Last year, Joan and I had solar power generation equipment installed at our home. Early in June of 2013, the new system was placed in service. Both the solar system provider  and the local power utility  have provided timely and reasonably detailed information on the solar power system’s performance. This post reports on actual performance during the first full operating year (July 2013 through June 2014).
We live in the high desert of north central Arizona, about 3,400 feet above sea level and about as far north as Los Angeles or Atlanta. Like the rest of Arizona, we enjoy sunshine much of the time. Temperatures here are rarely below freezing except overnight in mid winter. In the summer, temperatures often exceed 110o F during the day, sometimes for days or even weeks. Our home is a single story structure oriented roughly north to south — almost ideal for solar panels.
Refer to the chart labeled “Power Consumption by Month”. The blue curve indicates the total amount of electric power consumed (kilowatt hours), by month. The red line indicates the amount of that power provided by the solar panels and the green line indicates the amount supplied by the power utility.
Power consumption is quite seasonal due to air conditioning in the summer and electric heating in the jaws of winter. Power consumption ranged by almost a factor of three, from a low of 877 kwh in May and a high of 2,416 kwh in December. Solar power generation ranged from 674 kwh in the short days of November to 1,258 kwh in June.
The chart labeled “Solar Power Generated / Total Power Consumed” indicates how much of the power consumed in each month was provided by the solar panels. For the year as a whole, the solar panels provided 70% of total consumption, as designed. However, the high consumption winter months are also low generation months — during December, solar provided only 29% of the power consumed. On the other hand, in three months the panels generated more power than was consumed, reaching 143% of consumption in May. In those three months, the electric meter effectively ran backwards as the surplus power was delivered to the power grid.
The chart labeled “Monthly Power Bill” compares a year with solar (July 2013 – June 2014) with the same months a year earlier, before the solar system became active. As you can see, midwinter power bills changed little, while the other ten months improved markedly. Overall, our average daily power bill decreased by 67% — about as expected, since solar provided, on average, 70% of the power consumed. Most of the remaining 3% can be attributed to fees and taxes on monthly power bills that are not rigidly proportional to the power provided.
Obviously, those big reductions in monthly power bill payments need be balanced against the cost of installing the solar panels and related equipment.
View from the Power Utility
Widespread installation of distributed solar power generation capacity affects utility companies in negative and positive ways. On one hand, distributed solar installations like mine reduce peak demand loads at the most advantageous time — during long, hot summer days with high air conditioning loads. Similarly, when solar generation exceeds consumption, the utility receives clean, green solar power without capital investment on their part, effectively in exchange for base load power, usually delivered during times of low demand (at night, for example) from existing facilities.
On the other hand, the utility loses most of the revenues they are used to receiving from me and installations like mine. However, the utility’s power generation and power transmission facilities, for the most part, already exist. Their variable cost of generating power does decline, but their fixed costs and overheads don’t. As you can see from the green line on chart titled “Power Consumption by Month”, the utility provides (and bills) an average of about 500 kwh per month. However, they are obligated to be equipped to provide more than three times that much power in mid winter.
For Smaller Manufacturers
There are two reasons to consider solar power generation. The first is to reduce your power cost today and to hold that cost constant in the future, regardless what dramas befall fuel costs. The second is to provide your business, your customers and humanity generally with cleaner air to breathe. Both reasons matter.
That said, the economics of solar panels are likely to be most attractive for office facilities and light industry. In any case, manufacturers should be in regular contact with the service engineers at their local power supplier. They can, and will, help you evaluate installing solar generation. At the same time, they may suggest other avenues to lower your power costs, depending on the specifics of your facility and your power requirements.
Thoughtful comments and experience reports are always appreciated.
… Chuck Harrington (Chuck@JeraSustainableDevelopment.com)
P.S: Contact me when your organization is serious about pursuing Sustainability … CH
This blog and associated website (www.JeraSustainableDevelopment.com) are intended as a resource for smaller manufacturers in the pursuit of Sustainability. While editorial focus is on smaller manufacturers, all interested readers are welcome. New blog posts are published on Wednesday evenings.
 Our solar power generation system was designed, installed and leased through Solar City. They did a good, hassle-free job.
 The utility is Arizona Public Service (APS), www.aps.com
Note: The charts in this post were created from data provided by APS and from Solar City.