Renewable Energy: An Overview - The Greenhouse Effect

Ninety-three million miles away, the sun blazes energy toward Earth. When this energy reaches Earth, the energy transmitted in short wave-lengths (visible light, ultraviolet, etc.) penetrates our atmosphere and strikes the Earth's surface. Energy in long wavelengths (such as infrared, thermal radiation or heat) is absorbed by carbon dioxide and other gases in the atmosphere. When penetrating short wavelengths strike Earth, they are converted into long wavelengths (in the form of heat radiation) and reflected back toward space. Some thermal radiation escapes, but most of it remains trapped inside our atmosphere. These long waves build up and keep Earth warm. This phenomenon, known as the greenhouse effect, enables life to flourish on Earth.


Its future effects are also the subject of much discussion.As carbon dioxide and certain other gases increase in the atmosphere, more and more of the heat that should escape and radiate into space remains trapped. This trapped heat is the subject of debate within the scientific community. Scientists, lined up on each side of the issue disagree as to whether this heat may cause a rise in global temperatures.

According to the late Carl Sagan, a world-renowned environmental author, the typical global temperature difference between an ice age and an interglacial period is three to six degrees Celsius (5 degrees to 11 degree Fahrenheit). Sagan theorized that if global temperatures were to rise three to six degrees C, water would become warmer and expand, melt polar ice caps and raise sea levels. Under these conditions, many islands would disappear and the oceans would flood such coastal cities as New York, Los Angles and Tokyo. Just a three-foot rise in sea level would triple the size of San Francisco Bay.

Global warming may change precipitation patterns as well. Rainfall could decrease in some areas, causing water shortages and failing crops, while increasing in other areas with attendant flooding and soil erosion. Plants and animals that do not adapt quickly to the changing environment could become endangered species.

Some scientists, however, believe that an increase in global temperature could result in increased crop yields. Higher carbon dioxide levels associated with global warming could be beneficial for plants. If carbon dioxide levels doubled, it is theorized that plants could improve productivity by as much as one-third. Some evidence shows that a rise in carbon dioxide could increase a plant's optimal temperature and allow plants to thrive in warmer temperatures.

Those that subscribe to the greenhouse theory and global warming believe the primary cause of global warming is high emissions of carbon dioxide from industrial processes and the burning of fossil fuels. The U.S. is the world's largest carbon dioxide emitter. The greatest amount of carbon dioxide emitted comes from burning oil, coal and natural gas to produce the electricity that maintains the American standard of living. Transportation is the second largest contributor to the problem. Each car in the United State emits more carbon dioxide per year than the weight of the car.

Some models used by scientists support the theory that an increase in atmospheric carbon dioxide produces global warming. Scientists have been making attempts to measure any difference in global temperature. Researchers at NASA as well as other scientists believe there has been a 0.5 degree C (0.9 degree F) increase in the average global temperature over the last 100 years. Other scientists remain unconvinced. Researchers using the TIROS-N weather satellite to measure the temperature of the lower portions of the atmosphere during the 1980s did not find any detectable warming.

Despite the controversy over whether the global temperature is rising, the greenhouse effect is a well-established theory in atmospheric science. For example, Venus has a dense carbon dioxide atmosphere that could account for its surface temperatures of 426 degrees C (800 degrees F). Mars, with a thin carbon dioxide atmosphere, has an average temperature of -53 degrees C (-63 degrees F). This temperature difference, however, may also be partially explained by the distance of these planets from the sun.



APS STAR Center redeployed
(December 2011, text provided by APS)

For the last 25 years, the Solar Test and Research (STAR) Center is where Arizona Public Service has worked with manufacturers, universities and government labs to propel technological advancements in converting solar energy into electricity. The goal? To find technologies that would allow solar energy to become a viable resource option for customers.

Success on that front means the STAR Center takes on a new role.

Personnel and focus have transitioned from technology research to solar operations and maintenance. The chief focus is to provide cost-effective support to ensure optimal system production and research the long-term reliability of our solar investments.

Today, more than 21,500 megawatts of solar have been developed globally, with APS having more than 500 megawatts either online or in development. Manufacturers the world over produce roof-integrated tiles; mono- or poly-crystalline photovoltaic panels; solar box ovens; evacuated tube collectors and glazed flat plate collectors; hybrid solar-thermal systems; hybrid solar lighting systems; solar pumps, fans, and switchable windows; mirrors and tracking systems used in trough/parabolic mirror concentrators; and thermal storage systems. And while listing innovations, I’d be remiss not to mention the increasing deployment of passive solar design – well-known to historians and architects, but never studied on site.

This technological cornucopia has overflowed since the STAR Center opened in 1985, and innovation will doubtless continue.

Now, APS is looking to find solutions to the next set of challenges associated with renewable energy. Namely, how the intermittency from solar and wind resources affects APS’s ability to provide reliable and affordable electricity to customers.

So, while the STAR Center will no longer be open to testing and research of new solar technologies, the solar installations currently in place will remain in operation. A majority of the solar panels at STAR will continue to operate and provide clean energy to customers on the APS grid. Those panels that were removed were re-deployed to other solar projects or returned to the manufacturers.

Further, the STAR Center is now also serving as a working laboratory for those learning to install solar electric systems – or for installation companies who are pursuing continuing education opportunities. Though its mission has changed, APS STAR Center will enjoy a long future of service to APS customers and the solar industry.

Contributed by Renee Guillory, DE Partnership Manager, Arizona Public Service



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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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