cation (3 W/m2). The steady power of the lagoon system would be more
valuable than the intermittent and less-flexible power from the ordinary

A two-basin system could also function as a pumped-storage facility.


page no.

311Efficiency of 90%... Turbines are about 90% efficient for heads of 3.7 m or
more. Baker et al. (2006).

320Getting “always-on” tidal power by using two basins. There is a two-basin
tidal power plant at Haishan, Maoyan Island, China. A single generator
located between the two basins, as shown in figure G.12(a), delivers power
continuously, and generates 39 kW on average. [2bqapk].

Further reading: Shaw and Watson (2003b); Blunden and Bahaj (2007); Charlier
For further reading on bottom friction and variation of flow with depth, see
Sleath (1984).
For more on the estimation of the UK tidal resource, see MacKay (2007b).
For more on tidal lagoons, see MacKay (2007a).

Figure G.12. Different ways to use the tidal pumping trick. Two lagoons are located at sea-level. (a) One simple way of using two lagoons is to label one the high pool and the other the low pool; when the surrounding sea level is near to high tide, let water into the high pool, or actively pump it in (using electricity from other sources); and similarly, when the sea level is near to low tide, empty the low pool, either passively or by active pumping; then whenever power is sufficiently valuable, generate power on demand by letting water from the high pool to the low pool. (b) Another arrangement that might deliver more power per unit area has no flow of water between the two lagoons. While one lagoon is being pumped full or pumped empty, the other lagoon can deliver steady, demand-following power to the grid. Pumping may be powered by bursty sources such as wind, by spare power from the grid (say, nuclear power stations), or by the other half of the facility, using one lagoon’s power to pump the other lagoon up or down.