An instrument was developed to continually integrate the energy available in incident light on a specifically oriented surface. The unit was designed for outdoor use in remote locations and is capable of operation over a temperature range of -20 to +60 C with good accuracy. The unit is weather resistant, requires low power, has a high input impedance, is inexpensive, and has a visual readout and an analog output for recording

Masters, R. M.

English

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Produced by the NASA Center for Aerospace Information (CASI) 
https://ntrs.nasa.gov/search.jsp?R=19780006687 2020-03-22T05:42:56+00:00Z
September 1977
11926A'? GlJ 7 ^^ f^ ^l 
;x
ERDA/NASA/1022-77/21
NASA TM-73791
40LAR ENERGY METER
R. M. Masters
National Aeronautics and SpVAdministration
Lewis Research Center
Cleveland, Ohio 44135
(N4SA-T4-737 8 1)	 SOLAR ENHERGY ICT	 (NNASA)
12 p TfC A02/fi g 401	 CSCL 10A
N78-14630
Unclas
G3/44 55255
Prepared for
ENERGY PESFARCH AND DEVELOPMENT ADMINISTRA11ON
Division of Solar Energy
National Photovoltaic Conversion Program
Under Interagency Agreement E(49-26)- 1022I
I
1I	 Rsgxxt No ? Govran rent Accauon No 3	 Recrpre l's Cwlog Ne
NASA TM-73791
4	 Title ind Summit 5	 Re/tort Date
SOLAR ENERGY METER. September 1977
F	 Performing Organrtatrun Code
7	 Authorltl
	
8	 Perfuirnnp Orgsnitahon Report No
E -9358
R. M	 Mastery
10	 Work Unit No
9	 Pet tormmgOrgan,talion Name and Addins
National Aeronautics and Space Administration
I t	 Contract or Grant No
Lewis Research Center
Cleveland, Ohio 44135 	 —
_	 13	 Type of He{rort and Period Curered
12 Sponsor ,q Agency Name and Address 	 Technical Memorandum
Energy Research and Development Administration	 —
Division of Solar Energy	 14 Syoneoring Agency Report ho.
Washington, D. C.	 20545	 ERDA/NA° x1/1022-77/21
IS	 Supoementary Notes
Prepared under Interagency Agreement E(49-26)-1022,
16	 Abstract
An instrument was developed to continually integrate the energy available in incident light on a
specifically oriented surface.	 The unit was designed for outdoor use in rernole locations and is
capable of operation over A temperature range of -200 to +600 centigrade with good accuracy.
The unit is weather resistant, requires low power, has a high input impedance, is inexpensive,
and has a visual readout and an analog output for recording,
17	 Key Words (F ,.iggested by Author(s)l 18	 Distribution Statement
Solar energy Unclassified - unlitnited
Instrument STAR Category 44
ERDA Category UC-63
19	 Security	 Classif	 (of this report) 20	 Security Classif	 (of N.is pagel 21.	 Ne. of	 Peg, , , 22	 Fr^r
Unclassified Unclassifieu
For sale by the National Technical Irllomatlon Service, Springfield, Vlrpiiin 22161
i
AL
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i
J7
SOLAR ENERGY METER
ABSTRACT
An instrument was developed to continually integrate the energy avail-
able in incident light on a specifically oriented surface. The unit
was designed for outdoor use in remote locations and is capable of
operation over a temperature range of -20 to +60 0 centigrade with good
accuracy. The unit is weather resistant, requires low power, has a
high input impedance, is inexpensive, and has a visual readout and an
analog output for recording.
StM4A RY
An instrument was developed to integrate and totalize an instantaneous
analog signal that is directly proportional to the power available from
light impinging on a sensor surface. This was accoml.lished by using a
voltage to frequency converter plus an engineering unit divider that
sets each cycle of frequency equal to a given quantity of energy (i.e.,
1 cycle = 2.8x10-5 watt-hours/square meter). All cycles are then
counted and for each 3.6x105 counts (10 watt-hours/square meter), a
mechanical readout is stepped once to provide a visual display. An
analog output signal is provided fo: continuous recording purposes.
INTRODUCTION
In the design cf Solar photovoltaic power s;-;tems an important quantity
that is required is the amount of Sun energy available at the specific
location under consideration. Weather Atlas information is typically
used for such calculations but may be in error due to midi-climatic
variations in specific locations. Therefore, to establish a basis for
correctness of calculation data and to effect mor3 accurate energy
balance calculations for installed or future systems, an instrument to
measure the actual 'Sun fall energy on a surface at a specific location
is required.
This report describes an instrument using a silicon photovoltaic sensor
that has an output directly proportional to incident light (ref. 1).
The input from the sensor is integrated, totaled, converted to engineer-
ing units and displayed. The output display is now specified as energy
(watt-:ours/square meter) and is use-' directly for solar power system
calculations.
The output is presented two ways by the "Solar Energy Meter", a visual
display and an analog output. The difference between individual read-
ings of the visual display is the total amount of energy available
within the reading time interval. An analog output signal provides a
voltage level directly related to the integrated total and will totalize
1280 watt-hours/squar° meter before automaticall; resetting to zero and
starting over again.
V2
This instrument was designed fot specific use as a "Solar Energy Meter"
and is a special case. But the basic design is flexible and with modi-
fication may be applied to totalizing of any integrated analog signal.
Measurements may be made by totalizing such units as power (solar, wind,
electrical), heat. (temperature), volume (gallons, cubic feet) or any
other unit where a total reading is required. If used in multiples Ir.
a system, energy balance information may be read directly and continu-
ally.
INSTI MENT
General Description
The basic operation of this instrument is as shown by the block diagram
of figure 1. An analog output from the sensor supplies a signal to the
operational amplifier for amplification. That signal at a useable level
is presented to the Voltage to Frequency Converter (VFC) where it is
converted to a frequency dependent or the signal level. The unit 's so
calibrated that each cycle out of the VFC is equal to a specific quantity
of energy which, in this instrument, is 2.78x10-5 watt-hours/square meter
cycle.
Each cycle, the VFC produces an output pulse which is counted and con-
verted into engineering units by dividing the number of counts by
3.6x105
 to give an output calibration of 10 watt-hours //square meter.
Now, the number of calibrated output pulses are counted and displayed
by the following methods. First method is by stepping a six digit
me-nanical counter providing an output that is visually observable.
Delta readings are obtained by finding the difference between two con-
secutive readings. Also available in this unit is a binary counter
with outputs serving as inputs to a digital to analog converter to pro-
vide a 128 step analog output voltage that is directely proportional to
AL.	 the accumulated insolation.
Sensor - Ampiifier
The sencor for this instrument is a 2x2 centimeter silicon photovoltaic
cell. The sensor is calibrated by laboratory methods which provide an
I-V curve at an air mass one intensity of 100 milliwatts per square
centimeter. The silicon cell when loaded near short circuit current
with a 1 ohm precision load provides a millivolt signal across the
resistor. That signal is directly proportional to the Sun energy in-
cident on the sensor surface (ref. 1). This sensor output, if cali-
brated, integrated, and then accumulated, will be a measure of the
total energy incident on the surface o f the sensor and therefore a
surface in the same plane as ^_-he sensc.r.
N3
An amplifier is used to provide sufficient signal gain to allow the voltage
to frequency converter to work over a large frequency range for better
resolution of the input signal. The amplifier also provides one of the
calibration controls, offset adjust, which sets the frequency onset at
zero voltage.
If desired, the input to the amplifier may be ur gd with other signals
that need to be integrated and totalized. This may be done by using; a
simple voltage divider that will provide approximately 100 millivolts full
scale input to the amplifier. The input divider may be expanded into a
multiposition switch that would accept several levels of input voltages
coverinb several decaaes.
Voltage to Frequency Conversion
Voltage is converted to frequency by continually integrating the input
analog signal which is directly proportional to instantaneous power into
the sensor. Whet. the input analog signal is greater than zero volts it
is amplified and then applied to ate active integrator that continuously
accumulates the integration products. The integrator output provides an
output signal that is inversely proportional to the amount of accumulated
integrationbetween each integrator reset condition. Output voltage from
the integrator is applied to one input of a comparator located in the
Vol.tago to Frequency Converter (VFC) where it is compared to an accurate
stable reference voltage applied to the second input. When the integrator
voltage is higher than the reference volt-ge the comparator is in an "off"
condition. Conversely, when the integrator voltage is equal to or lower
than the reference, the comparator is "on" a<id triggers a precision one
shot circuit, in the VFC. The one shot provides a specific quantity of
energy into the integrator which charges the feedback capacitor to res°t
the integrator and initiate the next precision integration cycle.
Because the analog input voltage determines the rate of integrator feedback
capacitor discharge the following conditions prevail. When the analog in-
put voltage is zero the integrator is inoperative since the integrator feed- 	 i
back capacitor is not being discharged except by capacitor self discharge.
If the capacitor is of high quality this self discharge is low and errors 	 j
attributable to it are very small. As the analog input voltage is raised
the integrator discharges at a rate directly proportional to the analog
voltage level. Under this condition the integrator output voltage will
drop until the reference voltage is reached turning on the comparitor and
providing a precise amount of reset energy to the feedback capacitor to
start the next cycle.
Each cycle of integrated energy for this "Solar Energy Meter" is equivilent
to 2.7778 x 10 watt-hours/square meter and the following is :,he method
used to calibrate the unit. Using; the zero set control on the amplifier
set the VFC frequency output to zero. The full scale calibration control
is next sort + o 10,000 hertz with a full scale input corresponding to an input
equal to the milliampere output for an Air Mass one sensor calibration of
4100 milliwatts per square centimeter with the 2x2 centimeter sensor loaded
with a precise 1 ohm load. With the values of components as shown in
Fig. 2, the energy represented by each cycle is shown below.
(1) Cell Calibration = .1 watt
square centimeter,
When the voltage to frequency conversion is set to 10K hertz at the cell
calibration (1) the following calibration for one cycle is as shown in (2).
.1 watt	 10,000 cycles
square cen me of second
or 1 cycle	 .1 watt - second1 x 134 square centimeters
Convert to watt-hours/square meter
	
.1 watt - second	 X 1 x 104
 square centimeters X
1 cycle - 1 x 104 square centimeters square meter 
1 hour
3600 seconds
(2) 1 cycle = 2.7778 x 10 5 watt - hour
square meter
ENGINEERING UNIT DIVIDER
Having determined the amount of incident energy represented by each cycle,
it is necessary to put the output in terms that are useable. This is
accomplished by accumulating a sufficient number of cycles to be equal to
a specific engineering unit. The readout is desired to be in units equal
to 10 watt-hours/square meter; therefore, using the quantity in (2), the
following is determined;
10 watt-hours	 square meter-cycle	 5
(3) square meter	 X	 2.777 x 10 watt-hour	 = 3.6 x ]' cycles
In this instrument the accumulation is accomplished in two steps ',)-:cause
the amount required is lagge. The steps are 32 and 11250 giving the
needed amount of 3.6 x 10	 A programmable divide by N counter is used
to provide the more variable number needed while the 32 figure is obtained
by taking the output from stage 5 of a 12 stage ripple-carry binary
counter/divider.
At this point the positive going signal. is specified to represent 10 watt-
hours/square meter.
DATA ACCUMULATION AND DISPIAY
From the counter step specified to be 10 watt-hours/square meter a signal
is fed to a one shot circuit which provides,
 a pulse of energy sufficient
to step a mechanical counter providing a visual output.
c
i
4.
1^
5
r
The seven steps on the binary counter, from the 6th to 12th, are fed into
a digital to analog network. This network provides an analog :signal direct-
ly proportional to seven binary inputs which provide 128 discrete voltage
levels equal to a total of 1,280 watt-hours per square meter before resett-
ing to zero to begin again.
The display method used to display the accumulated information is dependent
upon the requirements of the user. It may range from the mechanical dis-
play included, strip recorders, and up to sophisticated computer readouts
if desired by the user.
CONCLUDING REMARK:
The basic instrument (figure 3) as described performs the design require-
ment of obtaining the total amount of solar energy impinging on a surface.
The instrument in conjunction with other measuring equipment (figure 4 & 5)
has been placed into operation in several areas such as Puerto Rico,
Arizona, New Mexico, Ohio, California, and New York with more areas to be
specified. At NASA Le RC a unit has been placed in close proximity to
laboratory type solar radiation detection devices and results are being
compared over long term operation.
Nominal supply voltage range of the Solar Energy Meter is 11 to 20 volts
with a power requirement at the 12 volt level of 0.1 watts. input-output
signals and operating power are supplit.d through a connector to a weather
resistant case that houses the electronics. Initial calibration of the
solar energy meter is made at 20 0C and provides ar input voltage to out-
put frequency curve that is a straight line of zero slope which is linear
within 0.1% o-rer the full input range. The meter is capable of operation
over a range of -200 to +600
 centigrade with a calibration curve change
that is less than ±1% of full scale reading. At all temperatures the
_inearity stays within 0.1% range. Errors may be reduced by use of internal
compensation if required.
This instrument may be configured as a completely self contained unit with
its own power supply as viewed in figure 3. An internal 12 volt nominal
Nickel-Cadmium battery is charged by a solar array panel located Just below
the sensor cell. This method provides continuous power for remote oper-
ation of the "Solar Power Meter".
Applications requiring integration and totalization are the uses to which
modifications of this instrument may be used. Specific uses such as
electrical energy, temperature, volume flow and others are dependent
upon the sensors and inputs available. Several units may be combined to
provide total energy balances of operating systems.
Reference
1. Selcuk, Kudret; and Yellot, John I.: Measurement of Direct, Diffuse,
and Total Solar Radiation with Silicon Photovoltaic Cells. Solar
Energy, vol. 6, no. 4, 1962, pp. 155-163.
SUN SENSOR,0PERAIIONAI
	
VOLTAGE TO FREQEENCY CONVERTER
0 100 mWlcm 2	AMPIIFER	 10 kMI • 100 mw sradcm2
ZERO	 FULL
ADJUST	 SCALE
CALIBRATE
r
t?-y
i
OF'pL)()R (41JA 
1,17TI
MECHANICAL	 OUT BUFFER BINARY ADDER ENGINEERINGMAX TOTAL
ixto$ W Wm2 AhlPllilfR lS8	 101y Km
UNIT DIVIDER
; 0. 36► 106
OUTPUTS
DIVISOR SET 10EN6INEERIN6 UNII
CONVERSION FACTOR DESIRED.
N
LNVERSIO
ANALOG'^P
1280 W	 1 "2
Figure 1.
	
• Block diagram of "Solar Ener iy Meter."
14
VOLTAGE TO
1	 ACTIVE	 FREQUENCY CONVERTERAMP 4 RV 3403	 INTEGRATOR	 +	 RV 4151
39 K	 10	 1 RV 3403A
+ K 100
P3(OXO) 
	
g 6 5K 5K
SIGNN:	 9– 	 T	 10 K	
6.8 K
IN
75 K 	 1	 4	 68001
=	 O
[i 
	 2 3
OFFSET
= ADJUST
FULL
	
SCALE	
25 K
ZR	
TRIM
4
_
13 12 STAGE
BINARY COUNTER
12 C04040	 +
To CD 4040 l6
8 VO:.	 78MO8HM 14 ()
2
R • 5 K	 1fRR
REGULATOR 7 4
^8 V DC 15 6 8
10
^	 REG 5 16
l 3 32
+ ANALOG ANALOG 2 128
12	 20 V DC OUTPUT
VOLTAGE
ADJUST 13 25615 MFU l2 512
MECHANICAL —_ 141024
COUNTER 15 2048
l0 K 1 4096
DIVIDE BY "M'
COUNTER CD4059
4, 6, 8, 9, 11,13, 14,17, 20, 22, 24	 +
1 CLOCK
23 OUTPUT
2, 3, 5, 7,10,12,15, 16, 18, 19, 21
N • 11250
I K	 11	
12	 10	 8	 It 8	 RV 3403A
—	
}MFD BY RAYTHEON
13	 9	
RV 415] 
	
4.7 MFD	 N • 112
2N3053
	 CD4001
COUNTER
DRIVER
Figure 2. - Schematic for "Solar Energy Meter."
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Figure 5. - Inner view energy measuring data system.


Solar energy meter

Abstract

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