A G Gelbert posted "Even Charles Hall (no defender of renewable energy), the creator of the EROEI (ENERGY RETURN ON ENERGY INVESTED) formula stated in his SUNY study that wind turbines have an EROEI of 18:1 at 1.5 MW and the return increases as the turbine size increases (they are now up to 7.5 MW)."
I was talking about Money return on money invested not EROEI which is a different thing altogether!
He also posted "And photovoltaic has an even higher EROEI. To put that in context both coal and gasoline have a lower EROEI without the fossil fuel subsidies."
He wrote "Undersea current has, unlike your wrong assumption, huge potential because it is close to large cities (smaller transmission line losses) and is available 24/7. "
Undersea current stops and reverses every 6.21 hours or so can hardly be considered a 24/7 resource. Real time tidal stream generators discard around 7/8ths of the resource and may convert about 30% of the remaining 1/8th into pretty worthless pulses of intermittent electricity with little or no monetary value without massive subsidies from gullible politicians who want to be seen to be green!
"So if you want to talk about government hand outs, look at fossil fuels for massive amounts of swag taken by the government and given to fossil fuel polluters."
That old trick of diverting blame somewhere else - without subsidies there would be no ROI at all in renewables because of the low outputs and low wholesale turnover.
The Gulf Stream is continuous but how do you get a cable 100s of miles all the way out there to tap into it?
I am no lover of fossil fuels which is why I have invented Gentec venturi, a tidal stream system that generates 10 times more firm electricity 24-7-365; and a mobile wave energy system, Gentec WaTS that will generate 2400 times more electricity 24-7-365 than a fixed near shore WEC.
Now it maybe that you think that just breaking even for an investor is brilliant but 10 and 2400 times more electricity respectively from tidal streams and deep ocean pelagic wavepower with very low CAPEX and medium OPEX will make investors £billions.
Why, you may ask, are these devices not in the water already - it is because I am prepared to wait until the gullible realise that solar does not work at night, and wind turbines do not generate when there is no wind and TSGs do not generate in real time at slack water.
One day ALL the world's electricity will be generated thermally from renewable heat using my system or a very close relative with the vital by-product of desalinated water. Fossil fuels such as coal and gas may run out as early as 2030 - then what?
I do not like the 'trend' to call electricity "energy" because it leads to confusion. Storing electricity once you have made it is one of the most expensive things to do. I was told this when I was an apprentice electrical engineer over 40 years ago - it was true then and it is true now.
Storing energy in the form of heat BEFORE you convert it into electricity is cheap and solves the intermittency problem with renewables. (PS you also get a lot more firm electricity and desalinated water as well)
There is nothing confusing or difficult about storing energy in the form of heat. Kinetic energy contained in 'cold' renewables such as wind, waves and tidal streams is easily converted directly into heat using a 'friction boiler'. For example, tidal stream generators convert just 3.8% of the total resource into intermittent pulses of electricity by electromechanical means which is pretty mundane 'engineering' - here I am using the word loosely. These geniuses discard more than 7/8ths of the resource and convert just 30% of the remaining 1/8th into pretty worthless electricity.
Simply converting 60% of the total resource into heat in the first instance gives you 15 TIMES more energy in the form of heat before storing in in insulated thermal accumulators. This allows you to convert it back into ~ 10 times more electricity as and when it is required even at slack water (as opposed to when the tide is running at +2m/s) using proven thermodynamics.
Thermal electricity accounts for almost all of the world's firm electricity (>90%) so it is pretty obvious to use renewable heat that is created from these cold renewables without burning fossil fuels and trees or anything at all
There is a mindset here; fossil fuel thermal stations have to pay hard cash for their fuel so thermal accumulators are a no-no in this context. Now, if you are putting (renewable) heat in to a store 20 times faster than it is escaping then there is no problem because you are not paying hard cash out.
Forcing liquid through a restriction will create heat in direct proportion - try touching a hydraulic ram casing after it has been used for a while - but be very careful not to burn yourself.
Re thermal efficiency, you can generate electricity not very efficiently with a dT of ~20C see OPEC for details - there is no need to go for a superheated 'sweet spot' as you put it - the raw heat is FREE at the point of capture - your points are, therefore, moot
There can be no medium future in intermittent marine energy converters, Wave and tidal have such low energy densities that it will never be economical to develop as investors are unlikely to see any return on investments. At present tidal stream generators convert just ~4% of the tidal resource into varying lengths of pulses of electricity depending on the Springs - Neaps' cycle.
Near shore wave energy converter fair worse with waves too small and waves to big; no wave machine has ever lasted two winters anywhere.
These marine activities have already been tried and tested in the UK and elsewhere and has been an expensive failed experiment. Generating electricity in 'real time' from tides and waves produces next to no useful consumable electricity. Only 5% of the total tidal kinetic energy is converted into electricity in small pulses between tides and wave power outputs hardly register on the same scale.
Yes, I realise that we all need renewables to work and so save the planet for our children but we are burning more and more coal, gas (natural and shale) and oil like there is no tomorrow and the best that mankind can deliver is intermittent pulses of electricity at all the wrong times!
Are you saying that tidal and wave power is going to save the planet by supplying intermittent pulses of electricity?
There is essentially two distict types of electricity; firm capacity (to supply on demand) and unfirm capacity (to supply subject to the vagaries of tide and weather)that requires constant fossil and or nuclear backup. Do you recognise the difference between the two types?
<5% of a resource into unfirm capacity will do more harm than good to our precious planet on which we all depend on for survival.
Philip, heat makes the world go round. Thermal energy from the Sun evaporates seawater, which create thermals, which create differences in air pressure, which creates wind, which creates waves etc etc.
Now CO2 in the atmosphere allows too much evaporation and creates stormier weather but also raises the planet's normal operating temperature above acceptable standards.
Renewable heat is the key to saving Earth from overheating. Renewable heat created directly from the kinetic and potential energies in marine renewable sources can be easily stored for thermal conversion into electricity later.
I notice that nobody has addressed the 'intermittency problem'. The irony is, of course, that these marine turbines are in the main asynchronous or induction type generators. These machines all induce pure synchronous electricity on to their windings; adding in some shaft power from wind, wave and tidal turbines and we get dribs and drabs of 'amplified electricity' out. These operate in the same way as audio amplifiers 'rubbish signal in; rubbish signal out'. No utility grid can handle any more than 10% of the dynamic generation portfolio at an given moment because the more rubbish electricity being induced is amplified and fed back onto the grid. This round robin feedback results in grid collapse.
In the UK we already have 'constraints payments' for not generating electricity to keep below the 10 to 100% ratio. The story for the gullible is somewhat different!
All talk of dodgy intermittent electricity from renewables accounting for any more than 10% of all electricity production is just pie in the sky!
Gary, The biggest problem with tidal streams is the lack of 'energy density' of the resource before you extract the energy from it. It works out at just 6kW(mech) per vertical square metre in a 6m/sec maximum tidal stream regime. By the time that you convert that into electricity you would be doing well to get > 1kW(e)/m^2. This figure discounts the area of the seabed required to provide the necessary separation; including this we would need to divide the numbers above by ~ 25! The wave energy resource in a fixed location near shore due to cabling considerations works out at 8kW/linear metre of wave front and you might get to convert a quarter of that into unfirm electricity. However, if you are prepared to travel to where the best and biggest waves are in the prospect area as outlined in my invention, then the wave energy resource jumps to a massive 1200kW/linear metre of the mobile beach. With that resource available to convert into heat and back into generator shaft power it is easy to see that real time generation by these 'cutting edge' devices is going to end in tears.