May Update

May is in the books and summer is here, along with the four months of the year when I'm subject to Time Of Use (TOU) rates during the afternoon hours.  I've tweaked schedules for the thermostats to pre-cool and then run the A/C less, and pool pump to not run at all during the 1pm to 7pm window where electricity is almost 5 times as expensive as the rest of the day.  Since those loads seem to be the biggest contributor to my utility bill, I hope the rescheduling will be helpful.  When I originally did my cost-benefit calculations and measured my historical peak afternoon usage, I had not been doing anything special to lower my afternoon usage, so any extra steps I take should add to my expected "real" savings, even if it's not accounted for in my calculations of how much power I'm generating.  And in addition to the major loads, I've also set a calendar reminder to go around the house right before 1pm and turn off any lights, fans, and other things people have left on.

The May electric bill was only $60, a nice savings from last year's $374.  Again, the "real" savings I'm seeing from TOU rates is almost double the savings I'm getting from solar generation itself... which still pays for itself.  The bottom line is I've got more money in my pocket this year than I did last year!

My spreadsheet model based on historical data predicted 2.273 MWh for May.  I actually generated 2.035 MWh, about 10% below my estimate, and bringing the 4-month total to 3% below my predictions.  Looking at my weekly average, it appears this trend may continue.  It might be that some of the assumptions I used in my model were off, or perhaps the panels are less efficient generating at higher temperatures.  However, I also recived a letter this month from the Public Utilities Commission of Nevada (PUCN) who is in the process of registering my system in order for me to earn Renewable Energy Credits (RECs) that I can sell on the market as a "Green Energy" producer.  They did their own independent calculation and while they differ month-to-month, the annual total is within about 0.2%.  So I'll hold off on making any adjustments for a while and see how the average works out.

The savings prediction at the beginning of the month was $118.82.  Actual savings off my bill due to generating power this month was $106.37.  This will be the last month for a while that my savings are less than my costs.  Now that the energy I generate between 1pm and 7pm (43% of my daily total) is worth 5 times as much, I will be making money for the next 4 months.  June will actually be the biggest profit, with energy generation actually paying for 2 months of loan payments!

May Costs:

Loan payment: $229.16

May Savings:

Reduced electric bill (2.035MWh * $0.05227) = $106.37

Tax savings from deductible interest: $41.63

Running total of costs: $1,474.96

Running total of savings: $665.70

A prediction for June:

Reduced electric bill (7.33 * 30 * 10 = 2.259 MWh) = $416.80

Tax savings from deductible interest: $41.50