solar powered electric car
Image: Australian government/Renewable Energy Agency

Solar-powered cars, and cars acting as batteries for a smarter electricity grid – there are many possibilities for EVs that lie at the “cutting edge” of technology.

A new report has revealed that solar charged, or “photovoltaic-powered” charging stations (PVCS) are on the rise, but careful planning is required to ensure roll-out at scale. 

The Australian PV Institute report focused on the opportunities, challenges and advantages of two aspects of PVCS power: connecting of solar arrays on electric vehicle charging stations, and installing solar panels directly onto EVs themselves. 

Solar technology can decrease CO2 emissions from electrified vehicles by reducing reliance on fossil fuel powered electricity, and encourage EV accessibility due to decreased dependence on the public grid. 

That means in remote areas, EVs might be able to charge straight from the sun instead of relying on the grid.

Generally speaking, PVCS allows the EV user to charge their car — both off-grid and on-grid — either with large PV power plants or a microgrid made up of a PV plant, storage, loads and power management.

Currently, not many PV installations are able to fully meet the energy needs of EVs, and their charging is still at least partly dependent on the public grid. 

“We can’t just abandon our EVs in the street when it rains… We can’t say that you may only charge your EV when the sun is shining.”

“We can’t just abandon our EVs in the street when it rains,” explained UNSW School of Photovoltaic and Renewable Energy Engineering associate professor Ned Ekins-Daukes, who is working on this research. 

“We can’t say that you may only charge your EV when the sun is shining. We need a significant solar array as well as a strong grid connection to back it up.

“The sun may not always shine, but PV power is quite cheap. So what that means is that if it’s sunny you have a happy situation, because the power can go straight into the EV. 

“On the weekend, when the sun is beating down on the multi-storey car park, the same grid connection gives you the ability to charge a number of EVs. During a rainy day, you can use it to feed power, in reverse, back onto the grid from the array on the roof of the car park.”

At UNSW for example there is a solar array on the roof of the car park for students and staff to charge EVs. But it is also connected to the grid, to allow for the cars to charge on a rainy day, and for the solar energy to go back into the grid on a sunny weekend when no cars are charging. 

But what happens when the car is fully charged but still plugged in? 

Ekins-Daukes said that many EVs are now coming on to the market with discharge capabilities. 

What that means is that the technology will detect when there is a power surge and the electricity is needed elsewhere, and it will take the charge out of your vehicle to where it is needed.

“When people get home from work at the end of the day and turn a load of stuff on, the electricity demand peaks. We could give the power system the discretion to discharge the car back onto the grid and give power elsewhere.”

“It’s where the cutting edge lies”

Don’t worry though – you won’t end up with a dead battery in the morning when you need to get to work. The technology will then sense when to recharge the battery of your EV in time for your morning commute. 

“The idea is that if you’ve got a whole street of people who get home and plug in their EVs, it’s got all night to charge. As a consumer, you just want to have a fully charged car in the morning when you go to work.”

Similar to Tesla’s Hornsdale Power Reserve (nicknamed “South Australia’s Big Battery”), the idea is that the cars would act like batteries that “smooth over blips in supply and demand of the electricity grid”.

The purpose of the large battery in South Australia is to provide continuity of electricity supply from the co-located windfarm. 

The battery “turns on and off quickly to fill gaps in the grid”.

Having an intelligent charger that knows when to give back to the smart grid is now technically possible 

Having an intelligent charger that knows when to give back to the smart grid is now technically possible, said Ekins-Daukes. 

“It’s where the cutting edge lies. A number of EVs on the market are already vehicle-to-grid compatible.”

It’s not just sunshine but also social behaviour that drives demand for PVCS. 

Research results in France indicate that most consumers would trust PVCS technology, although some aspects such as location, business model, and design require careful consideration.

Tesla’s Hornsdale Power Reserve (nicknamed “South Australia’s Big Battery”), is the largest battery in the world.

About the report: 

The Australian PV Institute (APVI) coordinates Australia’s representation on the International Energy Agency (IEA) Photovoltaic Power Systems Programme (IEAPVPSP), an advisory group to OECD countries. Associate professor Ned Ekins-Daukes of UNSW and Julia MacDonald of renewables consultancy IT Power Renewables are Australia’s experts for Task 17 of the IEAPVPSP. Task 17 is focused on possible contributions of photovoltaic technologies to transport, as well as the expected market potential of photovoltaic applications in transport. 

While the experts are Australian representatives, Mr Ekins-Daukes said that Australia did not contribute to this report. But he said that he is working on a separate study on how to charge EVs in the outback using solar power, which will be published in September.

The report findings: 

The two major charging capabilities and behaviours also affect the overall benefits to both the user and the environment: 

  • Slow charging mode: charging power of up to 7kW, based only on PV energy and optimised stationary storage energy, filling EV battery up to 6kWh on average, and requiring user acceptance of long, slow charging. 
  • Fast charging mode: charging power of between 7kW and 22kW based on public grid energy and stationery storage limited at 7kW, requiring user acceptance of the higher environmental impact of grid energy. 

For the roll out of PVCS at scale, the following requirements have been identified to optimise their implementation: 

  • Charging behaviour:
    • Daily charging over weekly charging 
    • Long and slow charging when possible 
    • Limit charging to the number of kWh required for the day, or charge more when PV power is available 
    • Limit charging power and stationary storage power to about 7kW 
    • Give priority to charging stationary batteries by PV over charging from grid 
  • PVCS Design 
    • Choose an optimal size for stationary storage 
    • Design methodologies and tools will be helpful for optimally sizing PVCS 
  • Local conditions and impact: 
    • Each PVCS needs to be designed to suit the local site requirements, weather conditions and user profiles in order to make full use of the PV energy 
    • Each PVCS needs to be assessed within the local area for societal impact and acceptance as well as aesthetic design impacts. 
  • Strategy: 
    • Well-conceived power management strategies with Vehicle to grid (V2G) and Vehicle to Home (V2H) integration to reduce the peak pressure on the public grid 
    • Long EV parking time to allow for slow charging 
    • Appropriate education around charging speeds and their environmental impact, 
  • Communication between the operators and the end-users: 
    • EV charge control software based on powerful algorithms, allowing intelligent communication 
    • PV production forecasting and communication 
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