Will Rooftop Solar Really Add to Utility Costs?

By Suma Jothibasu and Surya Santoso


Regulations in most states obligate utilities to derive some of their  electricity generating capacity from renewable sources. Unsurprisingly, the most  widely available options—wind and solar—dominate. The International Energy Agency (IEA) estimates that by 2050, solar photovoltaic (PV) power generation will contribute 16 percent of the world’s electricity, and 20 percent of that  capacity will come from residential installations.

By offering local generation, residential or rooftop PV reduces the need for transmission facilities  to move power from large generating stations to distribution substations. But the effect on the distribution grid is less straightforward. The conventional distribution grid is designed for neither two-way power flow nor large generation capacity. So the prevailing thought is that  the grid will need a costly upgrade to accommodate the high PV penetration. Our study within  the Full Cost of Electricity (http://energy.utexas.edu/the-full-cost-of-electricity-fce/) program aims to estimate the cost of maximizing residential PV capacity without any grid impacts. The bottom line? We found  that  even without hardware upgrades to the distribution circuits, such circuits can handle significant solar generation.

We looked at it three ways: Allowing the largest PV generation

1. without making operational changes to the circuit or upgrading the infrastructure;

2. with a few modest operational changes in the equipment already  installed; and

3. with additional infrastructure upgrades such as smart inverters and energy storage.

(Note that  accommodating the first two capacities does not require any integration costs, beyond  some minimal cost associated with the operational changes in the existing  devices.)

Depending on a distribution circuit’s characteristics, the maximum PV capacities it can handle range  from as low as 15.5 percent of the median value of the daytime peak load demand (2.6 megawatts in one particular circuit) to more  than 100 percent (3.87 MW in another circuit). These results suggest that  significant rooftop PV generation can be integrated in the grid with little or no additional  Photo:  Lester Lefkowitz cost to utilities and their  customers and without causing any adverse grid impacts. In fact, our study shows that  at such levels, impacts due to PV generation are either non-existent or can be addressed by appropriate circuit  operational changes.


The amount  of a photovoltaic capacity that can be added to a distribution circuit without violating its operating constraints depends on the specific nature  of the system. The minimum hosting capacity, shown as Circuit C, is 15 percent. The maximum hosting capacity with no changes to the distribution circuit, Circuit B, is 104 percent of median daytime peak  load.

In one example, an operational change was able to boost photovoltaic capacity from 15 percent to 47 percent. The PV hosting capacity of the circuit  in that  same  example can be boosted from 47 percent to 80 percent if as many  as one-third of the photovoltaic installations include smart inverter technologies.

Although adding energy  storage would also increase hosting capacity, we find that  the cost of energy storage systems would be significant, and so it is unjustifiable if the sole purpose is to increase PV penetration.

For details of which circuit  characteristics affect photovoltaic capacity, as well as other calculations, read the complete white paper “Integrating Photovoltaic Generation (http://energy.utexas.edu/files/2016/09/UTAustin_FCe_Int_PV_Generation_2016.pdf)[PDF], part  of the Full Cost of Electricity Study conducted by the University of Texas Austin Energy  Institute (http://energy.utexas.edu/). (IEEE Spectrum is blogging about the study  and linking to the white papers as they are released.)

 Suma Jothibasu is a graduate student and Surya Santoso (http://aspires.ece.utexas.edu/bio.html) directs the Laboratory for Advanced Studies in Electric Power and Integration of Renewable Energy Systems, within the Department of Electrical Engineering, Cockrell School of Engineering at the University of Texas Austin.

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The New Clean Energy Economy Invests in American Jobs

Published as a Arizona Solar Center blog 2013-08-31

Employment opportunities in the energy sector are exploding. New enhanced exploration techniques have created a boom in the oil and gas fields. Jobs in this sector are projected to double by the end of the decade.

But perhaps even more promising is the boom in the clean energy field. This emerging market sector involves a number of new technologies and industries such as wind, smart grid, energy efficiency, renewable fuels, electric vehicles, natural gas vehicles, hybrids, public transportation, and more.

Solar energy is also a part of the clean energy market sector. And as the solar industry grows, so does its beneficial effect on society, such as greater energy independence, improved environmental enhancements, and positive economic impact on jobs.

Research studies and reports examining the clean energy economy over the past couple of years include analysis from a wide variety of sources: public, private and non-profit. A common theme in these studies points out that as home-grown sources of clean energy have become more cost-competitive and mainstream, they are spurring the creation of more jobs locally than traditional fossil fuels.

Despite the fact that these studies have varying estimates as to the future size of this new energy sector, one thing that is not in dispute is that clean energy generates more jobs per unit of energy delivered than fossil fuels. And in the case of solar PV, the average employment is several times more per unit of energy produced than jobs in coal, natural gas or even nuclear.

The solar industry experienced explosive job gains throughout the great recession. According to the Solar Energy Industries Association, in 2012 there were more than 281 companies at work throughout the solar value chain in Arizona, employing 9,800 people. This was more than double the number of jobs in Arizona associated with the solar sector in 2011. By contrast, the coal industry has one mining operation and 16 power plant operations throughout Arizona. Coal is the largest source of electricity for Arizona consumers. But according to the Energy Information Administration, less than 1500 people are employed in coal mining and power plants in Arizona.

Make no mistake about it -- the clean economy is real. It's going to be the biggest job creating sector in the coming decades. Currently, there are approximately 120,000 full-time, permanent jobs nationwide related to solar and 1.2 million in the entire clean energy sector.

In July of 2011, the Brookings Institute, in collaboration with Batelle's Technology Partnership Practice, released the first comprehensive national clean economy study to quantify the clean job trends in the U.S. The study found 26 percent of all clean energy jobs are in manufacturing -- substantially greater than the nine percent of manufacturing jobs that comprise the whole of U.S. economy. Because manufacturing jobs require more specialized skills and pay higher salaries, the average clean energy worker earns 13 percent more overall than the average worker.

Community colleges, technical colleges, private and public universities recognize the jobs of the future are in the clean tech sector and are beginning to implement curriculum, programs and degrees for the sustainability professions and the clean economy.

Significant policy uncertainties, however, are threatening this economic boom in clean energy. Smart policy support is critical just as it has been throughout our history for the development of many of our modern industrial sectors, from the railroads to autos to the electric utilities and the internet. Government policy, money, expertise and coordination have contributed to the development of many beneficial industries; thus a strong argument can be made that helping the solar and the clean energy sector grow helps America prosper.

The major challenge facing us as these new technologies and industries emerge is whether or not our political leaders will continue to effect policies that provide certainty for private investment in a clean energy future. There are concerns that negative political pressure from vested interest groups and their lobbyists may force politicians to pull the plug, thereby allowing solar and clean energy and its associated jobs to develop elsewhere.

As we celebrate Labor Day, we must ask ourselves: Will solar energy, born here in the USA, carry a "Made in China" label in the future? Or will we take a stand in support of American jobs and ingenuity in a new clean energy economy?

Jim Arwood
Communications Director
Arizona Solar Center