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Published: 17th Nov 2023
Author: By H. Procter

Sustainability is a key requirement for tanneries with international customers. Conventional electricity supply in SA is a problem. 2 needs which can be met by the same technology

Solar power: It is difficult to understand whether what one reads these days makes sense, let alone whether the sustainability claims that technology makes are genuinely what they claim.
This article will explain some of the nuances of solar power for businesses and will list some balanced factors that a leather business needs to consider before investing in solar.

Southern Africa: As a temperate region (neither tropical, nor sub-tropical) and with an above average sunny skies count. Southern Africa is thus well suited to photovoltaic generation of electricity or solar generation of heat. Photovoltaic suggests the solar panels are converting sunlight into energy and the latest commercial technology is currently in its third generation – organic linked Perovskite, with multijunction cells (can use light in different wavelengths). These technologies mean more power in a wider range of conditions, using ingredients that are less dependent on rare materials and are more easily recycled at the end-of-life.
Perovskite is synthetic, made from ammonium compounds, lead, and a halide (Cl, I, Br). That means that the lead can pose problems, but is easily recycled (as a metal) if managed correctly.

Solar systems: A solar system is not just the panels. To generate power you need: solar cells, within a solar module, within a solar panel; the infrastructure to hold the solar panels to a building (which can be integrated into the structure); and a balance of system (BOS), namely connectors, a direct current (DC) to alternating current (AC) inverter that connects to the business fuse box, a battery charger, and a battery bank (for storage, optional) that can store power not used directly from the business.
Building mounted panels have a higher cost per watt compared to stand-alone field generation. So, wherever possible, businesses cooperate to build solar farms to create their power, unless the business has a large footprint that can carry a high number of solar panels. The land footprint (m2/MW) of solar is mid-range (solar is around 14 m2) compared to low nuclear (0.3 m2); and 21 m2 for coal fired and 99 m2 for onshore wind farm generation. So, whilst solar is land intensive it is better than wind.

Is it worth it in Africa? So, with cheap and consistent energy supply in doubt in Africa, the question about whether a company (or individual) should do some self-generation is becoming easier. Some parts of the world are so prone to storms, so careful thought of a large investment is worth it. A bad hailstorm in the Highveld could decimate a solar farm, and whilst there is usually comprehensive insurance that could cover losses, it does diminish the environmental advantages of solar if they are replaced every bad storm.
So, assume the risk from damage is low, what about theft? Fortunately, there is not a high demand for black market solar systems – yet, however there has been a noted increase, especially from “bakkie brigades” that install them and then steal them back. A reputable install company is thus a necessity (see Nedbank's list of accredited companies).

The following is given as a guide (please consult a solar expert for a more accurate breakdown).
Can the system supply the energy requirements of a small to large modern tannery? The answer is yes/maybe for small to medium; and maybe/no for large tanneries with a chunk of power required in night shifts. LWG defines a small tannery as producing less than 83,333 ft2/month and large tannery producing more than 83,333 ft2 leather/month. A small tannery (raw to finished) to get a bronze energy medal with LWG will need to only require 1.55 kWh/ft2 at a production rate of 83,332 ft2/month the total energy requirement will need to be less than 129,165 kWh/month or 4,245 kWh/day (1,556,103 kWh/year).

The typical size of a solar panel (building mounted) is 3.85 m2 (2.2 x 1.75 m). That means for a new generation solar technology the power rating will typically be 600 W. For a second-generation technology one can assume that the yield will be 15-25% so realistically the panel will produce 90W (15% yield).

The average amount of daylight in South Africa is 8.42 hours. Irradiation figures given for South Africa energy produced that can be captured by a solar panel per day range between 4.5-6.5 kWh/ Typical performance ratios are 75%.

This is a very generous rating and using this we can calculate that the number of 3.85 m2 panels needed to generate 4,245 kWh/day will be 877 panels which most tannery building could accommodate (3,377 m2, a building 60 m by 60 m has a roof 3,600 m2).

A tannery needs to understand what sort of land footprint that it has available. A factory should understand the maximum footprint that it has available so that it can overproduce and store excess energy into batteries that can be used at night.

Batteries: A large battery bank is going to be needed by a tannery if it is going to rely completely on stored power. The 877 panels calculated above will generate the 4,245 kWh of power needed per day, but the tannery will need to have capacity for what percentage of that power they will use at night. Typical commercial battery storage solutions range from 32 kWh to 320 kWh that can be stored. These are standalone units that can be upgraded by installing battery modules. So, assume that 25% of the energy needed (1,016 kWh capacity) will need to be stored, that means four battery storage units will need to be purchased to store enough energy for night operations.

Return-on-investment (ROI): Lastly, the consideration of the return on investment (ROI) is needed for all major equipment expenditure. The best price that was accessible for the cost of business rated electricity is R0.24/kWh (if it meets the threshold for business rate) but NERSA claims it is R1.73/kWh - so for the sake of this calculation let’s assume R1/kWh. The system costs, based on crude estimates for systems advertised in South Africa (without discounts for the large number of panels and storage units), will be as follows:
R10,000,000 for 877 solar panels
R27,841,000 for the four battery storage units
R3,420,000 for the BOS (connectors, inverters etc)
R1,500,000 for installation
TOTAL: R42,761,000

Table1. Return on investment calculation for full replacement of current energy with borrowed capital.

Additional running costs will include, cleaning and maintenance, insurance for breakages and final disposal costs for end-of-life. The systems are usually rated for 20 years’ service. There are government grants available for solar that should also be investigated further. The rate of electricity increase year on year in South Africa ranges from 11% to 32%, useful to use 20%. The commonly advertised SA bank interest rate is 8.25% so for an amortised bank loan, the amount of interest calculated on the total amount above, for 20 years, with a monthly payback amount of R364,315, will pay off the amount in 20 years. The aim is to pay that R87,435,476 (principal and interest) off faster with electricity savings.

Assuming no state subsidy and that the business will use all electricity generated, and that the power consumption will not change significantly the following table shows annual savings and when the cost of the solar system will be paid off. 

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