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Energy storage systemsFlow batteryReversible fuelcell

The share of renewable energy is steadily increasing around the world. But storing such intermittent energy source and utilizing it when needed has been a challenge. In fact energy storage makes up a significant part of the cost in any renewable energy technology. Many storage technologies are now available in the commercial market, but choosing a right type of technology has always been a difficult choice. In this article we will consider four types of storage technologies. The California Energy Commission conducted economic and environmental analyses of four energy storage options for a wind energy project: (1) lead acid batteries, (2) zinc bromine (flow) batteries, (3) a hydrogen electrolyzer and fuel cell storage system, and (4) a Hydrogen storage option where the hydrogen was used for fueling hydrogen powered vehicle. Their conclusions were:

”Analysis with NREL’s (National Renewable Energy laboratory)  HOMER model showed that, in most cases, energy storage systems were not well used until higher levels of wind penetration were modeled (i.e., 18% penetration in Southern California in 2020). In our scenarios, hydrogen storage became more cost-effective than battery storage at higher levels of wind power production, and using the hydrogen to refuel vehicles was more economically attractive than converting the hydrogen to electricity. The overall value proposition for energy storage used in conjunction with intermittent renewable power sources depends on multiple factors. Our initial qualitative assessment found the various energy storage systems to be environmentally benign, except for emissions from the manufacture of some battery materials.

However, energy storage entails varying economic costs and environmental impacts depending on the specific location and type of generation involved, the energy storage technology used, and the other potential benefits that energy storage systems can provide (e.g., helping to optimize

Transmission and distribution systems, local power quality support, potential provision of spinning reserves and grid frequency regulation, etc.)”.

Key Assumptions

 

Key assumptions guiding this analysis include the following:

Wind power will expand in California under the statewide RPS program to a level of

approximately 10% of total energy provided in 2010 and 20% by 2020, with most of

this expansion in Southern California.

• Costs of flow battery systems are assumed to decline somewhat through 2020 and

costs of hydrogen technologies (electrolyzers, fuel cell systems, and storage systems)

are assumed to decline significantly through 2020.

• In the case where hydrogen is produced, stored, and then reconverted to electricity

using fuel cell systems, we assume that the hydrogen can be safely stored in

modified wind turbine towers at relatively low pressure at lower costs than more

conventional and higher-pressure storage.

• In the case where hydrogen is produced and sold into transportation markets, we

assume that there is demand for hydrogen for vehicles in 2010 and 2020, and that the

Hydrogen is produced at the refueling station using the electricity produced from

wind farms (in other words, we assume that transmission capacity is available for

this when needed)?

Key Project Findings

 

Key findings from the HOMER model projections and analysis include the following:

Energy storage systems deployed in the context of greater wind power development

were not particularly well utilized (based on the availability of “excess” off-peak

electricity from wind power), especially in the 2010 time frame (which assumed 10%

wind penetration statewide), but were better utilized–up to 1,600 hours of operation per

year in some cases–with the greater (20%) wind penetration levels assumed for 2020.

• The levelized costs of electricity from these energy storage systems ranged from a low of

$0.41 per kWh—or near the marginal cost of generation during peak demand times—to

many dollars per kWh (in cases where the storage was not well utilized). This suggests

that in order for these systems to be economically attractive, it may be necessary to

optimize their output to coincide with peak demand periods, and to identify additional

value streams from their use (e.g., transmission and distribution system optimization,

provision of power quality and grid ancillary services, etc.)

• At low levels of wind penetration (1%–2%), the electrolyzer/fuel cell system was either

inoperable or uneconomical (i.e., either no electricity was supplied by the energy storage

system or the electricity provided carried a high cost per MWh).

• In the 2010 scenarios, the flow battery system delivered the lowest cost per energy

stored and delivered.

• At higher levels of wind penetration, the hydrogen storage systems became more

economical such that with the wind penetration levels in 2020 (18% from Southern

California), the hydrogen systems delivered the least costly energy storage.

• Projected decreases in capital costs and maintenance requirements along with a more

durable fuel cell allowed the electrolyzer/fuel cell to gain a significant cost advantage

over the battery systems in 2020.

• Sizing the electrolyzer/fuel cell system to match the flow battery system’s relatively

high instantaneous power output was found to increase the competitiveness of this

system in low energy storage scenarios (2010 and Northern California in 2020), but in

scenarios with higher levels of energy storage (Southern California in 2020), the

Electrolyzer/fuel cell system sized to match the flow battery output became less

competitive.

• In our scenarios, the hydrogen production case was more economical than the

Electrolyzer/fuel cell case with the same amount of electricity consumed (i.e., hydrogen

production delivered greater revenue from hydrogen sales than the electrolyzer/fuel

cell avoided the cost of electricity, once the process efficiencies are considered).

• Furthermore, the hydrogen production system with a higher-capacity power converter

and electrolyzer (sized to match the flow battery converter) was more cost-effective than

the lower-capacity system that was sized to match the output of the solid-state battery.

This is due to economies of scale found to produce lower-cost hydrogen in all cases.

• In general, the energy storage systems themselves are fairly benign from an

environmental perspective, with the exception of emissions from the manufacture of

certain components (such as nickel, lead, cadmium, and vanadium for batteries). This is

particularly true outside of the U.S., where battery plant emissions are less tightly

controlled and potential contamination from improper disposal of these and other

materials are more likely. The overall value proposition for energy storage systems used in conjunction with intermittent renewable energy systems depends on diverse factors.

• The interaction of generation and storage system characteristics and grid and energy

resource conditions at a particular location.

• The potential use of energy storage for multiple purposes in addition to improving the

dependability of intermittent renewable (e.g., peak/off-peak power price arbitrage,

helping to optimize the transmission and distribution infrastructure, load-leveling the

grid in general, helping to mitigate power quality issues, etc.)

• The degree of future progress in improving forecasting techniques and reducing

prediction errors for intermittent renewable energy systems

• Electricity market design and rules for compensating renewable energy systems for their

output

Conclusions

 

“This study was intended to compare the characteristics of several technologies for providing

Energy storage for utility grids—in a general sense and also specifically for battery and

Hydrogen storage systems—in the context of greater wind power development in California.

While more detailed site-specific studies will be required to draw firm conclusions, we believe

those energy storage systems have relatively limited application potential at present but may

become of greater interest over the next several years, particularly for California and other areas

that is experiencing significant growth in wind power and other intermittent renewable.

Based on this study and others in the technical literature, we see a larger potential need for

energy storage system services in the 2015–2020 time frames, when growth in renewable produced electricity is expected to reach levels of 20%–30% of electrical energy supplied.

Depending on the success in improved wind forecasting techniques and electricity market

designs, the role for energy storage in the modern electricity grids of the future may be

significant. We suggest further and more comprehensive assessments of multiple energy

storage technologies for comparison purposes, and additional site- and technology-specific

project assessments to gain a better sense of the actual value propositions for these technologies

in the California energy system.

 

This project has helped to meet program objectives and to benefit California in the

Following ways:

Providing environmentally sound electricity. Energy storage systems have the

Potential to make environmentally attractive renewable energy systems more

competitive by improving their performance and mitigating some of the technical issues

associated with renewable energy/utility grid integration. This project has identified the

potential costs associated with the use of various energy storage technologies as a step

toward understanding the overall value proposition for energy storage as a means to

help enable further development of wind power (and potentially other intermittent

renewable resources as well).

Providing reliable electricity. The integration of energy storage with renewable energy

sources can help to maintain grid stability and adequate reserve margins, thereby

contributing to the overall reliability of the electricity grid. This study identified the

potential costs of integrating various types of energy storage with wind power, against

which the value of greater reliability can be assessed along with other potential benefits.

Providing affordable electricity. Upward pressure on natural gas prices, partly as a

function of increased demand, has significantly contributed to higher electricity prices in

California and other states. Diversification of electricity supplies with relatively low-cost

sources, such as wind power, can provide a hedge against further natural gas price

increases. Higher penetration of these other (non-natural-gas-based) electricity sources,

Potentially enabled by the use of energy storage, can reduce the risks of future electricity.”

(Source: California Energy Commission prepared by University of Berkeley).

Wind energy is one of the fastest growing renewable energy sources in the world and in 2011 the global market grew by 6% with 40.5 GW new powers brought online, according to Global Wind Report. However storage of intermittent renewable energy is a critical contributing factor in renewable energy development. A study was conducted by University of California for California Energy Commission on the economic and environmental impact of for energy storage technologies and the ways to improve the energy efficiency of wind energy. When there is a strong wind there is no demand for power, and when there is a high demand for power there is no wind. This anomalous supply demand gap demands a reliable way of storing wind power during high wind velocity periods.

They examined for energy storage technologies namely 1.lead acid batteries, 2. Zinc Bromine flow batteries, 3.Hydrogen electrolyzer and Fuel cell storage system and 4.Hydrogen option to fuel Hydrogen cars with Hydrogen. By using NREL (national Renewable Energy laboratory) computer simulation model HOMER  for high wind penetration of 18% in California, they concluded that Hydrogen storage is the most cost-effective than other battery storage technologies and using Hydrogen to fuel Hydrogen cars is economically attractive  than converting Hydrogen into Electricity. The environmental impact of using Hydrogen is benign compared to batteries with their emissions.

“The key findings of this experiments are as follows: Energy storage systems deployed in the context of greater wind power development were not particularly well used (based on the availability of “excess” off-peak electricity from wind power), especially in the 2010 time frame (which assumed 10% wind penetration statewide), but were better utilized–up to 1,600 hours of operation per year in some cases–with the greater (20%) wind penetration levels assumed for 2020.

The levelized costs of electricity from these energy storage systems ranged from a low of $0.41 per kWh—or near the marginal cost of generation during peak demand times—to many dollars per kWh (in cases where the storage was not well utilized). This suggests that in order for these systems to be economically attractive, it may be necessary to optimize their output to coincide with peak demand periods, and to identify additional, value streams from their use (e.g., transmission and distribution system optimization, provision of power quality and grid ancillary services, etc.).

At low levels of wind penetration (1%–2%), the electrolyzer/fuel cell system was either inoperable or uneconomical (i.e., either no electricity was supplied by the energy storage system or the electricity provided carried a high cost per MWh).

In the 2010 scenarios, the flow battery system delivered the lowest cost per energy stored and delivered.  At higher levels of wind penetration, the hydrogen storage systems became more economical such that with the wind penetration levels in 2020 (18% from Southern California), the hydrogen systems delivered the least costly energy storage.

Projected decreases in capital costs and maintenance requirements along with a more durable fuel cell allowed the electrolyzer/fuel cell to gain a significant cost advantage over the battery systems in 2020.

Sizing the electrolyzer/fuel cell system to match the flow battery system’s relatively high instantaneous power output was found to increase the competitiveness of this system in low energy storage scenarios (2010 and Northern California in 2020), but in scenarios with higher levels of energy storage (Southern California in 2020), the electrolyzer/fuel cell system sized to match the flow battery output became less competitive.

The hydrogen production case was more economical than the electrolyzer/fuel cell case with the same amount of electricity consumed (i.e., hydrogen production delivered greater revenue from hydrogen sales than the electrolyzer/fuel cell avoided the cost of electricity, once the process efficiencies are considered).

Furthermore, the hydrogen production system with a higher-capacity power converter and electrolyzer (sized to match the flow battery converter) was more cost-effective than the lower-capacity system that was sized to match the output of the solid-state battery. This is due to economies of scale found to produce lower-cost hydrogen in all cases.

In general, the energy storage systems themselves are fairly benign from an environmental perspective, with the exception of emissions from the manufacture of certain components (such as nickel, lead, cadmium, and vanadium for batteries). This is particularly true outside of the U.S., where battery plant emissions are less tightly controlled and potential contamination from improper disposal of these and other materials is more likely. The overall value proposition for energy storage systems used in conjunction with intermittent renewable energy systems depends on diverse factors:

The interaction of generation and storage system characteristics and grid and energy resource conditions at a particular site The potential use of energy storage for multiple purposes in addition to improving the dependability of intermittent renewable (e.g., peak/off-peak power price arbitrage, helping to optimize the transmission and distribution infrastructure, load-leveling the grid in general, helping to mitigate power quality issues, etc.)

The degree of future progress in improving forecasting techniques and reducing prediction errors for intermittent.  Electricity market design and rules for compensating renewable energy systems for their output”. Hydrogen storage and Hydrogen cars hold the key for future renewable energy industries and Governments and industries should focus on these two key segments.

The city of Athens hosted its oldest tradition of lighting the Olympic torch for the 2012 London Olympic Games on Thursday in Olympia. The torch was lit by solar power; using parabolic mirror to redirect the sun’s light to light the flame with purest natural light. The thermal energy of sun’s light can be powerful when focused to a point and it can reach a temperature as much as 600C.The parabolic trough with reflective mirror focuses the sunlight on the tube called ‘collectors’ in which a fluid with high boiling point is circulated. The hot fluid in turn is used to convert water into steam in boiler. The hot oil transfers its heat to the water in a heat exchanger and returns back to the parabolic trough. It is a closed circuit system. The hot oil at 390C generates steam at 370C at 100 bar pressure, which is used to run a HP steam turbine. The standard steam condensing cycle generates power similar to fossil fuel fired power plant. A 50 Mw Trough plant in Israel (Negev Desert) is already in operation.

The capacity of such plant can be easily expanded by adding modular parabolic troughs and collectors and the plant can be designed to meet  specific power demands. This is a straight forward method to generate base load power using standard steam cycle. The efficiency of such system will be 41% maxium.However recently few companies are trying use a combined cycle. This increase the solar to heat efficiency from 50.5% to 53.6%.This nominal 50Mw power plant generates  a total peak power of 57.10Mw using a solar collection area of 310,028m2 with annual solar to electrical efficiency at 16.3% using a water-cooled condenser in the steam cycle. The cost of energy works out to $0.23 to $ 0.25 /kwhrs.

By using a central solar collection tower (Heliostat) and bottoming with Rankin/Kalina cycle ,it is estimated that the total installed cost can be reduced by 10%.The system can be configured from 2Mw up to 100Mw using both trough and tower system. The system can be installed in any remote, arid locations using air condensers, where cooling water is a problem. The estimated annual specific energy cost is less than 6 cents/kwhrs, comparable to low-cost fossil energy but with zero pollution and with zero carbon emission.

Solar thermal is a potential clean energy of the future for many countries around the world with yearlong sunshine with good intensisty.The solar thermal energy can also be used in many process industries where thermal heating is required. Solar salt pans can use solar thermal energy very efficiently to cut their production cycle. The concentrated brine can be used as a circulation fluid in solar collectors and also be used to generate power using low heat technologies like Kalina cycle, because concentrated salt brine can store thermal heat.

Gemasolar power in Spain is a base load power station supplying power for 25,000 homes 24×7 using molten salt (60% KNO3+40% NaNO3) as a thermal storage medium instead of batteries. Nine plants were built in 1980 in Mojave Desert with a combined capacity of 354 Mws.

Other examples of solar base load power plants are Blythe solar with capacity of 968Mw at Riverside County, California and Ivanpah power station with capacity of 370 Mw capacities in US. Large scale solar base load plants are no longer a theory but a commercial reality.

Direct solar lighting is also being introduced using fiber optics. The sun light is collected at a central point and directed through fiber optics to various rooms inside the building supplying direct sun light. This saves not only electricity but also provides natural light to work places because human body requires a certain amount of UV light exposure. Solar energy is here to stay and offer various clean energy solutions in the future.

 

 

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