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The first two plots here show watt hours generated per day by our solar panels and grid interactive inverter. The plot to the left shows the daily cycle for today and the last 7 days, while the second plot below shows the total daily energy every day since installation. Clicking each plot will show more detail.
The daily plot is restricted to the hours of 6am to 6pm, since input is negligible outside these hours. You will note the stepped nature of the plot - every 30 minutes the output appears to change slope, and output appears to limited by some factor other than insolation. I have not been able to find any explanation for this - there is nothing in the manufacturer's manuals, nor their web pages. If anyone can shed any light on why this occurs, I would be pleased to hear from them. My best guess currently (sorry!) is that it is some battery recharge regime.
There is a slight liberty taken with the data in the second plot. This was due to equipment failure over the summer of 2004/5. Data from the previous summer is substituted to maintain the shape of the graph. As the data shows a slight upward trend (more likely due to tree clearing than global warming!), this should not distort the analysis too much. The daily plot is generated by our house computer, and updated automatically every 10 minutes. The long-term plot is generated manually (last update 20090610).
The solar assembly consists of 20x75W panels (1500W total) feeding into a Trace SW3024 E 3300W inverter system, buffered by 4 Sonnenschein 6v 330AH gel cells (7920WH). In sunny weather, the system generates enough power that the meter is usually spinning backwards! Two of the house power circuits (including the refrigerator and all computers) are fed from this inverter, giving about 24 hours of autonomy (at normal current levels) in the event of grid supply failure. (see footnote *)
Our current electricity drawdown from the grid is about 14KWh per day (averaged over the year), and the solar system supplies an average of 4.6KWh (see chart above). That gives an average fraction of about one quarter of our electricity needs being supplied by the sun. That translates a saving of approximately $0.67 a day. The system cost about $6000 ($4000 for the inverter, $2000 for the rebated solar panels, not counting the batteries, which are only for UPS protection), and will therefore pay for itself (assuming no increase in electricity costs, an unrealistic assumption) in about 25 years! But of course, we are also saving about 2.5 tonnes of greenhouse gas a year, (roughly) the equivalent of not driving our car anywhere for the year.
We also have a rainwater system consisting of two 2250 litre Plastanks, fed from the house roof, and pressurised by a 240v Onga Riva-Flo TF30 centrifugal pump. This pump delivers 30 litres/minute at 8 metres head, and is quite adequate for our purposes. Delivery is to two toilet cisterns, and to a garden watering system (8 solenoid operated outlets and 2 standpipes). The garden watering system is driven automatically by cron jobs running on the house computer.
We used to have the water level in the rainwater tanks monitored electronically and displayed here as well; however corrosion problems forced the abandonment of this. There are plans to re-introduce the system, using 1-wire technology. Watch this space!
On the left is a plot of the inside and outside temperatures of the house. You can see the effect that the heating system has. The data is collected from a Dick Smith wx200 weather station and logged through an RS232 interface. The heating is controlled by a relay driven from the house computer (which also generates these plots). The cycling of the "thermostat" (There is no such animal, it is all soft controlled) can be clearly discerned when the heating is in operation. The actual "thermostat" temperature is controlled by a cron job, which can be overridden through a web interface.
Postscript: In Marysville, Victoria (Oz), there is an excellent Meccano Museum with many working models. It's called "Maniacal Mechanicals", in Murchison St (the main street). Worth a visit if you are in the area.
Postpostscript: Alas! "Maniacal Mechanicals" was destroyed in the disastrous Black Saturday bushfires (7 Feb 2009). See this collection of photographs of the place as a tribute.
(footnote *): The irony of this is that while my wife and I were away on a week's holiday, my son and his band cronies plugged guitars and amplifiers into the UPS circuit, and played so loudly that they overloaded the inverter, tripping its overcurrent protection, and turning off the fridge. He simply moved to another power point and thought no more about it, until he noticed all the icecream running out the bottom of the fridge! We came home to a disaster! Just goes to show, such systems are not 'fool-proof'!
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