Marine Energy: Next Generation of Renewable Energy?

In this blog post, I discuss the possibility of marine energy as a candidate for next generation of renewable energy (see picture below). But before I get to that, let me explain why we need to start exploring next generation of renewable energy.

Pelamis (wave energy capturing device)
(photo credit: Pelamis Wave Power Ltd.)

We all know that many nations have invested heavily in solar and wind power through various incentives and regulations such as feed-in tariff (FIT), renewable portfolio standard (PRS), and tax credits. These investments have somewhat fulfilled the intended purpose of improving the price competitiveness.

For instance, in many places, wind power is already at grid-parity, meaning that its lifecycle costs per production unit (e.g. kWh) is equalized with that of thermal plants. The costs of solar panel also fell dramatically in the past few years due largely to the emergence of Chinese manufactures, and it may not be far for solar power to achieve grid-parity as well (note that the installation costs, which relies on on-site skilled labors, may be an obstacle to grid-parity for solar).

So why these energy sources still supply a small fraction of total electricity demand? One reason is obvious: spatial constraint. Solar is an inherently unproductive way to produce electricity in a given area, and even if we install solar panel at the rooftop of every buildings, it satisfies a small fraction of total energy demand of the world. Wind power is more productive per area, but wind patterns and its impact on the environment such as noise severely limit its availability.

The other thing we need to consider is the stability of output; we all know that the output from solar depends on sunlight, so it can't produce electricity at night at all. Wind power also depends on weather conditions, and on low wind days, it doesn't produce electricity at all (see picture below). It is possible that advanced energy storage and smart grid technologies may be able to offset a portion of this problem, but the costs are prohibitably expensive for now.

Power Output by Generation Sources in US Pacific Northwest
(photo credit: Bonneville Power Administration)

What is the alternative then? Marine energy may possibly be the answer when thinking about the two problems of solar and wind power. Ocean is still largely untouched and its spatially availability is good. The continuity of marine energy is also attractive to utilities, who are responsible for stability in electric grid. For these reasons, I believe it is worth shedding light on marine energy on this blog.

Marine energy is not familiar to most people, and it is actually quite diverse. It can be harvested through (1) wave, (2) tide including ocean current, (3) thermal gradient, and (4) salinity gradient. Of these, power extraction using thermal and salinity gradient is structurally complicated and technically immature, and I don't expect them to be commercially viable in near future.

In contrast, the mechanism of electricity generation from wave and tidal energy is relatively simple, capturing ocean's kinetic energy by turbine (like wind) or absorber. The costs, durability to salinity and harsh climate, and transmission to land have been the major concerns to commercialization, but technological advancement has been achieved recently.
In the past few years, the costs have come down dramatically by the deployment of pre-manufactured devices instead of challenging assembling work on open water. Each device does not produce large amount of energy (around 100kW in most cases) but they are usually formed into an array like a wind farm. These devices are assembled in a factory and then towed to a desirable site, so the costs are expected to fall further as mass production begins.

OpenHydro (ocean current turbine)
(photo credit: OpenHydro)

The durability problem still persists, but a series of demonstration projects in Western Europe recently proved that when carefully choosing the materials, structural design, and mooring techniques, these devices can resist to saline erosion and storms for a long time, perhaps more than 20 years.

The transmission problem was also addressed in these demonstration projects in Europe, which showed that a single underwater cable can be shared by many generation devices at the same time. Furthermore, Ocean Power Technologies recently commercialized Underwater Substation Pod (USP), a device which converts a low-voltage electricity generated by multiple devices to a grid-quality electricity and sends it to the electric grid on land (see picture below).

Underwater Substation Pod
(photo credit: Ocean Power Technologies, Inc.)

Following the series of demonstration projects in Western Europe, several 10MW-class commercial projects become operational last year. UK, Spain, Portugal, Ireland are actively developing more commercial projects, and the US, Australia, and New Zealand are trailing them rapidly.

Asian nations, most notably Japan and China, are focused on other types of marine energy extraction techniques such as tidal barrage, oscillating water column, and thermal gradient. I believe that the environmental impacts of tidal barrage and oscillating water column on shoreline are too large, and all of these techniques are too costly and vulnerable to harsh climate.

While it is still too early to draw any conclusion, the recent success of clustered approach may enable massive deployment much sooner than previously expected. Many politicians and policy makers yet to realize the potential of marine energy, and I hope this blog post can draw a little bit more attention to the new comer.

1 comment:

  1. I attended AlChe Pacific Northwest Sustainability Conference 2 years ago, and there was a guy from PNNL that gave a talk about the feasibility of ocean renewable energy. In conclusion, there are great potential for ocean renewable energy, but there are as much uncertainties for the environmental impact on aquatic life.

    He talked about the impacts on marine life from electromagnetic waves generated by the machines, as well as the noise. I also wondered if those produce any amount of heat.

    I understand that "the ocean is still largely untouched", but because it's untouched, we have to find a sustainable way to implement.