Marine baseload power
Combining predictable tidal generation, geographically diverse arrays and complementary wave energy to create a smoother and more dependable renewable power supply.
Predictable renewable energy
Predictable does not mean constant
Wind and solar are essential renewable technologies, but their short-term output is strongly influenced by changing weather conditions.
Tidal energy behaves differently. The movement of the tide varies continuously, but the timing of that movement can be predicted far in advance.
At an individual location, tidal currents strengthen, reach a peak, slow towards slack water and then reverse direction. A single tidal array therefore does not generate continuously at constant power.
The opportunity becomes more significant when multiple marine-energy arrays are considered together.
Geographic tidal diversity
The tide does not peak everywhere at the same time
The dominant semi-diurnal tidal cycle around the UK repeats approximately every 12 hours and 25 minutes.
However, high water, low water and the strongest tidal conditions do not occur simultaneously around the coastline.
The tidal wave moves around Britain and is influenced by coastline geometry, water depth and local hydrodynamic conditions.
This creates significant differences in tidal phase between locations.
For a future portfolio of marine-energy arrays, these phase differences create an opportunity for generation from one location to overlap periods of lower output at another.
Source: British Oceanographic Data Centre.
Multiple-array generation
Different tidal phases can smooth combined output
A single tidal array has a predictable but varying generation profile.
If a second array is located where the tidal cycle is several hours out of phase, its strongest generating period may occur while output from the first array is reducing.
Adding further appropriately located arrays can increase the overlap between generating periods and reduce the amount of time when the combined portfolio is producing very little power.
This does not make tidal generation constant. The achievable result depends on the characteristics of each site, installed generating capacity, electrical connections and the economics of developing the selected locations.
It does mean that the location of each future array can potentially be chosen not only for the strength of its tidal resource, but also for the timing of its generation relative to other arrays.
A second tidal timescale
The strength of the tide also changes over the lunar cycle
Geographic phase diversity can help smooth the shorter tidal cycle, but tidal strength also varies over a longer period.
Around new Moon and full Moon, the gravitational effects of the Moon and Sun reinforce one another, producing spring tides with larger tidal ranges and generally stronger tidal currents.
Around the first and third quarter Moon, these effects partly oppose one another, producing neap tides with smaller tidal ranges and generally weaker currents.
The spring-to-neap-to-spring cycle takes approximately 14.8 days.
Bristol Channel example
A substantial difference between spring and neap tides
The Bristol Channel has an exceptionally large tidal range, making the spring-neap variation particularly noticeable.
At Hinkley Point, the published mean spring tidal range is approximately 10.7 metres, compared with approximately 4.8 metres during mean neap tides.
The mean spring tidal range is therefore more than twice the mean neap tidal range at this location.
Tidal-stream electrical generation cannot be calculated from tidal range alone. The important engineering parameter is local water velocity, together with the performance characteristics of the turbine.
The spring-neap cycle nevertheless illustrates an important point: even a geographically diverse tidal portfolio will experience a slower variation in the overall strength of the tidal resource.
Two natural cycles
Marine baseload must be considered at more than one timescale
The shorter tidal cycle and the longer spring-neap cycle affect generation in different ways.
Over approximately 12.4 hours, geographic phase differences between sites can be used to create overlapping generating periods.
Over approximately 14.8 days, the strength of the wider tidal resource rises towards spring tides and falls towards neap tides.
Developing a dependable marine-energy system therefore requires more than simply installing additional turbines at a single location.
It requires consideration of different sites, tidal phases, resource characteristics and electrical connections as part of one generating portfolio.
Complementary marine resources
Wave energy adds another source of generation diversity
Pliosaur Energy's floating platform is designed to generate electricity from tidal streams, ocean waves, or both resources together.
Wave energy is driven primarily by weather systems rather than the astronomical forces responsible for the tides.
Wave conditions should not be assumed to be strongest when tidal generation is weakest, and wave energy remains weather-dependent.
However, because tidal and wave resources are governed by different physical processes, combining them introduces another form of resource diversity.
At suitable locations, this creates the possibility of capturing predictable tidal energy alongside additional renewable electricity from waves through the same marine platform.
What we mean by marine baseload
A system-level objective
Marine baseload does not mean that every turbine or every individual tidal array generates continuously at constant power.
For Pliosaur Energy, marine baseload describes the long-term objective of combining predictable tidal generation, geographically phase-diverse arrays, complementary wave energy and appropriate grid connections.
The objective is to create a smoother and more dependable renewable power profile than any single marine-energy site could provide alone.
Portfolio development
Site selection becomes part of the generating strategy
The strongest tidal current is not necessarily the only consideration when selecting the next marine-energy site.
As the number of arrays grows, each potential location can also be assessed according to the contribution it makes to the wider generating portfolio.
Important considerations include tidal-current strength, tidal phase, spring-neap characteristics, wave resource, grid capacity, electrical demand, environmental constraints, navigation, installation, maintenance access and project economics.
This creates the potential to optimise not only how much electricity each array produces, but also when that electricity becomes available to the power system.
A broader renewable mix
Marine energy can complement wind and solar
Wind and solar will remain central to the transition towards renewable electricity.
The opportunity for marine energy is not necessarily to replace these technologies, but to complement them with a renewable resource that behaves differently.
Predictable tidal generation can add electricity whose timing is known well in advance. Geographic phase diversity can smooth the shorter tidal cycle, while wave energy can provide an additional marine resource with a different generation pattern.
Together, these characteristics could allow marine energy to make an increasingly dependable contribution to a renewable-led electricity system.
Technical note
Illustrating the principle, not forecasting output
The tidal-phase chart on this page uses historic tide-height data to demonstrate geographic differences in tidal timing.
Tide height is not the same as turbine electrical output. Project-specific current measurements, hydrodynamic modelling, turbine performance data, array configuration and electrical constraints would all be required to forecast generation from a particular site.
The generation illustrations are therefore intended to explain the physical principles behind the marine-baseload concept and should not be interpreted as forecasts of future Pliosaur Energy generation.