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Today Occidental's 1 MW solar array is 6 years old. Since "first-light" on March 4th, 2013 the array has produced 11.01 GWh of electrical energy, 12.0% of the college's use over the sameÌýtime period.

Good Morning Occidental!

Today Occidental's 1 MW solar array is 6 years old. Since "first-light" on March 4th, 2013 the array has produced 11.01 GWh of electrical energy, 12.0% of the college's use over the sameÌýtime period. ÌýFor equivalencies, especially regarding climate change, you can punch in 11.01 GWh = 11010000 kWhÌý.

In the last year the array produced 1.83 GWh of electrical energy. ÌýFor comparison here are the numbers from previous years,

1st year = 1.82 GWh
2nd year = 1.88 GWh
3rd year = 1.79 GWh
4th year = 1.82 GWh
5th year = 1.87 GWh
6th year = 1.83 GWh

The industry-wide expectation is that a solar array will lose about 0.5% of its production every year. ÌýSo by now I expected our production to be down by 3%. ÌýIt’s tough to tell from the numbers above because they are affected by lots of yearly systematics such as cloud cover, temperature, inverter failures, rain, dust, weeds, cleaning and weeding. ÌýIn preparation for a URC talk I gave last summer I downloaded NREL solar irradiance data, temperature data from ourÌýÌý(username = oxysolar, password = 1600solar on Chrome, Firefox, IE or Opera, no Safari) and inverter failures from the solar array log book for past years and used it, and a model for our solar array, to come up with a theoretical prediction for what the solar array should have been producing every day. ÌýThe results are shown below:
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The vertical axis is the ratio of actual production to expected production while the horizontal axis is the 2016 calendar year date. ÌýVertical light blue lines show days when the college received 0.1 inches of rain or more, vertical dark blue lines show days when the array was cleaned and vertical light green lines show days when the array was weeded. ÌýThe squiggly, black line shows the ratio of what the array actually produced to what it should have produced controlling for clouds, temperature and inverter failures (there were none in 2016). ÌýSomewhat arbitrarily I defined the array as “clean" if it received 0.1 inches or more of rain or after it is fully cleaned. ÌýThe data was provided by ourÌý, of course!Ìý I calculated a clean efficiency for 2016 to be 99.7+/-0.8%. ÌýAll of the yearly numbers for other years are consistent with 100% efficiency and with similar error bars so I see no evidence for a decline in performance. ÌýI recently ran across anÌýÌý(see Figure 11 IBC graph) which, after analyzing hundreds of solar arrays over many years, concludes that our SunPower panels decline at a significantly reduced rate of only 0.2% per year. ÌýSo maybe that’s it. ÌýTime will tell.
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Now then, you will notice a big dip in performance over the summer months. ÌýThat is a very consistent yearly effect and I attribute it, mostly, to dust accumulating on the panels, called soiling in the PV industry. ÌýFor the URC talk I did an analysis which attempted to balance soiling losses with cleaning cost losses and came up with a rule to minimize our losses. ÌýThe rule, which depends of cleaning costs, suggest we should clean the array about 1.5 times per year and facilities is now implementing that rule.

On the financial side of things, our electrical bills have been lower these last three years due to the energy generated by the solarÌýarray. ÌýOver the last year the solar array saved the college $280k. ÌýFor comparison here are the numbers from previous years,

1st year = $250k
2nd year = $293k
3rd year = $233k
4th year = $248k
5th year = $278k
6th year = $280k

The grand total savings so far is $1.600M on a purchaseÌýprice of $3.423M. ÌýThe calculated payback period is now 16 years, 10 years from now.
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I will leave you today with this important tiger-fact,
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Who knew?! ÌýGo Tigers!!!

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