Solar PV system research in Finland for export industry Seppo Valkealahti Professor Department of Electrical Engineering Tampere University of Technology

Solar photovoltaic (PV) system research in Finland for export industry Focus of the presentation: Status and achievements of solar photovoltaic system research carried out in Finland during the past years by (since 2009) • • • •

Tampere University of Technology Lappeenranta University of Technology Aalto University funded by ABB (Tekes)

with focus on • PV generator operation under varying climatic conditions • Interfacing PV generator to the power grid.

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Solar PV power research plant at Tampere University of Technology 69 PV modules with nominal power of 13.1 kWp combined with state of the art climatic and electrical measuring systems.

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TUT Solar PV research Plant

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String 1 (17 panels) Solar PV system research S5 S6 in Finland for export industry Strings 4 (6 panels)

– Temperature and Irradiance Measurement System

Strings 5 & 6 (6 + 6 panels)

Focus Status S7

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Weather Station S13

String 2 (17 panels) S11

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Photodiode SPLite2 Solar Sensor Thermocouple Temperature Sensor

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String 3 (17 panels) S17 24.3.2016

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Solar PV power research plant at Tampere University of Technology Continuous synchronized climatic measurements and data storing with 100 ms sampling frequency since 2011 • Various PV system models and simulation and analyzing tools have been developed Electrical measuring systems • I-V curve tracer based on controllable IGBT switches • PV generator simulators and emulators • Power electronics modelling and simulation tools • Electric measurement instruments

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Solar PV system research … Basic on PV power plants • From one to two thousand PV cells are connected in series to obtain high enough output voltage for power grid connection.

• PV modules have around 60 PV cells and typically three bypass diodes to protect PV cells.

• PV module is the basic building block of a PV generator (power plant) • PV power plants have typically around 20 PV modules connected in series forming a PV module strings.

• To increase the output power series connected PV module strings are connected in parallel.

• PV generator provides DC power which is converted to AC power for the grid by Solar Inverters.

• Climate conditions change all the time changing the operation of the PV generator and a continuous tracking of the maximum operation point is needed (MPP tracking). Seppo Valkealahti

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Solar PV system research … Basics: Partial shading of the PV generator Partial shading of 6 series-connected PV modules due to building structure

• Module temperatures varied over 20 °C due to shading • PV system can lose power by operating in a wrong voltage point No shading

Two modules shaded

Times of I-V curve measurements.

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Solar PV system research … Examples of research results Partial shading of a PV string generator causes many maximum power points.

The shading pattern of the PV module string.

The number of maximum power points on the P-V curve of the string generator of 18 PV modules as a function of system shading and shading strength. Seppo Valkealahti

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Solar PV system research … Examples of research results Partial shading of a PV string generator has a major effect on the maximum power points: IMPP and VMPP. • A global MPP tracking algorithm has been patented based on these results. Global MPPs Local MPPs

Global MPPs

Local MPPs

Maximum power point current and voltage pairs of the string generator of 18 PV modules operating under different partial shading conditions. • The same shading pattern was applied as in the previous slide. • The base value for the MPP current is 7.33 A and for the MPP voltage 466.2 V. Seppo Valkealahti

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Solar PV system research … Examples of research results Partial shading caused by moving clouds has a major effect on the operation of PV generators. Relative portion of time 0.08 % 0.62 % 0.73 % 4.29 % 27.78 % 66.50 % 0.004 % (Zero irradiance on the morning)

Number of Maximum Power Points (MPPs) in the measured P-V curves of the string generator of 18 PV modules during a half cloudy day. Seppo Valkealahti

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Solar PV system research … Examples of research results Solar PV power fluctuates. • On the average 20 times a day between 20 to 100 % of the clear sky power. • The average daily duration of fluctuation ramps is half an hour. Whole day

One hour

10 minutes

Power evolution of a 3.2 kWp PV generator on 15.06.2015.

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Solar PV system research … Examples of research results Compensation of Solar PV power fluctuations by energy storage (ESS) • A ramp rate limit of 10 %/min is applied below 650 600 550

Power (W)

500 450 400 350 300 PV generator output Battery compensated output

250 200 08:00

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08:10 Time (Hours)

08:15

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PV power fluctuations and the operation of energy storage for 20 minutes on 1st of July 2013 (1 kW nominal power). Seppo Valkealahti

Corresponding ESS energy evolution during 7.7.2012. 24.3.2016

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Solar PV system research … Examples of research results Enhanced state of charge control methods have been developed for PV power ramp rate limiting with energy storages.

PV generator power and grid feed-in powers using standard and enhanced operating control strategies of energy storage during a downward ramp. • The enhanced operating principle prevents power production outages. Seppo Valkealahti

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Solar PV system research … Examples of research results Sizing criteria for energy storage systems can be analyzed based on the developed state of charge control methods. • Power and energy capacity • Cycling tolerance and degradation of battery technologies

PV generator (PVG) and grid feed-in power, ESS power and ESS energy for a 1 kWp PV generator on 9.8.2012 with a ramp rate limit of 2 %/min. Seppo Valkealahti

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Solar PV system research … Examples of research results Shadows caused by moving clouds have been analyzed from the experimental database. • The average speed of shadows is around 18 m/s • Shadows move mostly towards North-East • …

The speed distribution of shadows during 15 summer months (457 days).

The polar histogram of the direction of movement of shadows during 15 summer months (457 days).

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Solar PV system research in Finland for export industry Scientific, technological and academic highlights • Clarification of the power-electronics-related interfacing constraints of the photovoltaic generator first time in the world. • Generating the real dynamic models for the PV and grid-interfacing converters first time in the world. • Solving the stability problems related to the size of inverter DC-link capacitor. • Revealing the origin of the grid-stability problems related to the PV inverters. • Proposing different methods to mitigate the grid-stability problems based on grid-voltage feedforward and different active damping methods. • Patenting five power electronic converters for PV interfacing applications. • Patenting multiple maximum power point tracking algorithm with no output power interruptions. • Explaining various phenomena related to PV system mismatch and MPP tracking related power losses under varying atmospheric conditions. Seppo Valkealahti

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Solar PV system research in Finland for export industry Scientific, technological and academic highlights • Inclusive dynamic thermal and electric simulation model of solar PV systems under varying atmospheric conditions. • Modelling and analyses of the operation of PV systems having various topologies under varying climatic conditions and their effects to the feeded power system. • Producing eight PhDs of which seven are working in industry and one as an assistant professor. – Four more PhD students are pursuing towards PhD degree.

• Publishing of 31 journal and 59 conference papers in the most respective international venues related to PV systems. • Major impact on the four majors in power engineering in the master degree program of electrical engineering at TUT. – 97 students signed up for the ongoing master level course “solar power systems”.

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Solar PV system research … What next? Finnish Solar Revolution! • A Tekes funded public research project is “starting” this Spring. – A joint project with Tampere and Lappeenranta Universities of Technology and Aalto University having parallel industry projects. – Planned in close cooperation with ABB, Efore, Ensto and Sola Sense.

• Main research themes of the project are: 1. 2. 3. 4. 5. 6.

Energy storage with renewables (PV) Micro grids Grid stability with high level of renewables (PV) Reliability of the PV system Future of the renewable (PV) business Preparation of EU funding applications.

• The following companies had notified their participation one week ago: – ABB, Efore, Ensto, Sola Sense, MX Electrics, Tampereen sähkölaitos, Tampereen sähköverkko, Caruna, Nocart, Convion and Eaton.

• More companies are welcome to join the project. Seppo Valkealahti

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Solar PV system research in Finland for export industry

Thank you! Questions?

More info: [email protected]

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