About

Brief overview of the project and some background information on why it is relevant

Carbon Emissions Reduction Strategies

Climate Change Act: 80% reduction in greenhouse gases by 2050 (Baseline 1990)
Reduce emissions from housing stock
UK Government target to make all new homes Net Zero Carbon by 2016
Reduce emissions from transport
Introduction of the Electric Vehicle (EV)

Integration of on site Renewable Energy generation to homes

Micro-generation Strategy
Currently being encouraged by Feed In Tariffs and Renewable Heat Incentive

Main Concepts of Project

This project is designed to explore a year in the life of a zero carbon home with an electric vehicle. The home is built to passive house standards (2016 Building Regs) to reduce energy demands through building structure and fabric. Energy demands (lighting, appliances, space heating and hot water) are met through Photovoltaic and Heat Pump supplies. Net zero carbon is achieved by generating enough PV energy to balance the energy required from the grid to meet household demands. A proﬁle of car use has been generated to represent the times vehicle is present and absent from the home, and the mileage covered when the car is away. A hypothetical electric vehicle was created for use in the project, based loosely on the Nissan Leaf.

Meeting the electrical demands of a home in the Vehicle to Home concept (V2H) involves a decision making process based on the best use of available energy sources; renewable technologies, the grid or the EV battery (Berthold et al, 2011).

Within the project, we aim to develop a control strategy which will

use renewable generation at the individual household level to meet domestic demands and assist with EV charging demands.
use the EV battery as a storage system, discharging to the home network during times of peak demand or low generation.
maintain EVʼs capability of operating as a mode of transport at all times.
shift bulk of EV charge demand to off peak period to assist in smoothing demand proﬁle in larger network, minimizing energy costs.

V2H has the potential to reduce the sharp peaks in energy use experience when high power appliances, such as kettles, are used for a relatively short period of time, leveling the electricity demand proﬁle of the house. This has beneﬁts for the larger electricity network by reducing peak demand and creating a more constant load during the day, improving the efﬁciency and cost effectiveness of electricity generation (Haines et al, 2009).

Generation of Proﬁles

There are few high resolution demand and supply proﬁles available, so we have used models and simulation tools to generate our proﬁles.

High resolution to pick up on high demand over short periods of time, i.e. use of kettle. These demands are only picked up in high resolution proﬁles. Some appliance and lighting demand based on occupancy. Others are occupancy independent and automatically cycle

Vehicle Use Proﬁle

Limitations related to energy density, cost and life cycle of lithium ion batteries restrict EVʼs to short journey times and ranges (Nair and Rajagopal)

Dependent on driver behavior and lifestyle. Vehicle use in reality will vary among individuals, and may not always be compatible with V2H. The project aimed to demonstrate how V2G would work in one speciﬁc case.

Assume full time employee, commute to work of 30 miles, leaving between 7-9 am, returning 4-6 pm. Additional journey added (recreation, social, etc) (Clement et al, 2011)

Commuter and business peaks - 7am - 9am, 4pm - 7 pm (Qian and Zhou, 2010)

Data from literature was used to derive the stochastic characteristics of the behavior of vehicles

Electric Vehicle

The electriﬁcation of vehicles is regarded as potential strategy for reducing green house gas emissions from the transport sector, driven by legislation and consumer pressure (Haines et al, 2009). This is of course dependent on the mix of generation technologies available to meet the charging demands of electric vehicle batteries. EV integration would also create a storage network, facilitating the integration of renewable energy sources, intermittent in nature (Lojowska et al, 2011). However, the charging of EVʼs create an additional demand on the electricity network.

Considering large scale integration of Electric Vehicles is out with the scope of our project. However, it is worth mentioning issues expressed in the literature. An EV network could provide storage for energy produced from intermittent renewable technologies, making this energy available during peak demand periods. This would reducing the need for additional generation from fossil fuel sources, and improve the efﬁciency electrical generation (reducing increases and decreases in production in centralized generators) (Berthold et al, 2011, Haines et al, 2009, Ma et al, 2010). Large scale EV integration could also assist in addressing frequency instabilities, caused by a mismatch between generation and demand due in part to the intermittent nature of renewable resources. Battery charging could be activated at frequencies above 50Hz, and discharged at frequencies below 50Hz, with a reaction time of a few seconds (Clement-Nyns et al, 2011).

EV are regarded as responsive loads and dispatchable electrical storage, due to the bi directional ﬂow characteristics of their batteries. Charging time could be shifted to suit network operators. Integration of an EV network could provide a useful mechanism for network support during periods where supply exceeds demand (Inglis et al, 2011). Incorporating responsive load and dispatchable storage into the grid would allow the load proﬁle of the larger network to be altered, resulting in a reduction in the time dependency of the supply (Inglis et al, 2011) and reducing the dependence on low efﬁciency, high emission “peaking” electric generation units, and associated ﬁnancial and environmental consequences (White and Zhang, 2011). Load leveling, rather than supplying peak power, is a more suitable use for the energy stored in EV batteries. Load leveling will shift some of demand to periods of low electricity use, minimizing losses and increasing grid efﬁciency (Clement-Nyns et al, 2011). Control of charge and discharge will become more complex and difﬁcult as the scale of EV integration increases (Haines et al, 2009)

It is estimated that, in theory, 90% of vehicles are available at any one time. If all these vehicles were EVʼs connected to the grid while idle, this represents a signiﬁcant energy storage resource (Clement-Nyns et al, 2011).

Objective of Control Strategy

Purpose of mains target - below mains target, grid supplies household demand, prolonging usefulness of battery. Above mains, battery supplies household demand, reducing peaks in demand) (Haines et al, 2009). Supervisory controls: Range buffer of 37% SOC, below which battery does not discharge to home.

Cost and CO2 Analysis

The battery can be charged either with surplus PV generation, or with Grid energy. The cost of renewable supply is taken to be zero, and CO2 emissions are also zero (ignoring capital and maintenance costs associated with technology installation, and embodied energy of technology). Grid energy cost varies depending on demand (peak/off peak) and CO2 emissions vary depending on the energy mix used to produce the grid energy (Berthold et al, 2011). EVʼs can be viewed as a type of distributed generation. As the load is close to the source of generation, transmission losses are also reduced in V2H (Haines et al, 2009). Ignore energy recovered during braking phases

Battery Life Cycle Impact

The effect of additional cycling on a lithium ion battery used in a V2H situation is not yet properly understood (Haines et al, 2009). Financial and economic implications of this type of battery use would have to be considered.

Additional Info

Fixed 3 kW battery charge rate - (Haines et al 2009)
For the health of the battery, only 80% of the capacity is available for use (Clement-Nyns et al, 2011)
Assume 88% energy conversion efﬁciency from AC supplied from grid, to DC energy stored in battery (Clement-Nyns et al, 2011) - We assume 90%.
Charge and discharge output varies between -4000 and 4000W. We assume +/- 7243.2 W for max of 200 mins. 3018W for charge (Clement-Nyns et al, 2011)
Charging and discharging at same price of electricity is uneconomical because of charge and discharge efﬁciencies (Clement Nyns et al, 2011).

The Nissan Leaf

The vehicle we are integrating into our Zero Carbon Home is a Nissan Leaf all electric vehicle. Leaf stands for Leading, Environmentally friendly, Affordable, Family car which is suitable with this project as the should be useable in a typical home with 4 occupants. The Leaf has won many accolades such as the 2010 Green Car Vision Award, the 2011 European Car of the Year award, the 2011 World Car of the Year, and the 2011-2012 Car of the Year Japan.

The car has the following statistics:

Production: 2010–present
Assembly: Local (Sunderland)
Body style: 5-door hatchback
Layout Front-engine, front-wheel drive
Electric motor 80 kW (110 hp), 280 N·m (210 ft·lb) synchronous motor
Transmission: Single speed direct drive
Battery: 24 kW·h lithium ion battery
Range: 117 km (73 mi)