PARTIAL SHADING DETECTION IN SOLAR PANEL

PARTIAL SHADING DETECTION IN A PV
PANEL
DONE BY: ARUN PS
CB.EN.P2PWE17001
M-Tech PWE
ASE
Department Of Electrical Engineering 1

INTRODUCTION
 The Industrial Revolution tapped full potential of fossil fuel energy
 Limited availability of fossil fuels
 Human activities have overloaded atmosphere with harmful gases.
 It resulted in climate change and global warming.
 Thus there was a need for a renewable source of energy which will
cause no environmental effects.

SOLAR ENERGY
 Solar radiation is readily available- 300 sunny days per year
 Eco friendly and less maintenance required as there are no moving
parts.
 Can be used in remote locations
 Modularity and silent generation of power
 DRAWBACKS – intermittency
partial shading

POWER CURVE
 Isc – short circuit current
 Voc – open circuit voltage
 Imp/Vmp – current / voltage at
maximum power point
 The solar panel should always
be operated at MPP point
 To achieve this MPPT algorithm (P&O) is used.
Power Curve for a Solar Cell

MPPT
 The MPPT algorithm will ensure the operation of PV panel at MPP, when
there is a change in load

PARTIAL SHADING
 Occurs when a solar cell/ a part of module is under shade
 It will lead to the formation of local hotspot
and the cell will not pump electrons
 A bypass diode connected in parallel to the
damaged cell will solve this problem

PARTIAL SHADING DETECTION??
VOLTAGE VOC
 During partial shading condition there will be formation of local peak.
 the current will decrease in
steps thus delivering a lower
than the rated value
 Such a condition can occur
during uniform irradiance
change
CURRENT/POWERIsc
Global peak
Local peak

EFFECT ON MPPT
 Partial shading results in a multimodal PV curve with several peaks
 The MPPT algorithm has to initiate a global peak search to extract
maximum power
 MPPT cannot differentiate between partial shading and a uniform
irradiance change
 As a result the MPPT will initiate a searching mechanism frequently
which will drop the efficiency of MPPT and the converter used.

HOW TO DETECT PARTIAL SHADING
 LITERATURE SURVEY
 checking sudden and large change in power and setting threshold Pth :
but the change in power between consecutive samples may also be
because of irradiance change.
 Setting a threshold for current Ith. : but no theory for setting Pth or Ith.
threshold values were set by trial and error method.
 If Pth is too large: MPPT cannot initiate global peak search
 If Pth is too small : MPPT will go to false triggering.

Literature survey contd…
 By interpolation technique Pth was selected to be 15% or array capacity
 Pth was set to be 0.1 – 0.2 PMPP
 Pth was set to be 5% of nominal power.
 Normalised deviation of power ⧍P/P was used as reference
All the above mentioned techniques does not have any theoretical support.
 Detection of voltage mismatch in PV modules : but this will require a
voltage sensor in each module

PROPOSED METHODOLOGY
Two designated points on IV curve is scanned ISC and IMPP
Calculation of Irradiance at these points
Find the mismatch in irradiance
Compare the mismatch with that of under normal irradiance

CONCEPT
 Equivalent circuit model of a PV panel
0
arg
tanB
Where
I reversesaturationcurrent
q ch eof electron
V applied biasvoltage
K Boltzmanncons t
T Temperatureof PN diode






CONTD..
Where G – irradiance, Ki – temperature coefficient of current, T – panel
temperature in K
 When the temperature is constant ⧍T = 0
 Always Impp will lie in the vicinity of 0.9Isc

Numerical computation
Thus value of G at
Isc and Impp are
equal

Contd..
 As per the analysis Isc is in the vicinity of 0.8Voc and Impp lies near
0.8Vocarray.
 Thus modifying the equation
 When the MPPT acquires samples
at 0.8Voc and 0.8Vocarray it records the respective current values and
calculates G at the designated points.

DETECTION OF UNIFORM
IRRADIANCE
 Under uniform irradiance the value of G1 is almost equal to G2
• There is an error of 16.7W/m2 under an
G of 1000W/m2
• For G=600W/m2 the mismatch is nearly 0
• For G=400 W/m2 the mismatch is again
17W/m2.
• Thus the mismatch between the G1
and G2 remains within a threshold

SURVEY TO FIND THRESHOLD
 To find the range of mismatch in G a survey was conducted for 10
monocrystalline and 10 polycrystaliine modules
Thus in all the cases the
mismatch was found to be less
than 40W/m2

UPDATING Voc
 Voc is required to initialise the sample points,perturbation size and to
predict the local peak position
 The effect of G on Voc will be less than effect of T. Here the computatioin
of Voc is through the value of G1 and G2
 This is done in 2 steps

Contd…
 STEP 1: prior to partial shading assume that MPP is tracked.
 At any temperature Vmpp is near 0.8Vocarray . While tracking MPP the
algorithm updates Voc under normal irradiance
Vocarray,u = Vmpp/0.8 Voc = Vocarray/Ns
 STEP 2: upon partial shading the MPPT scans currents corresponding
to 0.8Voc and 0.8Vocarray in order to calculate G1 and G2 and finally
Vocarray is updated

ALGORITHM

DYNAMIC SHADING

ADVANTAGES
 Increase in efficiency of MPPT and the converters
 Temperature sensor or irradiance sensor not required as irradiance
value is used to update Voc
 Less number of samples in MPPT – 3 samples. Thus increases the
transient efficiency.
 Lower implementation costs
 Versatile and adaptable
 Prediction error is less than 3%

The future is green energy, sustainability and renewable energy

PARTIAL SHADING DETECTION IN SOLAR PANEL

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