V2H System（Vehicle to Home System）：The V2H is a part of home smart micro-grid, in which the EV is connected to the building through bi-directional inverter and its char- ging-discharging regime is optimized by home energy management system (HEMS) . The V2H system charges the EV battery using renewable energy and valley power as much as possible and supplies power
to the family during the peak period of power consumption, in order to improve the energy efficiency.
Another mode, V2H and/or home distributed photovoltaic (HDPV) transferring valley electricity and PV by V2H can not only improve the utilization rate of valley electricity and PV, but also obtain considerable economic benefits.
Solution advantages:
- Smart charging function
- Intelligent discharge function
- Realize the function of peak shaving and valley filling according to the local power grid situation (load)
- When the power grid loses power, the power battery in the electric vehicle is converted to an emergency power source.
Has a friendly human-computer interaction interface.
Schematic of (and/or) HDPV-V2H concept :
Schematic diagram of HEMS in V2H sysytem：
Energy use scheduling strategy：
It is assumed that a household EV has its own bidirectional V2H device, and the EV will be connected to the V2H device once the driving is over. In order to reduce the cost of household electricity and use photovoltaic power as much as possible, the scheduling strategy of EV battery needs to meet the
following rules ：
⚫ Excessive PV power is preferred to charge the EV battery if the EV is parked at home during the daytime.
⚫ The EV battery is only charged from the grid during the low elec- tricity price period at night.
⚫ The EV battery supply power to the household load until the battery capacity drops to SOC min during peak hours.
⚫ The allowable discharge depth should be set for the guaranteed driving demand.
Multi-scenario scheduling mode:
It refers to four different cases in which the EV normal charging model and the V2H charging-discharging model are implemented in an ordinary house equipped with PV or not. These four cases are the cases of EV normal charging without PV, V2H charging-discharging without PV, EV normal charging with PV and V2H charging-discharging with PV. The basic load demand and the total travel demand of the family are the same in the above four cases.
Scenario A: A normal home without PV
This scenario is a normal home without PV, Household electricity is provided by the power grid.
Case 1: EV normal charging without PV
The household electricity is supplied by the grid and the EV is also charged from the grid in this case.
Case 2: V2H charging-discharging without PV
The EV interacts with the home power grid in this case. The V2H model can reduce household net expenditure by gaining peak-to-valley price difference.
Scenario B: A PV-equipped home :
A HDPV system is installed on the roof of the home in this scenario. The electricity demand in daytime is preferentially supplied by PV power. The grid
will provide power to the load when the PV power is insufficient to meet the household load.
Case 3: EV normal charging with PV
The PV can power the home while the EV is only a load rather than ahousehold power in this case.
Case 4: V2H charging-discharging with PV
The V2H-style EV is also a power source for the home load besides the PV and the grid in this case. If the PV price sold to the grid is much lower than the peak price of the grid, surplus PV is stored in the EV battery first, and then supplies power to the home load. It will bring additional revenue to the user.
EV battery parameters
In order to meet different driving demands of the EV, the lower limit of discharge for different driving distances is set as 0.5, 0.7 and 1.0, respectively. After the drive is over, the EV can supply power to the home by V2H if the EV battery still has enough energy.
one of the important determinant of battery lifetime is SOC range or depth of discharge (DOD). In order to minimize the adverse impact of V2H on battery life, the SOC range of EV battery is set as 30% ~ 80%, 50% DOD.
The impact of V2H and PV on the household energy utilization
EV charging in the valley hours at night can improve the utilization rate of valley electricity of power grid while the valley electricity stored in the EV battery can power the home by V2H, which can improve the energy utilization rate of the family. HDPV power supply for the home and the EV can improve the utilization rate of green power while the HDPV-V2H mode can store the excess PV in the EV battery and power the household load when the PV is insufficient, thereby maximizing PV self-utilization:
- Transferring valley electricity by V2H can not only improve the utilization rate of valley electricity, but also obtain certain economic benefits.
- Transferring PV by V2H can not only enhance the PV self-con- sumption rate, but also get more revenues than transferring valley electricity by V2H, because the former benefits from lower PV cost and higher PV price including PV subsidy, substitutable grid elec- tricity price and PV sale price while the latter is subject to lower peak-valley price difference.
- The HDPV-V2H mode can completely cover the electricity demand required by the household load in sunny and cloudy days without additional grid electricity. The combination of PV with transferred valley electricity by V2H is enough to support the household load demand in rainy days. In any case, the house equipped with the HDPV-V2H system no longer needs the peak grid.
