Tuesday, March 27, 2012

Solar photovoltaic milestone!


My solar photovoltaic (PV) system has been grid connected just over a year now and yesterday I reached the landmark of 1500 units of electricity generated of which 1113 units (74%) have been exported to the grid. I am now almost 70% self-sufficient with regard to my electricity needs and so the next task is to work on that last 30%! The system was installed by Elementary Energy from Corofin and my case study on their website contains more technical details.

(See my separate post for more on my home energy project)

September 2012. On 11th September, total output passed the 2400 kWh mark of which 1848 units were exported (77%). My strategy is to maximise exports for optimal financial benefit and I have been achieving over 80% during the Summer months. It has been a good start to September- here's hoping it can reverse the run of 14 consecutive months below forecast - the poor end to September resulted in missing the forecast target but at least, for the second month in a row, I exceeded my 2011 figures.

October 2012. Since my inport-export meter was installed by ESB Networks in February 2011, I have imported 2242 and exported 1918 units (kWh). This would indicate that I am 86% self-sufficient. However I think this is a bit flattering as this is at the end of summer and I prefer to use a rolling 12-month indicator = [output/(import + own use)] where (import + own use) represents total home electricity usage. The actual figures currently are 1234/(1644 + 253) which is 65% - still not bad!  As I log PV output and export data daily in a spreadsheet, 'own use' comes from this and is simply output kWh less exported kWh.

February 2013. A strange thing occurred this week, several days of cloudless skies. This afforded me an opportunity to measure the variation and trend in PV output over a day without the interference of cloud. The fact that this happened in the middle of February is surprising but less onerous than having to get up at the crack of dawn in mid Summer! I was not surprised at the basic results - I always assumed that the output over a day would be non-linear and I also expected my peak output to occur in early afternoon as my panels are facing SW. In the event, I was pleasantly surprised at the perfect curve I got and the peak output came about 2 hours after true noon. The falloff in late afternoon was more sudden than the slow build-up over the morning.

11 June 2013. The forecast output was reached in May after 22 consecutive months below forecast. There's also been a good start to June - the mini heatwave of the last 6 days produced 63.6 kWh (of which 58 was exported); this compares with the mini heatwave at the end of May last year which produced 61.6 kWh (of which 55 was exported). Postscript: the aforementioned good start provided the basis for my best June yet and target output reached again. 
July 2013. This was the warmest July on record in many stations and produced my highest monthly output yet of 211 kWh. Casement Aerodrome, the nearest station to me, had 150% of average sunshine (for the period 1981-2010) and touched 28.5 degrees C on the 12th July! 

February 2014. I was playing around last year with some of the data in my spreadsheets and came up with this indicator which I think gives a good picture of average monthly intensity of solar energy especially when graphed. I simply multiply the output for each month (kWh) by 1000 and divide it by the number of hours clocked up by the system in that month so obviously the unit for this indicator is Watts.

January 2015. Here are the output data for the last four years:
2011        1360 kWh
2012        1235 kWh
2013        1275 kWh
2014        1179 kWh
Target      1452 kWh

12 June 2015. Despite the fact that we had the coldest May in twenty years there was reasonable sunshine and I've had the best start to a year since 2011. Nevertheless, for the second year in a row the output for May was less than that for April - not what should be happening. My system has now generated 5650 units of electricity of which 4422 units (78%) have been exported to the grid and I am about 68% self-sufficient with regard to my electricity needs.  Pat 

(click to enlarge)

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