Intermittency of Solar Energy Sources

Solar Intermittency: The Keys to Solving Problems

This essay covers the issue of intermittency of solar and wind energy, describes its background, and distinguishes characteristics. Real initiatives and projects directed at decrease of intermittency will be provided and thoroughly analyzed. All their advantages and disadvantages will be shown below. These projects are oriented at improvement, salvage, and transmission of wind and solar energy.

The term intermittency itself undermines the extent of stoppage and absence of any power source. The intermittency of solar energy has a direct dependence on the amount of light in a particular area. It is also influenced by such factors as seasonality, time of a day, and weather conditions. During different seasons, the amount of solar energy also differs: it is bigger in summer and lower in winter. The amount of solar energy that can be obtained during noon hours is considerably higher than the amount of solar energy that can be obtained early in the morning. Weather conditions also have a considerable influence on the extent of energy, which can be obtained by using solar equipment. Cloudy weather reduces productivity of solar equipment. It should be mentioned that all of these factors can be predicted. Thus, the intermittency of solar energy is stoppage of obtaining of this type of source (for example, at night). The abovementioned intermittency of solar energy can be referred to intermittency of photovoltaics (PV).

The most reliable at in the same time the least intermittent type of renewable energy is solar energy generated by PV (Guest Contributor, 2013). This type of production requires the least maintenance and repair. The generation of solar energy is performed for about 98 per cent of the time. Other sources of renewable energy described in this paper (solar panels and wind turbines) require constant services and numerous maintenance procedures. Moreover, “the high degree of long-term reliability of wind and solar PV will partly offset the short-term variability that solar panels and wind turbines will experience” (Guest Contributor, 2013).

Notwithstanding these considerable benefits, the power obtained by PV is also under a risk of intermittency.
Wind energy has some distinct nature, which is why intermittency of this source of energy has some differences compared to intermittency of solar energy. Productivity of wind generators depends on such factors as speed of the wind in some particular location, time of the year, air density, temperature of the air, and characteristics of generators and turbines. The speed of wind, its directions, and density can be different in the same location in different periods of the year. Moreover, these characteristics are different for different areas of the country. The work of wind energy generators also depends on such factor as air temperature. Hotter air has lower density than colder air. That is why, it is less effective for energy production. That is one more background to say that wind energy is a seasonally dependent type of energy. Moreover, deficiency or surfeit of wind speed can lead to stoppage of wind generators. Turbines do not work during the periods with low wind speed because electricity cannot be produced. Besides, they cannot work during the periods with high wind speed in order to avoid overloading and damage.

David Talbot in his article “Lifeline for Renewable Power” (2009) provided the following explanations:
if there’s too little wind-generated power, the company’s engineers might have to start up fossil-fueled power plants on short notice, an inefficient process; if there’s too much, it could overload the system, causing blackouts or forcing plants to shut down.

Big turbines are less dependent from changes of wind speed than small ones, i.e. they cannot stop during the periods of too high speed or too low speed of wind. These factors should be considered during discussion of the topic of wind energy and its intermittency. Hence, the intermittence of wind energy means non-production of this energy during some period of time due to certain conditions. As it has been explained above, the intermittency of big wind turbines is considerably lower than the intermittency of small ones.

Dealing with Intermittency of Solar Energy and Wind Energy

There are several strategies of decreasing intermittency of solar energy. Among the most notable initiatives, there is decreasing electrical demand of people, creating the means of storage of power, as well as thorough planning and modernization of transmission lines.

The first initiative is reflected in minimization of people’s demand on electricity by increasing effectiveness and efficiency of its use. This can be obtained by development and implementation of different low consumption equipment. The example of such equipment is Xcrl Energy, an application that enables observation and control of electrical consumption through the web. During the periods of high demand, some electrical equipment can be shut down. This initiative provides a considerable reduction of electrical consumption (from 6 per cent to 27 per cent) and avoids overloading of electric lines (Talbot, 2009). However, this application cannot be applicable in manufacturing industries.

The second initiative is reflected in creation of different means enabling storage of obtained energy. Batteries represent storage facilities, which enable usage of renewable energy during the time periods when it actually cannot be produced (at night – for solar energy; during non-wind periods – for wind energy). The battery can be compared with a bucket of energy. The voltage can be replaced by pressure and the amperage by flow rate. Thus, the amount of energy necessary for charging the battery is bigger than the amount of actually stored energy. The efficiency ratio varies from 85 per cent to 95 per cent. Batteries consist of “flooding lead plates in sulfuric acid” (Dankoff, n.d.). Storage and transfer of energy is based on chemical reaction between “the positively charged lead plate and the negatively charged acid” (Dankoff, n.d.). The lifespan of the battery depends greatly on the thickness of a plate. A thicker plate provides a deeper cycle and longer use of the battery.

Main disadvantages of batteries include the fact that they cannot save the whole amount of energy and they have a limited time of use. The standard time of rating batteries is about 20 hours (Dankoff, n.d.). Batteries provide ability to withstand intermittency of solar energy because they enable saving of the energy. However, the main disadvantage of batteries is their high cost.

Nowadays, the American government tries to realize different alternatives directed at storage of the solar energy and at the same time reduction of expenses on it. The most notable projects include Solar Reserve in Santa Monica and Crescent Dunes Solar Energy Project in Nevada (Woody, 2011). The Solar Reserve project represents “a 110-megawatt solar thermal power plant in Nevada that can generate electricity 24 hours a day” (Woody, 2011). The project considers construction of incredibly big arrays of mirrors connected with a big boiler. The solar energy will create steam in a boiler. This steam will drive an electrical turbine. It is notable that the boiler will be filled by molten salt that will produce steam for driving a turbine. It is a rather unusual, but at the same time effective solution because “salt retains heat that can be released at night or when the sun is not shining to continuously to produce power” (Woody, 2011). The main disadvantage of these projects is their considerable initial cost. For example, Solar Reserve requires $ 737 million. Of course, this money will be returned in the course of time by use of solar energy; however, the government has been obliged to find these funds at once to start financing this project.

Issue Relating to Necessity of Dealing with Intermittency of Solar Energy

In his article “Solar Intermittency: How Big is the Problem?”, Hong Tan (2011) describes his doubts concerning the necessity of finding any solutions to intermittency of solar energy. He states that effective management of production and storage of solar energy comprises dealing with intermittency without any additional developments and projects. Development and integration of storage technologies can be unnecessary because of the nature of solar energy. This energy cannot be obtained at night and is becoming lower during the periods of cloudy weather. However, its production resumes during the day time and sunny weather. The intermittency of solar resources is very predictable. That is why, development and integration of grid into solar technologies is not the main problem of these technologies. Proper and efficient forecast enables predicting of solar energy productivity for the nearest hours and days. Hong Tan (2011) gives the following explanations: “integration of significant amounts of intermittent generation is entirely feasible with the existing grid,” due to the “ability of the grid to respond to changes in generation levels in real time using the existing generation and transmission system.” That means that “solar PV’s production curve is aligned with the peak demand during the day and therefore helps to shave the peaks within a utility’s generation profile” (Tan, 2011). However, people should clearly understand that in the course of time the demand for solar energy will be growing. Without any reliable and efficient sources of saving of this type of energy, the civilization can face a problem of deficiency of this resource. The amount of energy produced during daytime and favorable weather conditions will be not enough for covering increasing needs of the population. Hence, development and implementation of different methodologies of dealing with intermittency of solar energy are of paramount importance

Identifying Feature of Dealing with Intermittency of Wind Energy

The dealing with intermittency of wind energy should be considered through understanding that this source of renewable energy greatly depends on wind. Unlike weather conditions and changes of day and night, changes of wind force and directions are less predictable. Hence, the nature of intermittency of wind energy differs greatly from the intermittency of solar energy. Nowadays, the issue of their intermittency becomes rather sharp with the increase in the amount of wind stations. In his article “Wind Energy: Dealing with Intermittency Challenges”, Diffen (2011) states the following: “as more wind generation has been added, grid operators have been challenged to integrate a large amount of intermittent generation.”

There are different methodologies of dealing with intermittency of wind energy such as geographical distribution and electrical storage with using different applications.

Geographical distribution undermines building wind farms on immense territories. Such installment of wind stations increases the possibility of their work because the force of wind is different on different territories. This initiative requires much land resources and considerable money expenses. However, it provides such an advantage as increasing the possibility of production of wind energy and lowering non-production down time.

The last initiative to manage the intermittency issue is development of storage facilities (batteries) and usage of specific applications. Storage of wind energy can be performed by using batteries integrated into wind production turbines. This enables short-term energy storage in turbines. The principle of work of storage batteries has been described above. Use of special applications increases efficiency of these batteries. The first one is the GE Ramp Control application. This application presupposes incorporation of saving battery into wind turbine. It “lets the turbine catch extra power and then store it in the battery so that customers can access revenue that was previously unavailable to them” (Dankoff, n.d.).

Management of the Transmission Grid

As mentioned above, one of the methods of dealing with intermittency of the renewable energy is management of the transmission grid. Nowadays, researchers work on creation of a network of transmission lines, which will enable movement of energy obtained from renewable sources to different locations. Usually, renewable energy is obtained in the wildest and unoccupied regions. However, the highest demand for energy occurs in big cities and on plants and factories. Thus, well-planned and effective management of transmission lines will help to deliver energy from renewable sources from places where it is obtained to locations where it is necessary. Management of transmission grid implies creation of the shortest connections between the above mentioned locations for enabling quick and at the same time cheap transfer of energy. It is notable that the transmission system should be capable of a timely reaction to different load patterns.

Current transmission lines used for transportation of power from plants, which use non-renewable power sources, are not totally suitable for delivery of wind and solar energy. Usually, these lines do not connect locations where this power is obtained with power consumers (big cities and plants). Besides, often there are no any storage capacities.

The grid consists of “power generators, power lines that transmit electricity, and the components that make it all work, including substations, meters, homes, and businesses” (Dankoff, n.d.). The main issue of the use of wind energy is that it is produced in removed locations and sometimes even offshore. Travelling of wind energy though numerous transmission lines causes its loss. Effective management and implementation of new technologies can solve this problem. Below both initiatives will be described.

Wind energy is obtained by movement of wind turbines by wind. The passable system performance can be increased by integration of a great variety of compensated transmission facilities like series capacitors. Series capacitors are usually installed on line ends of a transmission line since “line ends are archetypal capacitor locations, because it is usually possible to use space available in the substation” (Palanichamy & Wong, 2015). This causes a considerable reduction of expenses on installation. These capacitors can also be installed in center of the line. However, this initiative has such a considerable disadvantage as a necessity of thorough planning and considerable expenses on building of a network of transmission lines.

Contribution of Each Methodology to the Process of Solving the Issue of Intermittency

Batteries are widely used as a means of storage of both solar and wind energy. They are convenient because they can provide storage of energy for about 20 hours on average. However, they cannot store all energy. Part if it is being lost during the storage process. As mentioned above, the efficiency ratio is about 85 – 95 per cent. Nowadays, solar batteries are widely used in a combination with PV. For example, a battery with capacity of 24 kWt capacity of about 3000 costs about $9,300 for the entire installation system. Hence, storage cost of one kWt/hour is about 31 cent (Rentzing, 2013). Usually, the cost of batteries varies from $3,000 to $10,000 depending on their capacity and size. It is a rather high price for individuals who install PV on their roofs. However, researchers state that the growing demand for energy storage and constant technological improvement will facilitate further reduction of cost of batteries and increase of their popularity with private users and industry. Brian Dumaine in his article “Storing Solar Energy for a Rainy Day” (2013) states the following: “battery storage costs will fall 57% a kilowatt-hour by 2020.”

The next initiative mentioned above is the so-called Solar Reserve project. The cost of this project is $737 million (Woody, 2011). The main benefit is that this project will provide power generation of 24 hours a day. This 110-megawatt solar thermal power plant “can power 75,000 homes at peak output” (Woody, 2011). Therefore, it is an example of complete solving of the issue of intermittency of solar energy.

The last initiative described above is modernization of transmission lines. In this essay, an example of real-life transmission line projects is shown in order to provide reliable and up-to date information. One of such projects is Grain Belt Express in Illinois, Indiana, and Missouri. It presupposes building of modernized transmission networks for delivery of wind power energy. Each line will deliver about 4,000 Mw of power produced by wind turbines located in Kansas. Realization of this project will lead to lowering of electricity process cost by more than $700 during the nearest 5 years after the implementation (Levesque, 2015). Carl Levesque in his article “Data Show Transmission + Wind = Cost Savings” (2015) describes the following future perspectives of building new transmission lines: “the U.S. could derive 20 percent of its electricity from wind by 2030 and 35 percent by 2050…annual consumer savings reaching $14 billion a year by 2050.” As per information presented in Lifeline for Renewable Power, the USA can cover about 20 per cent of its needs in electricity by using energy from wind turbines by 2030. However, this requires “60 billion investments in 12,650 miles of new transmission lines” (Talbot, 2009).

Evaluation of Solutions

The abovementioned solutions of intermittency of solar and wind energy have both negative and positive sides, different costs and applications, as well as different time of realization. Batteries can be bought by any person who has solar panels on the roof of a house and install them the next day. They are rather expensive for individuals, but they provide such benefits as storage of energy. Batteries can also be used in big saving energy projects as the GE project described above. However, this requires building of totally new wind generators. The use of batteries does not provide the total solving of the issue of intermittency because they do not save the whole amount of energy. They save it only for a limited time and batteries are placed not far from means of production of the energy. Thus, it is a kind of medium cost and temporary solution of intermittency.

The next initiative is the use of alternative means of saving energy (like salt in Solar Reserve). The efficiency of the project is rather high because it enables energy production 24 hours a day. However, this project requires considerable financing and areas (usually such big projects are situated in remote locations) and time for implementation (several years for realization of the project). The Solar Reserve project can solve almost entirely the problem of intermittency except for the problem of energy delivery from remote locations to consumers.

This essay also covers the problem of delivery of the energy by building new transmission lines. It is notable that such construction does not require sufficient single investments. That means that lines can be built step by step. Besides, creating an effective and efficient network of transmission lines requires time (depending on the amount of lines) and knowledge. This initiative can solve the problem of transportation and overload of the electric system.

Conclusion

This essay considers the problem of intermittency of solar and wind energy. These sources of energy have both similar and distinctive features. However, both of them are intermittent. Nowadays, this issue can be solved by implementation of several initiatives: use of batteries or other storage facilities for storage and development of the network of transmission lines. The main problem of these initiatives is high cost. However, these initiatives can provide considerable future benefits like a considerable decrease of the cost of energy, lowering of the overload of electric network, saving of energy, and increase in the use of renewable sources. All three main initiatives should be implemented jointly in order to provide maximum effectiveness and efficiency.