, more particularly, but not exclusively, to a method and system to overcome power loss in photovoltaic arrays due to mismatch loss.

Background art includes U.S. Patent Application Publication No. 2008/0238195 to Shaver, U.S. Patent Application Publication No. 2009/0020151 to Fornage, U.S.

Patent No. 8,013,472 to Adest, U.S. Patent Application Publication No. 2008/0150366 to Adest, U.S. Patent No. 7,900,361 to Adest, U.S. Patent Application Publication No. 2012/0037206 to Norman, and U.S. Patent Application Publication No. 2011/0273016 to

Adest.

SUMMARY OF THE INVENTION

According to an aspect of some embodiments of the present invention there is provided a device for power generation from a string of photoelectric generators including a collection circuit for collecting a first power from a string, and a substring harvesting path for harvesting a second power from a substring of the string and shunting the second power out from the string.

According to some embodiments of the invention, the device may further include a controller for regulating the first power separately from the second power. According to some embodiments of the invention, the device may further include one or more sensors configured for identifying a location in the string with excess generating capacity.

According to some embodiments of the invention, the sensors are located on an output path of the array.

According to some embodiments of the invention, the sensors are located within the array.

According to some embodiments of the invention, the location has increased insolation with respect to a string average.

According to some embodiments of the invention, the controller is configured for adjusting a current in the substring harvesting path thereby increasing a sum of the first power and the second power.

According to some embodiments of the invention, the device may further include a pulse width modulation circuit configured for performing the adjusting.

According to some embodiments of the invention, the substring harvesting path includes a DC to DC converter.

According to some embodiments of the invention, the DC to DC converter includes a pulse width modulation circuit.

According to some embodiments of the invention, the harvesting path includes greater conversion loss than the collection circuit.

According to some embodiments of the invention, the substring harvesting path is retrofit to the string of photoelectric generators.

According to an aspect of some embodiments of the present invention there is provided a collection circuit to collect a first power from a string of a plurality of photovoltaic generators of the photovoltaic array; a tracker configured to detect a photovoltaic generator having excess generating capacity from the plurality of photovoltaic generators, and a substring harvesting path to harvest an excess power from the photovoltaic generator having excess capacity and shunting the second power out from the string.

According to some embodiments of the invention, the collection circuit has lower conversion losses than the harvesting path. According to some embodiments of the invention, the tracker is further configured for adjusting a current in the substring harvesting path and thereby increasing a sum of the first power and the excess power.

According to some embodiments of the invention, the substring harvesting path is retrofit to the photovoltaic array.

According to some embodiments of the invention, the device may further include a switch for changing the substring.

According to some embodiments of the invention, the device may further include one or more sensors configured for identifying a location in the string with excess generating capacity.

According to an aspect of some embodiments of the present invention there is provided method for power generation with a string of photoelectric generators including:

collecting a first power generated in the string of photo electric generators; harvesting with a substring harvesting path a second power from a substring of the string, and shunting the second power out of the string.

According to some embodiments of the invention, a magnitude of the second power is regulated separately from a magnitude of the first power.

According to some embodiments of the invention, a net power output of the string is greater than the first power.

According to some embodiments of the invention, the method further includes detecting a location with excess generating capacity in the string and wherein the substring is selected to include the location. According to some embodiments of the invention, the location has an increased insolation with respect to an array averaged insolation.

According to some embodiments of the invention, the method further includes adjusting a current of the second power to increase a sum of the first power and the second power. According to some embodiments of the invention, the method further includes sensing an output of the string, and adjusting a current of the second power according to the sensing.

According to some embodiments of the invention, the method further includes sensing electricity within the string, and adjusting a current of the second power according the sensing.

According to some embodiments of the invention, the adjusting is by pulse width modulation.

According to some embodiments of the invention, the method further includes retrofitting the substring harvesting path to the string of photoelectric generators.

According to some embodiments of the invention, the first power is greater than the second power.

According to some embodiments of the invention, the collecting is done without introducing conversion losses to the first power.

Implementation of the method and/or system of embodiments of the invention can involve performing or completing selected tasks manually, automatically, or a combination thereof. Moreover, according to actual instrumentation and equipment of embodiments of the method and/or system of the invention, several selected tasks could be implemented by hardware, by software or by firmware or by a combination thereof using an operating system.

For example, hardware for performing selected tasks according to embodiments of the invention could be implemented as a chip or a circuit. As software, selected tasks according to embodiments of the invention could be implemented as a plurality of software instructions being executed by a computer using any suitable operating system. In an exemplary embodiment of the invention, one or more tasks according to exemplary embodiments of method and/or system as described herein are performed by a data processor, such as a computing platform for executing a plurality of instructions. Optionally, the data processor includes a volatile memory for storing instructions and/or data and/or a non-volatile storage, for example, a magnetic hard-disk and/or removable media, for storing instructions and/or data. Optionally, a network connection is provided as well. A display and/or a user input device such as a keyboard or mouse are optionally provided as well.

BRIEF DESCRIPTION OF THE DRAWINGS

Some embodiments of the invention are 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 embodiments of the invention. In this regard, the description taken with the drawings makes apparent to those skilled in the art how embodiments of the invention may be practiced.

In the drawings:

FIG. 1 is a schematic illustration of a first exemplary embodiment of an array of photoelectric generators with substring harvesting circuits;

FIG. 2A is a circuit diagram of a first exemplary embodiment of a substring harvesting circuit;

FIG. 2B is a circuit diagram of a second exemplary embodiment of a substring harvesting circuit;

FIG. 3 is a schematic illustration of an alternative exemplary embodiment of an array of photoelectric generators with substring harvesting circuits,

FIG. 4 is a flow chart illustrating an exemplary embodiment of a method of generating electricity with photoelectric generators and substring harvesting circuits;

FIG. 5 is a schematic illustration of an alternative exemplary embodiment of an array of photoelectric generators with substring harvesting circuits;

FIG. 6A is a simulated Power- Voltage diagram comparing the output of a solar array with a substring harvesting circuit to a solar array without a substring harvesting circuit; and

FIG. 6B is a simulated Current- Voltage diagram comparing the output of a solar array with a substring harvesting circuit to a solar array without a substring harvesting circuit. DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION

The present invention, in some embodiments thereof, relates to a method and system to improve power output of photovoltaic arrays and, more particularly, but not exclusively, to a method and system to overcome power loss in photovoltaic arrays due to mismatch losses.

In a photovoltaic array, a string of photoelectric generators (PEG's) is often installed in series with a single string current running through all of the PEG's of the string.

An aspect of some embodiments of the current invention is that power is harvested and collected along two paths from a PEG in a string of PEG's. Optionally, power is collected from the PEG along the main collecting circuit of the string and power is also optionally harvested from the PEG on a substring harvesting path.

Optionally, the quantity of power harvested can be adjusted separately from the power collected.

The terms string and PEG refer to relationships between structures that may exist on many scales. For example on a small scale, a single solar cell may be referred to as a PEG and a string of cells within a panel and/or a module may be referred to as a string. In an example of a larger scale, a PEG may include one or a few cells and a string may include one or a few modules and/or panels. On a larger scale, one or more modules may be referred to as a PEG and a string may include a large number of modules and/or panels.

In some cases, a substring of the string may have excess generating capacity. For example, the substring might work more efficiently and/or be capable of producing more power at a current different from the main string current. The reduction of power resulting from running the all the PEG's of the string at a single string current compared to the power possible when running each PEG at its optimum current is called mismatch loss. Mismatch losses can reduce solar energy by 10-30%. In some cases, mismatch losses can be even more than 30%. For example, in some cases, mismatch losses can reach 50% or even more.

For example, differences in power generation capacity within an array may occur because one or more PEG may experience higher insolation than other PEG's and/or the string average insolation. For example, differences in power generation capacity within an array may occur due to heterogeneous properties amongst PEG's in the array and/or differential heating of individual PEG's and/or due to differential effects of aging on PEG's. Such differential in generation capacity may occur in all kinds of photovoltaic arrays. Concentrated photovoltaic arrays (CPV's) may be particularly sensitive to increased local insolation (for example, when compared to the array average insolation). For example, a concentrator may focus light unevenly on a collector producing a highly insolated location on the collector. The unevenness of the illumination may range for example between 3% and 50%. CPV's may include high-concentrated and/or low- concentrated photovoltaic arrays. For example, hybrid photovoltaic-thermal solar arrays may be particularly sensitive to differential heating of PEG' s.

Consider a string of PEG's experiencing differential insolation. Driving all of the PEG's at the same current may be inefficient. Often, the string would work more efficiently (produce more power) if the more highly insolated PEG's were driven at a higher current than the less insolated PEG's at a lower current. In some embodiments, the current invention may supply a method and system to drive some PEG's of a string at a higher current and other PEG's in the string at a lower current.

For example, power may be collected at a first working current from a string of PEG's in a photovoltaic array. Simultaneously, additional power may be harvested from a proper subset of the string of PEG's using one or more substring harvesting paths.

The terms string and substring refer to relationships between structures that may exist on many scales. For example on a small scale, a string may refer to a string of solar cells within a panel and/or a module. On that scale, a substring may refer to a proper subset of those cells. In an example of a larger scale, a string may include one or a few modules and/or panels. On the larger scale, a proper subset of the modules and/or panels and/or some of cells within one or more of the panels and/or modules may be referred to as a substring.

Those PEG's not connected to an active substring harvesting path may, optionally, be operating at the first working current (that is collected from the entire string). Those PEG's of the substring that are connected both to the main string and to an active substring harvesting path may optionally be operating at a current equal to the first working current plus the additional current of the substring harvesting path. In some embodiments, the power harvested from the substring harvesting path may be controlled using a DC to DC converter to regulate the current of the substring harvesting path.

In some embodiments, a substring harvesting path may optionally shunt power directly to the output path of the entire string (then the substring harvesting path may be called a feed forward shunt path). Alternatively or additionally, the substring harvesting path may shunt power to an output path that is separate from the main collector output.

A substring harvesting path may optionally harvest power from four or more solar cells. Alternatively or additionally, a substring harvesting path may harvest power from between 1 and 3 panels. In some embodiments, a substring harvesting path will harvest power from a substring of a panel having from 18-50 solar cells. Optionally, a substring harvesting path may be installed in place of one or more bypass diodes and/or in parallel to one or more bypass diodes.

At some times, the power harvesting in substring harvesting paths will be less than 2% of the power collected along the main string circuit encompassing the entire array. At some times, the power harvesting in substring harvesting paths will be less than 30% and some time less than 100% of the power collected along the main string circuit encompassing the entire array.

In some embodiments, a controller and/or a maximum power point tracker (MPPT) may monitor and coordinate power distribution in the array. Optionally, sensors may be provided to monitor voltage drop and/or current across various portions of the array. For example, sensors may be used to find the maximum power point (MPP) of individual PEG's. For example, some or all of the individual PEG's may be driven near their MPP. In some embodiments, the additional sensors may also serve the additional benefit of helping to identify local malfunctions in the array. In some embodiments, additional power may be harvested from a portion of the array. In some embodiments the current invention may reduce mismatch power loss.

Some embodiments of the current invention may be well suited to concentrated photovoltaic arrays. Some embodiments of the current invention may also be useful in all kinds of photovoltaic arrays. The current invention may optionally be installed in new photovoltaic arrays and/or retrofit to old arrays.

Before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not necessarily limited in its application to the details of construction and the arrangement of the components and/or methods set forth in the following description and/or illustrated in the drawings and/or the examples. The invention is capable of other embodiments or of being practiced or carried out in various ways.

Figure 1 illustrates an exemplary CPV array PEG's including PEG's 112a-e.

Optionally, PEG's 112a-e of the array are installed in series along a main collecting circuit. Each PEG contributes a voltage potential to the main circuit at the same current. Power collected from the main circuit from point A to point A' includes the sum of the voltage potential by PEG's 112a-e and is output through output path 130. Optionally, a second power can be harvested from each of PEG' s 112a-e along a respective substring harvesting path 124a-e.

The embodiment of Fig. 1 illustrates an optional configuration wherein each PEG 112a-e is connected to both a main collection circuit and a respective fixed geometry harvesting path 124a-e. Optionally, power harvested on harvesting paths 124a- e is shunted out of the string. In the example of Fig. 1, the power is optionally shunted out of the system along an output path 130. Optionally output path 130 is the output path both for power harvested on substring harvesting paths 124a-e and for power collected on the main collecting circuit. In some embodiments, a maximum power point tracker 118 (MPPT) adjusts power in the collecting circuit and in each of harvesting paths 124a- e. In the embodiment of Fig. 1, optionally, power production and/or collection and/or harvesting is monitored using wired sensors 120a-c and/or wireless sensors 122a,b at various locations within the photovoltaic array. Alternatively or additionally, the system may include adjustable geometry harvesting paths (for example as illustrated in Fig. 3). Alternatively or additionally, there may be multiple output paths (for example as illustrated in the embodiment of Fig. 3). Alternatively or additionally, sensors may be located on the output path (for example as illustrated in the embodiment of Fig. 5).

In the exemplary embodiment of Fig. 1, each PEG 112a-e is connected to a respective substring harvesting path 124a-e. In operation, power may be collected from the entire string of PEG's 112a-e at a fixed, shared working current using the main circuit A-A'. Simultaneously, one or more of substring harvesting paths 124a-e may be activated to harvest additional power from a respective PEG 112a-e. The current in each substring harvesting path 124a-e is regulated separately using a respective DC to DC converter 114a-e. Optionally, each substring harvesting circuit is parallel to a portion of the main collector circuit A-A'.

For example, using the embodiment of Fig. 1, power may be collected from the entire string of PEG's 112a-e along from circuit A-A'. Simultaneously, additional power may optionally be harvested from PEG 112a using substring harvesting path 124a. The current in substring harvesting path 124a may optionally be regulated by DC to DC converter 114a separately from the current in the main circuit A-A' and/or the current in the other substring harvesting paths 124b-e.

In a more explicit example, 8 Amps of current may be collected along the main collection circuit A-A' from all of the PEG's 112a-e of the string. Simultaneously, a current of 4 Amps may optionally be harvested from substring harvesting path 124a. The resulting working voltage of PEG's 112b-e would be the main string current, 8 Amps. The working current of PEG 112a would be the sum (12 Amp) of the main string current (8 Amps) plus the current harvested by the respective substring harvesting path 124a (4 Amp).

Some embodiments may include only a single substring harvesting path. For example when the designer of a solar array knows that a particular substring of a solar is likely to receive higher insolation than the array average insolation, he may include a substring harvesting path for that substring only. When, in an existing solar array, it is found that a particular substring is consistently experiencing increased insolation; a substring harvesting path may be connected to that substring. In some embodiments, multiple substring harvesting paths may be located on different (possibly overlapping) substrings of the array.

In the example of Fig. 1, each substring harvesting path 124a-e includes a single dedicated DC-DC converter 114a-e respectively. In some embodiments, switches will be supplied and the size and geometry of substring harvesting paths will be variable.

Optionally, there may be fewer DC-DC converters than potential substring harvesting paths. When a particular substring of the array has excess generation capacity, for example when the substring is under higher insolation than other sections and/or than the array average insolation, the switches may be adjusted to create a substring harvesting path of that substring and include a DC-DC converter in the substring harvesting path. In some embodiments, the portion of the solar array driven at higher current, for example a more highly insolated portion, will be smaller than 50% of the entire array. In some embodiments (for example when some solar panels are installed on a roof and others on an external wall), the high current portion may be as much as 50% of the entire array or even more.

In the exemplary embodiment, maximum power point tracker 118 (MPPT) controls current collected across the entire array. Optionally, tracker 118 detects uneven PEG performance, for example due to uneven insolation. For example, tracker 118 tracks the voltage change across each of the PEG's 112a-e with hard wired sensors 120a, 120b, 120c and/or with wireless sensors 122a and 122b. Differences in performance between PEG's may signal, for example, uneven insolation. Optionally, sensors (120a-c, 122a,b) may be included in the respective DC/DC converters 114a-e.

In some embodiments, a tracker will have individual sensors for only one PEG and/or only for some of the PEG's in the array and/or for one or more groups of PEG's. In some embodiments, the tracker will detect uneven generation capacity by means other than individual sensors. For example, uneven generation capacity may be due to uneven insolation. For example a tracker may track current only on the main circuit, and may seek to increase the combined power output by an iterative routine (for example trial an error) adjusting of the current on the main circuit as well as a substring harvesting paths 124a-e.

In the example of Fig. 1, tracker 118 is optionally programmed to detect a PEG that would produce increased power at an increased working current. For example, tracker 118 may drive all of PEG's 112a-e at a single shared current and measure the voltage drop across each pair of sensor 120a-c and 122a,b. When one or more of the PEG's 112a-e produces a higher voltage potential than the other PEG's, tracker 118 may for example increase current in the respective substring harvesting circuit. Alternatively or additionally tracker 118 may include an iterative routine for adjusting output of individual PEG's. For example, tracker 118 may raise and lower the current in one of substring harvesting paths 124a-e (increasing and lowering the driving current of the respective PEG) and measure the response of the individual PEG and/or the system. If increasing the current in a PEG increases the power output (of the respective substring and/or of the sum of power collected over the entire string and the power harvested in the substring harvesting circuits), then the PEG will be driven at the increased current.

In some embodiments, the current in the main circuit and substring harvesting paths 124a-e may be adjusted almost continuously, for example every 1-10 milliseconds. For example, a solar power system mounted on a moving vehicle may be adjusted at a high frequency. In some embodiments, the current may be adjusted periodically, for example, once every 1-60 seconds. For example, in areas where moving clouds cause shadows that change every few minutes, an intermediate adjustment frequency may be used. In some embodiments, the current will only be adjusted from once a minute to once every ten minutes. For example, in a location where there are few shadows, adjustments may be made according slow changes in the sun angle. In some

embodiments, adjustments may be made at higher frequency at certain times of day (for example in the afternoon) or under certain weather conditions (for example when the sky is partly cloudy). Optionally adjustments may be made in response to a stimulus, for example, a significant change in the performance of the array and/or an acute change in the power output of the system. In some embodiments the current will be reset and/or adjusted when performance of the system is poor (for example when the current/power relationship is outside of a preferred working envelope).

In some embodiments, adjusting the current distribution (for example checking for a highly insolated substring) may be triggered by an event (for example the tracker may check for more efficient ways to distribute current at certain times of day as the sun changes location in the sky). Optionally, checking of insolation and/or adjustment of current may be done in a random manner. Optionally, checking of insolation and/or adjustment may use various known optimization methodologies, for example linear optimization, simulated annealing, dynamic relaxation, and the like.

In some embodiments, the tracker will include a controller and/or a DC to DC converter, and/or a transformer and/or a DC to AC inverter.

In the example of Fig.1 tracker 118 detects that PEG 112e has excess generating capacity. For example PEG 112e may be more highly insolated than other PEG's on the circuit. For example, when all PEG's 112a-e are driven at the same current, the higher insolation PEG 112e may produce a slightly higher voltage increase between sensors 120a and 120b than other PEG's 112a-d produce across their respective sensors. The higher potential may be taken as a sign of increased insolation.

Tracker 118 drives PEG 112e at the higher current. A portion of the current (the portion equal to the preferred current of PEG's 112a-d) is collected in the main circuit from A - A'. The excess portion of the power (the excess current) is harvested through substring harvesting path 124e and DC-DC converter 114e and shunted out of the string circuit A-A' and directly to the output circuit 130 (as shown for example in Fig. 1).

In the example of Fig. 1, power harvested in substring harvesting path 124e is adjusted to balance current in the main circuit for PEG's 112a-e while driving PEG 112e near its MPP. Optionally, PEG 112e is driven at a higher current than the current of the main circuit. For example, PEG 112e is driven at the sum of the working current of the main circuit plus the harvested current in path 124e.

Generally, use of a DC-DC converter may introduce a small conversion loss of power approximately proportional to the power converted (for example of the order of 5%). In the example of Fig. 1, the majority of the power of the array is collected from the main circuit A-A' without any additional converters, optionally, avoiding conversion losses on the main collecting circuit. Only a small portion of the power of the system goes through the substring harvesting path 124e and DC/DC converter 114e (the excess power of PEG 112e). The conversion loss power is then only 5% of a small portion of the total power output of the system. For example, the conversions loss may only apply to the harvested excess power of PEG 112e.

For example if PEG's 112a-d are each producing 40W at a preferred current of 5Amps and PEG 112e capable of producing 60W at 7.5Amp. Then substring harvesting path 124e may drain off 20W of power at 2.5Amp of current. The total power produced by the system would be 40*4+60=220W while the conversion loss of power due to DC- DC converter 114e would be 0.05*20=1.0W. In some embodiments, each substring harvesting path 124a-e will be designed for a capacity of less than the power producing capacity of the substring because only a portion of the power of the substring will go through substring harvesting path and the rest of the power will go through the main circuit. In the example of Fig. 1, DC to DC converters 114a-e may optionally be designed for a maximum power that is less than the full power of the respective substring. This may save money acquiring only low capacity components. Optionally a substring harvesting path may be installed on each individual PEG, and/or on some individual PEG's, and/or on one PEG and/or on one or more groups of PEG's. Extra sensors and/or substring harvesting paths may be installed as part of a new array, or they may be added to an existing array (retrofit). In some cases, it may be known a priori a location that likely to have excess generating capacity. For example there may be an area that is commonly exposed to higher insolation than the rest of the array. For example, near the center of a CPV array may be a likely spot of increased insolation. For example, a highly insolated PEG may receive between 10% and 200% more light that the average insolation of PEG's in the system. In some embodiments, extra substring harvesting paths may be added to locations where hotspots are expected. Optionally substring harvesting paths can be used in place of and/or in parallel to existing bypass diodes.

In some cases, the excess insolation of a cell may be a predictable time dependent occurrence (for example, due to geometry of the system and the daily cycle of changing sun angle). Optionally, the system may include a memory. Optionally the system may be programmed to apply a preprogrammed time dependent pattern of collecting and/or harvesting. Optionally a maximum power point tracking module (MPPT) may further adjust collecting and/or harvesting using the time dependent pattern as a starting configuration. In some embodiments, the system may make changes in the preprogrammed pattern over time. For example, the system may store the actual schedule of collecting and/or harvesting on a given day and apply it as an initial schedule for the next day. In some examples, the system may include a machine learning routine that adjusts the collecting and/or harvesting pattern. In some embodiments, there may be a multiple stored patterns each one used depending on some condition. For example, there may be a summer pattern and/or a winter pattern and/or a sunny day pattern and/or a cloudy day pattern.

After harvesting the excess portion from of the current from PEG 112e, the remaining current is similar to the preferred working current of PEG's 112a-d. In the exemplary embodiment, the remaining current is driven through the main circuit (from A to A') without additional converters. In the example of Fig. 1, substring harvesting paths 124a-e shunt power directly to output path 130. Power collected over the main circuit A-A' and the power harvested in substring harvesting paths 124a-e are combined and output through output path 130.

Figs. 2A,B illustrate alternative detailed embodiments of harvesting paths and DC/DC converters.

Fig. 2A depicts an exemplary version of a substring harvesting path including a

DC to DC converter. In Fig. 2a power from PEG 112c is optionally converted to an AC signal by a pulse width modulation (PWM) circuit including a capacitor C and a transistor MOSFET. The quantity of power drained from PEG 112c is controlled by the adjusting the PWM duty cycle. Optionally, the voltage in the PMW circuit is stepped up to the voltage of the entire array (as found in the collector circuit) by a transformer T and rectified by an output circuit including a diode D, a capacitor C_out and an inductor L. In some embodiments, the resulting power is fed into the output circuit of the entire array (as shown for example in Fig. 1). The current in the substring harvesting path (and consequently the power) is optionally controlled via pulse wave modulation by a transistor MOSFET.

Optionally, other methods may be used to control a DC to DC substring harvesting path. For example, a resonant converter with frequency control may be used. The DC to DC converter may be half bridge or full bridge. In some embodiments, current of the substring harvesting path may be adjusted by PWM, additionally or alternately current may be adjusted by changing the duty-cycle frequency and/or by changing the pulse shape and/or by other methods.

Fig. 2B depicts a second exemplary version of a substring harvesting path and DC to DC converter. The configuration of Fig. 2B may be applied where there is a common ground circuit.

Fig. 3 illustrates an alternate exemplary embodiment of an array of PEG's according to the current invention. PEG's 312a-e are connected to an MPPT 318. A single DC-DC converter 314 is connected to a variable geometry substring harvesting path 324. Fig. 3 also illustrates an exemplary embodiment of a system having multiple output paths.

In some embodiments, switches 328a-f may adjust the geometry of substring harvesting path 324. For example, switches 328a-f can be used to change which PEG's are included in the substring. Substring harvesting path 324 can harvest energy from various substrings of the array. Wired sensors 320a-c and a wireless sensor 322 are used by a controller 326 to measure voltage across some of the various sections of the array. In the example, switches 328f and 328b are closed and thus substring harvesting path 324 is harvesting the substring containing PEG's 312a and 312b. Power collected along the main circuit is output through MPPT 318 and an output path 330a. Substring harvesting path 324 shunts power out of the string via a second output path 330b. The net power produced by the string is the sum of the power output on output path 330a and output path 330b.

Figure 4 is a flowchart of an exemplary method for overcoming power loss in a photovoltaic array.

In some embodiments, a string of PEG's in series is provided 452. For example each PEG, in an exemplary embodiment 450, may be a substring of 30 photovoltaic cells. In embodiment 450, the array may include, for example, 15 substrings distributed over 5 solar panels.

In some embodiments, a subset of the PEG's in the array is selected 454.

Optionally, the subset will be selected 454 to include one or more PEG's that have excess generating capacity. For example, in the example of Fig. 4, three highly insolated substrings may be selected 454. In the example of Fig. 4, two substring harvesting paths are provided 456. A first substring harvesting path is connected to a first substring of the selected subset and a second substring harvesting path is connected to the other two substrings of the subset.

In the example of Fig. 4, a first current is set 458 for collecting power from the entire array of 15 substrings for example in an array collecting circuit. In the example of Fig. 4, the first current is adjusted to 10 Amps, which is low enough so that none of the PEG's is forced into reverse bias.

In the example of Fig. 4, a second current is set 460 for harvesting power on the first substring harvesting path. For example, the first highly insolated substring works more efficiently at 15 Amps working current. Optionally, the current in the first substring harvesting path is set 460 to 5 Amps.

In the example of Fig. 4, a third current is set 460 for harvesting power on the second substring harvesting path. For example, the second and third highly insolated substrings work more efficiently at 12 Amps working current. Optionally, the current in the second substring harvesting path is set 460 to 2 Amps.

In the example of Fig. 4, the voltage potential across the entire array of 15 substrings at 10 Amps is 12*5+2*5.5+1*6=77 volts DC. The power collected 462 across the entire array is 770 Watts.

In the example of Fig. 4, the voltage potential across the first substring harvesting path is 6 volts. The power harvested 464 on the first substring harvesting path is 30 Watts.

In the example of Fig. 4, the voltage potential across the second substring harvesting path is 11 volts. The power harvested 464 on the first second harvesting path is 22 Watts.

In summary of the example of Fig. 4:

• 770 watts of power is collected along the main collection circuit from the string of fifteen substrings.

• The twelve substrings that are not connected to a substring harvesting path have a working current of 10 Amps and an average potential of 5 Volts per substring producing 600 watts.

• Extra power is harvested from three substrings.

o The first of the three substrings produces a total of 90 Watts of power at current of 15 Amps at a potential of 6 volts. 10 Amps (60 Watts) are collected on the main circuit and 5 Amps (30 Watts) are collected on the first substring harvesting path.

o The second and third of the three substrings produce total of 132 Watts of power at a current of 12 Amps at an average potential of 5.5 volts per substring. 10 Amps (110 Watts) are collected on the main circuit and 2 Amps (22 Watts) are collected on the second substring harvesting path.

• The total power produced is 600+90+132=822 Watts of which 770 Watts are collected on the main string circuit and 52 Watts are harvested on the two substring harvesting paths. The power harvested on the substring harvesting paths is 52/822*100=6.3% of the power collected on the main string circuit. • The conversions losses due for example to 5% losses in the DC-DC converters on the two harvesting circuits is 0.05*52W=2.6W which is less than half a percent of the total power (2.6/822=0.003=0.3%).

In some embodiments, the main parallel circuit will not include a converter. In some embodiments, on the substring harvesting paths, there will be conversions losses associated with the DC to DC converters.

In some embodiments, a substring harvesting circuit may contain, for example, a few solar cells, and/or an entire solar panel, and/or a string of multiple panels. In some embodiments, the ratio of length of a substring to the length of the main string may be, for example, between 5% and 50%. In some embodiments, the ratio of the sum of power in the substring harvesting paths to the power harvested on main array may be, for example, between 1% and 50%. In some embodiments, the total power of a photovoltaic system may be, for example, from a few watts to a few kilowatts or a megawatt or more for commercial installations. In some embodiments, there may, for example from a single substring harvesting path to 100 substring harvesting paths or more.

Fig. 5 illustrates an alternate exemplary embodiment of an array of PEG's according to the current invention. In the example of Fig. 5, a controller 526 optionally monitors the power output of the array. Adjustments to the power in the collection circuit and substring harvesting circuit are optionally made to increase power in the output circuit.

In the embodiment of Fig. 5, a few PEG's, for example five PEG's 512a-e, are connected together along a collecting circuit E-E'. In the embodiment of Fig. 5, each PEG 512a-c is connected through a respective substring harvesting path 524a-e to a respective DC-DC converter 514a-e and to an output of the array.

In some embodiments, a controller 526 optionally may control the power outputs

572a-e by adjusting of DC-DC converters 514a-e. Optionally, a voltage sensor 520a and/or a current sensor 520b are mounted on the array output path and are used to measure a total array power output 572f. In the exemplary embodiment of Fig. 5, total array power output 572f is the sum of the power outputs 572a-e. A bulk capacitor 570 steadies power output 572f. For example sensor 520a may measure voltage across bulk capacitor 570. In the example of Fig. 5, PEG 512a may produce power efficiently at a lower current than the other PEG's 512b-e. For example, PEG 512a may have a lower insolation that PEG's 512b-e. Optionally, negligible power is harvested on substring harvesting path 524a corresponding to the lowest current PEG 512a (for example the power in harvesting path 524a may be less than 1% of the power collected from the cell on the collecting circuit and/or the power in harvesting path 524a may be less than 5% of the power collected from the cell on the collecting circuit). The power output of the lowest current PEG 512a is optionally collected along with a portion of the power from the other PEG's 512b-e in collective output power 572a along the main circuit E-E'. Optionally, the current of the collective power output 572a may be adjusted to a current close to the maximum power point of the lowest current PEG 512a.

In some embodiments, the more highly insolated PEG's 512b-e contribute to collective power output 572a and also to respective individual power outputs 572b-e on respective substring harvesting paths 524b-e. Harvested power outputs 572b-e are shunted to the total output 572f.

In some embodiments, controller 526 may optionally adjust converters 514a-e to increase total array power output 572f. Optionally, controller 526 may employ a multi variable iterative maximum power point tracking algorithm. The example the algorithm may include an extension and/or modification of a single variable algorithm such as "Hill Climbing", "Perturb and Observe", and/or others. To accelerate the convergence the algorithm might apply gradient descent, sliding mode control, and/or other methods.

Fig. 6A illustrates a simulated a power- voltage output curve 674b for a PEG array with substring harvesting and a simulated power-voltage output curve 674a for a conventional PEG array.

Fig. 6B illustrates simulated current- voltage output curve 676b for a PEG array with substring harvesting and a simulated current- voltage output curve 676a for a conventional PEG array.

Figs. 6A,B illustrate an example of a difference in simulated output between an exemplary photovoltaic array having a substring harvesting paths and a conventional photovoltaic array.

For the sake of illustration, Fig. 6A,B illustrates output of an array having 14 PEG's of which 13 of the PEG's are half illuminated and one PEG is fully illuminated. Alternative embodiments may have more or less PEG's in the array and/or alternative examples may include other lighting conditions.

In a conventional array, without substring harvesting paths, all of the power may be collected through a single collection circuit and all of the PEG's may run on the same current. For example, the highly insolated PEG may be forced to operate near the MPP current of the partially insolated PEG's (for example 4 Amps). This may result in loss the extra energy that could be produced by the highly insolated PEG at its MPP (for example at a higher current).

Using substring power harvesting, the partially illuminated PEG's may supply energy to a main collection circuit near their MPP (for example 4 Amps). The highly insolated PEG may optionally supply power to the main collector circuit at 4 Amp and also to a substring harvesting circuit (for example at 4 Amp). In the example the highly insolated PEG may run near its MPP (for example 8 Amp). For the exemplary embodiment, the array with substring harvesting may produce approximately 7% more power at the collective MPP 678 than the conventional array.

It is expected that during the life of a patent maturing from this application many relevant technologies will be developed and the scope of each term is intended to include all such new technologies a priori.

As used herein the term "about" refers to ± 10%

The terms "comprises", "comprising", "includes", "including", "having" and their conjugates mean "including but not limited to".

The term "consisting of means "including and limited to".

The term "consisting essentially of" means that the composition, method or structure may include additional ingredients, steps and/or parts, but only if the additional ingredients, steps and/or parts do not materially alter the basic and novel characteristics of the claimed composition, method or structure.

As used herein, the singular form "a", "an" and "the" include plural references unless the context clearly dictates otherwise. For example, the term "a compound" or "at least one compound" may include a plurality of compounds, including mixtures thereof.

Throughout this application, various embodiments of this invention may be presented in a range format. It should be understood that the description in range format is merely for convenience and brevity and should not be construed as an inflexible limitation on the scope of the invention. Accordingly, the description of a range should be considered to have specifically disclosed all the possible subranges as well as individual numerical values within that range. For example, description of a range such as from 1 to 6 should be considered to have specifically disclosed subranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6 etc., as well as individual numbers within that range, for example, 1, 2, 3, 4, 5, and 6. This applies regardless of the breadth of the range.

Whenever a numerical range is indicated herein, it is meant to include any cited numeral (fractional or integral) within the indicated range. The phrases "ranging/ranges between" a first indicate number and a second indicate number and "ranging/ranges from" a first indicate number "to" a second indicate number are used herein

interchangeably and are meant to include the first and second indicated numbers and all the fractional and integral numerals therebetween.

It is appreciated that certain features of the invention, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the invention, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable subcombination or as suitable in any other described embodiment of the invention. Certain features described in the context of various embodiments are not to be considered essential features of those embodiments, unless the embodiment is inoperative without those elements.

All publications, patents and patent applications mentioned in this specification are herein incorporated in their entirety by reference into the specification, to the same extent as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated herein by reference. In addition, citation or identification of any reference in this application shall not be construed as an admission that such reference is available as prior art to the present invention. To the extent that section headings are used, they should not be construed as necessarily limiting.

Claims

WHAT IS CLAIMED IS:

1. A device for power generation from a string of photoelectric generators comprising: a) a collection circuit for collecting a first power from a string, and

b) a substring harvesting path for harvesting a second power from a substring of said string and shunting said second power out from said string.

2. The device of claim 1 further comprising:

c) a controller for regulating said first power separately from said second power.

3. The device of claim 1, further comprising:

c) one or more sensors configured for identifying a location in the string with excess generating capacity.

4. The device of claim 3, wherein said sensors are located on an output path of said array.

5. The device of claim 3, wherein said sensors are located within said array.

6. The device of claim 3, wherein said location has increased insolation with respect to a string average.

7. The device of claim 2, wherein said controller is configured for adjusting a current in said substring harvesting path thereby increasing a sum of said first power and said second power.

8. The device of claim 7, further comprising:

c) a pulse width modulation circuit configured for performing said adjusting.

9. The device of claim 1, wherein said substring harvesting path includes a DC to DC converter.

10. The device of claim 9, wherein said DC to DC converter includes a pulse width modulation circuit.

11. The device of claim 1, wherein said harvesting path includes greater conversion loss than said collection circuit.

12. The device of claim 1, wherein said substring harvesting path is retrofit to the string of photoelectric generators.

13. A photovoltaic system comprising:

a) A collection circuit to collect a first power from a string of a plurality of

photovoltaic generators of the photovoltaic array;

b) a tracker configured to detect a photovoltaic generator having excess generating capacity from said plurality of photovoltaic generators, and

c) a substring harvesting path to harvest an excess power from said photovoltaic generator having excess capacity and shunting said second power out from said string.

14. The system of claim 13, wherein said collection circuit has lower conversion losses than said harvesting path.

15. The system of claim 13, wherein said tracker is further configured for adjusting a current in said substring harvesting path and thereby increasing a sum of said first power and said excess power.

16. The system of claim 15, further comprising:

d) a pulse width modulation circuit configured for performing said adjusting.

17. The system of claim 13, wherein said substring harvesting path includes a DC to DC converter.

18. The system of claim 17, wherein said DC to DC converter includes a pulse width modulation circuit.

19. The system of claim 13, wherein said substring harvesting path is retrofit to the photovoltaic array.

20. The system of claim 13, further comprising:

d) a switch for changing said substring.

21. The system of claim 13, further comprising:

22. The device of claim 21, wherein said sensors are located on an output path of said array.

23. The device of claim 21, wherein said sensors are located within said array.

24. A method for power generation with a string of photoelectric generators comprising: a) collecting a first power generated in the string of photo electric generators;

b) harvesting with a substring harvesting path a second power from a substring of the string, and

c) shunting said second power out of the string.

25. The method of claim 24, wherein a magnitude of said second power is regulated separately from a magnitude of said first power.

26. The method of claim 24, wherein a net power output of the string is greater than said first power.

27. The method of claim 24, further comprising:

d) detecting a location with excess generating capacity in the string and wherein said substring is selected to include said location.

28. The method of claim 27, wherein said location has an increased insolation with respect to an array averaged insolation.

29. The method of claim 24, further comprising

d) adjusting a current of said second power to increase a sum of said first power and said second power.

30. The method of claim 24, further comprising

d) sensing an output of said string, and

e) adjusting a current of said second power according to said sensing.

31. The method of claim 24, further comprising

d) sensing electricity within said string, and

e) adjusting a current of said second power according said sensing.

32. The method of claim 31, wherein said adjusting is by pulse width modulation.

33. The method of claim 24, further comprising:

d) retrofitting said substring harvesting path to the string of photoelectric generators.

34. The method of claim 24, wherein said first power is greater than said second power.

35. The method of claim 24, wherein said collecting is done without introducing conversion losses to said first power.