Tidal Power: The pros and cons

A derelict dry dock on the river Tyne. The last ship left in 1976 and the site has lain abandoned ever since. A turbine placed in the dock gate aperture (middle distance) would by now have generated over 5 gigawatt hours of electricity, purely by the daily rise and fall of the tide. Despite having been flooded and emptied by every tide, twice a day, every day for 45 years, there is less than 10 cms of silt at the bottom of the dock.  

By 2025 the site is currently being developed for housing. 

  In bygone times, the United Kingdom was industrious and found solutions to problems from its own resources. For power there was bounteous amounts of coal, then there was North Sea oil (and gas, gas also from Morecambe bay). This country has overwhelming natural resources. We do use some of these, we should use a lot more. With its natural resources the UK should be an exporter of power.    

   The development of dry docks is the basis. These are nothing more than big holes in the riverside banks into which ships were manoeuvred and grounded as the tide went out. Once in position the outer gates were closed, remaining water pumped out and work could begin on the hull or propellers or the rudder. A dry dock is 200 year old technology and is almost indestructible. 

  The amount of water flowing in and out as the tide rises and falls is substantial. Allowing a space like a dry dock just to fill and empty through a turbine could generate a lot of electricity. Basically, letting a hole in the ground fill and empty as the tide comes and goes.    

  Not just dry docks. There are similar sites all around the UK; industrial settling ponds and the sites of former salt panning operations as well. Former chemical works and loading stations for ships. Substantial areas of brownfield land.        

  The pros are ease of use and economy, that there is plenty of potential land available and it is usually near centres of population. This means that the cost of transporting the electricity from the point where it is made, to the point where it is used, is negligible. The cost of decommissioning is negligible as well. The unit could just be sold to a fish farm. Operation can be arranged to carry on continuously, the only environmental energy source that can do so. All day, every day. There are other uses the turnover of cold water could be put to.  Dry docks are simple and have around a 200 year history.

  There are many gigawatts available.

  The cons are that tidal power on its own is only marginally viable unless carried out on a large scale, although this statement is made looking at buy-in prices for electricity at around £50 per MWh, and without any subsidy involved. As the buy-in price increases the viability improves. And there are "other things" we can do on these sites, valuable things, that in fact make the generation of electricity a by-product. 

  Another "con" is the well known reluctance to embrace new ideas not only in the UK but Europe - wide. There are suitable turbines but they are expensive and only work in one direction, so better ones need to be developed. We have a plan to do this. Some of the output will be modest, maybe as low as 20 - 30 megawatts, but it is continuous. There will be an issue with silt, which will build up and will need to be periodically cleared out.

  It is cheaper in the short term to simply build houses on the land. Cheapest options are almost always selected. Tidal basins are a strategic development, but a lot of the cost of construction can be recovered by the dual use applications introduced in the earlier sections,  in which the site construction costs are fully recovered by another application and, as mentioned above, the electricity produced becomes just a by-product.