Time to take charge

by Melanie Basta
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Though uptake of electric vehicles is still currently low, parking facilities with vehicle charging points must now be planned for, because the market will grow and buildings must remain attractive to tenants and the real estate market, writes PAUL ANTONY.

The electric vehicle (EV) market is as yet small with sales of plug-in hybrids (PHEV) and entirely battery powered electric vehicles (PEV) at less than 0.1 percent of personal use vehicle sales. Unlike countries such as the Netherlands and Norway, the governments of which provide substantial financial incentives for EV purchase, registration, parking and running expenses, Australia presently lacks such market stimuli. Notwithstanding the current situation, the EV market will take off and office buildings, shopping and apartment complexes, as well as industrial premises, will need to have EV charging points as part of their parking facilities. Prestigious office buildings are already being equipped with EV chargers, but this is not happening as yet for much existing building stock. This article provides information on charger basics, installation, safety and maintenance requirements, and as such is useful for assessing the state of readiness of your facility for the increase in EV use.

Electric vehicles 101

The big difference between internal combustion engine vehicles and electric ones is energy density. By way of example, a 60-litre tank of petrol, weighing about 50 kilograms, can provide a cruising range of over 1000 kilometres; an 85-kilowatt hour battery, weighing 500 kilograms, will have a range of about 400 kilometres. However, before you conclude that electric vehicles have an insurmountable disadvantage, take into account that most personal vehicle trips are short range, taking place in metropolitan areas, and there their noiseless, fumeless properties, it can be argued, have it all over their fossil-fuelled mates.

‘Charging’ a petrol tank to its capacity is a matter of minutes, but for EV this can be a matter of hours. However, note that there are fast charging facilities (discussed below). Many personal use scenarios have the driver charge their vehicle overnight, at home, requiring only a ‘top-up’ while at work, shopping or other activities in the vicinity of their parking spot – thus obviating the installation of fast chargers.

Power and energy 101

A medium-sized EV may have a 30-kilowatt hour battery, which is the fully charged energy content of the battery. Charging that battery from empty to its full state in an hour would require the charging point have a 30-kilowatt rating (30 kilowatt hours divided by one hour). If charging to capacity were required in 15 minutes, the charging point rating would have to be 120 kilowatts. These are hefty numbers – even 30 kilowatts, for that matter, exceeds the power rating for the average home. Overnight charging, say over 10 hours, requires only three kilowatts for the charging point, and that level of power is more easily adaptable to domestic environments.

Electrical installations (or wiring) 101

Understanding this section is requisite to the scoping of future requirements in your facility, and in reviewing quotations for upgrades. Even ‘topping up’ charging when multiplied by a large number of charging points may well require upgrading to a very significant level.

At distribution board level (to which power outlets are connected), a 20-amp circuit can deliver a maximum power of 4.8 kilowatts. Obviously, if two charging points are to be connected, each one can only supply half, or 2.4 kilowatts. The foregoing example is a single-phase example. If three-phase supply is available, then a 20-amp circuit can deliver three times 4.8 kilowatts (14.4 kilowatts), or in case of two charger points per three-phase circuit, 7.2 kilowatts per charging point.

There are more electrical considerations that we’ll get to; however, it is obvious by now that providing multiple charging points in a car park requires evaluation of the existing electrical installation.

Slow and fast electric vehicle charging 101

There are two basic types of EV charging: alternating current (AC) and direct current (DC). The former is suitable for overnight and ‘topping up’ charging and the latter for fast roadside charging where the requirement is typically for adding at least 200 kilometres to the vehicle’s range in less than 10 minutes.

Electric vehicles have on-board chargers, and this will appear confusing because, that being the case, what are the essential functions of wall-mounted or free-standing chargers (in a roadside service station)? In slow charging, the vehicle’s on-board charger is connected to the external charging point, which is supplying alternating current (AC) to it. The on-board charger converts this to direct current (DC) to charge the vehicle’s battery bank. In fast charging points, DC rather than AC is supplied to the vehicle and the on-board charger is by-passed.

Vehicle on-board chargers have a low power rating (saving on manufacturing costs) compared to that available from fast DC charging points. For many buildings, if not most, AC charging points will be required.

Electric kettles and charging points

Electric kettles and other household electrical appliances require annual safety inspection and tagging. It is a very straightforward operation, taking about a minute. A charging point should be subject to more onerous testing and tagging, if only because the general public is holding onto a cable and connector capable of administering a lethal dose of electricity. Or a driver may, in a moment of distraction, attempt to drive off with the vehicle still connected to the charger.

The installation of charging points is covered by the Australian Standards (AS/NZS3000), but testing is essentially not covered. The distinction between electric kettles and charging points is to be borne in mind when it comes to the safety of the public! In essence, the testing of charging points is done with apparatus that mimics a ‘connected vehicle’ so that, among other things, electricity can’t be delivered unless interlock conditions have been checked. It is essential that regular testing take place using specialised testing gear.

Power quality 101

Charging points can cause power quality to deteriorate, possibly affecting other electrical equipment. This in turn can upset the poles-and-wire people connecting electrical power to your installation because of problems being caused to neighbouring consumers’ electrical equipment. Domestic charging points are not usually an issue, but the more sophisticated commercial application ones can cause power quality problems. Under ideal circumstances, the voltage in your electrical installation is a smooth sinewave. However, when that is not the case, problems including additional, unwanted heating of wiring and faulty operation of electrical equipment, can occur.

Just like rooftop solar, power to the vehicle is delivered via an inverter. This allows control of the charging current as the battery bank in the vehicle gradually charges up.

The disadvantage of the system is what is called ‘harmonic emission’ resulting from the charging current control causing voltage to change from a smooth sinewave to one that is ‘distorted’.

Planning for charging points

Planning is a specialised business. First, a power quality audit should be done, assuming that we’re talking about multiple charging points. Let’s assume single-phase charging points rated at seven kilowatts. Thirty charging points throughout the parking facility implies a maximum power requirement of 210 kilowatts. Each charging point will have to be protected by a 30-amp breaker. An assumption has to be made about the load factor, since the charging points are not all simultaneously in use. Assuming this is at 50 percent, 105 kilowatts are being added to the installation, which the main switchboard and the distribution transformer have to handle.

As to power quality, this will be heavily and negatively affected by harmonics. The proposed charging point equipment should be discussed with a power quality analyst, as well as the capacity of the existing electrical installation to cope with the added power demand.

Paul Antony M Eng (Elec), applications engineer, Power Parameters Pty Ltd.

Image: 123RF’s kasto © 123RF.com

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