1. Solar Energy
Calculating Energy Efficiency Lecture 3
Dr. Basman M. Hasan Alhafidh
Department of Computer Engineering
College of Engineering
Mosul University
2. Agenda
Solar energy basics
Overview of the major sources of energy
How solar Panel convert light into electricity
Calculating Energy Efficiency
Electrical and Mechanical components of a solar panel system
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3. Calculating Energy Efficiency
In a previous lesson,
- We looked at the maximum efficiencies of laboratory grade photovoltaic cells.
- We see efficiencies constantly going up and up and up.
- How is that efficiency calculated and how can we use that to our advantage as we begin
to select a photovoltaic module?
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4. Calculating Energy Efficiency
In this segment, we're going to
- Define the solar standard and Solar Test Condition (STC).
- We'll also learn how to calculate electrical power.
- We'll determine and calculate the efficiency using a photovoltaic specification sheet.
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5. Calculating Energy Efficiency
Brightness of the sun.
- Approximately 1,000 watts per square meter => Bright sunny day, around mid-latitude
on earth.
For a cloudless sky without any humidity:
- We measure the brightness within that one square meter and it is 1,000 watts.
- Dividing the 1,000 watts by one square meter, gives us this definition of 1,000 watts
per square meter. (we define this value as the solar standard = Power going in)
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6. Calculating Energy Efficiency
We combine that brightness with:
- The standard temperature of 25 degrees Celsius and Another term called air mass to
give a definition that combined solar and climactic conditions is 1.5.
these three pieces are what are going into determining the efficiency of our
photovoltaic modules.
1- The brightness.
2- The temperature.
3- and the air mass.
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7. Calculating Energy Efficiency
Now that we know how to measure the solar input, let's begin to look at how we
measure the electrical output from a photovoltaic module.
There are two fundamental units that we measure for a photovoltaic module to begin
to figure out how much power it's producing.
1) Voltage Unit: is as that push of electricity. How hard the electrical motion is
pushing from one side to the other side of the module.
2) Current Unit: is a flow rate or how fast the electricity is moving through the wire.
Power (output power) in watts = V (volts) * I (amps) 7
8. Calculating Energy Efficiency
If we want to measure the efficiency of a solar panel, we need to calculate
(output power/ input power) on the same unit of area.
For photovoltaic,
- we can measure V and I to get P, P(output power) = V * I.
- Then divide that by the area of the module.
- We then divide by the power of sunlight per square meter
to yield the efficiency.
Or we could use the listed efficiency on a manufacturer's specification sheet for every
commercial solar panel they produce which include five common terms.
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9. Calculating Energy Efficiency
The five common terms for commercial solar panel:
1) The voltage at maximum power (Vmp): The voltage being put out by the solar panel,
2) The current at maximum power (Imp): The current that's being put out under maximum
power
3) The maximum power (Pmax) is the power of the solar panel = Vmp x Imp.
4) Open-Circuit voltage (Voc), which is the maximum voltage that the cell will ever put out,
5) and the Short Circuit current (Isc), which is the maximum current the cell (Module) will
ever put out.
Note* Remember again that these are all under Standard Test Conditions (STC).
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10. Calculating Energy Efficiency
Under special conditions
1) A cloudy day: A photovoltaic module will still work but the output is less than its
maximum power because the current has gone down.
2) Temperature dependency value: Solar panel voltage decreases as the cell gets
warmer which is one of the biggest issues in IRAQ.
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11. Calculating Energy Efficiency
Under special conditions
So, the efficiency goes down slightly from standard test conditions.
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12. Calculating Energy Efficiency
let's calculate the maximum power (Watts) in the specification sheet,
30.1 (volts) x 7.7 (amps) = 232 (watts).
Note* However, the panel is not one square meter in size.
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13. Calculating Energy Efficiency
So, we'll have to adjust for the size of the actual photovoltaic panel.
For this particular panel, the length is 1.47 meters by 1.1 meters
wide.
=> 1.47 x 1.1 = 1.62 square meters.
232 𝑤𝑎𝑡𝑡𝑠
1.62 𝑠𝑞𝑢𝑟𝑒 𝑚𝑒𝑡𝑒𝑟
= 143 watts per square meter.
=> So, Efficiency =
𝑂𝑢𝑡𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
𝐼𝑛𝑝𝑢𝑡 𝑃𝑜𝑤𝑒𝑟
=
𝐸𝑙𝑐𝑡𝑟𝑖𝑐𝑎𝑙 𝑂𝑢𝑡𝑝𝑢𝑡
𝑆𝑜𝑙𝑎𝑟 𝐼𝑛𝑝𝑢𝑡
=
143 W/m2
1000 W/m2 = 0.143.
Solar panel would have an efficiency rating of 14.3%.
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14. Calculating Energy Efficiency
Summary, we should now be able to:
- Define the standard test condition and brightness of full sunlight.
- Calculate electrical power using current and voltage measurements to get wattage.
- Determine and calculate photovoltaic efficiency using a photovoltaic modules
specification sheet.
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