We have a 2kW 8 panel solar array (Panasonic HIT panels), mounted on a south-facing roof at approximately 35-40° angle from the horizontal, which was installed at the end of August 2013.
We now have two complete years of generation (Sep 2013 - Aug 2014 and Sep 2014 - Aug 2015).
These are the results for y/e Aug 2014 (in green) and y/e Aug 2015 (in red) and distribution by average sunlight 1971-2010 (met office stats) in blue:
Totals for August:
The panels have done 231kWh this month - down 18kWh on the month compared to August last year.
Average generation values for August 2014 and the year:
With 496 hours of daylight in August (sun up to sun down for all 31 days), the average kWh generated per hour of daylight this month was 0.47kW. August last year was 0.50kW.
Sept 2013 - Aug 2014: Sept 2014 - Aug 2015:
 |
| Sept 2014 - August 2015 |
Totals for the year:
The panels have generated a total of 2001kWh over the year 2014-2015. This is up 72kWh on the year compared to 2013-2014 (which was 1929kWh).
Anomalies and differences:
April 2015 generated more kWh per hour of daylight (0.63kW) than any of the summer months in 2014 and 2015. The main summer months July and August 2015 have both been poorly performing months in comparison to the previous year, yet the overall generation for the year is up.
Yearly average based on first two years:
The average of 1929 and 2001 is 1965kWh, which I shall use as the forecast for 2015-2016.
Any deterioration in the generation capability of the panels has been more than offset by the higher amount of sunny days in the year. Due to the huge variation in yearly generation between the 1st year and 2nd year, an accurate predication for the full 20-year generation total is not possible. However, here are the best case/worst case scenarios:
Best case scenario:
Assuming *no* degradation in generation capability, and using the 2-year average 1965kWh (as above), the 20 year total generation comes out at 39,300kWh (39.3MWh).
Best case scenario:
Assuming *no* degradation in generation capability, and using the 2-year average 1965kWh (as above), the 20 year total generation comes out at 39,300kWh (39.3MWh).
Worst case scenario:
Using the lower 1929kWh as the average per year, and assuming 1% degradation per year in generation capability (this is the value given by the manufacturers), the 20 year total generation would be 36,600kWh (36.6MWh).
Using the lower 1929kWh as the average per year, and assuming 1% degradation per year in generation capability (this is the value given by the manufacturers), the 20 year total generation would be 36,600kWh (36.6MWh).
Financial benefit - Feed in Tariff:
This year our generation payments have gone up from 15.3p/kWh to 15.45p/kWh (1% increase) and our export payments have gone up from 4.77p/kWh to 4.83p/kWh (just over 1% increase). This has netted us a total of £356.75 for the year, up £20.92 on last year's total of £335.83.
This year our generation payments have gone up from 15.3p/kWh to 15.45p/kWh (1% increase) and our export payments have gone up from 4.77p/kWh to 4.83p/kWh (just over 1% increase). This has netted us a total of £356.75 for the year, up £20.92 on last year's total of £335.83.
Financial benefit - using our own electricity and not having to buy from the grid:
A bit more difficult to arrive at a figure for this. We have two electricity meters, one which records how much solar electricity we have generated, and one which records how much electricity the household has used in total. But we don't know how much of the electricity used has come from the solar panels, and how much has come from the grid.
A bit more difficult to arrive at a figure for this. We have two electricity meters, one which records how much solar electricity we have generated, and one which records how much electricity the household has used in total. But we don't know how much of the electricity used has come from the solar panels, and how much has come from the grid.
I work from home, and we use a lot of electricity during the day, and last year I assumed the best case scenario (ie, that we used 100% of the solar electricity that we had generated). However I think this is a touch too optimistic - this year, I am going to use a figure of 80%. I have pretty much plucked this figure out of the air, using our electricity bills and gut feeling as a guide.
80% of 2001kWh is 1600.8kWh that we have not had to buy from the grid, which would have cost us 15.78p/kWh on our current tariff. Total saving: £252.61 for the year.
Financial benefit - total for the year:
Summing the feed-in tariff payments and the savings from using our own electricity, this gives a total financial benefit for the year of £609.36. This is down £15.64 on last year's total benefit of £623.98.
Summing the feed-in tariff payments and the savings from using our own electricity, this gives a total financial benefit for the year of £609.36. This is down £15.64 on last year's total benefit of £623.98.
Financial benefit - total so far:
The total financial benefit we have had for the first two years is £1233.34
Break even:
Assuming an average total yearly financial benefit of £616.66 (average of first two years' values) it will take us 8.4 years to fully recoup the original £5200 investment in the panels.
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