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On the financial side of things, our electrical bills have been lower this last year due to the energy generated by the solar array. ÌýEvery month I am able, with help from Facilities, to do a detailed and robust calculation of our savings. ÌýOver the last year the solar array saved the college $241,000. ÌýThis is a little smaller than the $283,000 I had predicted bumping up my predicted payback period from 12 to 14 years. ÌýRecall that the panels are warrantied for 25 years. ÌýThe payback period calculation, however, assumes a conservative 4% inflation rate for electrical rates, based on national averages. ÌýThe LADWP has been increasing rates at more than 6% for the last decade. ÌýIf I were to put 6% in we would be back to a 12 year payback. ÌýSo we will have to see. ÌýSo far the solar array has paid back 6.5% of the money we borrowed from the endowment (~$3.4M). Ìý

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1.81 GWh was 9% more than my simple solar model predicted. ÌýAs I said in my last email an excess might be due to sunny days, clean panels, conservative assumptions, simplistic assumptions or something else. ÌýUnderstanding the output of the array is important; in order to maintain it properly we need to understand it. ÌýTo that end I am aware of 3 student proposals submitted, 2 in physics and 1 in math, to the URC. ÌýWith their help we could make some headway on this problem.

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If you want to monitor the array yourself you can log into ourÌý,

Login ID = oxysolar
Password = 1600solar

The app can be found, for the iPhone, at the Apple's App Store by searching for AlsoEnergy.

In other news,

1) We made it ontoÌý.

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2) In October Facilities weeded around the array and cleaned all of the panels. ÌýI did a simple analysis and found that the combination, with a little rain thrown in to confuse the matter, produced at 30% bump in our energy production. ÌýIf you are interested I'd be happy to send you a memo I wrote about this. Ìý30% was much larger than I was expecting and got me to thinking about an optimal cleaning schedule. ÌýRamin Naimi, in Math, and I got talking about this one day and did manage to come up with an algorithm to maximize $. ÌýHowever it doesn't include rain. ÌýHey, you've got to start somewhere! ÌýAnyway the array has posed some fun and practical puzzles to solve.

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3) On 3 separate occasions we popped a fuse on the big 500 kW inverter. ÌýThe reason for this is still under investigation. ÌýIt is worrisome!

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4) Martifer went bankrupt! ÌýI am assured this is just an opportunity to get their finances in order. ÌýIn fact Martifer was up on the hill just a few weeks ago trying to track down the fuse problem.

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5) In October the DWP shut us down for a couple of days for electrical work nearby. ÌýIn total I estimate we were down for the equivalent of 11 full array days or about 3% of the year. Ìý97% uptime isn't too bad.

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6) On December 13th Facilities reported one of the panels had been broken. ÌýThis was fixed within a day. ÌýIt appeared to be some sort of projectile but we could never find it.

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