Two Years in the Sun

Just a year ago, a post to this blog titled A Year in the Sun reported on the initial performance of a solar power generation system installed at my home. Another year has passed and another full year of experience gained. This post updates A Year in the Sun and comments on performance over two full years. C.H.

Going Solar

Early in June of 2013, Joan and I had solar power generation equipment installed at our home. Both the solar system provider [i] and the local power utility [ii] have provided timely and reasonably detailed information on the solar power system’s performance. This post reports on actual performance during the first two full operating years (July 2013 – June 2014 and July 2014 – June 2015).

Sunny Arizona

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.

Capturing Photons

Our home consumes electric power from the solar system and from the utility. From minute to minute, we consume power from the solar system first, then from the utility. When we don’t use all of the solar power available, the remaining power is sold to the utility. When our requirements exceed the power available from the solar system, we buy power from the utility. Our solar system is designed to produce about 70% of our electric power requirements, on an annual basis.

Solar Power Generated

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 first year (July 2013 – June 2014) the solar panels provided about 70% of total consumption, as designed.  Solar power production ranged from 674 kWh in December 2013 to 1258 kWh in June 2014. In the second year (July 2014 – June 2015) our total electric power requirements were about 10% lower than the previous year. Solar power production was about 6% lower in total, ranging from 551 kWh in December 2014 to 1126 kWh in April 2015.

However, the high consumption winter months are also low generation months — during December 2013 and February 2015, solar provided only 29% of the power consumed. On the other hand, in three months of each year the solar panels generated more power than was consumed, reaching 159% of consumption in June 2015. In those months, the electric meter effectively ran backwards as the surplus power was delivered to the power grid.

Monthly Power Bill

The chart labeled “Monthly Power Bill” compares two years with solar (July 2013 – June 2014 and July 2014 – June 2015) with the year July 2012 – June 2013, 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 generation facilities, for the most part, already exist. Their variable cost of generating power does decline, but their fixed costs and overheads don’t. 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

Chuck on Wilson Mtn.Thoughtful comments and experience reports are always appreciated.

…  Chuck Harrington (

P.S: Contact me when your organization is serious about pursuing Sustainability … CH

This blog and associated website ( 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 weekly.

[i] Our solar power generation system was designed, installed and leased through Solar City. They did a good, hassle-free job.

[ii] The utility is Arizona Public Service (APS),

Note: The charts in this post were created from data provided by APS and from Solar City.