Raising the Standards for Solar Photovoltaics and Accelerating Deployment
Submitting InstitutionLoughborough University
Unit of AssessmentElectrical and Electronic Engineering, Metallurgy and Materials
Summary Impact TypeTechnological
Research Subject Area(s)
Mathematical Sciences: Statistics
Engineering: Materials Engineering
Economics: Applied Economics
Summary of the impact
A reduction in planning uncertainties and financial risks of
photovoltaics has been achieved by developing internationally accepted
standards. Non-standardised characterisation and unreliable energy
prediction caused a performance gap between expectations and realistic
yields. Loughborough University (Prof. Gottschalg, Dr. Betts) conducted a
series of research projects since 1999 which reduced this performance gap.
The team consciously transferred developed methods to international
standards for energy prediction and device characterisation.
Standardisation has, with significant contributions from this team,
resulted in the reporting period in a reduction of at least 2% calibration
uncertainty, which has a value at today's prices of $1.500,000,000 per
year (J. Wohlgemuth [5.1]).
The research at Loughborough University (LU), by Prof Gottschalg (at LU
since 1994, academic post from 2000 to date) and Dr. Betts (at LU since
2001, academic from 2010 to date) was undertaken as part of a variety of
different funded projects, all addressing the general area of energy yield
and characterisation of photovoltaic devices. The overarching question
answered in the research is how do photovoltaic devices interact with the
environment and how much energy these devices can actually contribute.
There are several key influences that were investigated, overall
contributing to uncertainty in the energy yield prediction:
- Device characterisation. Determining the output at certain
(standard) conditions [G3.3, G3.4 and G3.5] developed characterisation
methods for energy relevant performance characterisation. The quality of
these characterisations is typically proven in intercomparisons between
the leading laboratories, which were conducted in G3.4 and organised for
G3.1 and G3.2. These brought leading laboratories together and enabled an
exchange of ideas which resulted in a proven reduction in measurement
uncertainties in the field. It also enabled a modification of the
IEC6004-5 standard that was then written up as a standard by Prof.
Gottschalg. 3.3 & 3.5 are examples of the resulting work.
- Technology specific effects. Different PVg technologies behave
differently. G3.5, G3.3, G3.2 and G3.4 considered specific technologies
and how these could be measured in a standardised way to reduce
uncertainty. 3.2 and 3.3 are examples of the resulting work.
- Understanding the actual operating environments. One
overarching aim of the work conducted at Loughborough University is to
create energy rating standards. This requires the generation of
standardised data sets. G3.1, G3.4 and G3.5 worked on this, with a
particular link to the European Joint Research Centre's European Solar
Test Institute (ESTI) based in Ispra.
- Modelling the actual site dependent performance. The strength
of the Loughborough team is the modelling of the incident spectrum and the
input into the relevant standard sections can be attributed to the
submitting team. Work on this was carried out in G3.2, G3.3 and G3.5.
The detailed metrological research has resulted in a number of innovative
procedures of how to minimise the uncertainty in measurements or how to
assess the uncertainty in `non-standard' measurements, which were
previously assessed by broad assumptions. These measurements are key for
an accurate energy prediction as e.g. shown in G3.4 that the metrology of
devices is one of the two dominant sources of modelling uncertainty. The
detailed assessment methodologies, as e.g. presented in R3.6, enabled the
reduction of measurement uncertainty by working on the appropriate
It is not always possible to measure the required parameters for any
model. The team has developed new measurement apparatuses (G3.3, G3.5)
that allow the measurement of device parameters with to date unbeatable
repeatability and thus allows a much more accurate assessment of e.g.
spectral effects in the laboratory. As an example, the combination of
spectral, thermal and intensity changes demonstrated in 3.5, which was the
basis of G3.5, has not been achieved since and was the first qualified
solar simulator based on LED technology.
References to the research
Academic Papers Supporting the Impact:
The quality of the journals used for the dissemination is an indicator for
the strength of the research, as the journals indicated below are the
highest rated journals in the field of photovoltaics.
[3.1] Roy, J., T. Betts and R. Gottschalg (2012). "Accuracy of Energy
Yield Prediction of Photovoltaic Modules." Japanese Journal of Applied
Physics 51: 10NF01-11-10NF01-15; DOI: 10.1143/JJAP.51.10NF01
[3.2] Cole, I. R., T. R. Betts and R. Gottschalg (2012). "Solar
Profiles and Spectral Modeling for CPV Simulations." IEEE Journal of
Photovoltaics 2(1): 62-67, DOI: 10.1109/JPHOTOV.2011.2177445
[3.3] Monokroussos, C., M. Bliss, Y. N. Qiu, C. J. Hibberd, T. R.
Betts, A. N. Tiwari and R. Gottschalg (2011). "Effects of Spectrum on
the Power Rating of Amorphous Silicon Photovoltaic Devices." Progress in
Photovoltaics 19(6): 640-648, DOI: 10.1002/pip.1080
[3.4] Huld, T., R. Gottschalg, H. G. Beyer and M. Topic (2010). "Mapping
the performance of PV modules, effects of module type and data averaging."
Solar Energy 84(2): 324-338, DOI:
[3.5] Bliss, M., T. R. Betts and R. Gottschalg (2010). "Indoor
Measurement of PV Device Characteristics at Varying Irradiance,
Temperature and Spectrum for Energy Rating." Measurement Science and
Technology 21(11): 1-11, DOI: 10.1088/0957-0233/21/11/115701
[3.6] Strobel, M. B., R. Gottschalg, G. Friesen and H. G. Beyer (2009).
"Uncertainty in Photovoltaic Performance Parameters — Dependence on
Location and Material." Solar Energy Materials and Solar Cells 93(6-7):
1124-1128, DOI: 10.1016/j.solmat.2009.02.003
The journals these papers are published in have the most rigorous review
process and are amongst the highest cited in the field. Another quality
indicator is that the team was invited against significant competition to
join an European Metrology Research Project as one of two groups not being
National Metrological Institutes (the other being Fraunhofer Institute for
Solar Energy — the world's leading PV research institution). The team has
also been invited to be the only UK member in the EU-FP7 infrastructure
project Solar photovoltaic European research infrastructure (SOPHIA).
Further indicators would be that Prof Gottschalg has given invited
presentations on the three highest rated conferences in the world
(European PVSEC, Asian-Pacific PVSEC, IEEE-PVSC) on the topic. Thus the
international community seems to rate the work very highly.
Research Grants which provided the expertise and environment
||Stability and Performance of Photovoltaics (STAPP) PI – Prof Gottschalg
||PV-Catapult Lead Institution – EPIA
PI (Loughborough) – Prof Gottschalg
||Advanced Fellowship: Optimised Efficiency of Thin
Film Photovoltaic Device (ARF) PI – Prof Gottschalg
||A Science Base on Photovoltaics Performance for Increased Market
Transparency and Customer Confidence (PERFORMANCE)
Lead organisation – Fraunhofer Institute ISE
PI (Loughborough) – Prof Gottschalg
||Fast Energy Rating for Photovoltaic Devices and
Modules (FENRA) PI – Prof Gottschalg
Details of the impact
The research at Loughborough University contributed to an overall
significant reduction in the uncertainty in the photovoltaic market by
transforming research work into international standards. The impact has
been on reduced uncertainties in calibration and energy yield prediction.
The impact of calibration or power measurements is largely on the retail
value of photovoltaics. Energy impacts on the operation and finance side
of the business.
Photovoltaics (PV) is a new energy technology, and one of the key factors
slowing down market developments is a perceived risk in the installation
of these technologies. There are several different technologies competing
for market shares in the field. The devices are rated at standard test
conditions and one watt at these conditions would be termed watt-peak, Wp.
The overall market size in 2012 is of more than 28 GWp annual installation
in 2012, with an installation cost of slightly under 1£/Wp in the majority
Calibration uncertainty is a risk in the value of the overall market. In
today's market (June 2013), one percent uncertainty equates to 750M$/a
[5.1]. The team (Prof Gottschalg, Dr. Betts) was instrumental in reducing
this as demonstrated e.g. in the EU project Performance where the
calibration uncertainty of leading test laboratories was reduced from 5%
to less than 2% in standardised power measurements for crystalline silicon
and from more than 10% to about 5% for thin film photovoltaics [5.8]. The
underlying research which contributed to this was carried out during the
Fellowship and the FENRA project and was published amongst other papers in
[3.3, 3.5]. The transfer into standards was achieved by contributing to
the standard development and the participating bi-annual meetings and
appropriate working groups. Prof Gottschalg led the project team for
IEC60904-5, which is the most accurate method to extract the cell
temperature. Each degree measurement uncertainty in the temperature
contributes about 0.5% to the calibration uncertainty, the standard is
capable of sub-degree accuracy, while external measurements result in 2-3oC
temperature uncertainty. Prof Gottschalg was also on the project team for
IEC60904-7, IEC60904-3, IEC60904-9, IEC60904-10 and IEC60891. Each of
these standards is a crucial element of the calibration process and has
distinct elements linking to work carried out by the team in one of the
research projects. It can be assumed that at least 95% of the PV modules
produced in the world have been assessed based on the IEC60904 series of
characterisation standards and corrected to standard test conditions using
IEC60891. Most subsidy schemes require these numbers making the
application of these standards mandatory.
Energy yield uncertainty is a risk on the income generated from an
installation and thus the financial viability of any investment. The
impact claimed here is the better understanding of uncertainties [3.2,
3.6] and better measurements [3.5] and paving the way for standard
datasets [3.4]. The impact is difficult to quantify, as production and
costs vary for different countries. There are about 100 GWp installed
world-wide [5.9], and about 2.5 GWp in the UK. In the UK a system produces
around 850 kWh/kWp and the value of a kWh (FIT + self-consumption/ or
generation credit) around 0.2£. Thus the impact of one percent uncertainty
in production is well in the order of 34M£/a in the UK alone. Uncertainty
exists because of a lack of standardised simulations, lack of standardised
environmental inputs and lack of validation of existing methodologies on
statistical numbers of installations.
The work of the team has been utilised in the published standards
IEC61853-1 and the FDIS IEC61853-2. The work on mapping together with Huld
et al [3.4] is the foundation of the standard datasets (IEC61853-3). The
transfer of research work has been achieved by Prof Gottschalg being part
of the project teams and a general recognition of the work by the team.
Overall, the work carried out by the team or managed by the team
(PV-Performance, PV-Catapult) have resulted in an enhanced understanding
of the uncertainties involved and a subsequent reduction of the simulation
uncertainty by 2% [5.8].
Key in achieving this impact was participation in the international
standards body of Prof Gottschalg. Standards are developed by the
International Electrotechnical Commission (IEC) and CENELEC in Europe,
with collaborations between the two standard bodies. These normally get
mirrored by national standards, which is the responsibility of the British
Standards Institution (BSi) in the UK. Prof Gottschalg is active on all
these bodies as confirmed by [5.1-5.6].
These standards have been elemental in the market growth. Without these
standards enabling the PV deployment, the market would not have grown at
the current speed as other technologies have demonstrated with less
rigorous standards. In terms of overall market acceleration, the body of
work has been essential to further this sustainable technology.
Sources to corroborate the impact
The following sources of corroboration are available at request:
5.1 Chairman of IEC TC82-WG2
The email confirms the participation in the IEC standards body, the
contribution to the standards claimed and the value of standards to the
5.2 Chairman of CENELEC TC82-WG1
The letter confirms the participation in the EU fora, the contribution to
the standards claimed and the value of standards to the market.
5.3 Chairman of BSi GEL82
The email confirms the status as national expert on the relevant topics as
well as the impact on the national status.
5.4 Chairman of the German Society for Solar Energy (DGS)
The email confirms the impact of energy rating in the market as well as
the standing of the group in the international community.
5.5 International Electrotechnical Commission http://www.iec.ch/
gives official confirmation of Prof Gottschalg's position in the world's
5.6 CENELEC http://www.cenelec.eu/
gives official confirmation of Prof Gottschalg's position in the European
5.7 BSi http://www.bsigroup.co.uk/en-GB/
gives official confirmation of Prof Gottschalg's participation in the
standards development of the BSi
5.8 FP6 project Performance final report
demonstrates the achieved uncertainty improvements by the team as well as
others which have been achieved as part of the project and in comparison
to the PV-Catapult project. This verifies the claims of the improvements
in calibration uncertainty of the leading EU laboratories and the status
of the CREST team having a good standing amongst them.
5.9 IEA-PVPS, various reports on the status of the industry (http://www.iea-pvps.org/)
corresponding attempts to quantify impact figures.