Just got my first yearly bill from PG&E, reflecting the performance of our solar array.  Good news - right about where I expected it to be!  Here’s the stats for those that need encouragement to take the solar plunge:

• Power generated: 13,315 kWh
• Power bought from PG&E: 3,358 kWh
• Annual bill from the power company: $348.00
• Sum of monthly minimum payments for connected meters: ~$50
• Savings: $3,221.14 [1]
• Actual rate of return: 8.95% [2]
• Total payback length: 11.2 years [3]
• Extrapolated payback date: 11 Oct 2017

Notes:

1. This calculation takes into account the sliding price scale for energy over the baseline, and actual changes in the rates and baseline during the year.  Some straight-line averaging was necessary to correlate the readings taken from the meter with those from the power company.
2. Tax free!  And calculated only over the payback period - once the array pays for itself, I will continue to get free energy for many years.
3. Straight-line extrapolation based on assumed fixed consumption, and fixed energy prices.  It is virtually impossible that energy prices won’t rise substantially in the next 10 years, shortening the payback period and increasing the rate of return.

As far as I can tell, the solstice happened about an hour ago - placing it on either Thursday the 21st or Friday the 22nd depending upon your time zone.  These short days are pretty unpleasant, and I always look forward to lengthening days this time of year.  So the solstice is both a symbol of gloom, and a symbol of hope that it will all look brighter from here on.

Fitting with the gloom theme, the shortest day of the year was a cloudy, then drizzly, then outright gray and rainy day here in Auburn.  That adds up to the perfect opportunity to see what the bottom end of my solar panels performance is!  So as it grew dark I checked and found that in the worst imaginable conditions, I only generated 1.546 kWh - a far cry from our 40kWh average daily consumption, and probably just enough to power my laptop and monitor during the workday.  Depressing!

But true to the theme of hope, I updated my solar cost savings spreadsheet found that despite the lack of substantial solar output in these horrible conditions, during the first four months of operation I have still saved just shy of $1000.  Right on plan!  Even if electricity prices stay constant, inflation drops miraculously to zero, and for some reason the expected tax breaks don’t materialize, I’ll still break even in about 14 years; averaging about a 7% annual return on my investment.  I’m willing to accept that as the worst possible case!

By the spring solstice, I’m expecting much better news - the calculation (not just the forecast) of the value of this year’s tax breaks, longer and sunnier days, and probably some unavoidable electricity rate increases.  All adding up to a payback of under 10 years.  At least, that’s my solstice hope!

This summer marked a permanent reduction in our power bills, with the joyful completion of a 7.6 kW solar array!  I’ve wanted to invest in solar for years, but shopping for a reasonably priced yet competent installer always ended up on the back burner.  Despite the desire to do good by the environment and participate in an emerging distributed grid of clean energy, the costs are quite substantial, and is has proven quite difficult to determine what the payback on such an investment would be.  Between state rebates, federal and state tax credits, depreciation, choices of flat or time-of-use metering, a stack of rates based on consumption, which change seasonally and will probably increase in the future, figuring out the payback required too many assumptions to give me confidence in the resulting numbers.

My enthusiasm to figure this all out was renewed on a visit to the Horton Iris Farm, where they have a new 3+kW roof-top system.  The installer, Coy Ware of Coy Solar, has been a friend of the Hortons for a long time, and has a long history of general contracting, electronics, and eco-friendly technologies, so it didn’t take long for us to analyze our usage, figure out the parameters of the system, and get underway.  We calculated the payback at somewhere between 4.5 and 9 years - a pretty wide range but that was the best we could do.  At either end, I was willing to invest though.  Coy devised clever ways to move materials and equipment around the site since it isn’t very accessible by machinery.  It took about 6 weeks of steady and at times heavy manual labor to construct and install the system on the hillside below our pool, especially to Coy’s standards of excellence!

We switched it on about 6 weeks ago.  The system is a grid-tie, meaning that there are no batteries or other storage mechanism.  Excess power is pumped back into the grid, making the meter spin backwards - what a sight!

A new digital meter courtesy of the power company, and the System Lifetime readout on the solar has helped me keep track of how much I’ve saved - not a trivial proposition given the rate schedule involving baseline rates and increasingly expensive rates the higher over the baseline you go (the exact opposite of volume discounts).  I put together a rather complex spreadsheet simulating a virtual power bill and the resulting savings of $519.75 for the first 47 days.  Not factoring in the tax savings, a straight-line estimate at that rate puts the payback at around 8 years.  I hope to see that period shorten as rates rise (as they no doubt will within the timeframe), and the actual tax savings can be measured more accurately.  Over the life of the system, it should pay for itself many times over.

And the air is just a little clearer than it otherwise would have been. Those benefits will accrue for years as well.