The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
Aalto

Computational Studies on Variable Distributed Energy Systems

Jukka Paatero

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Faculty of Information and Natural Sciences for public examination and debate in Auditorium K216 at Helsinki University of Technology (Espoo, Finland) on the 6th of November, 2009, at 12 noon.

Overview in PDF format (ISBN 978-952-248-125-2)   [1419 KB]
Dissertation is also available in print (ISBN 978-952-248-124-5)

Abstract

In this work the large-scale integration of distributed wind turbine and photovoltaic power generation to medium voltage power distribution grid have been explored. The effects of the integration were mainly evaluated by steady-state power flow analysis. Compensation of unwanted overvoltage events was tested with the use of energy storage, utilization of grid topology, and redirecting of photovoltaic panels. In addition, this work examines the use of energy storage to compensate short and long term fluctuations in the power output of variable distributed generation. For this purpose three different storage control strategies were applied.

For simulation purposes a detailed bottom-up consumer load model and a distribution grid power flow simulation model were developed. The stochastic approach in the load model is based on the classic bottom-up load model by Capasso et al. However, the emulation of the activities of individual people has been replaced by statistical use of household appliances where reference data is more readily available. The grid simulation model is based on established power flow computation methods. The model is especially designed for easy implementation of grid details as well as various types of distributed generation and storage and their control strategies.

The distribution grid simulation results indicate that in a hypothetical crowded urban distribution grid an approximate limit for not causing grid disturbances for private households is around 0.5 kW of grid-connected photovoltaic power generation per apartment building household in both southern (Lisbon) and northern (Helsinki) climates. Using storage schemes the amount can be increased up to over 1 kW per household. However, grid details concerning storage size and siting topology greatly influence the exact limit. Further, the simulation results show that the integrated photovoltaic power generation can induce up to 34% reduction in the transmission losses of medium voltage distribution network. Corresponding analysis with wind power shows that if a MW-scale wind turbine is integrated to distribution grid the grid topology as well as the siting of distributed generation and storage are very important in avoiding unwanted overvoltage events. Overall, compensating power fluctuations of an individual MW-scale wind turbine needs to be viewed both on short and long time scales. Rapid minute-scale fluctuations can be most of the time smoothened by 50% with a storage unit in the capacity range of 25 kWh/MW. However, the long-term changes are difficult to compensate without large MWh-scale storage schemes. As a whole, the grid voltage issues proved to be much more crucial for the integration of variable distributed generation than the grid losses.

This thesis consists of an overview and of the following 5 publications:

  1. Jukka V. Paatero and Peter D. Lund. 2006. A model for generating household electricity load profiles. International Journal of Energy Research, volume 30, number 5, pages 273-290. © 2005 John Wiley & Sons. By permission.
  2. Jukka V. Paatero and Peter D. Lund. 2007. Effects of large-scale photovoltaic power integration on electricity distribution networks. Renewable Energy, volume 32, number 2, pages 216-234. © 2006 Elsevier Science. By permission.
  3. Jukka V. Paatero and Peter D. Lund. 2007. Impacts of energy storage in distribution grids with high penetration of photovoltaic power. International Journal of Distributed Energy Resources, volume 3, number 1, pages 31-45. © 2007 Technology & Science Publishers. By permission.
  4. Jukka V. Paatero and Peter D. Lund. 2005. Effect of energy storage on variations in wind power. Wind Energy, volume 8, number 4, pages 421-441. © 2005 John Wiley & Sons. By permission.
  5. P. D. Lund and J. V. Paatero. 2006. Energy storage options for improving wind power quality. In: Proceedings of the 3rd Nordic Wind Power Conference (NWPC 2006). Espoo, Finland. 22-23 May 2006, 7 pages. © 2006 by authors.

Errata of publications 1, 2 and 5

Keywords: distributed generation, network effects, simulation, photovoltaics, wind power, storage, consumption

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© 2009 Helsinki University of Technology

Last update 2011-05-26