Category Archives: Energy Efficiency

Earth, Wind, Fire, Water & Tyres


Grey Green recently completed a comprehensive energy audit at one of the largest tyre manufacturers in Africa. Our team investigated all energy and material flows. Excellent savings opportunities were found on:

  • Air compressors, plus compressed air distribution and use
  • Boiler, steam distribution and use
  • Effluent
  • Lighting
  • Materials handling
  • Solid waste
  • Water heating

The sixteen best savings opportunities gave payback periods between immediate (no Capex required, just improved control or maintenance) to ~3.9 years, with the average at less than 2 years. These were also quantified in terms of reduced carbon dioxide emissions and decreased carbon tax liability.

Annual financial savings were several millions of Rands.

The tyre company management shall also be able to use our Scenario Planning Tool to:

  • Graphically compare the savings produced by each savings opportunity
  • Decide when each opportunity should be implemented

Scenario Planning Tool

Grey Green also conducted pre-feasibility studies on various sources of renewable energy:

  • Earth – Biogas, from anaerobic digestion of locally sourced organic matter and biomass as a boiler fuel
  • Wind – Wind turbines opportunities in the region
  • Fire – Solar PV (i.e. photovoltaic) and solar water heating
  • Water – Hydro-electric options available.

As expected, the renewable energy opportunities have longer payback periods than energy efficiency opportunities, but once factory efficiency has been maximised, the only way of reducing energy costs further is by producing one’s own energy from renewable sources.

Fan of Energy Savings?

Grey Green has investigated the fans at numerous factories, including at several large grain mills. Often dampers are used to control flow rates and pressures. If so, removing the dampers or changing the fan speed produces good savings.

Case 1

A mineral processing works has six identical, belt driven fans. All operate against dampers which are approximately half closed.

Example of a Fan with Inefficient Control

Grey Green calculated that a simple change to the belt drive ratio with fully open dampers would:

  • Cost approximately R 7 500 to implement (equipment only – installation could be done by the factory’s own maintenance staff).
  • Produce annual savings of R 173 400 (No typos here the payback period is really only 0.04 years – i.e. less than 1 month).

Case 2

Another local grain mill has approximately 30 significant sized fans. None have damper control; whenever the mill is operating the fans run continuously at fixed speed.

Grey Green assessed 18 of the biggest fans. Our measurements and calculations showed that many of the fans were far from their optimum (maximum efficiency) operating points – i.e. when plotted on a fan curve like the typical one in the following diagram, their combination of flow rate and pressure rise was far from the best efficiency point.

Typical Fan Curve
Typical Fan Curve

Due to the age of the fans and their motors we recommended replacement of the worst performers.

  • For five fans replacement gave payback periods less than 1 year and total annual electricity savings of >R 2 million.
  • Six more fans could be replaced to produce payback periods between 1 and 2 years, with combined annual electricity savings of R 634 000.

Compressed Air Leaks – The Evil Hiss

Compressed air systems leak a bit, but not worth worrying about. Right? The shrug and ignore, business as usual approach is common. What a waste of an excellent opportunity to make big savings.

While assessing energy at factory, Grey Green’s engineers where able to measure compressed air leakage rate. Our client kindly agreed to leave all machines except their air compressor off for a few minutes. The photographs show the results.

The compressor is:
• An oil injected rotary screw machine
(by far the most common type used in SA factories).
• Relatively new, and fitted with a VSD (variable speed drive).

The photographs are of the display on the compressor when no other machines were running. The percentages show the speed of the compressor. Since it is a screw compressor, the percentages also indicate the proportion of rated flow rate which the compressor is delivering – an average of 41 %, when nothing else in the factory was on! 41 % of rated flow was feeding leaks!

• A 75 kW compressor supplying air to a system
with the same leakage rate
• Electricity cost of 65 c/kWh
• 2 shifts a day, 5 days a week, 48 weeks a year,
i.e. 3 840 hours operation a year.

• Wasted power = 0.41 x 75 = 31 kW
• Wasted energy = 118 080 kWh
• Wasted expenditure = R 76 750

Cost of locating and fixing leaks? Usually nothing more than time when a maintenance fitter is not busy with breakdowns.

Need help in getting started? Wondering what else could be improved on your compressed air system? Contact Grey Green now.


SARS’s 12 i scheme allows companies to claim tax rebates for capital expenditure which produces energy savings. Several requirements apply. One is a baseline report which shows the energy intensity before installation of the energy savings equipment.

Grey Green compiled a baseline report for a large dairy in the Eastern Cape.

The baseline report met all the requirements and the diary is proceeding with installation of energy savings equipment.

Baseline reports have to conform to the procedures of the IPMVP [International Performance Measurement and Verification Protocol) and SANS 50010 – South Africa’s standard for Measurement and Verification.

Producing the baseline included correlating energy usage with production. The following graphic is an example.

Effect of Production on Steam Usage

Effect of Production on Steam Usage

Seasonal variations in production and therefore energy are common with agro-processing. For our dairy client these were investigated by first considering how output varies from month to month. The following graphic shows that there is considerable seasonal variation.

Seasonal Variation in Production

Seasonal Variation in Production

Next month to month electricity usage was investigated. The following graphic indicates that it does not change much.

Seasonal Variation in Electricty Usage

Seasonal Variation in Electricity Usage

In addition to using a baseline report for tax rebate applications, the data will often reveal opportunities for energy savings. For example, comparison of the previous two graphics seems to show a mismatch between production variations and monthly changes in energy consumed.


Come Wine with Grey Green

Grey Green have audited six wineries in the Western Cape during the harvest period over the past few months with another two winery energy audits in progress and a further three in the pipeline.

On average, the energy saving opportunities identified at each site could potentially save the wineries approximately R 370 000 per annum with a promising average pay-back period of 3 years. We also calculated an average of 400 tonnes of equivalent carbon dioxide emissions saved through our recommendations.

Highlights of the proposed interventions included: 

  • Effluent Treatment Optimizations
  • Feasibility Studies for Solar PV
  • Waste-Heat Recovery System design
  • Energy Efficient Extraction System design
  • Efficient Lighting Retro-fit proposals
  • Chiller System Optimizations including. insulation

Interestingly, chillers (cooling/refrigeration) accounted for approximately 40% of the total energy consumption, with the exception of those wineries with a distillery. The distillery accounted for 18% electrically and when converting the boiler fuel into equivalent kWh (using the calorific value of the fuel), the fuel accounted for 94% of the total energy consumption!

Lauren almost overshadowed by grape skins
Lauren almost overshadowed by grape skins


Share a Coca-Cola with us

Penbev Coca-Cola logoWe have successfully completed a major lighting upgrade program at Peninsula Beverage Company in Parow Industria consisting of 5 sub-projects over a period of more than 2 years and including some 3000 fittings. Every high-bay and fluorescent in the plants, warehouses and offices was replaced with a more efficient alternative. As a result, Penbev are now benefiting from more than R1.1m in annual energy savings and an additional estimate of R270k in demand charge reductions per annum. Grey Green also managed to secure ESKOM rebates for our client in excess of R1.1m to help subsidize the client’s investment in the program.

FAURECIA Energy Efficient Lighting Upgrade

Induction Lighting

Grey Green has been awarded a contract for a major lighting upgrade at Faurecia’s Cape Town operation. The scope of the project includes financing, supply and installation of the new lights, before and after lux level drawings, as well as a 3 year maintenance program. This project shall save our client approximately R 2.5 M over 3 years and is expected to be completed by end June 2014.

Energy Efficient LEDs for Vector Logistics Cold Rooms

LED lights are a very good choice for cold room warehouses. After a very rigorous trial phase, Rick du Toit, regional plant engineer at Vector Logistics in Cape Town, decided on a LED light supplied locally by Lighting Revolution. The trial period involved testing different strength lamps with a various range of reflectors.

The light that was finally chosen was a 130W tunnel lamp, made up of two chips with separate cone reflectors at 120 degrees. These lights give a very even spread of light for warehouses with high ceilings of up to 13 meters.

The project was managed by Grey Green (as the ESCo), who made use of the Eskom Standard Offer Rebate Programme.  The project has been completed and the post assessment report has been published by the independent ESKOM appointed Monitoring and Verification team (M&V).

A summary of the changes that took place is given below:

  • 130 x LED Tunnel lamps were installed (130W each including electronic driver)
  • The lights are replacing 107 x 400W metal halide lamps (low bay fittings) and 23 x 1000W halogen wedge lamps
  • 27 of these lights are in areas where the ceiling height is 5 meters or less
  • 103 are in areas where the ceiling heights are between 11 – 13 meters high
  • Approximately half the lights are in cold rooms at between -4 and -6°C, the other half are in -25°C freezer rooms

Part of the project involved trialling the lights extensively, including switching tests as well as testing the lamp in the freezer rooms, which is the more severe operating climate. Based on the trial results the project went ahead using the tunnel lamp fitting from Lighting Revolution. The implementation was not without its challenges because of working in freezing room temperatures, but the installation team (FLASH Electrical) rose to the occasion. All battery operated equipment (lifting devices, drills and flash light) used needed to be warmed intermittently in order for it to operate correctly. This led to slight delays in implementation schedule, but overall the project went extremely well.  The results, measured in terms of increased lux levels on the plant floor as well as substantial energy savings, were quite incredible.

The M&V baseline report revealed that the metal halide lights consume on average 400W and the halogens 1080W. This fact may seem obvious but depending on the type of ballast and site’s average voltage the rated power drawn by a light fitting can vary by up to 50W or 10%.  The average lux within the plant rooms was between 70 – 100 lux before the implementation (due to degradation of the lux levels as the lights age).

After the post assessment measurements it was revealed that the LEDs performed better than expected in the cold environment. The 130W rated fittings on average drew 126W. The additional savings can be attributed to the cold climate within the cold rooms which helps dissipate heat from the fittings which is a typical weakness of LED lights. The average lux levels post the implementation was 180 lux even in the areas with 13 metre high ceilings.

The lights will thus save 51kW, equivalent to 447MWh per annum. This at current tariffs is equivalent to R 360 000 per annum. The Eskom rebates for LED interventions on the SOP programme are 0.55 c/kWh saved during the SOP qualifying times. This has resulted in the rebate subsidizing approximately 45% of total project costs!

The LEDs have IEC certification, and come with 50 000 hour or 3 year warranty. The indirect benefit of the LED lights is that they also have far less ballast losses and because of their lower operating temperatures there will be less heat dissipated into the cold room which should in theory lead to a slight saving in refrigeration load.

The project has served to demonstrate that using the correct light for a particular environment can be very effective leading to increased lighting levels as well as cost savings.