Solar EV Charging
A Guide to charging an EV from Solar Energy
There are several ways to minimise the cost of charging your EV. Some of the options include (in order of min to max cost):
New Car Free Public Charging: Make to the most of any free Public charging period that may have been 'priced into' your new EV. If there are convenient options between your daily home and work commute.
Workplace Charging: Make the most of any employer offered free charging at your workplace - if available.
Non-Networked Charging: Scour Charging Maps (such as Plugshare) for all of the freshly installed Stations, that are not connected to an EV Network Billing App (like Charge Hub) and/or offering initial 'free' charging.
Negative Energy Prices: Switch your home electricity provider to a Wholesale Electricity Rate retailer, such as Amber Electric (in Australia), and try to charge your EV when the market hits low or negative rates - when and if available.
Solar System: Install and/or connect your chosen charging method to an installed Solar System.
TOU Rates: Sign up to an electricity provider that offers cheaper Time-of-Use (TOU) - specific time-of-day off peak rates.
Plug in at home, with some 'system smarts' set up around selecting and automating charging times to minimize costs.
Plug in at home, whenever convenient, with minimal 'smarts'.
Utilise Public Charging Stations.
For most EV Drivers, they would ideally like to set up the best repeatable-with-minimal-additional-effort system from the very beginning. Thus, leaving Items 5, 6 and 7 as the most attractive options from this list. Additional considerations here are that statistics show that a high majority of suburban EV Drivers may already have solar installed.
Therefore, when deciding on which EV Charging Station to purchase, that could either connect to an existing Solar System, or that may be 'future proof' for the addition of a solar system in the future, in our view, will come down to following principles below. The concepts covered here will apply to any Solar EV Charging - Residential or Commercial applications.
The below sections will cover:
EV charging requirements vs the amount of Solar Panels required
Levels of Solar Integration and the recommended Charging Station
EV Charging from Solar
Solar Energy Basics:
The basic principles of a solar system is that photovoltaic solar panels are installed on the rooftop (or canopy) of a building (structure) facing a direction that will maximise exposure to the sun. The solar panels generate DC (direct current) electricity, which passes through the solar system inverter, to 'invert' the generated DC electricity into AC (alternating current). Which can then be used to run standard (240V) lighting and general appliances within the building. FYI - see here a Solar Calculator.
Consider that solar generated electricity are simply 'electrons'. There is no difference between the electrons supplied out of the solar inverter or taken from the electrical grid. If the electrons from the solar generation are not consumed by the building appliances, then the excess electrons can either be stored within a battery (EV or Solar System Battery Storage), or pushed back into the electrical grid - generating a electricity supply payment called a Feed-in-Tarif (FiT). As Feed-in-Tariff payments are getting reduced, then it is clearly wiser to find more financially smarter alternative pathway for the excess solar electrons - like hot water heating, air conditioning, swimming pool heating and filtering, or charging an EV or storage battery. So that you can avoid the high electricity costs of running these heavy energy consuming appliances when your options are higher.
EV Charging Requirements:
On average, most electric cars will get about 6km of range from 1kWh of electricity in their battery pack. For the average EV Driver who drives around 50km per day, an electric car will need about 8kWh of electricity to recharge what they use.
1kW of solar capacity (approx. 3 panels) will produce, on average per day over a year, 4kWh of electricity. So, it would seem that you would need to add around 2kW of solar or six panels to offset the charging of one electric car that is driven ~50km per day (give or take some efficiency losses).
Household Solar System requirements:
If you are going to charge your electric car via anything other than a standard wall socket, you will want to install at least 13kW of solar panels in total with a 10 kW inverter to make the most of solar energy. Distributed Network Service Providers, or DNSPs, are in charge of the local distribution of grid power and make the rules for connecting solar to the grid (see here). Their default position is generally to allow 5 kWs of installed (or export limited) inverter capacity per phase. Most homes in Australia are on single phase power, which means they can install 5 kWs of solar inverter capacity. An increasing number of homes now have three phase power which means they can install up to 15 kWs of inverter capacity and up to 20 kWs of solar panels. That is, if they could find enough space for all of the solar panels for such a system.
Solar System (Household) Batteries:
Adding a battery to your Solar System (such as a Tesla Powerwall) should be justified with consideration to your total electricity consumption needs - without EV charging. Charging a 70kWh battery in an EV from a 13kWh Powerwall, at any time other than an emergency, is simply inefficient.
How does an EV Charger charge from Solar?
Question - Can an EV Charger charge from only the electrons produced by a Solar System?
Answer - No, it can not. However, a 'smart' EV Charger measures the amount of excess (or total) energy generated from solar and then adjusts its own output to the same measured amount.
'Solar Smart' EV Chargers come with a bi-directional current transformer (CT) that is clamped around the incoming phase wire into your premises (or three wires in a 3 phase system). A CT is used to measure the flow of current (electrons). If the CT measures current flow from the electrical grid in to the premises, then this will indicate that the premises is drawing electricity from the Grid. If the electron flow is measured in the opposite direction, then this is an indication that there is excess solar that is being pushed back into the grid.
From this set up, there are now several expanded options:
Level 1: Solar Diversion:
With the above CT measurement arrangement, the CT will first of all measure total current (load). If the measured load is getting close to the set electrical system capacity, then the 'smart' EV Charger will ramp down its output accordingly, or pause it's output until the required capacity is available. Secondly, if the 'smart' EV Charger has an App with settings for something similar to 'Solar only', 'Solar with Grid support' or 'Full Throttle', then it will know from the measurement of the direction of electrons how much excess solar electrons that it can utilize. EV Chargers with an App and Solar Diversion are perfect for a simple solution, that doesn't foreseeably require connection to a storage battery or more complicated additional appliance management.
Level 2: Home Energy Management Solution:
As soon as you include a Storage Battery, or want to include wider appliance management (hot water, aircon, swimming pool), then you will need to consider an Home Energy Management Solution (HEMS). In the simple Solar Diversion example above, the 'system' wont know (so therefore won't allow) for you to be able to chose priority charging of your EV or Storage Battery. in the Solar Diversion example, if set to 'Solar only', the EV Charger will always take what is left over after everyone else has been fed. Therefore, if you want more control, a more complex (multiple CT and measurement device) system is required.
Level 3: Inverter OEM Integrated System:
An option to consider, if you haven't already installed either an EV Charger or Solar System as yet, is a fully integrated system from a solar/inverter manufacturer, such as Tesla, Fronius, or SolarEdge.
Note: For future proofing, we recommend to chose an EV Station to is third-party OCPP JSON 1.6 compliant. This will allow for integration with third party devices at a later date. Including App, Load Management, FBT reporting, vehicle Lease management.
An Alternative Option:
An alternative option to consider is the Charge HQ App. The App has a wide range of pre integrated EV Charging Stations and Solar Inverters. Offering one view of your Solar System and EV Charger, together with a connection to Amber wholesale electricity rates. At last report, we understand that they charge AUD$7 per month for their subscription. Note that the Charge HQ does not come with it's own measurement devices. Their system relies on connecting to your inverter and battery via an API (Application Programming Interface) to receive measurements and issue control commends remotely.
Note: Most 'smart' EV Chargers will require a solid internet connection at the EV Charger and Electrical Switchboard locations. For firmware updates and remote access. Connection strength is more critical if any load management calculations are done in the cloud.
Recommended Solar EV Charging Stations
Level 1: Solar Diversion:
Level 2: Home Energy Management Solution:
Smappee EV Wall with built-in Infinity Load Management. The Smappee Infinity Load Management system can be expanded over time with multiple CTs added to the one system, to be able to measure and control a range of devices, including your EV and Storage Battery.
Commercial Solar EV Charging
Solar Carports can add tremendous value to multi open-air car parking premises, to protect vehicles and offer a slow trickle charge.
Remembering our formula above @ 3 x panels = 1kW output. If the sun is at its highest point and full solar generation is produced solidly for an entire hour, then this becomes 1kWh. If an EV requires 8kWh to achieve an additional range of 50km, then that equates to 24 x panels producing at 100% for one hour (or 12 x panels for two hours). Most carport canopies are approx. 21 x panels per car bay. Assume a solar carport over a car bay, with an EV plugged in for 2 hours in middle of the day of summer sun will realistically, within this time, receive a battery/range top up of around 15%.
Therefore, ideally, Solar Canopies best suit applications where the EV Driver can plug in for 4 plus hours - i.e. at a workplace, airport carpark, etc. - and receive at least a 25% charge. Otherwise the EV Stations may not get utilized.
Higher power DC Stations, connected to solar will need to be supported by a storage battery and/or the grid. They just couldn't operate consistently all year round purely off of an average sized solar canopy.
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Image Credit: Canyon Solar