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Observations on Joining the AGL VPP

I am a retired electrical engineer and in my posts

 Statistical Analysis of Solar Energy Production in Adelaide


A Cost Benefit Analysis of the VPP Using 3 Years of Realime Data

I have developed an economic argument for joining the AGL VPP. I based my analysis on data obtained over the period 17/12/13 to 15/12/16, using downloaded data from our solar inverter, and our electricity bills. Please see the above posts for more information, and why I believe joining the AGL VPP makes good economic sense, given the subsidies being offered by AGL and the Australian Renewable Energy Agency, who have invested $5 million in the $20 million VPP project.


Incidentally, in the above cost benefit analysis, I made some projections based on increasing peak and controlled load power prices. Now that Hazelwood has shut down completely, power price rises are guaranteed almost immediately.


First, let me mention a few more general aspects of solar energy, and the AGL VPP, that have occurred to me during the writing of the above posts.


Some characteristics of solar panels are worth noting and are generally buried in specification sheets that may not be easily available to customers. I am not advocating any particular manufacturer, but suggest you buy the best quality panels you can afford. I have attached a link to the panels we have installed simply because it is a well written specification and highlights the important points I want to make.


The first things to note are a claimed efficiency of 15.1%, a 10 year product warranty, and a 25 year linear power output warranty. The efficiency figure is an indication of the ability to convert sunlight to electricity per square meter, and is not something to be concerned about from a reputable manufacturer. The second two warranties tell us that these panels are going to last quite a long time, and that the power output should be maintained for a very long time. That adds confidence to the economics of installing solar panels.


There are two Electrical Data Tables, one at Standard Test Conditions (STC) and one at Nominal Operating Cell Temperature (NOCT). The STC results are for a cell temperature of 25°C and a sunlight irradiance of 1000 watts per square meter. The NOCT results are for a cell temperature of 47.9°C (as shown in the Temperature Ratings table) and a sunlight irradiance of 800 watts per square meter.


Normal domestic solar panels have what is called a negative temperature coefficient, which means the warmer the cells get, the less efficiently they convert sunlight to electricity. These panels are quoted at ‑0.43% for PMPP, as you can see in the Temperature Ratings table, which means that the peak maximum power drops 0.43% for every centigrade degree increase above the specified test temperature. I think we could be fairly sure that Adelaide rooftop solar panel temperatures will rise well above 47.9°C at times.


The net result of all this is demonstrated when you look at the quoted Maximum Power at STC, and just how much lower it is at NOCT. The numbers at STC are what are normally quoted for domestic solar installations, so you might want to scale my real world energy figures in “Statistical Analysis of Solar Energy Production in Adelaide”, rather than believe the installer when he says you are getting 225 watt panels, or whatever the manufacturer’s specification states under STC.


Do solar panels need to be cleaned? There is plenty of reading on the web, but I think the following link is quite sensible.


The AGL VPP will allow for heavy night time and breakfast time energy users to charge their batteries at night on controlled load (off-peak). This will result in cycling the batteries twice a day; once from the mains, and once from solar power. The batteries being used in the AGL VPP seem to have a life of about 5,000 cycles, and cycled once a day should last about 13 years. That is presumably why they are warranted for 10 years. However, if cycled twice a day, that warranty may not be enforceable, and the expected life could be reduced to 5 or 6 years. I have covered some of this in Lifespan of Lithium Ion Solar Batteries, and am still waiting for AGL to release a data sheet on the batteries Sunverge are using, so we can all see for ourselves what the real numbers are. Clearly the depth of discharge each evening and each morning is the most important factor here, and is likely to be greater with 5.6 kWh batteries than with 11.6kWh batteries. Of course, all this assumes sufficient solar panel power to be able to fully recharge the batteries during daylight hours.


The economic benefit of the AGL VPP is but one part of this project for me. This is an engineering project attempting to test new ways of managing energy distribution and consumption into the future. As a retired electrical engineer, I am very happy to be part of something new and experimental which attempts to improve on what we have. The only aspect of this project over which we have no control is the extent to which AGL will draw on our batteries. This is something I’m not particularly concerned about, given the still relatively rare occurrences of grid instabilities, and the fact that the system does not appear to be designed to favour AGL over participants.


A big consideration in our decision to be involved in the VPP is the emotional reward in knowing that each night we will be using the power we have generated that day from the sun, and that in the event of a power failure, we will still have power to our critical loads. This is particularly relevant to me as a CPAP user, and to my partner who won’t have to listen to me snore my way through a blackout again! We find it hugely rewarding to think and feel that we will be a part of the solution, and not a part of the problem. I anticipate from my analysis that we will not have any net electricity and water-heating costs once the VPP batteries are installed, and that we will receive a small monthly return as well. We have found with this type of investment that one quickly loses sight of where the capital came from, and what else one may have done with that money, and that we start enjoying the benefits almost immediately, and for each and every day after that. It will be a powerful feeling being virtually off-grid.


One final consideration is that, as a result of joining the AGL VPP, we will have a smart meter and AGL’s advanced monitoring installed as part of the deal, so I will then have much greater access to detailed data, as well as the option of monthly billing, which I intend to take up. One of the exciting areas for the future is in the way electricity will be billed, and options to sell into AEMO at market prices. AGL have indicated that they are open to further developments once the initial VPP is bedded down and tested.


As long as politicians dominate the energy debate, and not the engineers, I anticipate we will have ongoing instabilities and blackouts. Why did we invest so much in poles and wires at a time when solar was growing significantly, and infrastructure was being asked to do less because of local solar generation? Why did we have a system that rewarded companies for investing in poles and wires and guaranteeing them a return, regardless of the engineering need? What is so hard to understand about base load and frequency stability?  Why sell all our gas overseas at prices we can no longer afford domestically?  Why don’t we have locally distributed gas-fired reserves around SA with no significant transmission losses? Above all, why have we had politicians running the “debate”, trying to score political points, rather than deferring to evidence based processes carried out by engineers and scientists who are far more likely to be focussed on the real issues, and able to develop rational long term solutions? Where is the hard data to show that spending possibly $2 billion, and almost certainly more, on expanding the Snowy Mountains scheme, with its 20% pumping losses, is not better spent on subsidising domestic battery storage? I suspect that a great many people, like us, would be prepared to pay a considerable amount for subsidised batteries. Whatever happened to evidence based bi-partisan policies for the long term?


I’m strongly in favour of a 50% renewable target, but not to the point of ignoring the engineering and scientific data, and the need to maintain grid stability and frequency via base load. Bear in mind that the Heywood Interconnector means SA is very vulnerable to weather, bush fires and human interference, and the cost of a new NSW connector is prohibitively high, and would still have the same vulnerabilities. Also, deriving power from interconnectors makes the assumption that there is power to share. The other aspect, often ignored, is that transmission lines have significant losses and the longer the lines the greater the losses. The Electrical Engineering Portal quotes overall technical losses in power distribution systems as 22.5%, with about a quarter to a third of that 22.5% in fixed losses (corona, leakage, dielectric etc. not due to current flow), and two thirds to three quarters of the 22.5% due to resistive current flow losses. It makes a great deal of sense to me to get rid of the distribution system as much as possible by generating and using most of the power needed locally. Local gas-fired base load makes sense on that basis as well, and the more local it is, presumably the less prone it will be to wide scale disturbances and distribution losses.


I would like to see energy policies based on well-funded, peer reviewed, engineering and scientific research and not on what are the best ways to ensure politicians get re-elected. Where is the data to show that spending $2 billion on the Snowy Mountain scheme would be preferable to subsidising domestic batteries? Where is the engineering evidence to support the current SA government’s proposed plans? Why had we not heard about the possibility of buying the existing Pelican Point generator instead of building a new one? Where is the evidence to suggest that a 100 MWh battery is better than a 200 or 300 MWh battery? Why do we not have public debates and transparency about the whole energy problem?


Sadly politics seems to dominate and we seem to be living in a fact-free political environment, something that appears to be a world-wide phenomenon.