Seven years of international collaborative research focusing on grid-interconnection of dispersed PV power systems (PVPS Task 5) culminated in a workshop in Arnhem in January 2002.

Since 1994, PVPS Task 5 has been working to develop and verify technical recommendations for safest, most reliable and lowest cost interconnection and operation of distributed, grid-connected PV systems.

Over the past three years, the priority has been to analyze the impact of high concentrations of PV systems on the electricity distribution network, with the purposes of defining recommendations for network operation and configuration and of optimizing PV inverter systems to ensure the distribution network can cope with widespread PV deployment. The conclusions of these activities were presented at the workshop 'Impacts of PV Penetration in Distribution Networks – Network Aspects on High Penetration Level of PV Systems and Islanding Analysis' on January 24-25 in the Netherlands. Over 75 experts from 15 different countries worldwide attended the meeting.

Islanding poses little risk
The main topic of the first day was islanding, a phenomenon whereby distributed generators like PV could potentially continue to feed power into the distribution network after the mains network has failed. A 'live' generator could pose a safety problem for instance for network technicians working to rectify the mains fault. The lively discussions amongst the workshop participants showed the keen interest in this issue.

Part of Task 5's work in this area has been to identify technologies for detecting islanding faults, though at the same time the group has effectively demonstrated that the probability of islanding is practically zero; normally the inverter will force a disconnect from the network if its voltage and frequency trip limits fall outside those of the mains for more than one second. There is a condition when load and generation are closely matched that could allow the inverter to operate outside these limits, but the likelihood of such conditions existing at the same time that the network fails is in the order of 1 in 1 billion, even at comparatively high connection densities. In terms of the likelihood of electric shock PV presents an extremely low risk – better than a 1 in 100 million chance.

PV penetration
The second day commenced with an overview of the state of the art of grid interconnection guidelines and inverter grid interconnection technology, the main conclusion being that guidelines and technologies are becoming less country specific. Another topic of particular interest to utilities and electricity delivery companies is the technical impact of high levels of PV penetration on the power network. Task 5 clearly indicated that networks can handle a large amount of PV, up to the daytime minimum load capacity of the distribution line, without significant problems. Slight modification of utility MV/LV transformer taps increases the limit of PV penetration significantly. A study of the power value of PV systems demonstrated that PV can have a good power correlation with electrical loads especially in business areas. All presentations showed that there are few technical barriers in power networks for the large-scale integration of PV systems. The focus is now on information dissemination and the removal of some old but persistent barriers – notably how to encourage proper consideration of distributed generators within energy companies’ network planning. The proceedings of the workshop are available electronically. Contact Bas Verhoeven: s.a.m.verhoeven@kema.nl. A set of reports presenting the full findings of the Task 5 studies will be available shortly.

Although the PVPS-specific research into this field has now concluded, the growing importance of distributed generation systems in general – a topic which has gained new significance in the wake of September 11th – is likely to result in a new IEA activity focusing on issues related to implementation of all distributed generation technologies.

Information:

• Tadashi Kanbayashi, NEDO
  Fax: +81 (0)3 35 90 58 03

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