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Optimization Chapter | 9 257

FIG. 9.13 Influence of level of development of the UK tidal stream resource on variability. (Data
from G. Sinden, Variability of UK Marine Resources, The Carbon Trust, London, 2005.)

multiple sites led to a reduction in phase diversity. A summary of the findings
of Neill et al. [30] is presented in Fig. 9.14. Because the high-energy tidal
stream sites are generally in phase with one another, there is high variability in
the resulting (aggregated) power—in agreement with previous studies [27,28].
In contrast, there is considerably more phase diversity amongst less energetic
sites. Therefore, an energy policy that seeks to minimize variability in the
developed tidal stream resource would be advised to include lower-energy sites
in the energy mix. Optimization, in this case the greedy algorithm with penalty
function, led to a proposed road map for the evolution of a UK tidal stream
industry (Fig. 9.15), with the key assumption that the Pentland Firth is the first
region to host an array—an assumption that has now been proven to be valid
with development of the MeyGen array. It is noted, in common with the Carbon
Trust report [27], that at very high levels of tidal stream development, limitations
on sea space would lead to an aggregated electricity signal that is dominated by
relatively few high tidal stream locations, with a particular focus on the Pentland
Firth. Incidentally, none of these studies included feedback between energy
extraction and the resource—a topic that is covered in Chapter 10. In reality,
at such large scales of exploitation, these feedback effects would be significant,
and so there is a gap in knowledge of how best to optimize at interarray scale.

9.3.2 Phasing of Multiple Tidal Range Power Plants
Few studies have considered multiple lagoon operation, never mind multiple la-
goon optimization. However, Yates et al. [31] considered (including feedbacks)
the operation of five tidal barrages in the Irish Sea, all operating in ebb-only
mode. The results show that all of the proposed tidal barrages in the northern
part of the Irish Sea (Dee, Morecambe, Solway, Mersey) are in phase with one