Storage and Simulation

Overview

This is the documentation of a session block at the Micro Perspectives for Decentralized Energy Supply 2013

In cooperation with:

NEK, Sustainable Energy Concepts
University of Paderborn
Session facilitator:

Yassin Bouyraaman, University of Paderborn

Sessions

Frequency Control Applying Plug-in Electric Vehicles Based on Costumer Behavior in Electric Power Networks and Micro-Grids

Introduction

The main idea is the use of Electric Vehicles (EVs) as power generating units and storage devices in Electric Power Networks and Microgrids taking into account the psychological aspects of the customers. The EVs can be charged when electricity is available and can give it back in case it is needed by the grid while the vehicle is connected. The use profile of the custumers must be taken into account in order to provide a system that will be used properly.

The following information is taken from the corresponding presentaion slides for the MES 2013 (will be attached soon).

A micro-grid mainly consists of distributed energy resources and energy storage systems. Electric vehicles (EVs) can be assumed as both appropriate power generation units and storage devices as it is shown in the following figure:

[....to be inserted...]

There is the plan to have one million EVs used in Germany by 2020 which could provide us with a great electric power potential.

The EVs could be very useful for secondary frequency control because of their battery’s characteristics of lower energy and quick response time. In other words, in addition to the technical benefits, this potentials could be applied for maintaining the power networks stability by mean of ancillary services. These batteries could easily replace fossil-fuel power plants for secondary frequency control and are very clean energy resources.
Micro-grids commonly consist of renewable energy resources like wind turbines or solar power units that have uncontrolled power output. A single battery could provide 4-20 kW which could be very advantageous for Germany’s power network frequency regulation or a part of its power grid such as available micro-grids.
An Aggregator is necessary to deal with the small-scale power of the vehicles for providing the regulation service on an appropriate large-scale power.

It is also inevitable to consider the psychological behavior of the human beings in using an electric vehicle and connecting it to the power grid. The minimum and essential requirement of the vehicle owners for joining the ancillary service is to guarantee them the charge of their battery to a desired level which matches their EV use profile. In addition some incentives such as direct payment or lifetime warranty of the battery should be given for voluntary participation of the vehicle owners.

Simulation and Study

The performed simulation in this research is based on the results of TU Chemnitz’s psychological studies. For the study, three categories were formed: P+R (park+ride, charge at home), P+C (park+charge, charge at public stations), public or sharing (no own car). These groups are separated into day chargers (5 am- 5 pm) and night chargers (5 pm- 5 am).

The following figure shows the distribution of the mentioned user categories in day and night chargers.

[... to be inserted...]

A large number of batteries will be available that could inject their stored power to the network at peak load times. Also at low load times they could consume the generated power of the base load power plants and the unplanned generations of the renewable energy resources. The simulation in this paper is based on the data of the previous figure and is carried out for different operation scenarios to show how the vehicles could maintain the power network’s frequency stability.

Each battery has three different states as follow: charging, discharging and standby. The aggregator must optimally choose and organize the state of each vehicle for the power grid’s regulation aspect. The IEEE 39bus Standard Network is applied for this research simulation to show the impact of the electric vehicles for secondary frequency control purposes. A full charging period of the batteries lasts 4-10 hours regarding the available power amperage. Each Mini E battery has a 28 kWh usable capacity which could provide us with circa 6 kW power per vehicle. We consider two aggregators in the network.

The simulation results show that for night chargers, the Aggregator1 collects 10000 available vehicles (60MW) and Aggregator 2 includes 5000 vehicles (30 MW). Different case studies were simulated during this period but just two main scenarios are analyzed in this paper:

The EVs as secondary frequency control devices are able to keep the frequency at 50Hz for a genreation increase of 70 MW and a load increase of 50 MW. They respond very quick and the oscillations are very small. The primary frequency control is only able to lower the impact of the genreation and load changes but there is a deviation even after 200 seconds which seems to tend to an offset.

For the related figures see slides 12-17 of the corresponding presentation (will be attached soon).

Conclusion

The simulation results show that the application of electric vehicles is very effective as secondary frequency controllers for the whole power network stability and its related micro-grids. In both scenarios were the vehicles able to bring back the frequency to its nominal value (respectively from 50.42 Hz in scenario1 and 49.62 Hz in scenario2 to 50 Hz). The available potential of these vehicles in 2020 (around 6 GW) could help Germany’s power grid operators in maintaining the stability of the network without any concerns.

Furthermore, the consumers can earn money by participating in the electric market using their vehicle’s batteries. In addition, these vehicles totally environment-friendly and are preventing the emission of greenhouse gases which is a very important constraint in any power network operation planning.
Hence, the use of EVs is strongly recommended for system operation issues like secondary control, power reserves and storing the extra power of renewable energy resources.

Questions and Discussion

Q: What about the voltage issue? Can the voltage be controlled by this approach, too?

A: Interesting aspect, but not discussed in this paper.

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Q: Why do we need this type of frequency control? Why do the governers not bring back the frequency to 50 Hz?

A: There is primary frequency control by the plants which can just produce more steam in order to control the frequency but it takes time. The EVs are used as secondary frequency control. It is much faster.

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Q: The night chargers need their energy during the day. How can they provide energy for the grid?

A: Example: The battery of the car is fully charged over night. The customer drives to work and connects the car. The grid can use as much energy as it needs as long as the car battery has enough energy left for the way back after work. A smart grid would have advantages when using this system. The incentive for the costumers is the money they get by selling energy to the grid. This is confirmed by the research study which has been the base for the simulation.

A Holistic Implementation Strategy for Storage Systems in Renewable Mini-grids

Company Profile – Autarsys GmbH

Autarsys GmbH is a newly founded company based in Berlin with long experience through the work at YounicosAG. They work with NaS, Vanadium Redox Flow and Lithium Ion batteries with focus on lithium ion-based energy storage systems (ESS) for mini-grids in the range 100-1000kW. In addition, they offer project accompanying services.

The Roll of Energy Storage Systems in Mini-Grids

An Energy Storage System consists of DC-Batteries, Battery Management System, Inverter, SCADA and Housing.

The Energy Storage system fulfills the following tasks in a grid:

1. Energy shifting for short term compensation of fluctuations and medium term shift such as day-night shift
2. Provision of short-circuit power
3. Control of the frequency to keep the balance – droop control.
   

Advantages of Li-Ion Batteries

is the long lifetime of 15 years,Depth of Discharge (DoD) of 80%. The disadvantage of the high investment cost is reduced in future. Within 7 years the price can drop to 250€/kWh.

The advantages of lithium-ion batteries is their high energy density up to 200 Wh/g, their long lifetime due to more cycles (3000-7000 Cycles @100% Depth of Discharge (DoD) or up to 15 years @80% DoD). They have a high efficiency (>97%) and low maintenance requirements. As they contain no or few heavy metals, they are environmentally friendly. The disadvantage of high investment cost is caused by the early stage of development which means high cost reduction potential. There are scenarios for the price to drop to 250€/kWh within the next 7 years.

Approach: Product and Service

The approach of Autarsys GmbH is to work with a Partner Company which has to have the experience in project development or as EPC for grid connected RE-projects, to have knowledge of local conditions and to be interested in going “off-grid”. Autarsys provides a modular ESS, which can be adopted to the needs of the project and has the expertise on storage system and isolated grids. They can do simulation studies and give off-grid specific consultancy services.
The result is a successfully joint project implementation.

Features of the Energy Storage System:

• „Plug ‘n play“ installation
  
• Power + energy scalable according to project requirements
  
• Hermetical sealed
  
• Connection + operation from the outside
  
• Remote monitoring
  
• A/C system + insulation to increase lifetime
  

The service works as follows:

Project Development

• Consulting regarding system layout and technologies
  
• Simulation studies
  
• Business case development
  
• Site-Assessment
  

Planning

• System planning
  
• Grid studies
  
• Execution planning
  
• Logistical planning
  

Construction

• Adaptation-Engineering for system integration
• Installation
• Commissioning
• Training of local personal

Operation

• Remote monitoring of state of health
• System updates
• System extension consulting

Maintenance

• Maintenance
• Supply part management
  

Questions and Discussion

Q: How big is the temperature effect that it is worth cooling down the system with a fan?

A: A 10° higher temperature can halve the lifetime.

Q: At what scale it is worth to use fans to cool down?

A: If there are 40°C outside, it is worth it! But of course, insulation and specific conditions are important.

Q: Isn't it contraproductive to consume energy using a fan to cool the system which produces energy?

A: Yes but the lifetime is important, too. Insulation and thermal mass also help to keep it cool.

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Q: How big are the AC systems?

A: Containers of 20 feet currently under construction is a 200kW and 150kWh storage system.

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Q: Voltage of the containers?

A: usually between 750-1050V_dc depending on the state-of-charge.

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Driving Rural Energy Storage: A Second Look at the Second-Life of EV Batteries

Rural Electrification: Business As Usual

Storage in current rural electrification applications are primarily Deep Cycle Lead-acid Electric Storage Devices (ESDs) due to their low initial capital cost (75 - 300 $/kWh). Disadvantages are the low energy density (30 - 40 Wh/kg), the short lifetime (3 - 5 years), the maintenance requirements and the environmental impact.

EV Battery Life Cycle

As the number of EVs in the world is constantly growing, a closer look should be given on the second-life possibilities of EV batteries. The life cycle of an EV battery starts with the manufacture and installation in the automobile. Afterwards it is employed in the vehicle. When the first life is over, it is removed from the vehicle and refurbished. Finally, the battery is employed in a second-life application. In the end it is recycled and disposed of.

Second-Life Applications of EV Batterie

The second-life applications od EV batteries can be off-grid such as backup or remote Installations; on-grid like renewable firming, service quality and reliability, load shifting; or mobile for transportation, recreational vehicles, commercial idling support.

Li-Ion vs. Lead Acid

	Used Lithium-Ion	Lead-Acid
Useful Lifetime (years)	6-10	3-5
Energy Density (Wh/kg)	100-180	30-50
Environmental Impact (Eco-indicator 99)	278	500
Cost ($/kWh)	? < $150	$75 - $300
Maintenance	NO	YES

Implementation Issues

One problem which can appear during the implementation is the charge regulation. Furthermore, the thermal management is important for the lifetime, the heat must be removed and the environment of the battery should be dry and cool. Repurposing costs is another issue which has to be considered. And the local technical know-how must be sufficient in order to make the system work in case of problems, exchange etc, which can be a problem, especially in remote areas.

Further Research

The following issues are future topics of research:

• Cost/impact of transport between point of origin, second-life, and end-of-life (EOL)
  
• What is the expected value of recovered materials and real cost of recycling/processing?
• What are the environmental/health impacts of unrestricted disposal in rural areas?
• What is the actual field lifetime of an average Li-ion ESD?
  

Questions and Discussion

Q: What are the factors the lithium price development is dependent on?

A: The money for research in these technologies depend on the e.g.on the oil price. The higher the oil price the more attractive alternative solutions become.

Q: How is it possible to handle all the different types of batteries and how to recycle them?

A: The lifetime is important, especially for remote areas. The maintenance cost can be reduced by 60%. Zou have to train local technicians who can deal with the batteries and there must be incentives for recycling.

Q: Why not burying them in the earth to keep them cool?

A: advantage: may be cool in the earth, disadvantage: we don't know the specific heat of earth, it may not be able to remove the heat produced by the battery; bad access in case of problems.

Final Discussion

Q: What is the necessary grid size for the EVs to work as frequency control?

Ameli: The idea can be applied in mini-grids or bigger networks. The scale is not important. The advantages are the onside service which is environment friendly. Further investigation will be the use of EVs as primary frequency control.

Q: How does the behaviour of the customers depend on the quality of the onside service?

Ameli: There are restrictions but instead the costumer gets incentives (e.g. money) to live with these limitations.

Q: There won't be 1 Million EVs in Germany by 2020. Who will buy an EV? They are expensive, etc. Is the optimism valid?

Gershenson:Tesla Motors is giving reports. The people see that it is possible to make money with EVs.There is going to be a shift. If the price is going down, we can go into rural public. There are many positive studies.

Ameli: 1 million EVs would provide 16 GW power, but 200000 would still provide 5 GW which is a lot of capacity.

Q: What about the batteries we have?

A: They last around 2 years and are not at all suitable for application in rural areas or for anz kind of long lasting storage device.

Further Information

• Micro Perspectives for Decentralized Energy Supply - Conference 2013