EFFECT OF POWER CHARACTERISTICS ON SOLAR PANELS: HANDS-ON PROJECTS FOR CLEAN ENERGY SYSTEMS CLASS

Birce Dikici and Javier Jalandoni

Department of Mechanical Engineering

Embry-Riddle Aeronautical University (ERAU), Daytona Beach

ABSTRACT

In this paper, experiments that can be introduced to Clean

Energy Systems classes are described. The experiments

investigate the effect of power characteristics (temperature,

shade and tilt angle) on solar panel electricity production. Solar

cell efficiency is the ratio of the electrical output of a solar cell

to the incident energy in the form of sunlight. The energy

conversion efficiency of a solar cell is the percentage of the

solar energy to which the cell is exposed that is converted into

electrical energy. Extreme temperatures can cause a decrease in

solar panel’s power output and airstream can dissipate the heat

and bring the solar panel to its normal operating condition.

Solar panel efficiency is undesirably affected by heat and

improved with introducing cooler medium.

As well as heat, solar panel loses its power when a part of it is

shaded by trees or surrounding buildings. Before solar panel

systems are designed for homes, usually a detailed shading

analysis of the roof is conducted to reveal its patterns of shade

and sunlight throughout the year.

By the same manner, how solar panels react to the direct and

indirect rays from the sun in order to produce electricity is

examined through experiments. Voltage, current and power

flowing into a resistor are measured when the angle of the solar

panel relative to the light source is changed. The tilt angles to

the electrical measurements are linked to the differences in

electrical generation.

Students can perform experimental procedures explained here

and gain the conceptual understanding of the Solar Energy

better. The investigations require student explanation of the

question, method, display of data with the critical response from

peers.

NOMENCLATURE

b, constant depending on the properties of the semiconductor

junction

q, electronic charge

H, incident light intensity

I0, the saturation current

ISC, short circuit current

k, Boltzman constant

R, temperature coefficient

𝑆, the solar insolation incident on the solar panel

𝑆𝑠𝑢𝑛, the solar irradiation

T, temperature

V, voltage

Voc, open circuit voltage

𝜃, tilt angle

Subscripts

amb, ambient

mod, module temperature

STC, standard test conditions

1. INTRODUCTION As energy crisis, climate change, ozone depletion, global

warming, and oil price fluctuation continue to increase; the use

Proceedings of the ASME 2016 10th International Conference on Energy Sustainability ES2016

June 26-30, 2016, Charlotte, North Carolina

ES2016-59384

1 Copyright © 2016 by ASME

of renewable energy will become an increasing trend that will

affect the next generation of society. However, it is apparent

that there is still not a general understanding about the benefits

of using clean energy sources. There is a need to educate

communities about sustainable energy to reach a large audience

in inventive and effective ways.

Instructors in engineering and related disciplines struggle to

find new ways to motivate and excite students about science

and technology and maintain the excitement of current students.

Although recognition of the active, hands-on science education

has been demonstrated clearly, implementation of such

pedagogy in engineering education has been slow. Student

achievement in science can only be increased by awareness,

appreciation for the technology for the tools, materials and

curriculum that support hands‐on learning [1].

In-class studies explained below examine the effect of power

characteristics (heat, shade, and tilt angle) on solar panel

electricity production.

1.1 Effect of heat:

Because the current and voltage output of a PV panel is affected

by weather conditions, it is important to characterize the

response of the system so the equipment associated with the PV

panel can be sized correctly. The average operating voltage and

current of a PV system is important parameters for safety

concerns, equipment capabilities and minimizing the amount of

wire required for construction. Engineers follows the

techniques to estimate how much energy a PV power plant can

generate over its lifetime by using the weather data, including

historical temperature and solar irradiation information [2].

Temperature affects how electricity flows through an electrical

circuit by changing the electron speed. This is because of an

increase in resistance of the circuit that results from an increase

in temperature. Since the weather changes during the day and

solar panels are installed in different climate regions, most

panels do not operate under ideal conditions [2].In some cases,

cooling systems are designed to keep the panels within certain

temperatures. Solar power panels in extremely hot climates may

pass a cool liquid behind the panels to absorb the heat. Cooling

systems that use outside air, fans and pumps can be designed

[2].

Solar cells exchange photons for electrons. Photons from the

sun with sufficient energy near the depletion region of a p-n

junction generate electron-hole pairs. When these electrons

have enough energy, they will move to the conduction band,

leaving holes in the valence band. The potential difference

across the depletion region creates an electric field that pulls the

electron to the n-region and hole to the p-region. The newly free

electron can flow from the n-region to the p-region and

recombines with the newly created holes. In this way the energy

of the incident photon is converted [3]. Since solar cells cannot

produce energy at a constant rate, the power delivered at a

certain instant is still very much a function of climatological

factors. The open circuit voltage and short circuit current

depend on parameters like solar irradiance and the temperature

as shown in Eqn. 1 and 2 [3].

𝑉𝑂𝐶 =𝑘𝑇

𝑞𝑙𝑛

𝐼𝑠𝑐

𝐼0 (1)

𝐼𝑠𝑐 = 𝑏𝐻 (2)

While it is important to know the temperature of a solar PV

panel to predict its power output, it is also important to know

the PV panel material since the efficiencies of different

materials have varied levels of dependence on temperature. The

temperature dependence of a material is described with a

temperature coefficient, R. as shown in Eqn.3 [2].

𝑉𝑂𝐶,𝑎𝑚𝑏 = 𝑅 × (𝑇𝑆𝑇𝐶[℃] − 𝑇𝑎𝑚𝑏[℃]) + 𝑉𝑂𝐶,𝑟𝑎𝑡𝑒𝑑[𝑉] (3) For polycrystalline PV panels, if the temperature decreases by

one degree Celsius, the voltage increases by 0.12 V so the R=

0.12 V/C. The general equation for estimating the voltage of a

given material at a given temperature is given in Eqn. 4. [2].

𝑉𝑂𝐶,𝑛𝑒𝑤 = 0.12[𝑉/𝐶] × (25[℃] − 𝑇𝑎𝑚𝑏[℃]) + 𝑉𝑂𝐶,𝑟𝑎𝑡𝑒𝑑[𝑉] (4)

1.2 Effect of shade:

As the angle of the sun changes through the year, trees and other

barriers may become shading problems. Shading depends on

the size, height, and proximity of surrounding objects. Proper

design will minimize shading during peak mid-day production

periods [4].

PV array is typically installed on the roof of a house, and partial

shading of the cells from neighboring structures or trees is often

expected. Partial shading of a photovoltaic array reduces it

output power capability. Some past studies assume that the

decrease in power production is proportional to the shaded area

and reduction in solar irradiance, thus shading factor is

suggested. While this concept is true for a single cell, the

decrease in power at the module or array is often not linear with

the shaded portion [5].Therefore, the relative amount of such

degradation in energy production cannot be determined in a

straight forward manner [5].

1.3 Effect of tilt angle:

In order to optimize solar isolation on solar collectors,

determining solar tilt angles at any given time is essential to

increase the efficiencies of the collectors. The position of the

earth relative to the sun changes with time. Therefore, the

change must be monitored well in order to increase the amount

of energy being received by solar devices. [6].

2 Copyright © 2016 by ASME

The magnitude of solar radiation received by a collector is a

function of several factors such as location latitude, the

declination angle (the angular position of the sun at solar noon

with respect to the plane of the equator), tilt angle, the sunrise

hour angle and the azimuth angle [6].The output power of a PV

panel depends on atmospheric conditions, such as direct solar

radiation, air pollution, cloud movements, and load profile, as

well as tilt and orientation angles. The tilt angle of the PV

module is the angle measured between the PV module and a

horizontal surface representing the x direction. PV modules

generate the maximum power when they are directly facing the

sun. For grid-connected installations where PV modules are

attached to a permanent structure, the PV modules are tilted at

an angle equal to the latitude of the installation site to optimize

their power generation throughout the year [7].

Solar trackers automatically move to “track” the progress of the

sun across the sky, thus maximizing output. Solar trackers are

slightly pricier than their stationary counterparts, due to the

more complex technology and moving parts necessary for their

operation [8].

2. EXPERIMENTS 2.1 Experiments for measuring the effect of heat: In order to understand the effect of heat on voltage output in a

solar panel, students assembled a circuit containing the voltage

sensor and the solar panel. They measured the temperature

change of the solar panel and corresponding voltage output of

the solar panel as the temperature changes. Temperatures

around a solar panel would be highest during the highest

daytime temperatures and with little to no wind circulation [9].

For observing the effects of heat, the voltage outputs were

measured using the equipment accompanied by the PV cell,

while current was measured using a digital multimeter (DMM)

from the Physical Sciences laboratory. These measurements

were done on Oct. 25, 2014 (between 11:30am-12:30pm with

an average temperature of 26°C) on two separate instances: (1)

with the solar cell without any cooling agent, and (2) with the

solar cell with a cooling agent placed behind it. The cooling

agent used was a MooreBrand Reusable Hot/Cold Compress.

The Gel Pack has a pliable gel formula that remains flexible

after freezer storage and is placed behind the solar panel.

2.2 Experiments for measuring the effect of shade:

To understand the effect of shade on voltage output in a solar

panel, students assemble a circuit containing the voltage sensor

and the solar panel. They are asked to determine materials to

use for soft and hard cover. Students consider conditions in

nature that partially block sunshine from falling on the solar

panel and their effect on voltage production. They also set

variable conditions, such as the distance of the light source and

the amount of solar panel to cover. They recorded and calculate

the mean voltage [9].

Two classifications of shade were used: (1) soft shade and (2)

hard shade. For the soft shade, a sheet of bond paper, and as a

hard shade 5 sheets of bond paper are used.

Bond paper is used to experiment the effect of shade. Bond

paper’s percentage air volume is given as 34.2, typical thickness

is given as about 60-80 μm and typical bursting strength is

between 150-200 kPa. Whiteness of paper is the extent to which

paper diffusely reflects light of all wavelengths throughout the

visible spectrum. The procedural standards for the

measurement of whiteness are described in ISO 11475. Bond

paper’s %ISO is between 70-92. Since paper is composed of a

randomly felted layer of fiber, its structure has a variable degree

of porosity [14].

1W photovoltaic (PV) cell (purchased from Horizon) and a

60W incandescent lamp is used. The voltage outputs were

measured using the equipment accompanied by the PV cell,

while current was measured using a digital multimeter (DMM)

from the Physical Sciences laboratory. These measurements

were performed on two separate instances: (1) without shade

covering the PV cell, and (2) with shade of various degree of

opacity covering the PV cell. The current and voltage was also

measured while the PV cell was under direct sunlight.

2.3 Experiments for measuring the effect of tilt angle: To understand the effect of shade on voltage output in a solar

panel, students can construct a circuit containing the voltage

sensor and the solar panel. Students set the tilt angle of the solar

panel and measure the output voltage at various tilt angles.

Students explore the relationship between the angle of solar

radiation falling on a solar panel and the production of voltage

by the panel. Students investigate the effect of solar insolation,

tilt angle, and voltage output, effect of axial tilt and seasonal

change on solar insolation [9].

For discussing the effects of tilt angle on a 1W photovoltaic

(PV) cell, the voltage outputs were measured using the

equipment accompanied by the PV cell, while current was

measured using a digital multimeter (DMM) from the Physical

Sciences laboratory. These measurements were done using a

commercially available 60W lamp as a light source to help

demonstrate the solar insolation incident on a solar panel.

Fig. 1 shows the test setup for testing the effect of heat, shade

and tilt angle.

3 Copyright © 2016 by ASME

Fig. 1. Test setup for testing the effect of heat, shade and tilt angles

3. RESULTS 3.1 Experimenting the effect of heat: To illustrate the temperature dependence of voltage across the

solar panel, a temperature vs. voltage graph is shown in Fig. 2.

The figure shows the experimental results for the experiment

and it indicates that if the temperature of the solar panel

increases, the voltage decreases and inversely, voltage remains

high if its temperature is remained relatively low. Fig. 2

illustrates the nominal response of the solar panel is due to the

heating of the solar panel surface.

Fig. 2. Nominal Temperature vs Voltage Profile

To further illustrate the temperature and voltage profiles, their

temporal response is shown in Fig. 3.

Fig. (3.b) shows a steady decline in voltage vs. time.

(a) Temperature vs Time (5 min.)

(b) Voltage vs Time (5 min.)

Fig. 3. The effect of heat on PV Cell

When the PV cell is exposed to the Sun, its temperature

increases (Fig 3a) while the voltage output (b) decreases due to

the temperature dependence of the dark current.

It is noted that there are slight oscillations in the temperature in

Fig. (3a). These oscillations are due to the gusts of wind that

were present during the experiment that would interfere with

the temperature profile of our experiment. Fig. (3.a) shows a

periodic disturbance every 10-20 seconds. However, these

effects were minimal and did not affect the overall expected

behavior of the solar panel; a general increasing trend was still

observed. Hence, it can be concluded that the voltage output

decreases from 2.3V to 2.18V as temperature increases.

(a) Temperature vs Time (10 min)

(b) Voltage vs Time (10 min)

Fig. 4. Effect of Adding a Coolant Pack

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Fig.4 shows the effect of adding a coolant pack. Notice the

decline in temperature in (a) and a high steady-state voltage

output shown in (b).

Fig. 4 displays the temperature and voltage profiles of the PV

cell when a coolant is added to the back of the PV cell to counter

the effects of solar thermal heating. Fig. (4.a) shows an overall

decreasing temperature profile with oscillating readings due to

the occasional gusts of wind. However, in this part of the

experiment the voltage output readings for the first 4 minutes

were fluctuating quite rapidly and a clear pattern was not

observed. After reaching the allotted time, it is observed from

Fig 4.b that the PV cell reached a final voltage output of 2.28

V. The effects of the coolant maintained the optimal voltage

output of the PV cell (indicated in Fig. (3.b) at 𝑡 = 0).

(a) Temperature vs Time (10 min)

(b) Voltage vs Time (10 min)

Fig. 5. Effect of Removing Coolant

Fig. 5. shows the effects of removing the coolant. Notice the

increase in temperature in (Fig. 5a) and a gradual decrease in

voltage in (Fig. 5b) once the coolant was removed.

After the measurements were taken of the effects of a coolant

on the PV cell, the coolant was removed to confirm that the PV

cell would be affected negatively. A ten-minute observation

time was performed to see the consistency with the previous

experiment. Once the coolant was removed, an increase in

temperature was observed by a decrease in voltage (as seen by

Fig. 5.a and 5.b).

3.2 Experimenting the effect of shade: The lamp was placed 4 inches directly above the PV cell with

zero angle of inclination. Using the voltage probe of Sparkvue,

a graph (Fig. 6) was produced indicating the voltage output

produced by the PV cell. The graph also indicates instances

where shade was added to block some light from entering the

PV cell.

Fig. 6.Voltage from 1W PV cell

Fig. 6 shows the voltage from 1W PV cell. In this figure, the

red line indicates the voltage with no shade present, the green

with soft shade, and the blue with hard shade. It is observed that

there is a significant decrease in voltage with increasing shade

opacity. In Table 1, a digital multimeter was used to measure

the current for each shade. Their corresponding power output is

also indicated.

Table 1: The current and power measurement depending on

shade type

Shade Type Current (mA) Power

(W)

None 144.4 0.3168

Soft shade 46.3 0.0926

Hard shade 10.7 0.0202

From the Table 1, it is observed that power output decreases as

the opacity of the shade increases.

3.2.1 Sun as a Light Source: Once measurements were performed for the 60W lamp, an

experiment was performed again to measure the voltage and

current produced by the Sun on a clear sunny day. (2:00 pm on

Sept. 21, 2014 in Daytona Beach, FL). The digital multimeter

was used to measure the voltage and current produced. Results

are shown on Table 2.

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Table 2: The current and power measurement on clear sunny day

Voltage (V) Current (A) Power (W)

2.2 0.76 1.672

3.3 Experimenting the effect of tilt angle:

Table 3. The voltage output versus tilt angle

Tilt Angle (degrees) Voltage Output

0 1.96 V

10 1.82 V

20 1.75 V

30 1.68 V

40 1.60 V

50 1.53 V

60 1.46 V

70 1.39 V

80 1.32 V

90 1.25 V

Table 3 shows the corresponding voltage output with the

respective tilt angle made by the incident light. The voltage

output is inversely related to the tilt angle, thus an increase in

the tilt angle results in a decrease in voltage output. Fig. 7

Fig. 7. Measured power versus tilt angle

4. DISCUSSION

In the ‘Effect of heat’ experiments, students compared solar

panel voltage outputs when exposed to lamp and a sunlight.

Students can also try different ways to cool the solar panels.

They could think about the ideas to cool a solar panel, such as

using a fan, liquid cooling, and water spraying,

Overheating due to excessive solar radiation and high ambient

temperatures will reduce the solar panel

efficiency. Research/design problem could also be posed here

to investigate an innovative ways to cool a solar panel and

suggest a preliminary design.

In the ‘Effect of shade’ experiments, students can also

investigate if shading a particular portion of the solar panel

affect voltage more than shading the other portions of the solar

panel. For completely opaque objects such as a leaf, the decline

in current output of the cell is proportional to the amount of the

cell that is obscured [10]. Students can use natural materials

such as soil, dirt (such as bird droppings), leaves, shadows that

can actually cover the solar panel. They can observe and

compare the effect of shadng of an opaque or transparent object.

As a research/design part of the project, they can offer designs

to wipe and clean the debris efficiently from the solar panels.

In the ‘Effect of tilt angle’ experiments students used different

tilt angles to observe the effect on power generation of solar

panel. Tracker systems follow the sun throughout the day to

maximize energy output. In these experiments, students can

also observe how tilt angle affect voltage production as latitude

changes. As a research/design problem, students can investigate

various ways of tracking and can design a solar tracker. There

are many different kinds of solar trackers, such as single-axis

and dual-axis trackers. Installation size, local weather, degree

of latitude, and electrical requirements are all important

considerations that can influence the type of solar tracker that

is best for the occasion [8].

Creativity, imagination, and knowledge are all required in the

work of science and engineering. Through the explained

experiments, students can decide between alternative solutions

and propose designs. Students can be asked to present their

results to classroom. Solving technological problems results in

new scientific knowledge [9].

5. CONCLUSIONS Solar panel experiments that can be introduced to Clean Energy

Systems classes are described in this paper. From the data, it is

observed that minimizing shade on a PV cell plays a critical role

in maximizing the voltage, and hence energy generated by a PV

cell. An object with a large opacity can greatly affect the

production of PV cell, and great care in minimizing the amount

of shade on the PV cell must be taken into consideration.

Furthermore, the power output of the PV cell does not depend

on just the voltage output produced (which can be affected by

debris obstructing incident light), but on current output (which

is affected by the intensity of the incident light).

It is observed from the experiments that the effects of heat on a

PV cell can be detrimental to the voltage output. From a voltage

output maximum of 2.3V to a voltage output minimum of

2.18V, an added 5% decrease in efficiency was observed and

calculated. Due to the inherently small efficiency of a PV cell

to convert sunlight into electricity (10% to 25% [13]), this

added increase of 5% is significant and shows the overall need

6 Copyright © 2016 by ASME

of a coolant for the solar panel. Cooling the PV cell is

demonstrated to control the effects of heat on the PV cell. The

coolant, the cold compress that can be purchased in any

pharmaceutical drug store would be a great addition as a

teaching material for future instructors to help demonstrate the

increment of the performance of a solar panel.

It is observed that the effects of tilt angle on a PV cell affects

its voltage output thus power output due to a change in incident

irradiance from the light source. It is imperative to have the

solar panel directly facing the light source to ensure maximum

power production. It is observed that a solar tracking device

would be useful in obtaining the maximum power a solar panel

is able to produce.

Mathematical tools and models help students gather data.

Students constructed explanations and communicated results.

Students were able to identify problems and tried to find

solutions or improve current technological designs.

Through the explained experiments, students formulate a

hypothesis for the scientific concepts and the designed the

experiment. They demonstrate procedures and conceptual

understanding of scientific investigations. The investigation

also require student explanation of the question, method,

controls, display of data and a presentation of results with a

critical response from peers. While students engage in

discussions and arguments, they learn scientific concepts better.

These discussions are based on scientific knowledge, their use

of logic, and evidence from their investigations [9].

5. ACKNOWLEDGMENTS All the work was conducted in the Clean Energy Laboratory

and Physical Sciences laboratory at ERAU. The grant and

support provided by ERAU is gratefully acknowledged.

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