United States Patent [I91 Ross

11 4,163,194 1451 Jul. 31, lW9

VOLTAGE-CURRENT-POWER METER FOR PHOTOVOLTAIC S O U R ARRAYS

Inventor: Ronald G. ROSS, La Canada, Calif.

Assignee: Califorsia Iastitote of Tsch.olo~~~, Pasadena, Calif.

Appl. No.: 818,122

Filed: Jul. 2 5 1977 ............................................. Int. (3.2 COlN 27/42 ..................................... US. C1. 324/29$ 320/48;

324/73 R Field of Surch ............... 324/29.5, 73 R, 73 AT,

324/1 13; 320/48

Refwmccs Cited U.S. PATENT DOCUMENTS

3,778,702 12/1973 Finger ................................. 324/29.5 ........................ 3,969,667 7/1976 McWilliams 324n9.5

............................... 4,021,718 5/1977 Konrad 324n9.5 Primary Exuminrr-M. Tokar Attorney, AgenL or Firm-Freilich, Hornkker, Wasserman, R o s a & Femandez

A meter is dkluscd for measuring thc voltagc, current, and power (VIP) parameters of a photovoltaic solar array, or array module, under sunlight operating wndi-

tions utilizing a variable load wnnected across the array and controlled by a voltage regulator which responds to the difference between the output voltage of the array and a programmed test voltage from a source which generates a single ramp volUgc for measuring and recording current as a function of voltage, repeated ramp voltages at a high rate for peak output masure- men& or a DC voltage for VIP measurements at lie- lectcd points on the f-V chrractmistic curve of the array. The voltage signal from a current sensing ele- ment, such as a shunt resistor in series with the variable load, is compared with the output current of a reference solar cell to providc a normalizing signal to be a d d 4 LO the signal from the current-sensing dement in order to provide a record of array current as a function of array voltage, i.e., for all load conditions from short circuit to open circuit. As the normalized current is thus mu- sured, an analog multiplier multiplies the uray voltye and normalized current to provide a mcrsurcment of power. Switches are provided to selectively connect thc power. P, currcnt, I, or voltagc, V, to n meter. directly or through a p k detector. At the same dnic any one of the parameters V, I and P may be recorded as a function of any other parameter.

X-Y OR 4 4 - I

U.S. Patent J U ~ . 31, 1979 Sheet 1 of 3

U.S. Patent J U ~ . 31, 1979 Sheet 2 of 3

U.S. Patent J U ~ . 31, 1979 Sheet 3 of 3

+v MANUAL SWEEP

J "'"' ,OFF

S6A PROGRAM 7 rv VOLTAGE GEN.

OUTPUT - 1

I -v I I GENERATOR ,

FIG. 4 L,,,,,,------------J

SUMMARY OF THE INVENTION The meter is adapted to be connected across the array, as bv conventional clins and insulated leads. to dace a . . I11 accordance with the present invention, a portable yrle&blc curre~it-sclrA~r~ clcrncrrt I4 u~rd variablc load

instrument for measuring the voltage, current and 16 in parallel with the array. The variable load may be power parameters of a photovoltaic solar array is com- 5 a large power transistor, or a plurality of power transis- priscd of a variable load connected across the array and tors in parallel, connected between the output terminal regulated by an ektronic m a n s thereby controlling of the array and the current-sensing element, but prefer- the voltage and current output ofthe array over the full ably the variable load is implemented by a pair of tran- range from subs-ti.lly short circuit current to open sistors connected in a double-emitter follower (or f i circuit. The vol tye at the output of the array and the 10 multiplier) configuration .s is well known in the art and signal voltage from a current sensing element represent m m w n l ~ referred to as a h l i n m n ~ i r . The config- fllc vc>ltngc nlld current pammctcrs, rcupcuiivcly, v uration consists of connecting thc collectors of two and I termin& connected to a recorder, and connected ~a"sisf0fS together, &id the emitter of one (the ~ ~ l i l r ~ l to an electronic multiplier, the output of which provides input transistor) to the base of the other. The emitter of power at a third termind p. ~h~ term,- 15 the other transistor is then the output terminal. Current rids V, I rind p be gelectively m e d to a pk between the common collectors and the emitter of the detector and meter, A voltage generator produces a other transistor is controlled by the input current to the selected program voltage for control of the variable base the input lad to outputs at the v I output ternin& to The input signal for control of the variable load 16 is sweep the full rPnOe between open and short circuit 20 derived from a feedback operational amplifiir 18 con- conditions once at a controlled rate for recording the nected the Output the may for c l d - 1 ~ ~ stabili-

HS a fUNtion Of vOlfage V, or utiOn of tlic viuiablc lorut. In practia, ttic power tr;w- edly a rate for + power through sistors are inverting amplifiers and therefore require

that the non-inverting input t c r m i ~ I (+) of the feed- the pd to terminal '. A DC 25 b.d; .mpWir be used for the c l o d loop, but in this progrun volude at seiected functional block diagram we ssurnc no polarity inver- lcvcls to pcrnlit ~ncusurcn~cnt of V, I und/or 1' nt sc- siorr irr Lliu loop across tljc vrrrlirblc loud st) tlrat t l~c lected points on the I-V charrtcristic curve of the mvmina input (-)of tk .mp,ifwr i. itdiuw being array. A reference connected to n O r m ~ n g connew in the loop for &pltCTative f--.; other- m a s for ' ~ 0 P r i . k ' ~ scd'nl the currmt '' the cur- 30 - regtnentive f e e d k k would occur. other rent output terminal I to provide a c u r r a t m- terminal of the amplirEr 18 receives a program voltage surement that corresponds to an array output (voltagc signal from a nt. and current) at a standard insolution level, such as 100 Tk program voltage from the ;EO is sldded mW/cm2. All I and P measurements made are continu- to the stnbilizing f e e d k k in the unplifKr to offset ously normalized to the nfcrcncc insolation level to 35 the point of - t h from 0 to v ~ . his is eliminate the effect of time variations in the in situ inso- accomplished by generating a voltage that is =ither (1) a Iation level. DC offset mmua.lly selected by a potentiometer 22, (2)

The rnvcl f ~ t ~ ~ that considered c h u w m c a linearly changing voltage to sweep the meter from of this invention Ue set forth with p t k u h i t y in the about V- 0.6 volts for -u-t of &a circuit append* chims. +l"k invention will best be understood UI current, 1, to open circuit voltage, V, at a dow rate, from the following description when read in connection ,h , 5 or 10 mends, or (3) an oscillating to with the accompanying drawings. rematedlv vary the array about between short circuit

BRIEF DESaIpTION OF THE D w W I N G S 'U;d circuit .t a fut ra te in order to ~ b t r i n an AC output for peak detection of puunden V, P .ad I.

FIG. 1 is a block diagram of the invention. 45 The parameter V, output voltage, is available at a FIG. 2 is a circuit diagram of a preferred embodi- jack identifd by Ule letters VJ in the drawing. Th.t

ment. jack is coupled to the array output terminal by an opera- FIG. 3 is a diagram of a normalizing circuit, tional amplifier 24 having a ftodbrck potentiometer 26 FIG. 4 is a circuit diagram of a program voltage for voltage gain adjustment of the Iwkr, and a b k S

generator. 50 of selectable coupling resistors lor voltage range selcc-

DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings. FIG. 1 illustrates the organization of a VIP meter 16 according to the present 55 invention. The VIP meter is capabk of measuring elec- trical performance chrractrcristics in situ for any m a y 12 within the specif'iatiom for which the meter is de- signed, such as the following: Open circuit voltage: 2

4,163,194 5 6

circuit of meter 40 to measure peak voltage current or input. of the operational amplifier 30A to assure that the power. operational limits of the amplifier 30A are not exceeded.

Any of the tl~rcc puramctcrs may be rccordcd on un Thc output of the operational amplifier 30l3 is thcn X-Y or strip chart recorder 44 while the switches 42 and applied to the multiplier 36 and to the terminal 1 of the 44 are in either position. Normally the parameters I and 5 switch 38 directly, and through a current-limiting resis- V are recorded to plot the I-V characteristic of the tor network 62 to the jack IJ for connection of the array, but sometimes it may be the parameters P and V. recorder 44 (FIG. 1). In either case, it is desirable to scan from short circuit The chosen voltage output of the solar array 12 is current, I , to open circuit voltage, V,, operation. That coupled to the operational amplifer 24 through the is accomplished by momentarily ciosine a sweep switch 10 bank of selectable coupling resistors 1 by a switch S2. which tr imen one cycle of a ramp voltlge in the gcner- Limiting diodes D3 md M assures that the signal ap- ator 2U to cause the output voltage, V, to drop to about plied does not exceed the operational limits of the am- 0.6 volts (for a virtual short circuit across the variable plifier. The input of the amplifier is also directly wn- load 16) and increase linearly to V, for a virtual open nected to the operational amplifier 18 where the output circuit across the variable load 16. The result is that in 15 of the program voltage generator 2Q is added to the the course of the ramp voltage sweep, the complete I-V, stabilizing negative feedback applied to the variable or P-V characteristic is recorded. The sweep time is load. Since the variable load is comprised of transistors controlled (5 to 10 seconds) for the operating specd of which effectively ~ rov ide sirnd inversion between the the recorder.

Since recording the I-V characteristic may take as much as 10 seconds, it is recognized that there can occur in that ilrwrval varistiorrr in the interroily of rcolur radiation due to waver or moisture, dust, etc., in the air. Although such variations are not n o r r d l y detectable by the human eye due to image perristencc in the eye, they will significantly affect the solar urray output, and thus introduce noise in the P rurd 1 meuurements. 111 order to normalize the measurements to a known solar intensity, a reference solar cell 5Q is wnncctcd to the nmplifir 30 through a normalizing circuit 52 that pru- vides a corrective offset to amplifwr 30 as a function of scriar radiation detected by the reference cell.

Since the fluctuatioas in radiation can occur during an I-V merrurwtent, it would be impossible to continu- ally adjust for normalization by m a n 4 muns. Conse- quently, the circuit 52 is designed so that after an initial calibration adjustment the amplifier offset is continually adjusted automatically for accurate normalization dur- ing measurements.

Referring now to FIG. 2, the preferred embodiment is slrowir using u pair of trurrsistora Q1 urrd (I2 itr s Dnr- lington configuration with two current-sensing ele- ments (resistors) 54 and 56, either of which may be connected through a switch SIB. The element 54 is selected for high current levels (5 amps) and the ele- ment 56 is selected for low current levels (0.5 amp).

The voltage signal across the selected current-sensing elmrcnt is cou~led to an o o e n t i o d amvli&r 30A which, togethe; with an operkional amplifkr SB, per- forms the function of the operational ampl i f~ r 33 of FIG. 1. A switch S l D is employed to selectively con- nect the element 54, either directly or through a resistor 511, and to connect the element 56 either directly or through a resistor 60 in order to scale the input to the operational amplifier 30A.

That arrangement is thus equivalent to that shown in FIG. 1 for placing a selectable current-sensing element

, 14 in series with the variable load 16. Consequently, the reference numerals 14 and 16 are employed in FIG. 2 to indicate generally the equivalence. Other reference numerals appearing in FIG. 2 which correlate directly with elements or functional. blocks shown in FIG. 1 are employed in FIG. 2 to indicate that direct correlation. Differences in this preferred embodiment vis-a-vis the configuration of FIG. 1 are obvious to those skilled in the art. Additional circuit elements arc included in the preferred embodiment for obvious and conventional purposes, such as the limiting diodes Dl and D2 at the

base and collect&& the n&ve feedback through the 20 operational amplifier 18 is through the noninverting

(+) input terminal of that amplifm. The output of the progrummod voltayc gcncraior is tlxn applied lo thc inverting (-) input terminal to provide at the output of the operational amplifwr 18 the difference between the

25 output signal applied to the amplifier 24 and the output of thc progri~mm~d voltagc generator 26.

A switch SIA irr tlw c l o d poailiorr slrow~r phccs a resistor 6) in parallel with a resistor 66 to scale the control current to the vu i rbk kmd 16 for a high current

30 output of up to 10 unpa In the opcn position of that switch, only the resistor 66 remains in the circuit to scale the control current for tow output currents as low as 0.316 amps or less. Limiting diodes DS, D6, D7 and Da protect the transiston Q1 and 4 2 from excessive

35 transient voltages. The operational amplifier 24 is provided with a differ-

ential input stage, and tbe inverting input terminal to which the feedback potentiometer # is applied for voltage gain adjustment is connected to a potentiometer

40 611 for introducing through voitage-dividing resistors 78 arid 72, ulrd il coupl~lrg r&sIor 74, lo provnlc 41 vol ln~c offset for adjustment of the output of amplifier 24. The output of the amplifier 24 is opplkd directly to the multiplier 36 and the terminal V of the switch 38. It is

45 also applied through a current-limiting resistor network 76 to the jack VJ for connection to the recorder. The multiplier 56 thw receives the current, I, the voltage. V, for multiplication to provide a signal proportional to power (P=IV) to a termirul of the switch 31) and

50 through a current-limiting network 78 to a jack PJ for connection to the recorder. In that manner, two of the three outputs V. I and P may k selectively connected to a recorder for plotting the I-V characteristic of the solar army, or for plotting power points at selected or

55 otherwise programmed output v01tagts of the solar m a y , while any one of the output sip&, V. I or P may be selected through the switch S for direct measure- ment by the meter 48, or peak detection and measure- ment by the peak detector 45 and meter UI.

60 An exemplary normalizing circuit is shown in FIG. 3. This circuit generates a molar m y current correction which, when added to the army current (I) measured at an in situ insolation _level of S(mW/cm*), results in a normalized current (I) cqresponding to a selected ref-

65 erence insolation level (S) such as 100 mW/cm2. The correction procedure is exprcsscd mathernatacrlly by the following equation wbcrc the superscript s denotes parameters evaluated at the insmtaneous in situ insola-

tion level (S) and the subscript sc denotes short circuit level is only 83 milliwatts per square centimeter, for condition: example. the instrument may be adjusted to compare

tlrc oulput ol' lirc illxny lo surlrc nrursurclrrenl llrrrl Wiis (1) made when the solar array was new and under some

5 known reference solar intensity, such as 100 milliwatts

tcrm added by normalizing circuit. per square centimeter, or for the particular solar insola- tion conditions of that day at some lower reference such

The exemplary normalizing ckcuit shown in FIG, 3 80 Or milliwatts PCr sqUPTe centimeter. implements the term (IS&) (S-Sl for three W r - This normalization is m m p l i h d autonutically selectable reference insolation levels (S) e q d to 100,80 lo once calibration adjustments are and WPlia to all and 50 mW/cmz. Constant voltages proportional to the s u h u c n t current mc t~remen t s of the may . So by negative of the= values are obtained from a fixed refer- measuring the solar intensity in the fuld on a given day, ence voltage and voltage-dividing network consisting .od then effectively forcing the dsu intensity to be of resistors 90, 92 and 94. An additional resistor % is 100% of standard, the circuit $2 ww a u t ~ t i ~ a l l y provided for fine adjustment of the reference voltage. l5 provide normalization. Then if for any r w o n the sun

A voltage proportional to the in situ insolation level intensity varies during measurement, such as might (S) is obtained from reference solar cell 50 by monitor- result from a cloud passing, or even a bird flying over ing its short-circuit currend through shunt resistor 80. A the solar cell, the normalizing circuit cuntinuowly m a - voltage roportiorul to (S-S) is obtained by connect- sures the output of the sun and adjusts in real time any ing the and S vol%W to the summing Junction of variation of the current input from the iolar array to the opetational m p l i f ~ 86 via WWliW resiston 82 and 84 operational amplifier 30A to maintain no-lizption to and switch SSB. 100 mW/cm2, or whatever was established as the stan-

An important fu ture of the correction procedure dard in the laboratory. In that manner, the normalizing defined by Equation (1) is the f ~ c t that the term (12Js) circuit will compenrirte for variations in solar intensity is independent of the incident bolation level (S) and 25 incident on the solar wfik the output of the solar thus is a constant for any given solar array. The term array is k i n g cheeked so that i f it is "83" in one instant (lZsc/s) is inlrduced by using potentiometer 98 lo up- and "85" in the next instant, then "81" in a propriatel~ scale the OutP"' of mplifier The nor- instant, the output of the o p e r a t i d rnplifEr SB is m_alization output thus achieved is equal to (IsJc/S) wnstandy normalized to ulOO" of whrt v.ri- ('-'land is ridded to the meuwed current ations ma9 be occurring in the solar intensity incident utilizi~rg the summing junction of amplifier 3f)A to- tin: ,,uriIlg tIlr ol. ~ u r e m c r r l . gether with coupling resistor 109 i~nd switch S5A. The normalized current output of the operational Before the nordixs t ion circuit can be used it must amplifier 3BB is the in real time be calibrated by setting potentiometer )(I equal to the value of (ISSc/s) for the m a y under test. This is f d l i - 35 plus correction vdue the norrmlizin~ circuit

introducing a Fition in 52 where this wrrcction value is a function of the mea-

swilch SSA-B-C. l,, tk cdibrate position switch sured solar intcrrsity througlr the refcrcoae 4 1 , which i s

(not shown) temporrrrily fo- the 801ar may under the value S while the ficld measuremejts of the solar m t into the condition of hart circuit current through m Y 12 are being mule- The vdue S is a refwmce vhable 16, iae,, p=I,, the same position a intensity set in an initial calibration when the meter is witch SSA shorts resistor 84 to ground, thercby actling first to Ihe but with a switch in s temporarily to zero. under dibration wndi- the calibrate position. The potentiometer 9# is thcn set tions Equation (1) revwts to the following form. to adjust the meter 18 to read zero as the mdtsu~cment

of current. That c~scntially sets within potentiomce 98 45 the value for the constant (I&)/S. The quantity S-S

Ilx I=&+- (-9

(2) may thereafter constantly change as the solar intensity of the sun on the array 12 m d reference cell SO changes, where S is nothing more than the ghr intensity mea-

Pfc = o (if is properly ulibnted) surement by the refemwe cell and S k a standard solar intensity for wnnallzation. The t a m L i n this constant

The &bration p-um is -4 out by gus t ing indicates that calibration of the normalizing circuit is potentiometer 98 so that the nomgd I eqds made under short circuit conditions of the solar array zero when switch 55 is in the calibrate position. 12, that is to say, while the variable load 16 is virtually

allow the incident insolation level denoted by Zero and the switch SlD is in the position shown. Since parameter S to also be monitored m operational ampli- 55 the short circuit current I, is always proportional to S, fier 102 is employed to couple that p.rameter to the if the short circuit current Is is then divided by S, the meter 40 through a switch S7A when that switch is result will be a constant independent of S. here fore, closed as shown, and a switch SIB which selects 1 of' a once this constant has been manually adjusted at any plurality of calibration potentiometers 104 for measure- given time, such as at the beginning of measurements on merit rung= of 31.6, 100 and 316 mW/=d. The djust- 60 the d a r array, the only W t of the enpression for tlrc lnents of those potentiometers are made under labom- output of the normalizing circuit h the term S-S. tory conditions. The output of the amplifier 102 is also which is the only term that ~ R S to be dynunicnll~ coupled to a solar intensity monitoring output by cur- changed during the measurement, and which is auto- rc~rt-limiting resistors 106 md 108. matically changed dynamicrrlly by the normalizing cir-

?'he rcsult of using the normalizing circuit during 65 cuit. Dwing calibration S is simply set to zero by the array measurements is nonnallzation of t h ~ output of switch SSB, and during operrth act to 100, 80 or 50. the array to a known solar intensity SO that if the Once the switch SSB is set to 100, 80 or 50 mW/cm2, instrument is used on a given day when the insolation the zeroing adjustment of the potentiometer 98 will

9 provide normalization of the solar intensity current n~easuretncnts provided to the meter, the multiplier and tire rcc~rdcr.

During operation, the program voltage generator 20 may provide a manually-adjusted voltage, V, through a potentiometer 110 shown in FIG. 4 which illustrates an exemplary circuit diagram for the program voltage generator. The switch S3A is set to the manual position while the program voltage is thus being manually set. The switch 38 is set to the V output terminal in order to observe the manually-set voltage. Once the desired vol~egc lrirs bccn rrra~rually set, tlrc switch 38 may bc sct to thc P or I terminals to measure the power or current produced by the solar array for the particular voltage sct. That is uscful in checking out and analyzing any problems present in the array, but what is more useful is to generate a ramp signal which will sweep the program voltage from virtually zero to a maximum value at a constant, rate over a period of about 10 seconds, in order to record the output current, I, or the output power, P, as a function of voltage, V. The sweep generator re- quircd for that purpose in the program voltage genera- tor is comprised of an operational amplifier 111, shown in FIG. 4, arranged as an integrator with feedback ca- pacitor 112 and input resistor network co~ected to --V comprised of resistors 115 through 117. A switch SGA is wrrndly closed to short out capwitor 112 so that the sweep begins at zero voltage corresponding to the array short circuit condition. Once the switch S6A is opened to initiate a sweep, the input terminal of the npwstional nn~plificr 111 is connected to the negative voltage sourcc to commence charging the capacitor 112 and thus drive the output terminal of the operational amplifier from an initial w o voltage to a predetermined level at a rate which depends up6n whether or not m y of the resistors 115 and 116 are in the input resistance network as selected by a switch S3B used to select three sweep voltage rates. The exact rate of increase is ad- justed by a potentiometer 118. Once the sweep has been completed, the switch S6A is closed to drive the pro- yr;rm~ncd voltugc ycncrator output back to zcro.

In some instances it is desirablp to have a sweep gen- erator which quickly and repeatedly drives the program voltage generator output back and forth between high and low limits, as when using the peak detector # with the mcter 40. That is accomplished by two operational amplifiers 120 iuid 122 with regenentive feedback through a resistor 124 from the output of the amplifier 122 to the input of the amplifier 120 and degenerative feedback from the output of the arnplif~r 122 to the inverting input terminal thereof through a capacitor 126 and a resistor 128. The operational amplifier has direct regenerative feedback through a resistor 130 in order to continually try to drive the operational ampli- licr 122 through a resistor 132 in a positive direction while the feedback circuit of the operational amplifier 122 continually tries to drive the positive input terminal of the amplifier 120 in a negative direction. The result is a silwtooth waveform with positive slopes substantially equal to the negative slopes. Other cyclical waveform generators could be used such as a sinusoidal waveform generator.

Although particular embodiments of the inveation havc becn dcscribcd and illustrated herein, it is rccog- nlzd that r~~odilications and equivalents m y readily occur to those skilled in the art and consequently it is intended t h t the claims be interpreted to cover such modifications and equivalents.

What is claimed is: 1. Apparatus for recording the voltage and current

output of a solar array conrprisiny signalcontrolled means for producing a variable load

5 across a solar array and a current-sensing element in series with said variable load acroas said array for sensing current through said variable load,

feedback control means for sensing the voltage out- put across said array and sensing element in series,

10 and for stabilizing the voltage output across the variabk load for a degired voltage output, mid fccdback control mcans including m e w s for sum- ming a control signal with the voltage outpul,

means for generating said control signal, thereby to I5 program said voltage output, and

means connected to said current sensing element and to said feedback control means for recording the current scnscd through said load as a functio~r or voltane outout.

20 2. ~ ~ p & a t u s defined in claim 1 including a refer- ence solar cell and normalizhn means connected to said - cell and said surrcnt-sensing element for scaling thc current to be recorded as a function of voltage output of said array so as to provide ;a normalized current that

25 corresponds to the array voltage output at a reference level of insolation from solar radiation, whereby all furrcnt rr~cirsurcrne~rlr iuu co~rtinuously trorr~~i~lizcd Lo the reference insolation levei.

3. Apparatus as defined in claim 2 including elec- 30 tronic multiplying means connected to receive said

voltage output and said nomalized currcnt for produc- ing a powcr output signal, means for measuring said voltage output, n o d u e d current or power output signal and switching means for selectively connecting

35 said measuring means to r d v e one of said voltage output, normalized current and power output signal for measurement.

4. Apparatus as defined in claim 3 wherein said mea- suring means includes peak dletccting means.

40 5. Apparatus as defined in clnim 4 wherein mid mea- suring mans includes rrwitclring mcuns for sclcclivcly bypassing said peak detecting means in making m a - surements.

6. Apparatus as defuKd in claim 5 wherein said means 45 for generating said control s i p l includes a ramp signal

generating means, a cyclic wave generating means, and a manually-adjustable static signal generating means, and switching means for selqkting as the control signal the output of the ramp d@ generating m a n s , cyclic

50 wave generating means or static signal generating means.

7. A portable inotrumwt for measuring the voltage, current and power parameters of a photwoltaic solar array comprising

55 a variable load connected iacrosf said array and regu- lated by electronic fecdtp.ck muns in response to a voltage-output signal of' said array, thereby to con- trol the voltage and current output of the array over the full range from substantially short circuit

60 current to open circuit, current scnsing means connected in series with said

variable load for sensin$ current through said load and producing a propohionate loPPd current signal,

multiplying means conncclted to said feedback means 65 and (a &d currcnt senvrng m a n s for providing a

power output signal t b t is the product of said voltage output across said load as regulated by said feedback means and said load currcnt signai,

- -

signal measuring means, and current measurements, or a DC voltage for power parameter selecting means for selectively connecting or current measurements at selected voltage output

su~d volluyc output rrg~lul. wid loud currc111 sitj~lul points, and said power output signal to said meter for a reference photovoltaic solar cell, measurement. 5 a current sensing element connected in series with

8. Apparatus as defined in claim 7 including peak- said variable load, detecting means, ud switching means for selectively means for comparing the output current of said sens- connecting said +detecting means in series between ing element with the output current of said refer- said parameter-selecting means and said signal-musur- encc solar cell to provide a normalizing signal, ing means. 10 means for adding said normalizing si@ to the signal

9. Apparatus as defined in claim 8 including means for from said current-senring element kr order to pro- gcneruting u programmod output voltage control signal vide normali;rcd array current ns a function of and means for adding said programmed output voltage array voltage output, control signal to said voltage output signal in said elec- multiplykg muuu for multiplyin8 the array voltage tronic feedback muns for programmed control of said I5 output and normalized current to provide a mca- voltage output surement of power,

10. Apparatus for measuring on a meter the voltage, switching meam for sdectively connecting the current, and power p u ~ c t c r e of a photovolt8ic solar power, nonnafized current, or voltage output to array under sunlight operating conditions comprising said meter, and

a variable I d comectad a c r m said array, 20 muns for selectively co-t- a peak detector in a voltage regulator which responds to the difference sMies with the selectad signal input to mid meter

between the output voltage of said array and a for peak mcasurcmenb. programmed test control voltage for control of 11. Appwtus as defined in claim 10 including voltage output across said l a , means for recording any of the thra puamcten of

means for selectively generating said contrd voltage 25 power, current and vol tyc thst w be m ~ ~ l ~ ~ o d . ns a single ramp voitagc at n low ratc for mawring 12. Apparatus ac defined in claim 11 wherein said mwer or current as u function of vollage from zero recording 111wrs plots one purunwwr as u I ' U I ~ L I ~ I ) ol' io a maximum voltage output, a repeated ramp another. voltage at a high rate for peak output power or * * I * *

30