April Update

April is time for "spring cleaning" and I took advantage of the concept to continue some energy efficiency improvements inside my house, to hopefully decrease my usage.  I've installed a few more occupancy sensors on the lights that are left on most often, and have replaced the lights I want on most often with lower-energy LED bulbs (on sale with rebate at Costco!).  I'll continue the slow transition to LEDs as the CFLs burn out.  (I've been rather disappointed with the lifespan of CFLs.)   My utility company estimates a percentage of my bill that comes from various usage (Not sure how they do that, but they do!) and lighting is about 15% of my bill.  The two largest loads are cooling and my pool pump.  I'll be sure to fine-tune schedules for those this month so that I'm ready for the high afternoon Time Of Use (TOU) rates come June.

A pleasant surprise arrived last week in the form of a $17 electric bill, compared to $254 last year!  Again, a large part of the savings is due to switching to TOU rates: a good thing that's actually saving me money, but I'm not considering it in my break-even analysis.

For the first month since I've been tracking, my monthly generation was slightly lower than I predicted.  It looks like April may have just been a cloudier month this year than historically, which is fine... the model was based on averages and in fact, if I take the last three months together, I'm nearly spot on.  I had been wondering if I needed to adjust my model, but it seems it working pretty well so far!

My spreadsheet model based on historical data predicted 1.983 MWh.  I actually generated 1.846 MWh, about 7% below my estimate.  For the last 3 months combined, I predicted 4.777 and generated 4.794, about 0.4% above my estimate.  Assuming this model consistency (on average) holds, I'm still looking for a September break-even.

The savings prediction at the beginning of the month was $103.69.  Actual savings off my bill this month was $96.49.  

March Costs:

Loan payment: $229.16

March Savings:

Reduced electric bill (1.688MWh * $0.05227) = $96.49

Tax savings from deductible interest: $41.76

Running total of costs: $1,245.80

Running total of savings: $517.70

A prediction for May:

Reduced electric bill (6.61 * 31 * 10 = 2.273 MWh) = $118.82

Tax savings from deductible interest: $41.63