1. The feasibility of solar parking lots for electric vehicles
Raquel Figueiredoa*, Pedro Nunesa, Miguel C. Britoa
a Instituto Dom Luiz;
Abstract
The coupling of solar photovoltaics (PV) electricity with electric vehicles (EVs) in parking lots is a promising solution to decarbonize the transport sector. This study explores the potential of it using a real park-and-ride lot. To ascertain the techno-economic feasibility of the concept, several sets of assumptions are analysed, including the use of energy storage and smart charging. For current market conditions, the payback time is found to be 14 years; a modest financial public incentive would significantly improve the project economics – it halves the payback –, enabling conditions to put this inescapable and green approach at the forefront.
The park-and-ride feature results on a very distinguished occupation during working days and weekends (Figure 3), due to the workplace daily commutes.
While the uncontrolled charging requires a battery to best use the PV generation,
the controlled charging allows its direct use for the EV charging.
All the scenarios are economically viable (IRR>discount rate of 7%). The reference scenario presents average results; it is followed improvements showed in A2, A3 and A4, which were allowed by the lower investment (due to equipment learning curves in A2 and the absence of battery in the latter scenarios). The most realistic case, A5, which considers a gradual deployment of the project increases the viability of the project comparing with the reference scenario.
Case study
Methodology
Energy analysis
Economic analysis
Park-and-ride outside Lisbon (Almada) with 1024 parking spots.
PV layout optimization (south-east oriented, 33º tilted)
Daily EV consumption: 6 kWh (less than 2 hours charging at 3.7 kW)
Uncontrolled and controlled (as function of PV availability) charging.
The PV production is primarly directed to the EVs; in case of surplus, it is firstly stored in a electrochemical battery (if the scenario considers it) and ultimately sold to the adjacent train station facilities. In the case of generation deficit, the park firstly uses the stored energy and then purchases energy from the power grid.
Figure 1. The parking lot and the metropolitan area where it is located.
1500 m
50 m
Reference
Optimal orientation
Delayed implementation
Uncontrolled charging
Controlled charging
Phasing deployment
Flat fee charging
Frequency’s secondary regulation
No storage
Storage
Figure 2. Parking lot system architecture.
DC/AC Inverters
AC/AC unidirectional chargers
Control Center
Train station facilities
1 MW-PV installation
Figure 3. Scenarios.
Results
40% subsidy
Figure 4. EV charging profiles for uncontrolled and controlled plans; and PV generation. The shadowed area correspond to the sizing of the storage battery.
Figure 5. Payback time (bars, left y-axis) and internal rate of return (IRR – line, right y-axis) for all scenarios. Dashed results correspond to the application of a public subsidy of 40%.
Conclusions
The main remarks provided by this study are:
There is a good correlation between the park occupation and solar electricity generation;
The payback times were found to be between 7 and 24 years, depending on the scenario;
Energy storage allows a greater fraction of solar EV charging; however, we concluded that financially it is not a good option because it is still expensive;
The phased deployment of the project (along with EVs market growing) is the most realistic approach, presenting a payback of 14 years, which decreases to 7 years when a public subsidy to the investment of 40% is applied.
For further studies, we suggest: a detailed discussion of controlled charging and of solutions to turn the project more appealing under current conditions; to test the concept on parking facilities other than park-and-ride (with different occupation profiles).
Aknowledgements
The authors gratefully acknowledge the financial support by the MIT Portugal Program on Sustainable Energy Systems, the Portuguese Science and Technology Foundation (FCT), grant PD/BD/114174/2016, project UID/GEO/50019/2013, and project SusCity MITP‑TB/CS/0026/2013.