|Title of Invention||
DIGITAL INSOLATION METER
|Abstract||Accordingly, there is provided a portable compact digital insolation meter for accurate measurement of incident solar radiation data, comprising a single crystal silicon solar cell adaptable as a transducer for generating a current directly proportional to a subjected insolation intensity; a shunt resistance for receiving an output from the solar cell and converting the output to a proportional voltage; a regression matching means for correcting the proportional voltage developed across the shunt resistance and transmitting a corrected signal; an analog to digital (A/D) converter for receiving the corrected signal and outputting a processed digital signal; and a display device for receiving the processed digital signal from the A/D converter and displaying measured data.|
HELD OF THE INVENTION
The present invention relates to solar renewable energy systems. In particular,
the present invention relates to instruments for measuring incident solar
radiation data. More particularly, the invention relates to a portable compact
digital insolation meter for accurate measurement of insolation data.
BACKGROUND OF THE INVENTION
Measurement of broadband and spectral terrestrial solar radiation is of
fundamental importance for the evaluation and deployment of solar renewable
energy systems. It is now well known that the uncertainty in economic analysis
of solar energy systems is directly proportional to the uncertainty of solar
resources data. Even after installation of a solar power system, a regular logging
of solar radiation data is mandatory to ensure efficient operation of the system.
Besides solar power projects, laboratories and solar technologies product
manufacturing industries need various kind of insolation (Incident Solar
radiation) data for their day to day operation. The success of products and
technologies delivered by such organizations are highly dependent on the
reliability and accuracy of the solar radiation data available to them.
Standard sophisticated instruments like pyranometer & pyrheliometer are not
suitable for large-scale use because of high cost, poor commercial availability &
need of specialized knowledge for their handling.
Measurement of solar radiation is generally based on the principle in which the
total hemispherical (solar disk + sky) solar radiation (G), received by a horizontal
surface, constitutes sum total of two components - (i) Direct beam radiation (B)
from the solar disk projection on the surface (being modified by the cosine of the
incidence angle of the beam, I); and (ii) Diffused radiation or Sky radiation (D),
which is scattered by atmospheric layers of the sky dome. Relationship can be
G = B cos (I) + D
The typical instruments used for terrestrial radiation measurement are usually
Pyranometer, Pyrhellometer, Shaded Band Pyranometer etc. (Refer figure - 1).
Total hemispherical radiation can be measured by pyranometers, that respond to
radiation within 2P steradian (hemispherical) field of view. Pyrheliometers, being
a narrow field of view instrument (5-0° to 5.8°), can measure nearly collimated
radiations from the 0.5° diameter solar disk and small part of the sky.
Hemispherical sky radiation or diffused radiation can be measured by shading a
pyranometer with a disk located to subtend the same angular field of view as a
The aforesaid sophisticated instruments, although providing more or less
accurate insolation measurement, however are not suitable for large-seale use
because of two main reasons:
a) They are quite expensive and stability is restricted.
b) They can be handled only by skilled persons with specialized knowledge.
These restrict the use of such instruments for collecting sufficient amount of
solar radiation data.
A plurality types of hand held solar radiation meters are available, which
measures the intensity of global incident solar radiation (G) in units of watt/m2.
But many of them are analog meters (moving coil type). So they suffer from
typical limitations like sluggishness of response, backlash error, error caused by
non horizontal position of resting, parallax error of reading etc. Simple digital
insolation meters, though free from aforesaid limitations, mostly cannot offer a
measurement quality which is comparable to the Pyranometers. So the readings
collected by such hand-held meters are only meant for indicative purpose and
not suitable for laboratory / industrial application. These meters also cost
substantially high besides scarce commercial availability.
OBJECTS OF THE INVENTION
It is therefore, an object of the invention to propose a portable compact digital
insolation meter which is capable of capturing a wide range of measurement
data enabling analysis and processing of the captured data to arrive at an
Another object of the invention is to propose a portable compact digital
insolation meter, which can be adapted by any person of average intelligence.
A further object of the invention is to propose a portable compact digital
insolation meter, which is simple in construction and offers sufficient ease of
A still further object of the invention is to propose a compact digital insolation
meter, which is cheap and easily maintainable.
An yet another object of the invention is to propose a portable compact digital
insolation meter, which provides direct readout and ready for use insolation data.
A still another object of the invention is to propose a portable compact digital
insolation meter, which eliminates the initialization requirements like zeroing or
SUMMARY OF THE INVENTION
Accordingly, there is presided a portable compact digital insolation meter for
accurate measurement of incident solar radiation data, comprising a single
crystal silicon solar cell adaptable as a transducer for generating a current
directly proportional to a subjected insolation intensity; a shunt resistance for
receiving an output from the solar cell and converting the output to a
proportional voltage; a regression matching means for correcting the
proportional voltage developed across the shunt resistance and transmitting a
corrected signal; an analog to digital (A/D) converter for receiving the corrected
signal and outputting a processed digital signal; and a display device for
receiving the processed digital signal from the A/D converter and displaying
BRIEF DESCRIPTION OF THE ACCOMPANYING DRAWINGS
Fig. 1 (a) - shows a black and white pyrometer of prlor art used for
measurement of solar radiation data.
Fig. 1 (b) - shows a pyrheliometer with tracker of prior art.
Fig. 1 (c) - shows a shaded pyranometer of prior art.
Fig 2 - depicts a relationship between intensity of insolation and current of a
single crystal silicon solar cell according to the invention.
Fig 3 - shows a flow chart including operation of a portable compact digital
insolation meter according to the invention.
Fig. 4 - shows a pictorial view of the insolation meter of the present invention.
Fig. 5 - shows a graphical representation of the comparative performance
characteristic of the insolation meter of the present invention in respect of the
prior art instruments.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE
The basic requirement for insolation measurement is a suitable transducer, which
can generate a voltage or current directly proportional to the available intensity.
The linearity of this transducing characteristics affects the level of accuracy of
the insolation meter. Single Crystal Silicon Solar cell is a good choice for such
transducer. Short Circuit Current of a crystal silicon solar cell (Ise) changes
linearly with change in insolation level. It is noted that the aforesaid opticat
current can be obtained by short circuiting the two terminals of the solar cell
even when it has no biasing voltage. Based on this principle, a circular single
crystal Silicon Solar cell (1) has been used as the main transducing sensor of the
digital insolation meter. Figure - 2 shows a linear relationship between insolation
level and Ise of the sensor cell as verified in an experimentation stage of the
As shown in fig. 3, the insolation (Is), received by the sensor solar cell (1) from
the Sun disk and the sky, is converted to a proportional voltage (Vs) across a
shunt resistance (2). The voltage developed across the shunt resistance (2) is
corrected through a simple regression matching means (3) applied for calibration
purpose. The corrected signal (Cs) is applied to the input of a standard dual
slope integrating A/D converter (4) and the digital output signal (Ds) of the A/D
converter (4) is read through a display device (5).
The innovative digital insolation meter can be put to actual use in roof top or
laboratory environment by just holding it in such a way that the sensor (1)
remains horizontal. There is no scale selection or zeroing requirement. As the
meter is switched on, insolation measurement is carried out continuously with
the display device (5) updating the measured data 3 times every second without
any flicker. The insolation meter is powered up by a standard 9 volts dry cell &
power consumption requirement is similer to that of a standard multimeter. The
relevant technical parameters of the meter are as under :-
• Auxiliary supply : 9 (7-11) VDC
• Display : 3-1/2 digits
• Display refreshing rates : 3 readings / sec
• Resolution of measurement : 10 W/m2 i.e. 0.01 kW/m2
• Accuracy : ± 2% with respect of reference pyramometer
• Dimension : L 120mm x W 80mm x D 45mm (approx.)
• Weight: 200gms (max)
PERFORMANCE ANALYSIS AND COMPARATIVE EVALUATION
To assess the actual performance of the innovated meter, the measured data
have been compared with concurrent measurements taken by a prior art
Pyranometer. The experiment has been carried out over a period of almost one
year (November 2004 to October 2005) to verify the performance of the digital
insolation meter under changing climatic conditions round the year. Such
environmental conditions include scorching summer vis - a - vis chilled winter,
humid days during rainy seasons vis- a - vis dry days around winter, dear,
partial cloudy and overcast sky conditions etc. To take care of the spectral
content variation of sunlight from sunrise to sunset, reading during a day have
been collected in multiple sessions, spreading from 8:00 am to 5:00 pm.
The performance of the present meter has also been further compared with an
internationally adapted digital meter of prior art. The comparative scatter plots of
concurrent measurement amongst the present meter, a pyranometer of prior art,
and the internationally adapted digital meter of prior art, are shown in Fig - 5. It
can be clearly understood from these plots that the measurements taken by the
three instruments have high degree of equality. In fact a high value of
correlation coefficient (R2 > 0.99) in each case gives enough confidence about
the matching performance of the present meter with respect to any pyranometer
of prior art.
It has also been assessed from the above comparative study that the
measurement accuracy of the present Digital Insolation meter in within ± 2% of
the reference pyranometer.
In this context, it is worth mentioning some different constructional features of
this digital insolation meter with respect to the other reputed (brand X) digital
meter available in the market.
• In brand X meter, a high quality calibrated silicon solar cell from reputed
source has been used as the insolation sensor. In the present meter, any
small size single crystal silicon solar cell can be used. No calibration of the
cell is required according to the present invention.
• The sensor silicon solar cell, used in the branded meter, has parallel grid
structure (3 gridlines/cm) with a central bus bar, whereas the present
meter uses a circular cell with simple annular grid.
• In the branded meter the sensor is covered with a special coating of
transparent lacquer. In present inventions no such coating is required.
• Key parameters of the two sensor cells are shown in table - 1. It can be
clearly seen that the present invention is capable of adapting a sensor
with much less efficiency & fill factor. This in turn indicates that much
cheaper cells can be easily used in the present invention compared to
prior art meters.
• Temperature compensation circuitry is used in the prior art meters. In the
present meter such correction is done by a statistical regression matching
TABLE 1 : Comparative chart for the key parameters of the sensors,
used in the two digital insolation meters (at insolation = 500W/m2).
Accordingly, the innovative meter constitutes a simple and economic one, yet
can deliver high quality of insolation measurement. Thus by virtue of its user
friendliness & affordabillty, this meter can have wide applications across the solar
industries, power stations, field engineers, academic scholars etc. Laboratories
lacking in high-grade infrastructure can also use it for their solar radiation data
collection purpose with adequate confidence.
1. A portable compact digital insolation meter for accurate measurement of
incident solar radiation data, comprising :-
- a single crystal silicon solar cell (1) adaptable as a transducer for
generating a current (As) directly proportional to the subjected
insolation intensity (Is);
- a shunt resistance (2) for receiving an output (As) from the solar
cell (1) and converging the output to a proportional voltage (Vs);
- a regression matching means (3) for correcting the proportional
voltage (Vs) developed across the shunt resistance (2) and
transmitting a corrected signal (Cs);
- an analog to digital (A/D) converter (4) for receiving the
corrected signal (Cs) and outputting a processed digital signal
- a display device (5) for receiving the processed digital signal (Ds)
from the A/D converter (4) and displaying measured data.
2. The isolation meter as claimed in claim 1, wherein the sensor (l)
constitutes a circular single crystal sillcon solar cell.
3. The insolation meter as claimed in claim 1, wherein the sensor (1)
comprises a simpler grid structure silicon solar cell.
4. The insolation meter as claimed in claim 1, wherein the display device (5)
is a 3-1/2 digit LCD with refreshing rate = 3 readings /sec.
5. The insolation meter as claimed in claim l, wherein the resolution of
measurement is not less that 0.01 KW/m2.
6. The insolation meter as claimed in any one of the preceding claims,
wherein a standard 9 volts dry cell supplies the required power to operate
7. An accurate portable compact digital insolation meter for accurate
measurement of incident solar radiation data as herein described and
illustrated with the accompanying drawings.
|Indian Patent Application Number||247/KOL/2006|
|PG Journal Number||31/2009|
|Date of Filing||23-Mar-2006|
|Name of Patentee||BENGAL ENGINEERING & SCIENCE UNIVERSITY|
|Applicant Address||SHIBPUR, HOWRAH|
|PCT International Classification Number||G01W 1/00|
|PCT International Application Number||N/A|
|PCT International Filing date|