Power from the Moon?

We’ve talked previously about how tidal energy could be a great solution for the New Zealand Electricity Sector of 2050. The idea of effectively using the moon to power our homes is very attractive. Tidal energy is very similar to wind energy but instead of air you have tide driven water rotating the turbines – although there are some more  novel designs than you would see on land .

The history of tidal energy in New Zealand is a little rocky. A few key sites have been floated: Te Aumiti / French Pass, Cook Strait and perhaps the most ambitious, Kaipara Harbour. The Kaipara Harbour plans were granted resource consent in 2008 for 100 turbines, later increased to 200 turbines in 2011. There is massive potential with two billion cubic metres of water passing through the entrance channel at 10 km/hr per tidal movement. These 200 turbines were expected to produce around 200 MW which would have put the station in the top ten of New Zealand’s biggest power producers. However, like all other major tidal projects in New Zealand to date, no construction has taken place.

Elsewhere in the world, tidal energy is picking up steam. The biggest installation worldwide is in South Korea where the Sihwa Lake based facility has a 254 MW capacity. Interestingly it’s only a one-way turbine due to the complex nature of the water systems. Scotland is also taking on the mantle with the Pentland Firth having been described as the “Saudi Arabia of Tidal Power” with the potential for over 1.8 GW of power (although the Cook Strait is purported to have 12 GW of potential which would dwarf this). Work in the Firth is underway for the world’s biggest tidal project with plans to have 400 MW capacity by the time of completion, currently 6 MW is already operational.

The attractiveness of tidal power is already clear but there are significant environmental and engineering challenges that must be addressed for it to be cost effective. Unsurprisingly one of the key aspects are the materials used. A high salt environment combined with the force of the water (given it’s around 1000x more dense than air) can cause significant mechanical design issues. Environmentally the impact on marine life also requires consideration.  This includes the obvious risks of animals colliding with the turbines, but also less obvious potential issues such as electromagnetic radiation from the turbines interfering with the in-built navigation systems of certain sea creatures.

The Ministry for the Environment has investigated why there has been minimal implementation of tidal energy projects in New Zealand. A few options are discussed but the main cause appears to be a lack of incentive for many investors, with low growth in electricity demand in recent years and uncertainty around the future of the Tiwai Point Aluminium Smelter. However, with the shift to decarbonisation and the expected impact this will have on electricity demand (as discussed in a recent report by Transpower), perhaps New Zealand’s age of tidal energy will soon arrive.