Marine Renewables: How Hard Can It Be? (Part 2)

 

To build upon the previous post (link) marine renewables have a fantastic and readily available resource in the waves and the tides, yet while fossil fuels have to be found, extracted, transported and refined prior to use, marine renewables still seem to come out worse off; why is this?

Energy density

Starting with energy density, yes, water is better than the air used by a wind turbine - a similar output tidal turbine is about 1/4 of the diameter of a wind turbine - but this is still much, much less than found in fossil fuels. Fossil fuels pack around 34-39MJ/l whilst a tidal flow of 2.5m/s is an order of magnitude less than that.

The power density of fossil fuels represents a challenge to other emerging technologies such as electric vehicles, where in this case batteries are struggling to compete with the power density of petrol and diesel. Again, the power density in MJ/l is similar to that of a tidal flow, so an order of magnitude less than these "conventional" fuels.

Yield and Reliability

In power generation yield and reliability are fundamental, but often conflicting. In order to generate a large yield, which means lots of income, there is a tendency to pursue more advanced, complex or novel designs which may not be as reliable. On the other hand, there are devices that are developed from well-established technologies and are very reliable, but often these are not best optimised for energy extraction and return a lower yield. This engineering balance is a fundamental challenge for marine renewables.

CorPower WEC Deployment

Image Source: EMEC

Marine Operation

Image Source: offshorewind.biz

Cost of Marine Operations

Building upon the reliability issue identified in the previous point, if a marine energy device has an issue, it often results in an expensive and/or complex marine operation to access, retrieve or repair the device. This highlights the need for high reliability, which often comes at a cost or to the detriment of yield. The alternative is to have designed for marine operations, which is becoming more popular; i.e. buoyant nacelles, floating devices to move away from heavy lift operations.

Lack of Large Scale Generation

To date marine energy has been showcased in single device demonstrators or small pilot arrays; the lack of large farms generating power has prevented cost reductions through economies of scale and restricted the learning to the few devices deployed. Having more devices in an array not only facilitates the benefits of economies of scale, but also the potential for shared tooling and maintenance equipment, effectively reducing the cost of each asset.

Hopefully this blog has brought to attention the significant challenges facing marine renewables and a better understanding of how hard it really can be. However, whilst there are challenges, it is a fantastic natural, sustainable resource that we should make efforts to exploit. Given that marine renewables get three out of the four power generation OPEX costs for free (cost of fuel, transport of fuel, carbon taxes, O&M), it has great potential to succeed. Many clever minds are tackling the problems we have highlighted in this blog and real progress is being made in the field of marine renewables, so expect them to form a significant part of the renewable energy mix in the future!

1 comment on “Marine Renewables: How Hard Can It Be? #2Add yours →

  1. Some of the earliest WEC (wave energy conversion) devices, when extrapolated out to 1000 MW powerplants, floating in the ocean, used something akin to “one year’s production of copper wire, world wide”. In principle, ideas are often viable, but at a usable scale (not to mention the ships and manpower cost to deploy the device, might be more money than the revenue earned from electricity production and sales) these electricity-from-waves-and-tides deices never lift off.

    I have two unbreakable rules in the designs I create: (1) devices must be self-deploying, with no humans going out to sea for anchoring and hookup, and (2) no electricity generated offshore. Power should be brought ashore, as pressurized water is brought from miles away to run through a spillway and large-size hydraulic turbine onshore.

    I have been at this since 2006, and now I’m 69. I refined my “captured energy storage” system, but I am not enough of a qualified engineer to say if the LCOS for my system is “a go”. Need help with that!

    I will be bringing my website up to date, in the next two weeks.

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