Balancing multiple electricity sources, to eliminate downtime at the lowest cost, is the holy grail for many companies. Why is this not very common, given our current electricity crisis in the country?
The situation
The current South African power generation grid consist of multiple sources: coal-fired generation, nuclear generation, solar generation, wind generation, open-cycle gas turbine generation, and more. With the availability and reliability of the Eskom supply continuing to degrade, more and more focus is shifting towards other private generation sources, with solar generation leading the charge. Solar, however, does not come without its own drawbacks, especially in availability, as you only have a finite amount of sun in a day. Diesel generation is the more conventional answer, but diesel generation is costly due to the price of fuel. In developed countries, the mass-produced power, or grid, is stable enough to supply power 24/7. In these countries the push for solar is purely for cost saving and environmental purposes. It does not matter if a business cannot produce its own solar power during the night, business will continue, unaffected by power outages.
In South Africa however, the reliability and availability of power is the main concern in industry. Most industries cannot function or produce without power, so they turn to one of two places. For industries that produce only during the day, such as shopping malls or small-scale manufacturing, the easy answer is either solar or diesel generators. For larger scale industrial manufacturing which runs 24 hours per day, the answer is more complicated. Any solution will have to include some form of generation which can function at night, and the majority of this would typically be via diesel generation.
The balancing act
The ideal private power generation solution is a combination of multiple generation and storage methods that allows for flexibility in its operations. This would allow the consumer to control the electricity capacity available and therefore the outcome. This generation solution will typically firstly target availability first to ensure that there is never a gap in production, and then it will target generation cost to ensure the lowest possible running cost. A system as flexible as this would allow the consumer to run at full production, with power availability downtime greatly reduced or eliminated, at the lowest possible cost.
Current private power generation methods and technology in South Africa make it difficult to implement such systems. Eskom does not receive (or care about) any information on the capacity requirements of manufacturing sites, nor does it share any information regarding capacity availability, except for a loadshedding schedule.
Solar generation in South Africa works on a principle called ‘islanding’, which in effect means that when the grid is active, the system does not export to the grid and when the grid is not active, it will run on an island, completely independent from the grid. In other countries where the grid is more stable, feeding back into the grid is encouraged and compensated for.
Diesel electricity generation ranges from manual start systems to auto start systems, with integrated GSM modules and change over panels for when grid power falls away. However, even these top-of-the-line diesel generators do not natively allow for external control. These systems are typically closely tied to the grid for control purposes, but do not have the facility to take into account the availability of solar power for instance.
Battery storage is another source of electricity capacity. Battery packs are typically connected to solar panels through inverters to store electricity for periods when there is no sun. Batteries are also used in smaller applications tied to the grid to charge using grid power. Although most battery packs have their own management system, they typically take only one power source into account. Other alternative generation methods such as wind, biogas, etc. have a similar drawback in that they tend to be standalone systems with little thought of integration into a complex power generation solution.
The most optimum solution should be able to balance current available capacity with current consumption and storage replenishment needs, all at the lowest cost possible. An example of an optimum solution would be for sufficient solar generation to allow for low-cost energy during the daytime and grid usage during the night, with diesel generators only covering the grid availability gaps when there is no solar generation. In cases where production runs only during the day, this would make up a significant portion of power usage. An even better alternative would be to make use of large battery banks to be charged with low-cost solar energy during the day. These could take the place of the generator to cover the availability gaps, which would leave the diesel generator as pure standby. In this scenario, alternative generation methods, such as wind generation or biogas, could replace the grid component and the system could run with the following hierarchy: solar, wind or biogas, Eskom, and then diesel generator.
The solution
To eliminate the risk of downtime, an automated system would be required. To automate such a system two main components are required: communication between systems and the ability to control the different systems. Eskom is a generation entity with known shortcomings, and this makes efficient communication difficult and unreliable. Solar systems communicate via networks such as RS-485, CAN bus or others, and their communications protocols are sometimes proprietary, making integration difficult. Diesel generation is primarily built to be used in areas where there is no communication, or where simple notifications and auto start functions are sufficient. These units generally make use of GSM modules to send notifications of generator status. Battery packs typically have proprietary management units, sometimes without the ability to connect to a network.
For optimum use of available electricity capacity, it is necessary to know the current generation capacity available from all sources, the cost of each capacity component, and the current and future load required. In a perfect world, systems would be supplied by the grid, which acts as an infinite supply as the required system capacity is far outweighed by the grid capacity. In a private system containing multiple generation methods, the alternative generation methods are limited or finite. This would mean that if there is a reduction in generation from one generation method, such as solar or wind, it may not be possible to accommodate the entirety of the load, and it will have to be supplemented by a second, or possibly third generation or storage method. Deciding which generation method to use will require knowing the real-time capacity and availability of that method, and integrating it seamlessly.
The solution would be a centralised control system which could accommodate multiple communications methods. This would allow detailed data sharing and accurate measurement of the current power consumption and the power generation ability. It would have control of all the available generation and storage systems to efficiently change between different generation and storage methods based on algorithms determining the most efficient and lowest cost use. Where the system contains storage in addition to generation capacity, an additional factor that would also need to be included in the algorithm is the replenishment need of the storage solution.
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