Solar Energy’s Solstice Problem

The Global Solar Power Explosion

By any count, solar electric generation is a huge success. Solar cells, like the ones on the roof of my house, are being installed in accelerating numbers by residences, public buildings, commercial facilities, industries and electric power utilities around the world. The cost of solar installations continues to decline, while environmental concerns affect the operational viability of existing fossil fueled electricity generation.

AEO 2016 ER Solar Power GenerationThe graph to the right, from the U.S. Department of Energy, [1] projects that solar generation capacity will increase by about ten times from 2015 to 2040, without considering any new technology, laws, regulations or other factors that may well accelerate the rate of solar installation further over the coming years. Solar power generation capacity in countries other than the U.S. – including less economically developed countries – is likewise increasing.

Closer to Home

My Home Viewed from Space

My home, as viewed from Space

My home is in the high desert of central Arizona, about as far north as Los Angeles or Atlanta. Climate here is sunny and dry almost year around – almost optimal for solar power. Here is a Google Earth picture of my house, as seen by a satellite. The solar panels, which you can see in the picture, have been in service for three years now.  My solar power system has on-line data collection, so I now have some pretty reliable performance numbers.

The graph below, from my actual experience, demonstrates solar’s “solstice problem”. The blue curve indicates the total electric power consumed at my house, by month. The red curve indicates the amount of solar electric power generated at my house, by month. The green curve indicates the net amount of electricity I purchase from my local electric power utility, again by month.

Home Solar Power Graph

My solar power system is designed to produce 70% of my electric requirements, taken over a full year (which it does). However, as the blue curve indicates, my total power consumption varies widely from month to month, with strong peaks in mid-summer (air conditioning) and mid-winter (electric heating).

However, my solar power generation (red curve) also varies strongly from month to month, with high peaks during the long days of mid-summer and low peaks during the short days of mid-winter.  As you can see, my solar system produces about half as much power in mid-winter months as it does in mid-summer months, near the solstices.

The Solstice Problem

To appreciate the impact of the solstice problem, it is useful to zoom out from considering a single solar installation (like my house) to thinking from the perspective of a power utility or the perspective of the power grids. Solar power is going to continue to grow as a fraction of total electric generating capacity. But, solar power facilities only generate electricity while the sun shines. At the same time, residential customers like me and you, as well as commercial and industrial customers, expect all of the power they need to be available whenever they need it.

Obviously, the sun doesn’t shine at night. But nights only last a few hours. Batteries and other technologies are available to manage the overnight problem. The solstice problem – generating capacity varies dramatically over weeks and months from solstice to solstice – is another matter. The solstice problem is just that – a problem that needs to be solved for solar energy to become truly practical on a massive scale. There are lots of possible avenues toward a solution, or sets of solutions for different geographic areas. These avenues might include demand management and innovative large scale energy storage technologies. Or, there may be approaches that nobody has thought of yet.

For Smaller Manufacturers

The electric power industry is in a state of transition. Manufacturers, especially those with substantial electric power requirements, need to remain aware of your utility’s situation and your own options. You might consider producing some or all of your own power (solar, of course). In any case, develop and maintain an on-going rapport with your utility’s customer service engineers.

Thoughtful comments and experience reports are always appreciated.

…  Chuck Harrington

(Chuck@JeraSustainableDevelopment.com)

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 weekly.


[1] This graph is from Energy Information Administration’s Annual Energy Outlook 2016, Early Edition, published 17 May 2016. Available for free download at: http://www.eia.gov/forecasts/aeo/er/index.cfm