With South Africa rapidly moving up the electricity cost league tables, SA Instrumentation and Control tapped into the local grid for a few pointers for readers to act on in 2010.
The June 2009 report ‘2008–2009 International Electricity & Natural Gas Report & Cost Survey’ from NUS Consulting Group shows energy costs declining at anything from 8 to 30% in most major economies covered by the survey. South Africa’s cost increase of 33% for the year is anomalous.
The report showed that at US cents 4,90 per kWh (approximately R0,37/kWh at US$1=ZAR7,5), South Africa ranked a favourable 14th in terms of electricity cost.1
Subsequent to that survey NERSA granted Eskom a 31,3% increase.
Extrapolating that revised unit cost for the next three years with annual increases of a minimum of 33% means that by November 2012 this will be US cents 15,1 per kWh (approximately R1,135).
That will probably put South Africa’s electricity cost in the top three most expensive countries of the survey and certainly well ahead of Australia, Canada, Finland, Sweden, France and the USA.
South African manufacturers will need a massive shift in attitude in terms of energy awareness to remain competitive under these circumstances.
SA Instrumentation and Control features editor Andrew Ashton and editor Steven Meyer got together with Fred Gibson of Gibson Technologies and Conrad Muller of Beckhoff South Africa to brainstorm some practical tips that manufacturers could follow to achieve power-related savings or squeeze extra production out of constrained supplies.
In summary there are four main strategies to consider:
* Pay less per kWh.
* Reduce base load.
* Reduce peak load.
* Improve awareness.
Pay less per kWh
Tip
Know what tariffs are available from your supplier, know at what tariff you are being billed and be aware of tariffs in other areas and/or from other supply authorities. Consider how you can use these facts to move to a more advantageous tariff, negotiate an improved rate or relocate your business to an area where costs are lower.
To reduce electricity bills consumers need to pay at the lowest cost per kWh. There are instances where industrial consumers are billed at the wrong tariff or where small municipalities take advantage of a limited number of manufacturing businesses to subsidise other consumers. One large manufacturing site in which Gibson was involved was even being charged at a domestic tariff and was subsequently able to negotiate a 30% saving.
Look at load profile, MD and tariff – if you can change your process and hence profile there can be a lot of benefit in moving to a different tariff. You must be on the right tariff and for that you need history.
In her keynote address at the Association of Municipal Electricity Undertakings (AMEU) Convention in September 2009, Minister of Energy, Ms Dipuo Peters, noted there are approximately 2000 different tariffs in South Africa and that these need to be consolidated.
Reduce base load
If you are serious about energy management, you have to look at the whole process. It takes a while – you cannot just say, let us put a variable speed drive system in here – you have to look at the whole layout of the factory – where the wind blows, where the sun shines into the building.
Energy management requires a big picture approach – knowledge of mechanical and electrical engineering, thermodynamics and business if you want to get the maximum benefit.
Common sense
Think about and apply common sense to your plant and processes. For instance, if you have an annealing furnace make sure it is insulated properly and is not situated in a draught – keep the doors closed.
Apply common sense and work from first principles before reaching for high-tech solutions. Look at the mechanical part of your process, the thermal side – because that is where the losses happen. You also have electrical losses, but they are much less than the mechanical losses.
Efficiency
Run power consumers efficiently. This may be at or above design capacity and may mean resizing motors.
Design and run your process efficiently – operate at full capacity. Rather run at full capacity for three hours and then switch of for the rest of the day than run at part capacity for the full day.
When designing a new plant, spend more time on the mechanical aspects to more closely match motor no run a mechanical device more slowly.
Most electric motors are oversized – many motors run at 50% of their design load and consequently at very low efficiencies and poor power factor.
Switch off
Turn power consumers off or slow them down when you do not need them.
People do not switch machines off – they have this idea that starting up a motor consumes more energy or is going to negatively impact their maximum demand. If you are not using the motor, switch it off. And that comes back to the control system. When you do not need a device to run, switch it off – that is easy to incorporate into automated control strategies.
If you do not switch something off, you do not save energy: the biggest savings are made by switching off non-essential consumers when not in use.
Tap change
Make sure that your MV supply or distribution voltage is correct.
If your plant is located close to a substation the supply authority may be running overvoltage to compensate for distribution losses to more distant power consumers. Overvoltage will lead to more heat losses on active distribution components and motors and reduces their lifespan.
If regulation is poor then online step changers may be cost-effective.
Power factor
Improve your power factor.
This has a dual benefit of also reducing maximum demand.
You pay for all the power you consume, but it is kW that make things happen.
If a user has a small installation then 0,991 is a good goal for power factor (PF), but the problem with power factor correction banks is the step size – if you can achieve 0,98 or better then that is OK. To design a power factor bank properly is not that easy – you cannot just go and buy a generic solution off-the-shelf and expect it to perform well and give long service. It needs to be tailored to the plant’s load profile if you want it to last 20 years.
One of the reasons for poor PF is the tendency to over-specify motors. Motors run most efficiently at full load. The motor plate might say that it runs at 0,92PF at full load. But the motor never runs at full load. For this same reason, just replacing the existing motor with an energy-efficient motor is not going to help much if it is over-designed. And, of course, many motors do not run at constant load, so they have to be rated for maximum. Take a hammer mill – if you equip it with a high efficiency motor you need to invest in a proper control system to ensure that the feed into the mills causes the motor to run optimally. This not only improves production throughput but also saves energy.
If you are starting with nothing then a payback period of less than one year is often achievable.
Power quality
Improve power quality – reduce harmonic distortion.
Harmonics heat up cables and transformers and consumers pay for that:
* Motors become less efficient.
* Impacts on life of PF capacitors.
* Can impact on measurement accuracies of instrumentation.
Harmonics in distribution networks can be expensive to fix, often requiring redesign of the distribution system (harmonic filters) to isolate harmonic loads in one transformer and new rectifier switching technologies.
Earth currents
Monitor earth leakage paths.
Every bit of current leaking to earth is paid for in the electricity bill. When you have an earth fault at home, your earth leakage trips – but many factories do not have Transcore earth fault protection relays on their distribution. If you are serious about energy management you have got to see what is flowing to ground. Sometimes it is the simple things that get overlooked.
Reduce peak load
Reducing peak load is a little about power factor improvement and a lot about daily and monthly scheduling.
“It takes a certain amount of energy to boil a litre of water: you cannot change that, but you can change when you choose to boil it.”
Avoid peak periods
Schedule production with due consideration of peak tariff periods.
Before they invest in anything clients should look at their process. You do not need fancy power meters and power management systems to know that your workforce arrives in the morning and switches the plant on. Everyone starts at seven and so they switch their machines on. All you need to do is look at the equipment data sheet to know approximately how many kW it draws. Why not schedule production a little differently? Take a smelter that can do three runs a day – it does not matter whether it starts at eight o’clock each day or at nine o’clock – it will still do three runs over 24 hours.
Plan to succeed
Establish energy budgets in terms of kWh per minute and maximum demand.
Think about and apply common sense to your processes. For instance schedule high peak loads to reduce or eliminate overlap.
Schedule maintenance for the end of a tariff month.
System designers should give their clients the ability to prioritise loads on a scheduled basis. The starting points are the production plan and an energy budget. In a planning meeting MD requirements can be discussed to prevent avoidable peaks and these requirements can be prioritised accordingly.
Configurable scheduling allows the user to determine how and where his energy will be used.
The budget in kWh per minute becomes a sloped target on a monthly kWh vs. time graph so that at any time production personnel can see whether they are under or over target. As the end of the metering month approaches, management can make an informed decision, based on business principles, whether to go into penalties (if the plant is over budget) or to schedule a maintenance shutdown to allow the final figure to remain within budget.
Automate appropriately
Reduce loads automatically by taking control away from the users.
Where it is appropriate, remove or override user inputs to allow control systems to keep demand within budget. This may be by briefly reducing current drawn by a furnace, slowing down large drives or disconnecting non-essential equipment.
Business context
Put energy management into the business context.
You cannot replace people. Energy management technology is there to help, but the people have to run it.
Competent systems provide management with the tools to develop energy budgets and choices in terms of how to expend those budgets. They do not try to fully automate load shedding. Energy management systems must complement the company’s business goals, empowering management to take business decisions in context.
Keeping management involved in energy usage on a daily basis develops a culture of energy conservation. Once people take ownership of these tools they will use them efficiently.
At one of Gibson Technologies’ client sites each production manager has an energy budget. When a plant area has used 25%, 50% and 90% of its budget the system sends an e-mail to the relevant production manager. Once 90% is reached a message is sent at every additional 2% and once the whole budget has been used up an e-mail is sent to both the production manager and the managing director.
Improve awareness
An awareness of energy costs and energy consumption is something that everybody in an organisation needs to subscribe to.
When you propose an energy management system you have to have an insight into the business. You have to speak to the employees – find out who is going to analyse the data; who is going to look after the IT side of things; who is going to get buy-in. Put big screens displaying energy usage in places like the canteen to raise awareness and get buy-in across the board. Employees hear about Eskom in the news – they know the risks of not getting their energy usage under control. People understand that an energy cost increase of 45% has a big impact on their employer’s profitability. They know that this threatens their livelihood.
Project justification
Here are some of the motivators that can be used to justify energy management projects:
* Base load savings.
* Maximum demand savings and reduced MD penalties.
* Overcoming production capacity vs. supply constraints.
* Green image/brand building.
* Maintenance savings.
* Equipment longevity.
* Production and quality benefits.
* Reduce man-hours per unit of production.
Reference
1. The NUS survey was based on prices as of 1 June 2009 for the supply of 1000 kW with 450 hours use. For deregulated supplies, 1 June contract pricing was obtained during the week of 27 April 2009. All prices are in US cents per kilowatt hour and exclude VAT.
For more information contact Fred Gibson, Gibson Technologies, +27 (0)82 325 5653, [email protected], www.gibsontech.co.za or Beckhoff Automation, +27 (0)11 792 3374, www.beckhoff.co.za
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