Securing your power supply
Working out the cost of electrical power loss to your business puts you in a position to scope your standby power needs, as DAVID CARDOZO reports.
When Virginia Woolf wrote A Room of One’s Own in 1929, emancipation of women was some time off. It could be said their dependence on men back then is replicated by a similar, suppliant attitude that businesses have today towards electricity supply – essential infrastructure supplied by ‘electricity authorities’ on whom they have to depend.
Yet in the present climate there are good reasons for freeing business from the control – the absolute control, that is – of electricity suppliers. Here, we explore some specifics of power supply for your business that you can rely on when disruption occurs.
Let’s start with oft-heard statements. ‘My business is too small to investment in expensive standby gear’ or ‘there is no reason for assuring my own power as we haven’t experienced any blackouts’. These ignore the cost of a day without electricity, or shorter periods that have similarly bad results on business operations.
Interruption to electricity supply is not a rare occurrence. A typical example was a power interruption of some hours, and longer in some areas, in Citipower’s system during a couple of very hot days in Victoria in early February 2018.
The explanation given – that there would have been plentiful supply by way of generation capacity if it hadn’t been “for distribution system failures occasioned by high temperatures” – somehow doesn’t compensate for the lack of electricity. Does it really matter how a system fails? It’s the business of the electricity supplier, but you as a business cop the damage! Basically, assuming that having your own source of power is too expensive is a cop-out.
There are two ways of securing your own supply – batteries or standby diesel generators. There is no preferred way, the choice being dictated by:
- your total power requirement
- the proportion of essential loads, and
- the maximum time you can afford to be ‘off air’.
For businesses with a power requirement of at least 100 kVA (note: kVA, the unit for power demand, stands for 1000 volt-amps), which implies an annual consumption as high as 600 megawatt-hours, investment in power plant may well require a capital expenditure of $150,000-plus. And the figure can easily double when building changes are required. Although not necessarily eye- watering amounts, they are major investments for many businesses and therefore require careful evaluation.
POWER SUPPLY SYSTEMS
The preferred storage medium is valve regulated lead acid (VRLA) batteries. These entail little or no maintenance, no fumes and no fire hazard. They are, however, very heavy batteries.
The energy storage density is typically 30 to 50 watt-hours per kilogram. Lithium batteries have much higher energy densities, of the order of 1000 watt-hours per kilogram, but require tender loving care.
These are reliable and have power density of the order of 10 to 30 watts per kilogram. Typical fuel cost is 40 cents per kilowatt-hour. As to kilowatt-hours that can be extracted, this is only limited by the capacity of the fuel tanks. They therefore have to be used where power interruption periods outstrip the capacity of batteries. Although there is no absolute rule, power interruption periods exceeding 30 minutes or so may require standby diesel generation.
ESSENTIAL AND NON-ESSENTIAL SERVICES
Hospitals, airports, air traffic control, server rooms and rail transport signalling require 24/7 energy security. This not a requirement for many business operations and, in specifying some form of electricity security, there has to be sensible trade-off of risk versus cost.
For many companies, the battery solution is the simplest and least costly one. However, it requires a careful analysis of essential and non-essential loads because of limited back-up time. The definitions are entirely determined by individual businesses. Having classified the electrical loads, an analysis should be undertaken, requiring little else than a reasonable knowledge of functions and kilowatt or kVA requirements of various processes and building services etc.
Rather than working on the basis of the length of a piece of string, a sensible way of assessment is to plug in interruption periods of one, five, 10 and 20 minutes. For IT functions, depending on size, there may already be an uninterruptible power supply, or individual ones for towers etc. The latter normally have very limited support periods. As for centralised IT, you should also take into account power interruptions of an hour or longer.
The importance of undertaking this task – which does not require highly specialist knowledge – cannot be understated, and the outcome may be that no emergency or back-up supply is needed. On the other hand, you will have meaningful data for discussion with potential suppliers of equipment, and engineering and installation services, ending up with a solid proposal to take to your capital expenditure committee.
Admittedly, risk analysis is not easy, especially because network failure statistics are very hard to come by, and are not necessarily neatly carved up into detailed geographical areas, so that you may have a picture for your particular location. Then again, when it comes to fire insurance, you have to take your insurer’s data based on industry claims history as the basis for your premiums, which do not necessarily recognise your location or particular circumstances etc. And there’s something else: all insurance risk assessment is based on historical data, but premiums take into account the uncertain future. When it come to electricity, we face disruptive times, requiring an article of faith when it comes to not factoring in the need for back-up supply. One way of looking at back-up supply is as a capitalisation of premiums to cover the contingencies of loss of electricity.
Battery systems use inverters to supply alternating current at normal voltage and frequency available from the poles and wires that connect to your business. During normal availability of the electrical network, the battery charge is maintained (topped up).
When the network fails, the batteries discharge, powering the inverter. When network power is restored, the batteries are recharged, sometimes via a supplementary charger. Larger systems, the ones more likely to be used in supermarkets, office buildings and industrial plant etc are so called ‘in line’ types that are continuously operating, in effect insulating your facility from network disturbances.
Diesel generator systems (DRUPS, which stands for diesel rotary uninterruptible power supply) comprise a diesel engine driving a generator/motor. During normal availability of the network, the generator/ motor functions as an electric motor with power supplied by the network, spinning under no load and storing rotational energy. When network power fails, the motor switches to generator mode, supplying power for a short period of time while the diesel engine runs up to speed and takes over the task of driving the generator.
WHAT ARE YOU LIKELY TO REQUIRE?
In the first place, an analysis of your business under power failure conditions is necessary. Second, before jumping to technology solutions, it’s necessary to look at emergency plans – those that may alleviate the power loss situation for a limited time without requiring investment in hardware. Finally, the task of standby plant scoping should commence, taking into account essential business activities.
This is a two-stage project whereby the first stage, not requiring engineering expertise, is undertaken by you, segregating essential and non-essential services, and assigning their power requirements. With that data in hand, consultation with electrical engineering people can proceed. The result of that exercise is the basis for system specifications, and subsequent calling for quotations.
David Cardozo is a Melbourne-based energy writer.
This article also appears in the April/May issue of Facility Management magazine.