Green power halts coastal erosion

The erosion of our coastlines is a becoming a serious problem in many areas of the world. This is mainly due to dying reefs and waves becoming more powerful. The issue with the reefs is that climate change has caused rising sea temperatures, leading to acidification and coral bleaching. As for waves, total wave energy is growing by 0.4% per year, again due to the rapid warming of the oceans. Globally, around 70% of the world’s coastlines are eroding, and 200 million people worldwide rely on the protection that coral reefs offer. With 99% of remaining reefs projected to disappear by 2040, communities and livelihoods are at risk in areas such as Mexico, Indonesia and numerous smaller island habitats around the world. That erosion is not benign, it causes the loss of land, which can damage buildings and infrastructure, which in turn can damage the economy of the areas affected. It can also increase the risk of flooding and storm damage, as beaches can offer some protection from both.

As a practical example, in Mexico, warmer temperatures are causing parts of the Mesoamerican Reef near Quintana Roo, Mexico to be affected by 'white syndrome,' which can kill corals in under 40 days. That region of Mexico is particularly reliant on tourism. The loss of beaches there could have a devastating effect on the local economy. For example, the resort of Playa del Carmen is one of the worst of the areas affected. It is estimated that the resort has currently lost between 30 and 50 metres of beach, as shown in the image.

One way of alleviating the damage caused by erosion is to restore reefs, or create artificial ones. Restored or generated reefs have the potential to reduce the energy of waves by 5 – 8%, and it could be possible to revert the impact of waves hitting the shore to levels from nearly 20 years ago. As a result, coastline erosion would be stopped or even reversed.

CCell Renewables is one company that is using renewable energy in Quintana Roo and other locations to combat coastal erosion by patching existing reefs and growing new ones. The technique that the company uses is based on the electrolysis of seawater. In five years it can potentially produce strong limestone rock that would normally take hundreds of years to form. The limestone structure on which coral grows must be created on a large scale without impurities, with a strong molecular structure and grown at an optimum rate. The electrolysis process needs to be precise. If it is too slow nothing will grow, too fast and the limestone will not be tenable. That means delivering large power quantities precisely.

To accomplish that job, the CCell engineering team has developed solutions using renewable energy sources such as solar, wind and wave energy to power its reef-growing systems. To effectively combat erosion, ocean waves need to be dissipated around 300m from the shore. The company’s technique uses a steel frame, passes the low voltage, high current power between the structure and a small metal anode. At the anode, oxygen is generated. At the cathode the pH rises which induces precipitation of dissolved salts in sea water on the steel surface. The rock formed is mainly aragonite (calcium carbonate) and brucite (magnesium hydroxide), which seals the steel structure and protects it from corrosion. After the rock has formed, divers can attach corals grown in local hatcheries to the rock. These corals grow at two to three times faster than normal because of the optimal conditions.

The renewable power sources have one thing in common: their power generation creates a widely varying output voltage due to constantly changing environmental conditions. That power then needs to be converted to a voltage that can be used for electrolysis.

Dr. Will Bateman, CEO of Ccell describes the conversion process in Mexico by saying, “It is mostly driven by solar panels that are installed on one of the residents homes. At night we use a little bit of energy from the grid hich which is sent out to sea as DC is a lot safer to operate in water. The next stage is to step down the power to around 20 volts. Then there is a further conversion down to a lower voltage depending on the requirements for electrolysis. That conversion increases the current by a factor of eight and takes the voltage down by the same factor.”

In practice, this requires a power delivery network (PDN) with a front-end conversion and regulation stage followed by a downstream point-of-load (PoL) regulation stage for the systems monitoring and control electronics. Power is delivered via a long cable to the electrolysis system which is placed very close to the steel frame located on the ocean floor where the reef will be rebuilt or created.

For the Mexican project, Ccell chose Vicor’s Factorized Power Architecture (FPA), which incorporates a current multiplier with a fast transient response. The Vicor Factorized Power Architecture factorized the DC-DC function into two separate modules, a PRM regulator and a VTM current multiplier. The PRM buck-boost regulator is capable of operating over a wide input voltage range, which accounted for the variable voltage from the renewable source.Its zero-voltage switching (ZVS) topology has very high efficiency and power density and is easily paralleled to deliver higher power. The power delivery to the reef is so far offshore it requires almost 2kW, but the higher voltage allows reduced cable size and a cost saving. The PRM is optimized for delivering higher regulated voltages for the downstream VTM.

The VTM is a resonant, high-switching-frequency, fixed-ratio converter (non-regulating) with an output voltage that is a fixed ratio of its input voltage. The transformation ratio is called the K factor. The VTM operates like a DC-DC transformer such that if the K factor was 1:8, the output would be 1/8 th of the input and the current multiplication from input to output would be 8. The two modules work together with the PRM handling the tightly regulated voltage required for the reef, and the VTM handling the conversion and current delivery to the electrodes.

Taking into account the measured voltage drops in the power cables to the reef, the PRM would regulate the 36 – 70V input from the wave energy converter to deliver between 9.6 and 32V on the input of the VTM modules, which have K factors of 1:8, to provide a 1.2 – 4V output. As environmental conditions are constantly changing, the PRM is regulating the input to the VTM to maintain the desired output voltage.

As the power is already delivered to the frame, some of it can also be employed for a different purpose. Ccell has employed devices along the new reefs to perform real-time monitoring of marine ecosystems using acoustic beamforming to track and measure marine life.