A small residential PV-system of 1.5 kWp is analysed for yield and failures after running during 5 years: Easy to understand example on terms such as specific yield, annual yield, irradiation and solarPV electricity. Typical 'camel back' curves stand for high summer yields and low to nothing in winter.

1. Solar power analysed
A close lock into 5 years of operation of a small
residential PV-system
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brought to you by goMicromorph PV-School

2. Energy Yield of a PV-system
Average Annual Energy
Annual Energy (kWh)
2000
1'878
1600
Energy (kWh)
1'564
2008
2009
1'644
1'603
1'653
2012
2013
1'479
1200
800
400
0
2010
2011

3. Annual specific yield
2000
1'878
1600
Energy (kWh)
Formula 1:!
Specific Yield = energy yield / nominal
solar power
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Example:!
A PV-system of 1.5 kWPeak installed power
(6 modules à 250 W) generates in a good
year 1800 kWh of electricity.
a) calculate the annual specific yield.
b) calculate the average monthly specific
yield.
Solutions:
a) Ya = 1800 kWh / 1.5 kWp
Ya = 1200 kWh/kWp = 1200 h/a
b) Ym = Ya / 12 = 100 h/m
Average Annual Energy
Annual Energy (kWh)
1'564 1'603
1'644 1'653
1'479
1200
800
400
0
2008
2009
2010
2011
2012
2013
The most meaningful figure of a solarPV system is the specific yield, indicating the energy
per installed power - or the number of full operation hours per year or per month.

4. Annual specific yield
Average Annual Energy
Annual Energy (kWh)
2000
1'878
Energy (kWh)
1600
1'564 1'603
1'644 1'653
1'479
1200
800
400
0
2008
Nominal PV power: Pg = 1.5 kWPeak
Installed: 2007
Thin-film silicon (aSi) modules,
new micromorph modules installed 2012
New nominal power: Pg = 2 kWPeak
2009
2010
2011
2012
2013
Specific Yield (kWh/kWp)
Ya
Pg!
1043
1069
986
1252
1096
827
1.5
1.5
1.5
1.5
1.5
2.0

5. Monthly energy yields
Spec.Yield 2010
Spec.Yield 2011
Spec.Yield 2012
Spec.Yield 2013
Average
8
10
Spec.Yield 2009
Specific Yield (kWh/kWp)
180
135
90
45
0
1
2
3
4
5
6
7
9
11
12

6. Monthly energy yields
Spec.Yield 2010
Spec.Yield 2013
180
Spec.Yield 2011
Average
Spec.Yield 2012
Spec.Yield 2009
Average
Specific Yield (kWh/kWp)
180
135
135
90
90
45
45
0
0
1
2
3
4
5
6
7
8
9
10 11 12
1
2
3
4
5
6
7
8
9
10 11 12

7. Average yields
Spec.Yield 2011
Average
Spec.Yield 2012
Spec.Yield 2009
Average Annual Energy
Annual Energy (kWh)
2000
1'878
1600
135
Energy (kWh)
Specific Yield (kWh/kWp)
Spec.Yield 2010
Spec.Yield 2013
180
90
1'564 1'603
1'644 1'653
1'479
1200
800
45
400
0
0
1
2
3
4
Monthly values
131 149 146 156 148
16
19
82
19
25
49
28
5
6
28
7
13
8
7
9
13
2008
10 11 12
118
76
36
4 Average
15
13
19
4 Std. Dev
119% 135% 60% 21% 19% 9% 5% 9% 13% 17% 52% 97% Std. Dev %
2009
2010
2011
2012
Yearly values
1637
kWh/kWp
134
kWh/kWp
8%
%
Large variations on monthly basis, less variation from year-to-year comparison.
2013

8. 0
Year
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
Sum(Max(Energy/
Wpeak (Wh/W)))
Monthly energy yields
Energy (kWh/kWp)
100
2
2008
3
2009
2010
4
2011
5
2012
6
2013
7
Year within Month
8
9
10
11
12

9. 0
Year
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
Sum(Max(Irradiation (Wh/m2)))
Monthly irradiation
200000
Irradiation (kWh/m2)
100000
2
2008
3
2009
2010
4
2011
5
2012
6
2013
7
Year within Month
8
9
10
11
12

10. 0
Year
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
0
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
2008
2009
2010
2011
2012
2013
Sum(Max(Irradiation (Wh/m2)))
Sum(Max(Energy/
Wpeak (Wh/W)))
Energy - Irradiation
Energy (kWh/kWp)
100
2
2008
3
2
3
2009
2010
4
2011
5
4
2012
6
5
6
2013
7
7
Year within Month
8
8
9
200000
9
10
10
11
11
12
Irradiation (kWh/m2)
100000
12

11. Do the sun-hours and the
electricity-hours correlate?
Average Annual Energy
Annual Energy (kWh)
8
2000
1600
6
Energy (kWh)
Electricity (kWh/kWp/day)
1'878
4
1'564 1'603
1'644 1'653
1'479
1200
800
400
2
0
2008
0
0
2.25
4.5
6.75
Irradiation (kWh/m2/day)
Daily energy Yield versus
irradiation 2008-2013
9
2009
2010
2011
2012
2013
Specific Yield (kWh/kWp)
yearly
1043
1069
986
1252
1096
827
monthly
87
89
82
104
91
69
daily
2.9
2.9
2.7
3.4
3.0
2.3

12. Linear fits of daily
energy-irradiation
Irrad'08 (kWh)
Irrad'11 (kWh)
Irrad'09 (kWh)
Irrad'12 (kWh)
Irrad'10 (kWh)
Irrad'13 (kWh)
Electricity (kWh/kWp/day)
0.830
-0.059
0.872
-0.096
0.733
-0.013
2013
y = 0.8194x - 0.1653
-0.030
2012
4 y = 0.7335x - 0.0134
0.895
2011
y = 0.8723x - 0.0956
0.129
2010
6 y = 0.8298x - 0.0591
0.914
2009
y = 0.8949x - 0.0299
d
2008
8 y = 0.914x + 0.1291
m
0.819
-0.165
2
0
0
2.25
4.5
Irradiation (kWh/m2/day)
6.75
Lowest system performance in the
year 2012 due to broken PV9
modules.

13. Conclusions
•
Energy yields vary:
- strongly looking on a monthly basis (up to 135% for some
months)
- less on a year to year basis (only 8% over the past 5 years).
•
A convenient figure comparing solarPV systems is the
specific yield (Ya) on an annual time scale. It gives
comparison of all sizes of PV-systems.
•
Yields correlate well with the sun irradiation.
•
Correlating irradiance with yield brings up operational
problems of the PV-system.

14. Further reading
See us on
www.gomicromorph.com
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http://gomicromorph.blogspot.ch/
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twitter.com/goMicromorph
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ch.linkedin.com/in/gomicromorph/
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http://www.youtube.com/user/
goMicromorph
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http://www.slideshare.net/PVschool
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https://itunes.apple.com/ch/artist/
luc-feitknecht/id513205568?
l=en&mt=11

15. More reading
You may like also
•
•
Cloud enhancement: a few slides
on the surprising effect of clouds
boosting the solarPV yield
http://www.slideshare.net/
PVschool/clouds2-25195039
!
!
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The cost of solar electricity: the
key to solar electricity is sun and
cheap money
http://www.slideshare.net/
PVschool/cost-of-solar-electricity
!