Tidal Energy

Energy storage through tidal energy is primarily controlled by government and municipal entities in South Africa, as access to the coast is typically limited to recreational purposes and ownership below the high tide mark is prohibited. Tidal energy, generated by the natural ebb and flow of tides influenced by the gravitational forces of the Earth, sun, and moon, is often likened to a battery. For tidal energy to be effective, it requires a range of at least 5 meters. Additionally, other forms of marine energy, such as wave energy and sea currents, could also be classified under the umbrella of “Naval Energy.”

Tidal power falls between solar and wind power in terms of its variability, with factors such as high and low tides, spring tides, and neap tides influencing its generation. Similar to hydro power, tidal power has high availability due to water being incompressible, leading to a higher power factor. This brief overview highlights the potential of naval power.

Agulhas Pulse

The Agulhas current flows southward along the eastern coast of Africa, extending from 27°S to 40°S. This current is characterized by its narrow width, rapid speed, and strong force. As it approaches the South Point of Africa, it encounters the cold Benguela current moving northward from the Antarctic, causing it to deflect eastward. The core of the Agulhas current is identified by surface velocities exceeding 100 cm/s, with an average peak speed of 136 cm/s. During the summer months, the prevailing South Easterly winds and weakening of the Benguela barrier can result in the phenomenon known as the “Agulhas Pulse,” where peak speeds can reach up to 245 cm/s or 8.8 kph.

Although it may not seem significant, water’s incompressibility means that the power factor of velocity to wind is 10 times greater. In practical terms, a translated wind speed of 88-90 on the Beaufort Scale is equivalent to a Whole Gale or Storm. This difference in speed may require advanced technology such as variable pitch blades used in Wind Generation – or the Kaplan Turbine. For more detailed calculations, visit the Hydro Power Blog.

Tidal Power Types

Despite the numerous ideas being considered, traditional hydro-based methods like the Rance Tidal Power Station, which utilizes a Bulb-type dam across the entire river, continue to be favoured. The focus not on minimizing the footprint and civil works required. However, the Rance Tidal Power Station has not seen the return of Plaice since 1966. The Sihwa Lake Tidal Power Station, now the largest, has already displaced agriculture due to increased salinity and has also accumulated high levels of PFOS.

There are too many scars to count when it comes to the environmental damage caused by politicians, developers, and local municipalities. This is due to the ingrained mindset that bigger is better in the utility industry.

Hydropower is often considered the cleanest form of energy, but some installations are not environmentally conscious and fail to consider the triple bottom line. However, with the increasing influence of renewable energy sources like wind power, even traditional utility companies can adapt and become more sustainable by embracing smarter, smaller increments. This shift towards a more interconnected and efficient energy system can be likened to building an Internet of Power.

I disagree with the common belief that the Grid is unable to store power. I won’t go into detail now to avoid going on a long rant, but I firmly believe that battery storage is crucial. Hydro power is an ideal form of battery storage, as demonstrated by El Hierro – proving that where there is a desire, there is a solution.

Grid Storage:

I have an idea that came to mind while studying RE Systems: many people believe that the grid cannot store power, but I disagree with this notion. I may not be able to provide a mathematical proof, but I have occasionally searched on Google and may be using the wrong terms.

The South African household power operates at 220V with a frequency of 60 Hz. When a unit is activated, it undergoes a synchronization process to match its frequency with the grid. This is crucial to prevent a dead short in case the frequencies do not align.

Transmission also monitors the grid for frequency variations. A drop in frequency indicates strain on the system, requiring an increase in Generation to meet power demand or an increase in load shedding. Conversely, an increase in frequency indicates excessive generation, which must be reduced. If generation is already at a low Maximum Continuous Rating (MCR), some turbines may be used as “Dump Loads.” The reference point for frequency variation is typically 0.5 Hz.

In terms of power, the equation P=V*I applies to both DC and AC power. However, AC power consists of two components: Real Power and Reactive Power.

Real Power and Reactive Power components of AC Power

An electrical engineer will say AHH thats simple, but all Greek to me. But with 325 000 km of overhead line in South Africa I am sure there is a Capacitive storage component that can be used a latent power bank to absorb Renewables… the VIcos(2⩊t), with ⩊ being the line frequency.

Energy Storage:

Some of the various types of energy storage [and Acronyms] looked at on a utility scale are:

1. Compressed Air Energy Storage (CAES)
2. Flywheel Energy Storage (FES)
3. Pumped Hydro Energy Storage (PHES)
4. Battery Energy Storage (BES)
5. Flow Battery Energy Storage (FBES)
6. Superconducting Magnetic Energy Storage (SMES),
7. Super Capacitor Energy Storage (SCES)
8. Hydrogen Energy Storage (HES)
9. Synthetic fuels (Biodiesel and Ethanol)
10. Thermal Energy Storage (TES)

Just a side note, currently Pumped Hydroelectric Energy Storage (PHES) accounts for 1% of the energy profile in South Africa, yet it remains largely untapped. Can you name any dams in the area that are used for hydroelectric power generation? Chances are, there are none.

Battery Energy Storage (BES/BESS)

The battery uses a chemical reaction to convert the stored chemical energy into electrical energy and produce voltage between the terminals. DC, or Direct Current, has a positive [cathode] and negative [anode] terminal. It has become the most common direct current source for many industrial applications and household. This has not changed much since the Voltaic Cell, with two electrodes and an electrolyte to convey charge.

For Utility sized projects though the following Systems installed that use chemical conversion:

• Lead-acid (LA) – 35MW
• Nickel battery – 27 MW, NiCad
• Sodium-Sulphur (NAS) – 316MW
• Lithium battery – 20 MW
• Redox Flow Battery – <3MW (Not a BESS, actually a FBES)

Lead-acid batteries, the oldest and most developed battery, are a rechargeable battery type and are composed of a sponge metallic lead anode [-], a lead-dioxide cathode [+] and a sulfuric acid solution electrolyte [called battery acid]. Having a lot of advantages such as relatively low cost, simplicity of manufacture, quick electrochemical reaction kinetics and good cycle life under measured conditions made them quite attractive and dominate the market. The 35 MW listed above is actually far from reality as virtually every car is a SLI LA battery, and many modifications have been done and released to market:

• Lead Antimony Batteries
• SLI Batteries (Starting Lighting and Ignition)
• Valve Regulated Lead Acid (VRLA) Batteries
• Lead Calcium Batteries
• AGM Absorbed Glass Matt Battery
• Gel Cell
• Deep Cycle Batteries
• Ultra-battery [New]

Lead batteries are a cause for concern due to the presence of heavy metal. However, because they have been on the market for a long time, there is a recycling system in place. Another issue is their low energy density, which results in them being large and bulky. For renewable energy sources, the main concern is their low energy storage capacity. If they are drained too much, their lifespan is significantly reduced. Additionally, lead batteries have a lower ability to hold a charge compared to other types.

Nickel Batteries: Rechargeable Nickel batteries are made of an active material – Nickelous Hydroxide as the positive electrode. Among all types of Nickel based battery, Ni–Cd and Ni–MH are the most developed. NiCad had come to dominate the portable market, think AA batteries. Compared to the same size Ni–Cd cell, Ni–MH batteries offer 30 to 40% more energy capacity and power capabilities and the Ni-MH are used in Hybrid Electric Vehicles [HEV] such Toyota Prius.

Lithium batteries are primary batteries composed from lithium metal or lithium compounds as an anode. The advantages such as lightweight, safe and low cost cathode material make them a promising technology for future mobile applications. Li batteries offer higher charge densities of 100–150 Wh/kg and have limited environmental impact since the lithium oxides and salts can be recycled. Often called LiPo, or Lithium Polymer. With its high charging density these often drive drones.
One disadvantage of Lithium batteries is Thermal Runaway of the lithium-ion battery initiating an unstoppable chain reaction. The temperature rises rapidly within milliseconds and the energy stored in the battery is suddenly released.
New LiFePo4, which addresses Thermal Runaway of lithium batteries – but still possible, only at a much higher temperature of 246C, compared to LiPo of 104C. Specially designed for RE applications, with over 6000 charges if fitted with BMS (Battery Management System)

Urban Battery Storage Systems.

Currently, the options for urban renewable energy setups are primarily limited to Lead-Acid, Lithium, and LiFePo4 batteries. LiFePo4 is commonly chosen for renewable energy installations due to its high energy density, despite concerns about natural resource depletion and high costs. However, the longevity of LiFePo4 batteries, particularly in regions like South Africa with frequent power outages, offsets these drawbacks.

Let’s examine the current situation in South Africa, where the average national energy consumption is 300-400W. To be conservative, we will plan for a 500Wh usage, which equates to at least 1kWh required for the 2-hour Load Shedding period. We will size the batteries to ensure they can supply this load during each operational regime, using the full load nameplate capacity.

This little exercise was quite intriguing for me. Initially, SLI batteries seemed like a good option, but it’s important to note that they have a long recharge time. These calculations were based on Load-shedding stage 3, so they may not be sufficient for anything above stage 1 load shedding. The prices were sourced from a popular online retailer that carries a variety of items. I made some adjustments to the lifespans, as they can vary depending on battery maintenance, which is automatically managed by the BMS (Battery Management System). A quick calculation at the end shows the benefits of having a BMS in place for your system.

What is load-shedding

I have referred to this Blog on “South African Energy Crises“, but I think many of our international clients do not know what this is? In our situation we have not built enough power stations for the number of people that we have electrified. Onus for this fall fully on Ideocratic Government and State-Owned Company Eskom. Eskom regulates the grid and powers all, virtually no feed-ins are allowed. To avoid a national failure of the grid, which would happen if a unit was dropped at peak demand, the so-called ‘reserve’. But with Ideocracy it would just be a veld-fire along one of 325 000 km of power lines to have a catastrophic dropping of the grid as the 2019 Venezuelan Blackouts [Wiki Link]

Eskom only provides information in PDF format, which is difficult to read. You can view an example of a PDF at this link. While searching for this information, I discovered that Lusaka, the capital of Zambia, is experiencing four-hour load shedding periods, which is impacting the entire SADEC region.

However, another consideration is the potential increase in cost associated with implementing a Battery Energy Storage System (BESS). Given that load shedding for stage 3 occurs every 6 hours, the most practical option would be to use LiFePO4 batteries.

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