There has been mention in these forums about our nominal 230 volts being a joke when we notice that it's often (usually?) in the order of 250 volts, if not higher.

On that point, the Publisher's Letter in the December 2011 issue of Silicon Chip, under the subject title, makes interesting reading. It begins:

"With all the controversy over solar grid feed-in tariffs and renewable energy certificates, yet another problem with domestic solar panels has arisen. According to a story in The Australian newspaper on 13th October 2011, 'The runaway take-up of rooftop solar panels is undermining the quality of electricity supplies, feeding so much power back into the network that it is stressing the system and causing voltage rises that could damage household devices such as computers and televisions. Power distribution lines and home wiring were designed for electricity to flow from power stations to appliances, but households with solar panels do the reverse of this'”.

and concludes:

"Ultimately, this problem might be solved by a change in the design of grid-feed inverters: once the voltage coming in from the street rises above (say) 245VAC, the inverters would be switched off and would no longer be able to generate power. This would protect other consumers but of course, those people who invested in solar panel installations would not get the full benefit. Worse, they might have to pay for power which, if the system voltage was below the threshold, they would otherwise be generating. This is yet another instance of the impracticality of the Green’s advocacy of Australia generating all its electricity from renewable sources. For this and a whole host of other technical reasons, it just ain’t ever going to happen."

Link to article: http://www.siliconchip.com.au/cms/A_112704/article.html

I read, with some interest, the article mentioned and whilst the Editor in Chief, Mr Leo Simpson, raises some good points, it isn't as simple as it sounds.

Mr Simpson is correct in many ways though some of the story is yet to be told. Instability in the electricity grid is due to quite a few causes.

The first is the small matter of the load constantly varying. This is due to loads on the grid being turned on and off and includes things as simple as the family fridge cutting in and out to maintain its temperature right up to furnaces at steel-making facilities being in use.

In between there are loads such as heating, ventilation and air conditioning (HVAC) plants in large buildings. I once worked at a large private hospital in Sydney, a freestanding building with seven floors, including the underground carpark, all requiring forced ventilation of one kind or another - most floors serviced by huge water chiller units for cooling, boilers for heating and large pumps to circulate the chilled and hot water around the building to feed to air handling units, which then circulated the climate-controlled air to patient rooms, etc.

Then there were the sump pumps in the carpark to prevent flooding, smoke fans to extract air in case of a fire, the machines for the four passenger lifts and pumps for the warm and hot water services that feed patient showers, clean and dirty utility rooms, etc.

This hospital had one switchboard for general light and power and included the ATS switchboard for the emergency generator and uninterruptible power supply and another switchboard for 'mechanical services', that being the HVAC loads. The mechanical services switchboard was by far the larger of the two. The underground substation had three transformers, one for each switchboard and one spare.

Remember that this is one one of thousands of large buildings that contains similar equipment and most of the electric motors were rated at between 30 and 50 horsepower and the only motors that had any form of 'soft start' were for the heat rejection fans, fed from VSDs.

The essence of this story is that in this one building, there would have been enough electrical interference and variation in the load to be noticed by the operators of the grid. When monitoring the load, the grid operator, Transgrid, has to compensate by adding and subtracting supply from the State's power stations. This is mostly automatic but there is some human intervention at times. There is more to instability in the electricity grid than solar installations

The next thing, regarding the grid itself, is that its capacity becomes gradually less between the power station's main substation and the consumer's switchboard. This is on a sliding scale from gigawatts down to about 24kW, which is usually the maximum capacity of a domestic switchboard.

Mr Simpson's point, I think, is that the tail end of the grid is not designed to have generation equipment connected to it. He's right. It's not. There is definitely the potential for overloading to occur, particularly in the odd case where one or two homes in an area are consuming very large amounts of electricity and numerous others have spare solar capacity.

The only misgiving I do have is relating to this comment:-

Ultimately, this problem might be solved by a change in the design of grid-feed inverters: once the voltage coming in from the street rises above (say) 245VAC, the inverters would be switched off and would no longer be able to generate power...

This would have to be very carefully engineered to prevent an infinite loop of surging. The last thing we'd need or want is hundreds of solar installations cycling on and off in response to the overall voltage output.

As the owner of two server clusters, one of which powers the mighty Vintage Radio and Television, I need to feed this equipment from a UPS to make sure of two things:-

1. To safeguard against blackouts, even those that only last a few moments.
2. To safeguard against instability in the electricity grid, namely surges, spikes and brownouts.

Any or all of these phenomenons can damage computer equipment beyond repair and none are predictable. UPSs are designed to absorb this instability up to a point. My UPS makes a lot of noise throughout the day, clicking to battery power each time there is a surge or spike due to equipment owned by other electricity consumers in my area or brownouts when substation switching occurs.

I don't think it is my imagination that the UPS has got busier since consumer solar installations have become more commonplace.

Whilst I am not a believer in the Prime Minister's climate change agenda, I am a strong supporter of solar power and have been since before the words climate and change were put together for political reasons. I still maintain an open mind with regard to grid connectivity due to the 'unknowns' - the issues we are yet to discover.

This is yet another instance of the impracticality of the Green’s advocacy of Australia generating all its electricity from renewable sources.

Whilst I am a supporter of solar power, it is a well known fact that it won't be the only source of electricity in the years to come. At some stage, if we are to stop burning coal we only have two options for baseload power stations, gas or nuclear. Gas is easier and cheaper to retrofit into existing stations but nuclear does provide the option to generate without tainting the air. Australia has had three nuclear reactors; all at the ANSTO facility in Lucas Heights, NSW for scientific and research purposes; and all have been run safely so there is no reason why this wouldn't continue on a larger scale for the production of electricity providing there was a great degree of government regulation involved.

I think what will end up becoming of domestic solar installations, once government handouts come to an end in the future, is that the number of these will increase but feeding back to the grid will ultimately cease as there'd be no economic benefit to customers continuing to provide their excess capacity to others.

Having had a relative who worked in power stations I remember him telling about receiving calls from System Control to warn of big changes of load both up and down, or generating capacity that was about to be shut down or reduced for whatever reason. They would then have time to "run up" the generation which cannot happen instantaneously. The big load items then were Sydney's electric trains and big industrial loads like electric furnaces and steel mill motors. But most loads changed steadily and predictably when averaged over the system.

The system is resilient - in the sixties an earthquake in the NSW southern highlands caused Tallawarra power station units to trip out because of misalignment (waves - and not of water! - could be seen going down the turbine floor of the power station). The unused steam went out the safety valves. But the system survived without widespread blackouts.

Presently about 20% of South Australia's power comes from wind, and this apparently hasn't caused a failure of the system there. But it has reduced the cost of power there by something called the merit order effect whereby the cheapest producers at the time are used first (wind) and the others bumped up the order. For this reason some Victoria generators have opposed a new transmission link between Vic & SA because it would effect their margins. Evidently they make a large proportion of their profit from times of high demand when power cost can increase to as high as $10,000 per megawatt hour!

In my travels to and from work each day I head past White Bay Power Station, which once provided most of the electricity for Sydney's light and heavy rail networks. One day I am sure that due to a failure of the Government to convert it to a museum it'll continue to deteriorate to the point where it'll fall in on the security officer designated to try and keep vandals and squatters out.

The system is resilient...

I think in the overall scheme of things, we do take our elecricity supply for granted and with good reason. It's almost always there, to the point that outages are very noticable. There's a lot to rely on electricity for these days. Up until I was about 14, the only thing in my bedroom that required electricity was the light hanging from the ceiling and my Hornby Railway. Most kids now have numerous toys and appliances that require electricity to run or charge batteries and they are in receipt of these things well before the age of 14 - laptops, Xboxes, televisions and in many cases a video player in one format or another.

Even in the comparitively austere 1970's, I remember the rolling blackouts we used to suffer under the stewardship of the strikes (often primary and secondary boycotts) that were more common at the time. Bus drivers would want more pay and would strike for days at a time to get it and they'd be followed off the job by train drivers, milk, bread, power stations, nurses, teachers, builders and even the bloke that would walk from one phone box to the next with a rag and some ammonia washing spit off the handsets.

Apart from those industrial issues of days gone by I think we've done pretty well. The trick may well just be trying to mesh new age technologies with those that have existed for 100 years.

For this reason some Victoria generators have opposed a new transmission link between Vic & SA because it would effect their margins.

There is some papertalk that some of Victoria's power stations will close in the next ten years. Apart from their age they burn brown coal which has a thermal efficiency of 10%. They make money but are facing pressure to close from more than one direction. One problem is a lack of a service to replace them though. The Commonwealth has put a thinly-veiled ban on the construction of new coal-fired stations - a ban it can't enforce as electricity is constitutionally a state responsibility. The owners of the power stations would also be unlikely to vanish from the scene without being compensated.