Solar Energy – What is it and How is it Used?

“That sun is trying to kill us” is something I hear every other day from my wife. Growing up and settling in the Midwest of the USA, she is used to the beating heat from our local star. I remember a particular summer when the consecutive number of days over 100F (~38C) was well over 60.

As you can imagine this post is about the sun. (By which, I mean the star closest to us, but similar principles would apply to other solar systems). The emphasis will be made on understanding what this energy is, and how we can harness it.

First, let’s discuss solar energy in general. As its name suggests, this type of energy comes from the sun. (Solaris means sun in Latin and is where our word solar comes from). So far, so good. Now, even though “radiation” gets a bad reputation, this is actually how the heat and energy from our star reaches us. The radiation is produced by nuclear reactions in our sun’s core. Two hydrogen atoms get fused together to form one helium atom. The chemical reaction releases heat and light. And all of this is occurring inside the sun 93 million miles away in space. The light and heat travel through space. Then some of that energy, in the form of radiation, reaches us here on Earth.

Now that we know what energy solar energy is and where it comes from, let’s briefly discuss the processes we currently have to capture this energy and what uses we can make of it.

There are primarily two types of sun power harnessing systems:

  1. Solar panels
  2. Concentrated Solar Power (also known as CSP)


Solar panels are typically photovoltaic (PV) which means that they will convert photon energy (photo) into electricity (voltaic). When you think of such technology the roof of houses and office buildings (PV panels – comprised of several PV cells) is usually the first example to come to mind. But, don’t forget the small solar cells used to power your calculator (PC cell), or the much larger installations on the side of the highway (PV arrays – comprised of multiple PV panels). After capturing this solar energy, you can either use it for your personal needs, or in some cases you can sell it back to the grid. Note: Amazon recently completed its 17th rooftop solar project by installing a 1.1 MW array on its Las Vegas fulfillment center (https://www.renewableenergyworld.com/articles/2018/05/amazon-s-onsite-solar-just-went-up-a-notch.html).Another way solar panels work for domestic application is to circulate a liquid through the panels to heat the home (air heating, water heating, and so on).

CSP use a different technology altogether. Fields of mirrors (that rotate with the sun) are used to concentrate the energy from the sun into what is called a “black body”. In heat transfer terms, this refers to something that has a high thermal coefficient (emissivity) and typically sits at the top of a tower. If you have ever used a magnifying glass to concentrate solar energy on some dry twigs to start a fire, you have seen how effective this approach can be.

Figure 1 CPS project
Figure 1 CPS project – http://helioscsp.com/2017/02/

The previous blog post of this series mentioned that both nuclear and solar sources were considered clean energies with solar being renewable while our sun still shines. What makes it clean exactly? I am glad you asked! (I know you did not, but let’s pretend you did.) To quote my last post, clean energies are defined as “energies that do not pollute the atmosphere when used.” With solar energy, the process of energy creation is indeed harmless to the surrounding. The environmental impact of the systems to manufacture items needed to capture the solar energy and recycling/disposing of waste products from that process may pollute. Some will argue that solar arrays can be a visual pollution, but that objective opinion does not make solar a “dirty” energy since gathering the energy neither produce pollutants nor emits carbon dioxide.
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Clean Energy

As turbomachinery engineers, it is not always easy to tell non-technical folks what we do. If we start with “I design turbines,” the first thing most people think of are those giant wind turbines, and we are stuck with the nickname “wind guy/gal”. What we do is far more complex than putting 3 blades on a stick and confusing bystanders with why the turbine is rotating on a seemingly windless day; and don’t even get me started on the claims that wind turbines are a non-visually pleasing ploy from the government to make use of our taxpayers money.

Clean Energy

Okay, maybe I will get started on those topics, but not in this series. Today, I am introducing a new series of blog posts related to clean energies and how turbomachines tie in with this not-so-novel concept making a lot of noise nowadays.

Throughout this series, we will be discussing the different “clean” technologies in power generation which people have been using for hundreds of years, some more recent “hipster-y” applications, and look at what could make a difference in tomorrow’s world. These short posts will cover general and practical information, which students as well as seasoned engineers can use to better understand the topic at hand. Some articles/parts will be more technical than others, and no matter what your current level of proficiency, you will be able to pick out some useful takeaways.
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Concentrated Solar Power

As time goes by, the demand for energy rises while finite resources gradually diminish. The concept of going ‘green’ or using infinite resources has become more and more common in the marketplace. With this in mind, the abundance and reliability of solar energy makes for an attractive alternative. This is because solar power is different. This statement, of course, begs the question of HOW solar power differs.

Common traditional power plants still utilizes finite fuel. Steam power plants, for example, use the fuel as an energy source to boil water which, in turn, allows the the steam to turn the turbine and drive the generator to produce electricity. Concentrated solar power systems, however, use heat energy from the sun as a heat source – which is renewable. This system works by using utilizing mirrors or mirror-like materials to concentrate energy from the sun and then takes that energy to produce steam. The system can also store the energy that is absorbed during the day, to be used at night when the sun is not present. There are a few different types of concentrated solar power systems which one can choose from.

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The Economic Optimization of Renewable Energy

clean-blog-postGlobal warming is a very popular topic at the present time. With the upwards trend of clean technology and the realization that strict climate policy should be implemented, demand of renewable energy has sky-rocketed while conservative plant popularity continues to fall. Additionally, the number of coal power plants have significantly dropped since its peak era, as they are now known as the largest pollutant contribution, producing nitrogen, sulfur oxide and carbon dioxides.

Renewable energy comes from many sources: hydropower, wind power, geothermal energy, bioenergy and many more. The ability to replenish and have no limit on usage and application makes renewable energy implementation attractive. To make this even better, it also produces low emission. Theoretically, with the usage of renewable energy, human-kind should be able to meet their energy needs with minimal environmental damage. With growth rates ranging from 10% to 60% annually, renewable energy is getting cheaper through the technological improvements as well as market competition. In the end, the main goal is to maximize profit while minimizing our carbon footprint.  Since the technology is relatively new, capital costs are still considerably higher compared to more traditional (–and naturally harmful) implementations. This begs the question of exactly how we maximize the economic potential of a renewable energy power generation plant.

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The Economic Optimization of Renewable Energy

Global warming has been a very popular topic these days. With up-trend of clean technology and realization that strict climate policy should be implemented, demand of renewable energy sky-rocketed as conservative plants popularity falls. Number of coal power plants have significantly dropped since its peak era, being known as the largest pollutant contributor as it produces nitrogen oxide and carbon dioxide, the technology is valued less due to its impact on nature. Renewable energy comes from many sources: hydropower, wind power, geothermal energy, bio energy and many more. The ability to replenish and having no limit in usage and applications make renewable energy implementations seems attractive. Aside from that, they also produce low emission, sounds like a win-win solution for everyone. Theoretically, with the usage of renewable energy, human-kind should be able to meet their energy need with minimal environmental damage. With growth rate ranging from 10% to 60% annually, renewable energy are getting cheaper through the technology improvements as well as market competition. In the end, the main goal is still to generate profit, though these days taking impact on nature into the equation is just as important. Since the technology is relatively new, capital cost still considerable higher compared to some cases with more traditional (–and naturally harmful) implementations. So the question is: how to maximize the economic potential of a renewable energy power generation plant?

The Economic Optimization of Renewable Energy

Living up to the maximum potential of any power generation plant starts in the design process. Few examples for solar power plant: designers should take into consideration type and quality of panels, it’s important to see the economic-efficiency tradeoff before jumping into investment; looking into the power conversion is also one of the most important steps, one should take into consideration that it would be worthless to produce more energy than the capacity that are able to be transferred and put to use, though too low energy generation would mean less gross income.

Another example, for a geothermal power plant, many studies have shown that boundary conditions on each components play a big role in determining the plant’s capacity and efficiency. High efficiency is definitely desired to optimize the potential of a power plant and minimized the energy loss. Though, should also be compared to the economic sacrifice; regardless of how good the technology is, if it doesn’t make any economic profit, it would not make sense for one to invest in such technology. Low capital cost but high operating expenses would hurt the economic feasibility in the long run, whereas high capital cost and low operating expense could still be risky since that would mean a higher lump sum of investment upfront, which might or may not breakeven nor profitable depending on the fluctuation of energy market.

Modern technology allows investors and the engineering team to make this prediction based on models developed by the experts. SoftInWay just recently launched our economic module, check out AxCYCLE to optimize your power plant!

Reference:

[1] Optimal design of geothermal power plants 

[2] Strategies in tower solar power plant optimization

Explaining the Binary Power Cycle

Geothermal energy is known to be a reliable and sustainable energy source. As the world gives more attention to the state of the environment, people lean towards using more energy sources which have little to no impact on nature. Where it is true that currently no other energy source can outperform fossil fuel due to its energy concentration, geothermal energy is a good prospect as a temporary substitute until a better form of energy supply is found.

There are two types of geothermal power sources; one is known as the steam plant and the other is the Binary cycle. Binary cycles have the conceptual objectives of: high efficiency — minimizing losses; low cost to optimize component design; and critical choice of working fluid. This particular type of cycle allows cooler geothermal supply to be used, which has a huge benefit since lower temperature resources are much more common in nature.

blog - binary power1blog - binary power2

 

 

 

 

 

 

The way a binary cycle works can be explained using the diagram shown above. Since the temperature of geothermal source is not high enough to produce steam, hot water is fed into a heat exchanger. From there, secondary liquid with lower boiling water than water i.e. isobutane, absorbs the heat generated. As the steam of secondary liquid moves the turbine, electricity will then be produced. This whole process repeats in a cycle since the secondary fluid will then condense back to its liquid state and being used for the same process.

From the process described above, it can be seen that binary cycle is a self-contained cycle — ‘nothing’ goes to waste. This fact leads to the potential of having low producing cost energy source from binary power cycle. That being said, due to the lower temperature, the conversion efficiency of the geothermal heat is also considerably low. Consequently, Carnot efficiency of such process is lower than most power cycles. Large amount of heat is required to operate a binary cycle, leading to a better and larger equipment. Not only that since a bigger amount of heat energy has to be let out to the environment during the cycle, a sufficient cooling system must be installed. Although the production cost is found to be lower, the investment cost for installation would be very expensive. Then, the main question to this particular technology implementation would be how to improve the quality of production and economic feasibility?

First, one of the main aspect of binary power cycle is to overcome water imperfection as a main fluid. Consequently choosing optimal working fluid is a very essential step. Characteristic of optimal working fluids would include a high critical temperature and maximum pressure, lower triple-point temperature, sufficient condenser pressure, high vaporization enthalpy, and other properties.

Second, it was studied on multiple different events that well-optimized ORCs perform better than Kalina cycles. The type of components chosen in the cycle also affect the cycle performance quite substantially, i.e plate heat exchanger was found to perform better in an ORC cycle in the geothermal binary application compared to shell-and-tube. Addition of recuperator or turbine bleeding also have the potency to improve the overall performance of a binary cycle plant. It is important to model multiple thermodynamic cycle to make sure that the chosen one is the most optimized based on the boundary conditions. While designing ranges of thermodynamic cycles, it is common that the cycle is modeled based on ideal assumptions. For binary cycle in geothermal application, plant efficiency would be the most important parameter. In order to achieve a desired plant efficiency, both cycle efficiency and plant effectiveness should be maximized.

Additionally, pinch-point-temperature between condenser and heat exchanger is a substantial aspect to pay attention to, even the smallest change of in temperature is considered a significant change. Thus, including this parameter is a very important aspect.

This particular cycle has many potentials which haven’t been explored. Enhance the advantages of your binary power cycle using our thermodynamic tool, AxCYCLE.

Ref:
https://en.wikipedia.org/wiki/Binary_cycle
http://www.technologystudent.com/energy1/geo3.htm
http://www.researchgate.net/publication/229148932_Optimized_geothermal_binary_power_cycles

Throwback Thursday Webinar – Green Energy and ORC

It’s #ThrowbackThursday and we’re sharing one of our past webinars called “Green Energy – Turbomachinery for Organic Rankine Cycles.”iStock_000015544357Medium

Growing global demand for energy coupled with environmental concerns from the prevalence of fossil fuel usage has created a strong demand for new sources of clean energy. This demand has inspired scientists and engineers to search for and propose new solutions to generate greener, cleaner energy. One of the new methodologies which has been proposed is generating electricity from low temperature heat sources, the Organic Rankine Cycle being among the most widely used. Such popularity encouraged innovation in the area, and inspiring various design modifications in conjunction with low temperature heat sources and with a wide range of power rates. Continue reading “Throwback Thursday Webinar – Green Energy and ORC”

Sustainable Turbomachinery

iStock_000015544357MediumThis past Tuesday was the 44th celebrated Earth Day. On Earth Day, more than 100 countries join together to literally stop and smell the roses, appreciate the splendor and beauty of Mother Nature and take extra efforts to be more conscientious for our shared home.

Turbomachinery, though not always the first thing that comes to mind when speaking on the subject of green technology, plays an important role toward our efforts for a more sustainable environment.
Continue reading “Sustainable Turbomachinery”

Working Fluid in Organic Rankine Cycles

orcfluid
ORC Fluid

The choice of the working fluid for any given application is a key issue and should be done based on specific applications to achieve maximal efficiency. For working fluids in ORC, a green energy alternative, there are some requirements to keep in mind:

•Thermodynamic performance
Low pump consumption and high critical point

•Positive or isentropic saturation vapor curve
Avoid wetness in flow path, i.e. avoid damages of flow path elements

•High vapor density
Decrease sizes of equipment (expander and condenser)

•Acceptable pressures
High pressures usually lead to higher investment cost and increasing complexity

•High stability temperature
Prevent from chemical deterioration and decomposition at high temperatures

•Low environmental impact and safety level
•Good availability and low cost Continue reading “Working Fluid in Organic Rankine Cycles”

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