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 SILICON CHIP www.siliconchip.com.au Publisher & Editor-in-Chief Leo Simpson, B.Bus., FAICD Production Manager Greg Swain, B.Sc. (Hons.) Technical Editor John Clarke, B.E.(Elec.) Technical Staff Ross Tester Jim Rowe, B.A., B.Sc Nicholas Vinen Photography Ross Tester Reader Services Ann Morris Advertising Enquiries Glyn Smith Phone (02) 9939 3295 Mobile 0431 792 293 glyn<at>siliconchip.com.au Regular Contributors Brendan Akhurst David Maddison B.App.Sc. (Hons 1), PhD, Grad.Dip.Entr.Innov. Kevin Poulter Dave Thompson SILICON CHIP is published 12 times a year by Silicon Chip Publications Pty Ltd. ACN 003 205 490. ABN 49 003 205 490. All material is copyright ©. No part of this publication may be reproduced without the written consent of the publisher. Printing: Hannanprint, Warwick Farm, NSW. Distribution: Network Distribution Company. Subscription rates: $105.00 per year in Australia. For overseas rates, see our website or the subscriptions page in this issue. Editorial office: Unit 1, 234 Harbord Rd, Brookvale, NSW 2100. Postal address: PO Box 139, Collaroy Beach, NSW 2097. Phone (02) 9939 3295. E-mail: silicon<at>siliconchip.com.au ISSN 1030-2662 Recommended and maximum price only. 2  Silicon Chip Publisher’s Letter Anti-islanding in grid-tied inverters is a big drawback In the past, I have touched on the frustration of homeowners with solar panel installations who have no electricity during blackouts. They have this wonderful shiny panel installation which is prevented from generating power during black-outs by the “anti-islanding” feature of grid-tied inverters! This disadvantage was greatly magnified for many people in the aftermath of the severe weather in Sydney at the end of April. Many thousands of people were without power for more than a week. Just imagine that: no power at all for a whole week – nothing for light, cooking, heating, computers, TV and other entertainment or cordless phones – you could not even charge your mobile phone! And this was in Sydney suburbs, not somewhere out in the sticks! No-one was to blame for this situation as the storms downed many thousands of trees and the electricity linesmen were flat out reconnecting whole districts. Even as I write, the clean-up of felled trees is still going on and is likely to continue for another month or so. Now we all know why this “anti-islanding” feature is incorporated into grid-tied inverters. It is there to protect linesmen who may be working on the system when there is a power outage. On the face of it, this is a good idea. But is it really necessary to also prevent the home-owner from having any electricity at all when there is a blackout? There are other ways of protecting linesmen. The most obvious method would be to use the anti-islanding feature of the inverter to switch a contactor, so that the home-owner’s system was disconnected from the grid but still leave the inverter itself to generate power. Sure, the home-owner would not get any benefit from feeding power into the grid but at least he (or she) would still have power while the Sun was shining. While there would still be no power available at night, most home-owners would be happy to work around this, knowing that food in their refrigerators was not going to spoil and many other power-using tasks such as clothes washing could be done during the day. No doubt some people would argue that relying on a contactor to isolate the home-owner’s system could be a recipe for a fatality. But surely a contactor could be arranged to “fail-safe” so that if it did not work, the system would be isolated anyway. I am sure that it would possible to arrange for redundancy in the monitoring and switching to make sure it was always safe and reliable. Of course, it would be necessary for the grid-tied inverter to still be able to monitor for the presence of power on the grid, so that the system would automatically switch back when grid power was restored. If you concede that this idea has merit, then it is only a small step to allow solar systems which are grid-connected (no longer “grid-tied”) to have battery storage so that home-owners can generate their own power during blackouts at night. The release of the Tesla PowerWall lithium battery system (see article on page 25 in this issue) makes this a practical scheme. The solar panels would charge the PowerWall during hours of sunlight and feed the excess power into the grid. Then if there is blackout, the system automatically isolates itself from the grid and the home-owner can enjoy electricity as normal. The PowerWall would also have the benefit of smoothing the peaks in electricity demand from the grid, as it could supply at least some power after the Sun goes down. Of course, the Tesla PowerWall might also persuade some electricity customers to disconnect themselves entirely from the grid and thereby avoid paying daily service charges. Leo Simpson siliconchip.com.au