Newsletter No. 11


Today, Occidental's 1 MW solar array is 8 years old.

Since "first-light," on March 4th, 2013, the array has produced 14.46 GWh of electrical energy, 12.1% of the college's usage over the same time period.  That amount of clean energy represents 23 million pounds of avoided CO2 emissions.  For other equivalencies you can punch in 14.46 GWh = 14460000 kWh.

In the last year the array produced 1.68 GWh of electrical energy, a record low for us following last years' record low.  Last year the problem was faulty equipment and some weather issues.  This year the problem was COVID; no the array didn’t catch it.  Last summer when we were due a cleaning the college was overwhelmed with COVID related issues and the cleaning we normally do at that time fell through the cracks. 

On the financial side of things, our electrical bills have been lower due to the energy generated by the solar array.  Over the last year the solar array saved the college $311k, our second best year for savings with increasing electricity prices compensating for lost production.  To date the array has saved the college $2.2M on an investment of $3.35M.  Accounting for lost investment opportunities (endowment) the payback period for the array is 15 years, unchanged from last year.  We are now more than halfway through paying off the array.

It's not good that we didn't clean the array last year and, as a consequence, lost a lot of energy and savings to dirt.  But, to a scientist, it is an interesting data point.  Our average production over the other 7 years has been 1.83 GWh.  The difference is 1.83 - 1.68 GWh = 0.15 GWh or 150,000 kWh.  A typical house uses 20 kWh per day for comparison.  The difference multiplied by our overall average electricity rate, 18.38 cents/kWh, is $27.6k.  With only one exception, the very rainy 2015, we have cleaned the array once every year.  So, roughly speaking, $27.6k represents the loss from not cleaning the array one time.  The last time we had the array cleaned it cost us $4.5k, illustrating the economic advantage of cleaning.  As I discussed in 2019 the optimum is about 1.5 times a year.  This number is driven by the large cost of cleaning the array.

What if the cost to clean the array were zero or near zero?  How much more energy could we produce and how much more money could we save?  From modeling of the output of the solar array we know that it could be producing 1.96 GWh per year on average with surprisingly small, 2% (RMS), variance from year to year.  In this optimal, zero-cost-to-clean scenario the increased energy savings would be 1.96 - 1.68 = 0.28 GWh = 280,000 kWh or $51.6k savings per year.  Relative to our overall savings, $311k, this is a significant chunk of change.

Today we don’t need to worry about cleaning.  That 0.25” of rain yesterday restored our efficiency to 100%.  With the gorgeous sunshine this morning it looks like the array is going to be cranking today.  I hope you have a chance to go outside and enjoy some good old-fashioned fusion-produced solar energy today.