Scotrenewables update

A tweet from Scotrenewables claims 20MW output over 24 hours.  With a 2MW device, that equates to a capacity factor of 20/(24*2) = 41.7% over the period.

The period was September 21/22, when the moon was new and tides were therefore at their springiest - especially as it's around the autumn equinox, when springs are at their springiest.

But either way, a capacity factor of better than 40% is comparable with offshore wind.

Tidal devices - performance review

Following the Scottish Renewables Marine Energy conference in Inverness, a couple of interesting performance metrics emerged.

Atlantis recently announced that the MeyGen project had generated 700 MWhr during August, apparently from 2 AndritzHydroHammerfest (AHH) turbines.  We thought it might be interesting to extract an average capacity factor from these figures.

2 turbines at 1.5 MW - 3 MW installed capacity.

Number of hours in August: 31 * 24 = 744

Total potential output = 744 hours * 3 MW = 2.232 GWhr

Actual output: 700 MWhr

Capacity factor: 0.7/2.232 = 31.4%

This may be a slight over-estimate, as the third AHH turbine may have made a minor contribution late in the month following its re-installation, but even with that proviso, these are not bad figures for a full month (i.e. neaps and springs).

ScotRenewables made a similar claim - that its 2.0 MW SR2000 had generated 116 MWh over week.  This equates to a capacity factor of 116/(24*2*7) = 34.5%, and we understand that this period was intermediate between spring and neap tide.

As runtimes extend and reliability improves, we hope to see these numbers go up too.

Revisiting the Marine Current Turbines capacity factor

Some while ago, in this blog post we calculated an apparent capacity factor for Marine Current Turbine's SeaGen in Strangford Narrows of 38%.

We've been rooting around in OFGEM's ROC database to see if there's further information available on SeaGen's performance.

Looking at the ROC register, which reports the number of MWh generated for ROC-accredited projects, it seems that the SeaGen achieved monthly average capacity factors of up to 58% in its best years.

This analysis is based on SeaGen having a capacity of 1.2 MW and is consistent with another blog analysis we did of the capacity factor of the technology.



This analysis begs some other questions though - what went wrong in 2011?  and has the technology been abandoned since 2014? It also seems that the capacity factor was pretty variable, pointing to a lack of reliability - fair enough in a prototype technology.

We'll be using this approach  to look at other technologies too, in the upcoming Redfield review of tidal technologies and its companion volume - Redfield review of wave technologies.  Contact us for details: info(at)redfieldconsulting.co.uk

Hours on the clock

Marine Current Turbines have now racked up 1000 hours of export to the National Grid, as reported here.

MCT claims an average capacity factor of 66% for the period of operation. We have calculated a capacity factor, based on ROC register figures, which shows a steady(ish) increase to around 25% in November 2009. This calculated CF does not make any allowance for downtime, availability of marine mammal onservers, or (crucially for MCT) the limitations imposed by daylight-only working.

Since daylight in November is less than 50% of the time, and the trend is upwards, we can see that a claimed 66% capacity factor in December could be realistic.

If true, it's excellent news for the company and the technology, as it's always all about cost per MWhr, and more MWhrs means a better metric.