Newsletter No. 10


Today Occidental's 1 MW solar array is 7 years old. Since "first-light" on March 4th, 2013 the array has produced 12.75 GWh of electrical energy, 11.9% of the college's usage over the same time period.

Good Morning Occidental!

Today Occidental's 1 MW solar array is 7 years old. Since "first-light" on March 4th, 2013 the array has produced 12.75 GWh of electrical energy, 11.9% of the college's usage over the same time period. That amount of clean energy represents 20 million pounds of avoided CO2 emission or the equivalent of the carbon sequestered by 150 thousand seedlings planted or 1.1 billion smartphones being charged. For other equivalencies you can punch in 12.75 GWh = 12750000 kWh here.

In the last year the array produced 1.77 GWh of electrical energy, a record low for us. This was due, in part, to an intermittent and persistent problem with the inverter for the carport solar panels. I estimate we lost 0.02 GWh over that incident spanning, luckily, December and January, our lowest producing months. Our average yearly production is 1.83 GWh so the inverter can’t account for all of the shortfall. An unusually cloudy last spring and fall and a late August cleaning of the array probably account for the remainder. My most recent (2018) e!ciency analysis (see last year’s Solar@Oxy News for details) shows us at 102 +/- 3% so it likely is not the panels degrading.

Like all things, the array is requiring more maintenance as it ages. This year, during routine maintenance, it was discovered that 9 panels were broken. One was clearly a projectile as the shattered glass surrounded a particular point in concentric circles. We never found the projectile. The others were, mysteriously, shattered the whole way across. The good news is that we were able to purchase 27 used, replacement panels with some to spare for the future. That’s important because panels with this particular form factor are not being produced any more. And then there was the carport inverter failure. That took awhile to figure out and then to get the spare parts to fix it. Overall we spent $20.7k maintaining the array this year, including one cleaning. Since “first-light” we’ve spent $85.8k or $12.3k/year or 0.35% per year relative to the price of the array. An extensive study of commercial arrays operations and maintenance suggest we should expect maintenance costs of between 0.5% and 1.0%.

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 $319k, a record high, expenses are included. How is it possible for us to have maximum savings but minimum energy generation? About 80% of our savings comes from energy charges and they have been skyrocketing lately. Here is a plot,

The green, red and blue represent charges for different times of the day. The purple curves is the weighted average. So each kWh that the array generates is worth more this year than in previous years. This is good news for solar savings but bad news for the college’s bottom line. Here’s a plot of our yearly usage though,

The dashed brown line shows all of the electrical energy we’ve used per year since 1998. The orange line shows the amount we are billed for with the break in 2013 due to the solar array. Our overall usage has been falling for the past 2 years. This is due to, among other things, the installation of LED lights for campus lighting. The grand total savings from the array so far is $1.919M on a purchase price of $3.423M. The calculated payback period is now 15 years, 8 years from now. This payback period estimate is shorter than last year's due to rising electricity costs.

Reading the news in the morning over co"ee and breakfast is often distressing so, for some time, as a pick-me-up, I’ve been reading online articles about renewable energy. To me this is one of the truly bright spots in today’s world. Here’s an example discussing a new way for farmers to make money, agrivoltaics. And speaking of bright spots, Gretchen North had her Biology 380 - Plant Physiological Ecology class plant 12.5 pounds of poppy seeds around the panels on the hill a few weeks ago. If Google is to be believed that is ~20 million seeds! With a little more rain we may have a huge orange and black tapestry to enjoy this spring.

Until it rains enjoy the Rayleigh-scattered blue light on this sunny Wednesday!