[thedoc (OP)]

We need to increase performance of wind and wave powered systems to better harness the potential of these free, clean sources of energy.
Read a transcript of the interview by clicking here

or [chapter podcast=1000866 track=14.10.07/Naked_Scientists_Show_14.10.07_1002799.mp3] Listen to it now[/chapter] or [download as MP3]

[thedoc (OP)]

Read this interview by clicking here [chapter podcast=1000866 track=14.10.07/Naked_Scientists_Show_14.10.07_1002799.mp3] or Listen to it now[/chapter] or [download as MP3]

[evan_au]

A video on development of the "Salter Duck" (8 minutes):

They claim it could absorb 80% of the energy in a wave.

One problem with wave power is that there is an enormous amount of energy in the waves from a big storm, which is likely to tear apart the wave-power collection device.

[alancalverd]

The problem with all these technologies is

1. The source is unreliable: it produces power when it wants to, not when you need it

2. The product is electricity, which only accounts for a fraction of our energy needs

3. Adding an unreliable source to a grid, destabilises it and reduces the economic and physical efficiency of the reliable sources

4. The lifetime cost per unit energy is absurd

5. The environmental impact is unpredictable

6. The total available power is negligible

7. The mean power is about 5 - 10% of the installed capacity, so the capital investment is uneconomic

8. Maintenance costs "climb the bathtub" very rapidly

One could go on, but as long as the public can be conned into subsidising these absurdities, people will make money out of them, so politicians will raise taxes to pay for them.

[evan_au]

One method touted to deal with unreliable generation is variable consumption (or "Demand-Side Management", in the jargon).

Given that:

• almost every electronic appliance today contains at least one computer,
  
• within a decade, most new appliances will be networked (the "Internet of Things")
  
• Then that opens up a lot of opportunities to save power by switching to an energy-saving mode when generation capacity is marginal (some devices or organisations may even be able to switch to an energy-producing mode). 

[chiralSPO]

I think judicious use of a combination of flywheels, capacitors and rechargeable batteries or fuel cells can even out any variability in power generation on the scale of seconds, minutes and months (respectively).

Can it be done economically? Not with existing technology, but I think we will see major shifts in the next decade or so. Also, wide adoption will also be able to take advantage of the economies of scale, increasing the "bang per buck."

[alancalverd]

Last month (a warm September)  there was no wind above 5 knots over England for more than 10 days. As wind turbines produce power accordiing to a v³ law, this means that if , say, 20% of grid power was generated by wind, we would need a storage capacity of about 500 kWh per capita to maintain our present standard of living under perfectly normal circumstances. That's 500 car batteries per person, assuming 100% efficiency. You would need to double that to cope with average winter conditions, and at least double it again to cope with peak demand, like cooking breakfast.

So if you are an average family you will need to find space for 8000 car batteries just to cover the 20% of your electricity that comes from wind. At £40 each, that more than doubles the cost of your house. And the batteries will need replacing every 5 years or so.   

[nicephotog]

The problem is private enterprise reselling, Wind power is more a problem of equipment reliability than cost for a DIY consumer, true it is expensive but it is quite possible with only mild care at choosing modern household appliances to be able to live the same life as grid electricity with 8Kw hybrid kit.
In Australia the electrical utilities are privatised government sector that own or lease back the generators and power stations e.t.c. BUT, it does not mean that if you are more than 80 meters away from a neighbour that an OFF GRID 8Kw power system cannot supply everything required for 1:1 against grid electricity!
Another great feature of off grid is a small 2500w 12v blackout power system, that also serves as a computer network attack protection by not being connected to grid power.
NOTE: To truly understand "wind charge controllers" and "generation efficiency / time unit" most wind turbine generating always occurs in the lower 10% trickle of the wind turbine wind speed rating(You are so right if you know wind turbine ratings that the wind does not always reach that speed [usual rating size is  10m/s to 12m/s]).
http://www.windsolarhybridaustralia.x10.mx

alancalverd: So if you are an average family you will need to find space for 8000 car batteries just to cover the 20% of your electricity that comes from wind. At £40 each, that more than doubles the cost of your house. And the batteries will need replacing every 5 years or so.

I rest my case! Not to be demeaning in front of you, and not 8000 automotive starter type, but, "deep cycles" anything from "16"x 80Kg 250ah to "80"x 25Kg 80ah for 10 to 12 years use, if you read the article windsolarhybridaustralia.x10.mx they do not use "car batteries" they use either special "2v (two volt) deep cycle batteries e.g. 230Kg 3000ah" or standard "12v deep cycle" and you would need quite a few things but there is much more to know about deep cycle batteries such as lead acid , GEL , silicon, (Lithium deep cycle(*deep cycle - synonym for "industrial") is way too expensive). While "float charge" is 30% in a lead acid type, for off grid you are trying to get an average days complete use on 10% - 15% "battery bank" discharge(down to 90% full - called D.O.D. Depth Of Discharge). Other requirements , not to be UPS batteries, able to last chemically for 10 years at or above 20 degrees Celsius on float.

chiralSPO: Can it be done economically?

They are cost efficient by self import at this very time - pending exchange rate(be your own customs broker - broke the deal and fill out the form yourself all DIY).
In import deals, the more you buy(batteries(correct name "accumulator"), pv panels e.t.c.) the cheaper it gets but costs do "add up" so use your calculator from start to finish.
You need a 3 tonne hydraulic tail gate van and palette jack trolley to pick up from customs warehouse.

[alancalverd]

If I read your figures correctly, a 230 kg 2volt deep cycle unit will give you 3000 Ah. That is 6 kWh, so you need 24 of these to supply 20% of one person's energy needs  for 5 days. Add in the controller and connectors, and we are talking about 40 tonnes of battery pack per household. Most believable price today is about $500 per cell, so $50k or so per household for the batteries alone. And then there's the small problem of dealing with 4 tonnes of scrap lead and a few gallons of sulfuric acid every year. 

Compared with an oil tank (20,000 kWh, 2 tonnes) at $5000, it's a nonstarter.

[chiralSPO]

Car batteries are not the solution, for many obvious reasons, as Alan has laid out quite well. However, power to gas conversion might have a chance. Electrolysis of one liter of water will produce 4.5 kWh worth of hydrogen, so only about 120 L of water would be required to store that 500 kWh value put forth earlier. Of course the hydrogen takes up space too--at atmospheric pressure, 500 kWh worth of hydrogen gas would require 141 m³, or a sphere of radius of 3 meters. This is unreasonable to have in a house or apartment, but if large wind or solar farms had a substation to store and dole out energy, it would make sense to produce and store highly compressed or even liquified hydrogen (or methane).

A small town could have a substantial fraction of their energy needs backed up with a single water tower, a couple MW-scale electrolyzers, a compressor/liquifier and a liquid hydrogen tower capable of holding a few hundred m³ of liquified hydrogen. None of this is cheap, but it is all durable (MW electrolyzers require some annual maintanence, but can last well over 40 years).

Changing our energy infrastructure will be incredibly expensive and slow, but consider the amount invested in building up the oil and coal industry. The infrastructure and manpower required for prospecting, extraction, processing, transportation, distribution and use of fossil fuels isn't exactly cheap either. And we are not even considering the cost of environmental damage (direct and indirect).

[alancalverd]

The hydrogen economy can be set up at very low cost as we already have the necessary distribution network for most stationary purposes. Centralised storage isn't a problem: oldfashioned gasholders worked at low pressures, modern LPG farms can handle several atmospheres' compression, and the bigger the storage vessel, the more economical it is to fill it with liquid hydrogen.

You can burn hydrogen in a conventional gasfired power station any time you need electricity. Indeed the maintenance costs of a hydrogen furnace are much lower than for fossil fuels or even methane.

The only real difficulty is using it for transport as the losses from small liquid hydrogen tanks are significant and the specific energy of the gas is too low for aviation, though adequate for urban transport. .

[chiralSPO]

The hydrogen economy can be set up at very low cost as we already have the necessary distribution network for most stationary purposes. Centralised storage isn't a problem: oldfashioned gasholders worked at low pressures, modern LPG farms can handle several atmospheres' compression, and the bigger the storage vessel, the more economical it is to fill it with liquid hydrogen.

You can burn hydrogen in a conventional gasfired power station any time you need electricity. Indeed the maintenance costs of a hydrogen furnace are much lower than for fossil fuels or even methane.

The only real difficulty is using it for transport as the losses from small liquid hydrogen tanks are significant and the specific energy of the gas is too low for aviation, though adequate for urban transport. .

Agreed. So if we had a 100 MW wind or solar (or wave) farm producing hydrogen, and feeding that to a hydrogen-burning power station, would that not solve the problem of intermittency? (provided that one could store enough of the hydrogen to smooth out the seasonal variation in energy capture and demand).

[allan marsh]

Read energy or extinction by Fred Hoyle from the 1970's its a great small book.
See the power if a mile of sea  compared to the windmills.

It's a great starting point

[evan_au]

no wind above 5 knots over England

That's why several High-Voltage DC cable connections between France, Norway and Germany (and into Spain and North Africa) are recommended for efficient use of renewable sources (as well as efficient use of non-renewables).

When it is blowing a gale in the North Sea, the Spanish can turn their coal-fired generators back to "idle".

[alancalverd]

Agreed. So if we had a 100 MW wind or solar (or wave) farm producing hydrogen, and feeding that to a hydrogen-burning power station, would that not solve the problem of intermittency? (provided that one could store enough of the hydrogen to smooth out the seasonal variation in energy capture and demand).

Yes but. The problem with a 100 MW wind farm is that it only produces, on average, 5 - 10 MW. Now we lose 60% of that when we convert the hydrogen back to electricity (40% thermal efficiency is pretty good for a small station) so we have installed 110 MW of generating capacity to yield 6 MW overall - just enough to run one locomotive (Eurostar uses 12 MW).

Still it's better than wave power, which has been in development now for 40 years and produced no energy at all.   

[alancalverd]

When it is blowing a gale in the North Sea, the Spanish can turn their coal-fired generators back to "idle".

Alas, no. Wind turbines are generally shut down when the predicted wind speed exceeds 35 - 40 kt. They are usually rated at a steady speed of about 30kt but can be damaged if they are hit by a gust, so they don't work in bad weather. Or in good weather.   

[peppercorn]

Real world capacity factors
UK Wind average (2007-2012): 27.5%

"...best capacity factor of any offshore wind farm - 46.7%, having produced 1,278 GWh over 1.5 years".

I think making ammonia efficiently could be an alternative (better) use of excess electricity from intermittent renewables, instead of producing hydrogen.

[alancalverd]

The problem with capacity factors is that they are arbitrary. If I put a 100 kW blade on a 150 kW alternator (which makes sense, because blades are a lot more expensive than alternators, and you certainly don't want to do it the other way round!) I can put a 50 kW rating plate on it and claim 20% capacity factor even though it only produces 10 kW.   

[chiralSPO]

Real world capacity factors
UK Wind average (2007-2012): 27.5%
I think making ammonia efficiently could be an alternative (better) use of excess electricity from intermittent renewables, instead of producing hydrogen.

Interesting. Are you thinking of creating ammonia for use as a fuel/energy storage medium, or as a useful product to make when there is excess electrical energy available, and then finding some other source of energy when there is a deficit?

I know of a company that pays industrial electro-refineries to up- and down-shift their electricity demand as the grid energy balance fluctuates--they never sell any electricity back to the grid, but because the operation is so energy intensive, and would otherwise be going 24/7, a reduction is consumption is equivalent to increasing the available energy for the grid.

[peppercorn]

The problem with capacity factors is that they are arbitrary. If I put a 100 kW blade on a 150 kW alternator I can put a 50 kW rating plate on it and claim 20% capacity factor even though it only produces 10 kW.

I am unclear, following your logic, how you get a nameplate rating would be 50kW in your example. It could conceivably be 100kW, based on the size of the generator installed.

And I would question why such a turbine would use a 50% larger generator anyway. Any increasing in size and weight of electrical machinery in a nacelle, a couple of hundred metres in air must also scale up everything else up as well (tower rigidity etc); there will an additional increase in maintenance costs and, off-shore, this is obviously a serious overhead - thus, a generator, say, 10-15% larger than the blade's continuous rating seems somewhat more realistic.