The Mark 2010

As renewable power sources become more and more important, we need to consider the full costs associated with them.

Renewable energy is a hot topic these days. But not all forms are equally viable. Solar power is only cost-effective in dry sunny places with climates that are not highly seasonal. Power generated by tides, waves, and ocean thermal energy (the temperature difference between warm surface water and cold deep water) is impossible away from coasts, and only windy places can produce wind power.

In Canada, there is an abundance of hydroelectric power. There is also a great potential for tidal power generation. However, all costs need to be tallied when considering these forms of energy.

For example, hydroelectric power is often costed without considering the full price of maintenance, especially considering such long-term factors as reservoirs silting in.

There are also many indirect costs. The evaporative loss of water reducing downriver flows and changes in the seasonal pattern of those flows can also have severe impacts on fish and human water use. The dams themselves impact migratory fish such as salmon, and remedies such as fish ladders are often better at impressing the public than they are at allowing fish to complete their life cycles.

Since much of Canada's hydro power potential is on Precambrian Shield, many of these costs are lower – for example there is less silting in of reservoirs. But in some places, the building of dams for power generation has been much less cost-effective than expected.

In 1976 Manitoba Hydro diverted the greater portion of the Churchill River flows into the Nelson River which flows into Hudson Bay. The sprawling shallow dead-tree-filled reservoir of an expanded Southern Indian Lake was formed, and became more eutrophic and variable in water level due to seasonal patterns of holding backwater and releasing it.

The result was that shallow water biota, e.g. eggs and young of species that breed in the shallows during the fall, were killed. The native community of Southern Indian Lake, approximately 700 people dependent on the whitefish fishery, was severely impacted. There was a general collapse of the fishery over the period from 1976 to 1981.

The downriver Churchill River water flow has been changed because the dam holds back water at high flow times and releases it during normal low flow times. The flow down the Nelson River has correspondingly increased. Mercury was released in the newly flooded reservoir and Hg concentrations in the fish tripled and remained high for three decades after impoundment. This is not an isolated example. Many of the same impacts resulted from the James Bay Project in northern Quebec.

On a larger scale, the increased numbers of dams augments water loss through evaporation and decreases water flow in the outlet river. It is thought that the St. Lawrence River's flow has decreased significantly over the last century because of dam-building throughout the St. Lawrence drainage area.

Tidal power generation may also have high costs. Dams across tidal estuaries are called “barrages.” Because there is a cycle of water flowing in and out, and because estuaries are typically much wider than rivers, barrages are expensive to build and have great environmental impact. Turbines on the seabed are the latest technology. The power of tides is being harnessed around the world, but none with the potential of projects underway at the Bay of Fundy.

Twice a day, 14 billion tons of seawater – roughly the equivalent of the combined flow of every river on earth – pours up the Bay of Fundy to Minas Basin and back out again. The land adjacent to it and underneath it sags slightly under the weight. Tapping Fundy tidal power has been discussed for a long time. In 1984, Nova Scotia Power (NSP) began a small tidal power project at Annapolis Royal NS which is still running, producing about 20 megawatts every day.

In 2007, NSP paired up with the Irish company OpenHydro to plan a new pilot project involving large turbines mounted to the floor of the seabed in the Minas Passage. The results from an environmental assessment were released in 2008, concluding that the project should proceed but must include ongoing monitoring. This project will hopefully be in operation by 2010, and two other technology providers also hope to have tidal power generators of different designs in operation the same year. All three have design features that are supposed to protect fish, marine mammals, and other marine life.

Everyone wants to see how these new power-generating turbines will withstand the scouring currents which are not just sea water but also suspended sediments and ice in the winter. Installing and maintaining the turbines will be a major challenge.

The costs will determine whether Fundy tidal power is a cost-effective proposition. We already know that power can be produced from Bay of Fundy tides. But can it be competitive with other sources of power? Perhaps it will be when fossil fuels start running out. If so, it is probably a good thing that we will have some time to further improve tidal power technology.

The long-term environmental concerns are mostly to do with the consequences of removing tidal energy from the Bay of Fundy, but this will only be a real concern when the deployment of underwater turbines greatly exceeds this pilot project stage.

When it reaches commercial production scales, the tidal currents could be slowed considerably. This may be difficult to imagine, but the “reversing falls” near the Bay of Fundy end of the Saint John River have noticeably lost energy over recent decades because of the river's increased silt load sapping the tidal energy.

The Bay of Fundy ecosystem, supporting life from diatoms to the fishery to whales, as well as various human activities, has evolved for centuries with existing tidal patterns. The key question is how much tidal power can be generated without impacting that ecosystem.