DIY Solar EV Charging Station Design | Charge Electric Cars With Solar Panels

DIY Home Solar EV Charging Station Design

If you already own an electric vehicle (EV) or plan to do so, you should seriously consider charging it with the sun. Solar power is fast becoming the good guy on the block as far as clean energy is concerned.

If at the moment you charge your electric vehicle with electricity from the grid, your utility expenses will definitely increase and also you’ll be putting more demand on the grid. It´s often said that EV driving is completely green but of course this isn´t true.

All of the raw material that comes out of the ground to manufacture an EV has to be mined and processed, which at the moment is done using machines powered by hydro-carbons. If the electricity grid in your country is fired by hydro-carbons as well, then the problem is compounded.

In fact it’s been calculated that an electric car running from a ‘dirty’ grid is about as eco as a modern diesel car – there’s a long way to go! The future may see electric vehicles with solar photovoltaic panels embedded in them but at present plugs and sockets are used to charge EVs so that’s what we have to deal with.

When did electric cars become popular?

Electric cars early 1900s

The heading is a bit of a trick question. Most people think of electric cars being a modern inventions, but not so.

If we look back at the records from Dept. of Energy, USA, from the time when vehicles were powered by horses, patents using electricity to power vehicles were filed initially in Hungary, the  Netherlands and the USA during years 1828-1835.

Five decades later the first electric vehicle built by William Morrison was shown to the amazed public in the USA. During the end of 19th century electric vehicles actually gained popularity against gas and steam powered vehicles because of their environment friendly nature and ease of driving.

At the beginning of 20th century around 1900-1912 about one third of all vehicles in the US were EVs. During the same time Thomas Edison actively worked on batteries for electrical vehicles and Ferdinand Porsche built the first hybrid EV. In around 1920-1935 petroleum-based vehicles overtook the EV share and EVs went extinct from the roads.

“Dr. Evlyn Farris and her Electric Car in 1919” by jurvetson is licensed under CC BY 2.0

Three decades later when gasoline prices touched their peak, EVs were again  considered as worried industrialists could foresee a time when hydrocarbons disappeared.

The first electric rover on moon in 1971 made also an impact, many people realizing that the vehicles were viable in all kinds of environments. Since then the momentum has gather pace until we can see a time when all vehicles will be electric.

Warming of the planet and dirtiness of fossil based fuels is enticing automobile manufacturers and buyers to turn their heads more and more towards EVs, but this uncovers another problem – how are we going to charge millions of EVs with our national grids? Solar energy has to take up the slack!

What types of EV are there?

In general, electric vehicles are categorised as follows:

Hybrid electric vehicles (HEV) in their pure form are those which use regenerative braking and a gasoline engine to charge the battery. There are different types of HEVs but none of them charge their batteries from an external charge point or socket. Specifically, in full HEVs an electric motor assists the engine to drive the wheels. This makes it more energy efficient than conventional vehicles and also more environment friendly.

Plug-in hybrid electric vehicles (PHEV) are those HEVs which can be plugged in to be charged. They also have a gasoline engine and battery powered electric motor to move the vehicle.

Additional battery charging makes PHEV an all electric vehicle when it runs only on battery and the engine assists when the battery capacity is exhausted. It is better than HEV for its energy efficiency and environment friendly design.

All Electric Vehicles (AEV) do not have a gasoline engine in them and are totally dependent on an electric motor and batteries to drive them. Regenerative braking and other energy efficient features with external charging equipment make it an all electric vehicle or AEV.

In conventional vehicles the engine and its capacity defines the power of that vehicle and that capacity is to explode gasoline or diesel with force and speed to drive the shafts turning the wheels of that vehicle. The gasoline or diesel is required to be poured in the vehicle to store it there and use it while driving.

Similarly in EV, electricity is to be poured in and stored in batteries. This electricity or electrical energy is stored in form of chemical energy in batteries. This chemical energy is again transformed to electrical energy to turn the electric motor which drives the shafts turning the wheels of that EV.

The battery is the most important component of an electric vehicle if it is an all electric vehicle (AEV). HEV and PHEV still have combustion engines in them so that makes engine and battery both essential components depending on usage. If we just concentrate on the EV and battery part of the subject, there are different types of batteries.

Electric Vehicle Battery Technology

What type of batteries are in EV cars?

The number and types of batteries available makes a long list indeed, all with different chemical compositions, usage and design.

Out of that list lithium ion batteries currently power the ‘All Electric Vehicles‘ or AEVs. The lithium ion batteries are again split into various types depending on their mineral components.

The chemical symbols are used as identifiers, like Lithium Manganese (LMO) and Lithium Nickel Cobalt Aluminium Oxide (NCA) batteries which are currently the best rechargeable batteries in use in AEVs today.

What technology is used in electric car batteries?

Nickel Metal Hydride (Ni-Mh) batteries are used in hybrid electric vehicles or HEVs because of their performance but are not very good if used as rechargeable battery in AEVs because of high cost and high self discharge.

Lead acid batteries and Ultracapacitors are also used in EVs to take care of electrical load other than the main drive train of the vehicle – they do so in a very efficient and cost effective manner. Ultracapacitors also help in additional power boost to the vehicle, if designed to do so.

Electric Vehicle Battery Capacity Comparison

Let us have a look at some basic characteristics of Nickel Metal Hydride (NiMH), Lead-acid and Lithium ion (Li-ion) batteries in the table below.

What is the capacity of electric car batteries?

From the table above the superiority of Li-ion batteries over other NiMH and Lead-acid batteries can be understood easily. The energy delivered per kg of li-ion is much higher, which means more battery can be carried for the same power output significantly giving more range than the other types.

They have several times the life of other types which is a huge plus given the price of EV batteries. Li-ion batteries hold their charge longer than the other types and they are more efficient (and therefore quicker) to charge, by grid or solar.

The list of HEV’s, PHEVs and AEVs using these batteries is very long – the table below displays some popular models from leading manufacturers:

Solar Charging Station For Electric Vehicles – How Many Solar Panels To Charge A Nissan Leaf?

For this case study I’m going to go through the design stages for building  an EV solar charging station suitable for a  Nissan Leaf. The technical specifications of Nissan Leaf S 40 kWh are laid out below:

*EPA – Environment Protection Agency
**MPGe – Miles per gallon gasoline equivalent. 1MPGe ~ 1 mile per 33.7 kWh

What amount of energy (kWh) is required to charge Nissan Leaf S EV?

I have seen calculations done to cover recharge of the whole battery capacity, which doesn’t make much sense to me. No one drives their cars until the tank had run out. In general, with our work commute to work and other regular journeys, we can pin down our daily mileage fairly accurately.

It is much more realistic to consider this Nissan Leaf S EV covering the average US range of 30 miles per day. Using the combined drive range of 111 MPGe as the average efficiency of this vehicle, this equals 3.3 miles per kWh.

So to drive Nissan Leaf S EV for 30 miles per day, approximately 10 kWh of energy is required if efficiency of this vehicle is 3.3 miles per kWh.

If we consider different drive ranges of the same vehicle then the amount of energy required will change accordingly:

Solar EV Charging At Home – How much does it cost to charge an EV at home?

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Let us consider Nissan Leaf S 40 kWh again to calculate this cost for an average US household.

If we consider average residential US electricity price of 13.3 cents / kWh, then to charge a 40kWh battery of Nissan Leaf S, it will take $5.3 per full charge.

Solar panel system design to charge Nissan Leaf S EV

Solar panel system and EVs are a marriage of the most modern ways to generate and consume electricity. Combining both makes renewable energy independent and secure – it makes perfect sense. A solar panel system can power the EV in its own right – it doesn’t have to be connected to the grid. In this design brief we are looking at an off-grid solar panel system to power a Nissan Leaf S with 40kWh battery capacity.

Just for reference:

• the Nissan Leaf S can take 20 hours to be fully charged if a Level 1 charger is used with supply voltage of 120V.
• Using a Level 2 charger with supply voltage of 220/240V this can be done in 4-8 hours time.
• If Level 3 charger or DC fast charger is used, Nissan Leaf S can be charged in about 30 minutes.

The length of time it will it take to charge an EV with solar panels depends on:

• Geographic location where the solar panels are placed
• Irradiation level of that location
• Number of solar panels
• Energy required from solar panels

Let us assume the EV i.e. Nissan Leaf S is used to travel 30 miles per day and again assuming the drive range of EV is combined range of highway and city. As discussed above for this scenario, 10kWh of energy is required as input to battery everyday if it travels 30 miles each day.

The components required for such a design are:

• Solar photovoltaic panels
• Solar inverter (micro or string)
• Charge controller
• Energy storage batteries
• Electric vehicle supply equipment (EVSE)

IMPORTANT NOTE: In a DIY design, you might think direct current (DC) from solar panels could be used to charge batteries and also charge EV with a DC connect charger for very fast charging and improve in efficiency of the whole system by cutting down a DC to AC inverter, but this is still under research.

EVs or EVSE are not designed by companies to be directly charged with solar panels or batteries. It is not a safe option to opt for such a DIY design and it is better to use the mature and proven existing technology for charging EVs. DC charging is available for Nissan Leaf S but from commercial charging ports and we are considering this design to be at home.

The Nissan Leaf S EV is equipped with DC fast charger equipment which uses CHAdeMO charging technology, known as Level 3 charger. This fast charger uses DC to fast charge the EV in few minutes when connected to high power (50kW or more) supply from a commercial charge point.

These commercial charge points convert AC to DC to charge the EV and are expensive to install, more than 7 to 10 times compared to AC chargers.

For home EV charging equipment, the Nissan Leaf can be charged with Level 1 (120V) and Level 2 (240V) chargers. For this design we will consider 240V charging from solar panels which takes 8 hours to fully charge 40kWh battery of Nissan Leaf S.

The on board charger on Nissan Leaf S EV is 6.6kW and this is the maximum power it will take to convert AC to DC to charge the Li-ion 40kWh battery.

Now, the calculation for design of solar panels is for 10kWh of energy required to drive 30 miles each day. Let us assume the location where this system is to be installed is Burns, Oregon, USA. Here direct sun’s normal irradiation or insolation level is 5.81kWh/m2.

Here the PCU (Power Conditioning Unit) will consist of battery, inverter and MPPT solar charge controller. It’s a usual design practice to add 35% of the power requirements to compensate for the various ‘line losses’ inn the system, so the requirements in watts will be multiplied by 1.5.

• 10kWh /day x 1.5 = 15kWh /day is to be supplied by PCU to the EV on-board charger.
• Consider combined efficiency of inverter and battery used to store and supply energy from the solar panel system as 90%.
• The amount of electricity to be supplied by solar panels to inverter and battery = 15/0.9 = 16.6 kWh /day.
• Considering average normal irradiation to be 5.81kWh/m2, 16.6 kWh of electricity can be generated by 16.6/5.81 = 2.86 or 3kW of solar panels.

If each solar panel is considered to be 300W each then 10 solar panels will be required to supply 10kWh of electricity to drive 30 miles in Nissan Leaf S each day.

The time it will take to charge EV with solar panel will be the same as connected to home AC socket. It will depend on the charge available in the EV battery itself and solar energy storage and the power conditioning unit will substitute the home AC supply of 120V or 240V as designed.

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Solar Charging Station For Electric Vehicles

Solar EV charging station cost analysis

As per the design discussed above a 3kW solar system will power a Nissan Lead S with 40kWh battery to run 30 miles each day in Burns, Oregon, USA. The cost of this system is as follows:

• Solar panels: $9000
• Off-grid inverter: $5000
• Battery: $10000
• Charge Controller: $500
• Ancillary equipment like wires and cables: $300
• Miscellaneous expenses: $200

Total cost: $25000

This cost is an estimation using current average component prices (2020) in the USA, which can obviously be more or less. The cost depends on the solar system design with a defined battery storage. The major cost in an off-grid solar power system is of the battery, and the electricity backup desired defines the cost of such a solar system.

If battery is not wanted by the consumer, the solar system can only charge the EV during daylight with good amounts of sunlight. This reduces the cost of installation of the solar system but also limits the time within which the EV can be charged.

Other factor which determines the cost is the type of solar panels. If highly efficient mono-crystalline solar panels are installed the price will be high compared to low cost poly-crystalline solar panels. In the same way the area required for the same wattage of mono-crystalline panels will be less than poly-crystalline solar panels.

Related Questions

How many solar panels to charge a Tesla?

10 to 12 solar panels rated at 300 watts each should be able to charge a Tesla EV if the daily mileage was around 30 miles, which is the average commute in the USA.

Can solar panels power a car?

Solar panels can be used externally to recharge an electric vehicle’s batteries, but they cannot power a car for any great distance. The roof area available isn’t enough to produce the kWhs for the electric motor. Roof mounted solar panels will help to extend the range by feeding into the batteries while running, but as yet there is no commercial system to do this.

Why don’t they put solar panels on electric cars?

There is not enough roof area on the average electric car to make it worthwhile mounting solar panels. The cost of doing so would be greater than the gains in mileage range due to the solar panels charging the batteries. Future improvements in solar panel efficiency may make this a viable proposition in years to come.

Other resources relating to EV charging station design

Site-Design-for-EV-Charging-Stations.pdf

Electric Vehicle Charging Station Design and Development

EV Charging Station Installation Guidebook