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1. Solar Photovoltaic Theory

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1-2. Potentialassessment

- Contents

1-2. Potential assessment1-2-1. Basic principle of assessment1-2-2. Insolation measurement1-2-3. Estimation of annual power generation1-2-4. Case practice

Sun light from any direction

PV

REFLECTED

1m

1m

Horizontal plane

- Insolation

Solar radiation (Insolation ) is “light energy” from sun.

- Solar radiation (insolation) reaches the ground as:
- direct radiation
- diffused radiation

Global Radiation(Insolation)

Energy received within a unit time

Energy: kWh/m2

Power: kW/ m2

1.00 kW/m2( 0.093 kW/f2 )

1.35 kW/m2(0.125 kW/f2 )

Green

Out of atmosphere( 1.35 kW/m2 = 0.125 kW/feet2)

Ground surface on the equator( 1.00 kW/m2 = 0.093 kW/feet2 )

Absorbed by H2O , O2 , O3, CO2

Visible

- Insolation spectrum on the surface of ground

- Various effects for insolation

- Local latitude effect
- “Air mass” effect( Atmospheric path length effect)
- Seasonal effect
- Weather effect
- Face rotation effect
- Surrounding obstacles effect( Shading effect )

: Local latitude

I0

I0

I0

I0

Earth

-90 deg(S pole)

0 deg(Equator)

+90 deg(N pole)

- Effect of Local Latitude

Actually, you can measure this value

Local Horizontal Insolation

mathematical Cosine curve

1.0 kW/m2(0.093 kW/feet2)

about 1.0 kW/m2(0.093 kW/feet2)

(kW/m2)

I0 (kW/m2)

1 m

m

1 m

- Effect of Local Latitude

Rectangle plane towed sun light

Meaning of convert equation

Horizontal plane

Insolation energy of the tilted plane(yellow) and the horizontal plane(blue) is same.

Tilted plane(yellow plane)

Horizontal plane(blue plane)

B

c

a

A

C

b

- A-2 Triangle Function ( Cosine Function )

Please calculate by your handy computer

Example

Ideal tilt angle = local latitude

Ideal PV plane

Your horizontal plane

I0

You are here

I0

Local latitude is

Earth

- Best tilt angle

Best tilt angle is almost same as “local latitude”

Lp (Light pass length)

Air

Air Mass =

I0

At (thickness of air)

I0

mathematical Cosine curve

I0

With Air mass effect

I0

Earth

-90 deg(S pole)

0 deg(Equator)

+90 deg(N pole)

- Effect of “Air mass” ( Atmospheric path length )

At

Lp

about 1.37 kW/m2( 0.125 kW/f2 )

about 1.0 kW/m2( 0.093 kW/f2 )

- “Atmospheric path length” depend on its latitude.

Air mass effect

LatitudeMax.Min.

Japan+35degJun.Dec.

Singapore 0degMar.Sep.Jun.Dec.

Australia- 35degDec.Jun.

- Effect of Season

- Effect of Season

Seasonal effect is more strong in high latitude

-13 Samoa

+1 Kiribath

-17 Vanuatu

-21 Cook Is.

kWh/m2day

-8 Tuvalu.

+34 Japan

Month

Data in JAPAN

Fine day

Cloudy day

Actual output / Rated capacity

Rainy day

Time

- Effect of Weather

Daily output curve of various weather condition

- Key factor of solar resource
- Latitude
- Atmospheric path length
- Length of daytime

- Opportunity of fine day.

- Latitude

Almost same in PPA countries

Depend on the geographical aspect.

Insoration6822 (MJ/m2year)Utilization15.8%

Fine day77.5%Cloudy day17.9%

Nandi

Fiji

Insoration6131 (MJ/m2year)Utilization14.2%

Fine day68.4%Cloudy day21.2%

Suva

- Effect of Weather

Location = 35N

Face to S

W

E

Face to SE

Face to SW

S

Insolation

610121418

Time

- Face-rotation effects on daily insolation curve

- If you rotate PV module face to East, output peak will shift to earlier.
- If you rotate PV module face to West, output peak will shift to later.

Northern hemisphere

Face to S

Face to SE

Face to SW

Insolation

Face to S

Face to SE

Face to SW

Insolation

Face to S

Face to SE

Face to SW

Insolation

610121418

- Face-rotation effects on daily insolation curve

- This effect is more strong in high latitude.
- Low latitude area (under 15deg), this effect is negligible.

Latitude15N

Latitude35N

Latitude60N

- Latitude effect

- Seasonal effect(depended on sun height angle)
- Air mass effect

Insolation

- Weather effect

Summer

- Seasonal effect

Winter

Time

61218

Day light time

- Various effects on daily insolation curve

- Necessity of on site insolation measuring

Key factor of solar resource

- Latitude dependent
- Atmospheric path length
- Length of daytime
- Seasonal sun height-angle

- Weather dependent
- Opportunites of fine day
- Mist in the air

- Site situation
- Shade of mountain, tree, buildings
- Contamination by dust, salty gusts

Easy to estimate

Easy to estimate

Easy to estimate

Un-known

Un-known

Difficult

Un-known

On site insolation measuring is necessary before planning.(at least 1 – 3 years. Use meteorological observatory data)

PV

- Basic theory of PV panel adjustment

Basic theory of PV panel adjustment

- You cannot avoid these effect.
- The best things you can do are to:

Latitude effect

Air Mass effect

Seasonal effect

Daily effect

Weather effect

Obstacle shad effect

- Tilt PV plane the same as your latitude.- Face true north or true south.

Face to N or S (as possible as you can)

same angle as latitude

Avoidable. Try to find good location

+deg

At 45N point, Optimum tilt angle is45 – 7 = 38 deg

45 deg

local latitude

difference between local latitude and optimum tilt

-7deg under

In low latitude region such as 10 to 20 deg, error is negligible

-deg

- Basic theory of PV panel adjustment

(Note)

- In high latitude locations, the optimum tilting angle is slightly lower than the local latitude.

By using computer, you can calculate accurate tilting angle easily.

- Insolation of the world

1 (kW/m2)

Output 1 kW

Rated Capacity “1 kW”

1 (kW/m2)

Generate 1 kWh for 1 hour

Rated Capacity “1 kW”

- Definition of PV’s Rated Capacity

Note: This is the definition that,we use metric system here.

“Rated capacity 1kW” means

( Power )

If insolation is 1 kW/m2, this PV can output 1 kW.

( Energy )

If PV has 1 kW/m2 insolation in 1 hour, this PV can generate 1 kWh

1 (kWh/m2day)

Generate 1 kWh for a day

Rated Capacity “1 kW”

- Definition of PV’s Capacity

“Rated capacity 1kW” means

( Accumulated Energy )

If PV has 1 kWh/m2day, this PV can generate 1 kWh for a day

In resource assessment, “Accumulated Insolation (energy)” is used widely.

Daily accumulated insolationkWh/m2day

Monthly accumulated insolationkWh/m2month

Annual accumulated insolationkWh/m2year

1 (kW/m2)

Generate 1 kW

Rated Capacity “1 kW”

1 (kW/m2)

Generate 1 kW

Rated Capacity “1 kW”

- Definition of PV’s Capacity

“Efficiency” parameteris already included in “Rated Capacity”.

- High-efficiency PV ( Single crystal PV 15% )

If you use “rated capacity”, you don’t have to consider about efficiency.

- Low-efficiency PV (Amorphous PV 8 %)

Module is larger.

- How to observe Insolation

Pyranometer for Horizontal Global Solar Radiation (Insolation)

Pyranometer

Horizontal plane

- How to observe Insolation

Pyranometer for Horizontal Global Solar Radiation (Insolation)

Sun window (receives light from all directions)

- Place Pyranometer on thehorizontal plane.
- Make sure no shadow is cast all day long.
- Clean upper window frequently.

20 cm

Instant valueXX.XX (kW/m2) orAccum. valueXX.XX (kWh/m2)

Data logger

Insolation data is very common in meteorology. Ask your meteorological observatory for local insolation data.

Metric(m)Imperial(feet)

MJMJ / m2yearMJ / feet2year

kWhkWh / m2yearkWh / feet2year

x 3.60

x 1 / 10.76

Pyranometer for Global Solar Radiation

- There are many units of Insolation data.

Be sure to note which unit your pyranometer is using.

- Example of raw data (monthly data)

Date

January

Accumulating Time

Average Insolation for a day

(kWh/m2day)

- Example of raw data ( Annual data)

Daily average Insolation

Summarize

Annual total insolation

I0

I0

I0

Earth

- Convert “horizontal insolation” to “tilted insolation”

Raw insolation data( Horizontal insolation )

Horizontal to Tiltedconversion

Plane ofPV Panel(Tilted same as local latitude)

I0

Hj

I0

I0

Earth

Hj : Tilted insolation

Hj(kWh/m2year)

PV Module Plane(Tilted as local Latitude)

I (kWh/m2year)

Measured Plane (Horizontal)

(kWh/m2year)

(kWh/m2year)

- Convert “horizontal insolation” to “tilted insolation”

(Note) This conversion can be used in low latitudes (less than 20deg.)

- Convert “horizontal insolation” to “tilted insolation”

Meaning of convert equation

(kW/m2)

I

Hj(kW/m2)

1 m

Insolation energy of the tilted plane(yellow) and the hori-zontal plane(blue) is same.

m

1 m

Tilted plane(yellow plane)

Horizontal plane(blue plane)

Local Latitude = -10 (deg)

Horizontal InsolationI = 2,000 (kWh/m2Year)

(kWh/m2year)

(kWh/m2year)

(kWh/m2year)

- Convert “horizontal insolation” to “tilted insolation”

(Example)

Hj = 2,031 kWh/m2year( Tilted insolation )

I = 2,000 kWh/m2year(Measured raw data)

10 deg.

Actual generation energy

Hg = 70% (System Efficiency)

- Converter Loss8%
- Surface Contamination7%
- Temperature Rise 15%

Pu = Rated Capacity of PV Module (=1.0 kW)hg = System efficiency (= 0.7 depending on type of PV cell)H = Tilted Plane Insolation in kWh unit.

- Actual generation energy of PV

(Example)

Tilted InsolationHj = 2,031 (kWh/m2Year)

PV rated capacityPu=10 (kW)

(kWh/year)

- Calculate “Load Factor ( Syaytem Utilization parameter)"

- To estimate various capacities of PV system, calculate Unified Parameter,called"Load Factor (System Utilization Parameter )".
- This parameter means “Annual average output power” of unit capacity of the PV system.

p = Annual Available power for Unit Capacity of PV Module

Pu = Unit Capacity of PV Module (=1.0)

(Example)

Annual power generationp= 14,217 (kWh/Year)

PV rated capacityPu=10 (kW)

16.3 (%)

(kWh/year)

- Calculate annual power by System Utilization Parameter

(Example)

If you install a 50kW PV system in this place, how much power can you generate?

System utilization parameterUg= 0.158 (%)

PV rated capacityPu=50 (kW)

Local Latitude = -15 (deg)

Horizontal InsolationI = 1,800 (kWh/m2Year)

PV CapacityPu = 5kW

- Exercise

(Insolation data)

Step1Convert “horizontal insolation” to “tilted insolation”

Step2Calculate annual earned energy

Local Latitude = -15 (deg)

Horizontal InsolationI = 1,800 (kWh/m2Year)

PV CapacityPu = 5kW

(kWh/m2year)

(kWh/m2year)

(kWh/m2year)

(kWh/year)

- Exercise

(Insolation data)

Step1Convert “horizontal insolation” to “tilted insolation”

Step2Calculate annual earned energy

- Exercise

Step3Calculate “Load Factor"

Step4If you install 50kW PV system in this place, how much energy (kWh) can you earn?

14.9 (%)

(kWh/year)

- Exercise

Step3Calculate “Load Factor"

Step4If you install 50kW PV system in this place, how much energy (kWh) can you earn?

Case Practice

February has 28 days