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Archives: about solar power

Although most of us perceive solar to be more sustainable than conventional sources such as coal or gas, traditional analysis methods rarely consider the full value that solar generation provides. As a result, economically viable solar power generation that achieves apparent parity with conventional energy sources1  – commonly referred to as “grid parity” – can seem an elusive goal. By taking a closer look at all the economic benefits of solar generation, however, it’s clear that grid parity is within reach. 
 
Let’s start by looking at just one of the many hidden benefits of solar generation. Solar power generation often coincides with peak demand periods, providing substantial value by generating power when it’s needed most. Take for example the August 2003 blackout in the Northeast. Not surprisingly, demand for power peaked during the day when temperatures were at their warmest and air conditioners were working their hardest. Solar generation is ideally suited to mitigating these peak conditions as the sun fuels both the heat wave and solar power generation. In this case, as little as 500 MW of solar PV installations dispersed throughout the region could have averted the outage.
 
One reason PV value is largely unrecognized is that it is usually defined solely in terms of the investment return it provides the owner of a system. That leaves out the value solar generation provides to utilities and ratepayers who purchase power, as well as taxpayers who have contributed to the installation of new PV systems via incentives and to society in general. Recently, I undertook the task of analyzing  the value of solar power generation to all constituencies in a particular area – in this case New York State – and demonstrated that solar generation can indeed reach grid parity.
 
So what are these hidden benefits? For utilities and ratepayers, benefits come in the form of reduced costs associated with obtaining power, whether it’s from the wholesale market or through increased power generation capacity needed to meet peak demand. In addition, because PV systems can be spread across a distribution system, power loss through long-distance transmission and wear-and-tear of feeder equipment such as transformers is reduced. PV generation also can act as a price hedge to volatile commodity prices for electricity. 
 
Taxpayers and the society at large also realize tangible benefits. Solar generation improves grid security by reducing the chances of power outages. Going back to the 2003 Northeast blackout example, a $3 billion investment in PV could have prevented the outage, which is estimated to have cost $8 billion. Solar generation also benefits the environment and public health through reduced pollution, and it employs more people than conventional energy production, creating jobs.
 
As Figure 1 shows, by quantifying these benefits for the State of New York, we estimated the combined value of distributed solar generation to the state’s rate and taxpayers to be in the range of 15 to 41 cents per kWh. Since the unsubsidized cost of PV is in the order of 20 to 30 cents in New York, the effective grid parity gap is essentially bridged in this state, and likely in several others as well. This a fundamentally different conclusion than arrived at when applying the traditional grid parity definition without any context, comparing unsubsidized PV to least-cost (gas) generation at 6 to 8 cents/kWh – let alone coal at 4 cents per kWh – and showing a large apparent solar grid parity gap. 
 
Richard Perez Grid Parity
 
Understanding the full value of solar better equips us to support the growth of solar generation. We all stand to gain from a healthier, more sustainable world – economically, environmentally and in terms of energy security.


 
Richard Perez co-authored the paper, “Solar Power Generation in the U.S.: Too Expensive, or a Bargain ?” with Tom Hoff, Founder and President, Research and Consulting at Clean Power Research, and Ken Zweibel, GW Solar Institute, George Washington University. 

1Specifically, apparent grid parity is the point at which unsubsidized solar competes with the cost of new gas generation capacity, sold at wholesale. 

Richard Perez
Richard Perez
Senior Research Associate, University of Albany, Atmospheric Sciences Research Center
Albany, NY, United States

Variability of photovoltaic systems is an important and often misunderstood topic.  SunPower has been a pioneer and leader in efforts to better characterize variability and its impacts, and has helped develop a substantial body of work on the topic.  It has been consistently demonstrated that the variability of a single, relatively small PV system is much greater than that of many distributed PV systems – and that large, utility-scale PV systems demonstrate substantially lower variability than small systems in the same location.  The following article by guest blogger Richard Perez provides an excellent introduction to the topic.  
 
Owners of PV systems know first-hand that passing clouds cause rapid changes in the amount of energy produced from second to second. The impact of this short term power “variability” on system owners is usually seen rather than felt because during times of low production, electricity from the grid picks up the slack. This is good for PV system owners, but makes it difficult for grid operators, who are charged with providing reliable energy for their customers. 
 
One way for utilities to manage variability is to ramp up other power plants, but that increases the costs and complexity of managing the electric power distribution system. Fortunately, recent studies have found that renewable energy sources that are distributed across a wide geographic range greatly reduce the effects of weather-related variability to the overall electric system. This means that more “dispersed” residential and commercial PV is good for utilities. 
 
Electric grid operators became aware of the difficulty variability posed when information about short-term variability in a 3.5-megawatt plant in Springerville, Arizona was widely circulated in 2009. The analysis revealed frequent ramping up and down of the plant’s production as a result of passing clouds. This prompted utilities and agencies across the U.S. to ask themselves: “How would power fluctuations be handled if PV reached a sizeable fraction of power production?” The implication of the Springerville analysis was that short-term fluctuations in power production within a particular region are an obstacle to large-scale PV deployment. 
 
As a result of the Springerville analysis, the questions about short-term variability were taken up by the U.S. Department of Energy and the California Solar Initiative. Unsurprisingly, research confirmed that conditions can be highly variable at any given location. But on the positive side, research also revealed that spreading PV systems out over a larger area mitigates the problems of short-term variability. The truth of this finding is supported by the probability theory’s law of large numbers, and has been proven through recent studies. 
 
The following image illustrates this principle by showing how distance can “smooth” variability. The data in the top part of the figure shows 10-second solar radiation (irradiance) at a single location in Napa, California, on November 21, 2010. The data in the bottom half of the figure presents the same irradiance data, but measured at 25 locations in a 1.5 square mile grid rather than at a single location. The data in the bottom half of the figure is much smoother, without large short-term fluctuations.
 
Richard Perez Irradiance Data

A similar study in New York compared the variability of a single PV system versus a large number of systems deployed over a 25 square mile area. The study found that power output variability of PV systems distributed across a region is similar to the demand-side variability impacts that utilities have experienced for many years. Namely, that a single customer might be quite “noisy,” with local fluctuations caused by the starts and stops of systems and equipment, while the city-wide load experiences almost no short-term fluctuations. In the same way, the power fluctuations at a single PV system location can be substantial, but fluctuations decrease as the footprint of distributed systems increases. 
 
The efforts taken over the last few years to observe, understand and quantify the influence of space and time on PV energy production are making it easier for grid operators to manage short term variability.  These findings, and the introduction of tools to assess the impact of new PV systems on the overall electric grid, support the continued expansion of dispersed residential and commercial PV systems, and the ability for grid operators to get the most from their solar resources. 

For further reading:

Richard Perez co-authored the paper, "Solar Resource Variability: Myth and Fact," published in the September/October 2011 edition of Solar Today, with Tom Hoff, Founder and President, Research and Consulting at Clean Power Research

Richard Perez
Richard Perez
Senior Research Associate, University of Albany, Atmospheric Sciences Research Center
Albany, NY, United States
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