Thank you.

David

It is worth noting that in Australia peak demand is on summer afternoons, when wind is more reliable. Many of the low wind events are in evening and early mornings. You can see from Figure 5, between 8am and 8pm, 80% of the time >27% capacity and 90% of time >18% capacity(ie 47% of expected power). Although they don’t give a breakout(figure 10) of low wind events in daytime, low wind events(<5% capacity) average 2hours and <20% capacity only 5hours.
Based on this( ignoring reduced variability with TAS and WA included,) we would not need to store more than 6hours power to make up the difference between 20% and 38% capacity( ie less than half) or to store 90% of power for 2-3 hours.

Because solar delivers at peak demand, and less low wind events are in the day we are really talking about storing a small amount of power for unexpected low wind off-peak periods(no solar) and a defined 4-6 hour peak period.
Most hydro dams in Australia run at 40% capacity, for months without rain, delivering 8.5GW peak power for 6 hours/day. If the existing dam capacity was increased 6fold, they would be able to provide for all of those 2-6hour low wind events even without any solar energy. Adding just 3 hours storage to below dam rivers would enable half of that to be recovered and pumped back over the next few days. Some locations can recover all of the water because they have a lower dam.
Solar energy storage is only needed to use turbines and transmission lines more efficiently, but would allow solar to exactly match daily peak demand by shifting the solar peak by 3hours.

The storage of (intermittent) renewables is obviously a very important issue in the debate going on around us and you reiterate your solutions to the problem in reply to Ted Trainer’s comments. The thoughts below are how I clarified the issue for myself. You will doubtless have to reiterate your ideas again and again in the future and may want slightly different ways of explaining the same problem. I doubt whether there is any new knowledge for you below.

You distinguish between within day variability, within season variability and short term variability due to e.g. large scale weather systems. Of these the latter is the least predictable but its effects are mitigated if the area from which the renewable is being sourced is large. Additionally there is also for us in Australia El Nino type variability.

CSP smoothed through steam storage seems well suited to short period (within day) predictable variations. The predictable between seasons variability is simply a problem in the appropriate mix of winter and summer efficient sources.

The relatively unpredictable short term (weather system) variability is probably best solved as you say with pumped hydro storage. If that is so then you need storage for a week or fortnight. This has implications for how small your lower storage dam could be before you lose significant water from the upper dam. I guess that if you have sequential large dams on the same water course as in the Snowy and Tasmanian systems you have this form of variability covered.

I don’t know how you handle El Nino variability. I guess the problems it causes for hydro is offset by the extra sunshine. The ultimate lower storage dam is the ocean – but I do not know whether there are appropriate storage sites in Australia which could be used in this way. I guess that turning a favourite recreational site from a freshwater to a saline environment might not go down too well.

Your article and the associated discussion at the Oil Drum were a tonic. Just the sheer quantity and quality of thought that the American conversation can stimulate is impressive.

Kind regards,

David Murray

I have addressed these comments on Ted Trainer’s comments to you. I think the electrified transport and battery issues are central to the carbon free economy.

Ted writes:

(a) “Neil says I have not dealt with the use of car batteries. I have had a look at this and see it as problematic because of the need to have the battery full again when the user wants to use the car. Lithium is not abundant if we are thinking about 9 billion.” and
(b) “I don’t think that he [David Mackay] deals adequately with the fact that almost all renewables only electrify, which is only 50+ (sic, ? %) even if you electrify all transport.”

Electric motor cars and transport (or some other alternative to fossil fuels) in one form or another is a critical part of our future. The need to have a car fully charged and available all the time is often mentioned as a drawback to the V2G and G2V solution. In principle smart metering (or even low tech time switches) can solve the problem. If you have to have a full battery always you leave the G2V switch on and the V2G switch off. Time controlled switches with say V2G on until 3 am and then off, and G2V on from 3 am until drive time would seem to be a low tech solution which would solve the problem and earn some dollars.

The lithium supply problem has received some attention. It doesn’t seem to be a problem in the short term. In the longer term there are competing technologies such as NiMH, hybridized lead acid and sodium/sulphur as Neil points out. Nickel and lead are in abundant supply. NiMH has patent problems (with Chevron!). Lead’s discharge problems are being solved by adding a capacitator to the anode (or cathode). Zinc air (not zinc slurry) is another active technology based on an abundant material.

David MacKay’s treatment of energy to drive motor vehicles has been scrutinized extensively. If we calculate the energy in the petrol used by a petrol engined motor car we include the energy for traction and the energy for heat. If we calculate the energy in the electricity used by the electric engined motor car we calculate the energy required for traction only – we don’t need the energy used for the unnecessary by-product heat. The energy used for traction appears to be less than 20% of that required for traction and heat. This is a remarkable untapped energy inefficiency.

Electrifying interstate motor transport appears difficult to visualise. Electrification of interstate rail is plausible but without big volume increases is probably very expensive. Commercial intra-city transport is ideally suited to electrification. Short distances, lots of stopping and starting and return to a depot at night. If the vehicles can earn dollars at night from V2G then commercial operators will have few qualms about setting the appropriate time switches.

Kind regards,

David Murray

The issue of storing several days supply of electricity is only relevant to local renewable energy. The study by Robert Davy and Peter Coppin CSIRO( 2003) illustrates for wind in just SA,VIC and NSW,only has a few hours of low wind at any one time, but we would have wind from WA to QLD and TAS and as well solar. In winter solar is very reliable in the north(winter dry season) and very reliable in summer in southern WA and SA. So its really only storage for wind demand at night with normal hydro peak capacity. Possibly 30GW for 4hours. Increasing hydro capacity by 400%(not new major dams) would be adequate, and increasing Bass-Link from 600MW to 6GW.
“My figures indicate that world hydro capacity could possibly be doubled; not multiplied by 10.”
If Tim is referring to Australia that may be correct, I was referring to the world, where according to DOE_ Idaho Lab, the US alone has 400Gw average undeveloped potential( about the same as the worlds developed). Canada has another 180GW and China possibly 300GW( 80GW capacity is under construction post 3 Georges).

MacKay’s scenario G(no FF or nuclear) only uses a small amount(15%) of solar from N Africa, remember in UK wind is strongest in winter, solar would be used in summer. He does have another scenario using a lot of solar but not much wind energy.

The issue of efficiency gain is important, for example Tim’s scenario of Australia needing twice as much electricity in 2050 is only valid if efficiency gains are less than GDP growth. California is a good example of high GDP growth, very slow growth in energy use. If energy becomes expensive( as we all expect) then efficiency gains will be similar to GDP growth.

The only long term transport issue I see is for air travel. If we cannot replace the 900Million vehicles with battery power in 30 years we may need fuel rationing, the extra cost electric batteries will seem like a bargain. There is certainly enough Li for 1000 million vehicles, possibly not every one will be able to afford Li and have to use Ni or Pb or sodium/Sulfur.

“Here are some thoughts on some of the useful comments you forwarded; if convenient can you feed these back to their senders.

Neil’s figures on hydro are important to take into account; yes peak hydro output can be bigger than average annual contribution. But the contribution from hydro as a storage system isn’t settled by this; it depends on physical plant required to be ale to store pumped water, and get hold of it to pump and store. In other words I think the big limit is the availability of low dams. You must have access to a lot of water that’s down, close to the high dam, to pump up when surplus wind and sun are available. One would imagine that the number of locations enabling that and the associated generating capacity is a lot less than the normal hydro generation capacity, or what it can put out at peak load.

My figures indicate that world hydro capacity could possibly be doubled; not multiplied by 10.

Tasmanian capacity to supply to the mainland is very interesting. I think the magnitude issue is important here; if Australia was to run on renewables, then by 2050 with maybe double present demand, there will be times when sun and wind are down and we’d need to get maybe 60 GW from storage — taking into account conversion losses — and this is just to meet electricity demand, not including electric transport. Where can we store and get hold of anything like this quantity. (You might recall my thoughts on the task this would set for nsolar thermal; ,to cover 4 days plant would need perhaps 25 times normal 12 hr storage.)

Neil says I haven’t dealt with use of car batteries; I have had a look at this and see it as problematic, because of the need to have the battery full again when the user wants the car. Lithium is not abundant if we are thinking about providing for 9 billion.

I lam not interested in “efficiency gains” defined as energy use per dollar of GDP. What matters are trends in energy use. Nor do I think there is any value in attending to measures of annual achievement in the past, e.g., 1% p.a. gains in efficiency. We are in a critical era where all bets are off, the conditions to come will be very different to those in the past, and so extrapolating familiar trends will be unwise. For instance the cost of energy will surely rise a lot and this will feed back into everything, for example cutting lots of minerals out of what was thought to be the recoverable category.

Mackay is good on ocean currents, which I haven’t gone into much, but these are limited; good for some countries such as UK, but not likely to make much global difference I think. He concludes that the UK can’t run on renewables, unless it draws on Africa for a big proportion. I don’t think he deals adequately with the fact that almost all the renewables supply only electricity, which is only 50+ of demand even if you electrify all transport.

He is interesting on solar thermal for Europe from Africa, but doesn’t go into it very deeply. Not sufficient to draw those little squares representing small proportion of the Sahara that could meet demand. What about net supply. What about winter. What about runs of cloudy weather.

I see Gregor Czisch is making another fuss about how Europe could run totally on renewables. I haven’t been able to find his recent writings, but have his c 2004 papers. His discussions are quite valuable I think but I don’t think he clinches it; for instance he talks about averages, when what matters is the variability and how often the renewables will leave big gaps.”

Overall, Mackay’s book is a really excellent contribution, but naturally imperfect given the breadth of fields he is trying to cut across — each area has its many nuances, as we are discovering in these many useful comments.

Thank you for your comments on the Tesla and for the confirmation of David MacKay’s apparent accounting error in dealing with the energy usage of private transport.

I was simply not aware of the enormous wastage of high grade energy by the internal combustion engine. The Boron car would go one step further and remove motor vehicles right off the high grade energy energy budget.

Kind regards,

David

“This figure quoted of about 2kWh/person/day as the “practical” resource just doesn’t add up to calculations, of energy in average wind speeds of 12 m/sec at 100m height( at least 3% of UK). gives 1200W/m^2,energy and assuming a wind farm only recovers 1.5%of this is 18MW/km^2 for 7,000km^2(3%of UK)=126GW or 2kW average(48kWh/person/day). I think that’s about twice the present UK per person electricity consumption, so perhaps only 1.5% of UK would be OK. That’s still going to leave a lot of wilderness, as well as very low impact on the actual environment on regions having turbines( 4-6 turbines /km^2)”.
MacKay relies very heavily on the 2 kWh/person/day figure. He derives it from his conclusion that for all practical purposes wind farms won’t get much above 2.2 W/sq m. (B.10). I redid his calculation using your 12 meter/sec, and his standard windmill (54 meter diameter blade) and windmill spacing (a five diameter 270 m square). With those figures my windmill generates 17 W/sq m. That coincides very neatly with your statement that the best 1 % of sites produces X 8 more energy than the average wind speed sites.
His 2.2 W/sq meter and 10% of the UK surface area give him 20 kWh/d/p (Figure 10.3) of onshore wind power, decimated by Nimbyism and nay saying into 3 kWh/p/d in Figure 18.7
Your 17 W/sq meter and 3% of the UK surface area give you 46 kWh/d/p. You would rightly argue that this 3% is much less open to the NIMBY and nay saying arguments.
MacKay uses the critical assumption of 3 W/sq m for shallow and deep offshore wind farms. This is fifty per cent better than the (B.10) assumption he uses for on shore wind, but nowhere the ball park for your top 3% of 12 meter/second wind farms of 17 W/sq meter. If he is out by the same order of magnitude on these technologies the figures (and conclusions) change beyond all recognition.
I think David MacKay’s method is invaluable – but the assumptions in his numerical calculations seem to have led us astray. Barry had the same reaction to his treatment of nuclear, particularly with respect to uranium resources.
I apologize for the length of this reply – but the topic does not lend itself to too many shortcuts.
Kind regards,
David Murray

PS I read recently that wind produced 40% of Spain’s energy needs in early March during a particularly breezy weekend. Fantastic. Did they have to load shed a lot of this monstrous surge or how did the matadors manage to keep it corralled in a safe place?

I was responsible for the motherhood statement that ‘You can have lots of carbon free energy without nuclear or coal’. Your comments are very relevant and Neil has replied to your points (a) to (d) in much the same way as I would have.

I would want to write two versions of your second paragraph.

‘1. There are enough uncertainties to convince me that any risk averse portfolio would have to include nuclear and renewables. The relative mix in the portfolio should depend on cost, feasibility, convenience, safety etc.. Our ideas on these will change as the new zero carbon economy rolls out over the next few decades, and we may alter the mix in our portfolio in the light of this extra evidence. My (I mean your) view is that nuclear power has sufficient advantages that it should dominate the mix.’

‘2. There are enough uncertainties to convince me that energy production activities (in say 2020) will include nuclear and renewables. The relative mix in this outcome will depend on cost, feasibility, convenience, safety, market forces, political forces and the regulatory environment. These will change as the new zero carbon economy rolls out over the next few decades. My (I mean your) view is that it is likely that nuclear power will dominate the end result, and furthermore in the meanwhile I (you) will move heaven and earth to change the political forces and the regulatory environment that will determine the mix of energy production activities in line with my (your) preferred result in paragraph 1.

My (I mean my) view would reverse the role of renewables and nuclear.

Thank you for taking time to communicate in this way. I noted that you submitted a large number of posts around midnight last night.

Kind regards,

David

I was 99%, but not 100% sure what you thought Mackay’s serious error was.

Is he wrong in saying (in order of magnitude terms) that a conventional ICE motor car would use 80 kWh/ 100 kilometres and an electric car would use 15 kWh/100 kilometres?

Or is he wrong in using the 40 kWh/d/p figure for cars in his red box on page 103 for example?

Kind regards,

David

You made a minor error – you could have down loaded MacKay’s book for free rather than paying money. Not even Tom Blees was as kind as David Mackay – he only let you have one chapter for free.

MacKay’s book is a great little book – but be careful about the analysis between pages 109 and 112.

I think Neil dealt with your concerns about the Tesla. I find the difference between the energy usages of petrol and electric vehicles that MacKay gives truly amazing – and want to double check the sums with him.

Kind regards,

David.

Yes, I was reasonably sure it was a different technology. The problem is that it was the result of the same industry and regulatory structure that we are relying on to implement the rapid expansion of Gen III reactors and Gen IV technology and reactors.

Kind regards,

David Murray

‘Sure you are…’. Yes, it is up to me to promote my ideas – and I appreciate your providing the forum to do so. Thankyou.

On The Beach seriously stressed a lot of people for a long time. We still hear of people using ‘energy’ reactors to piggyback into ‘weapons’ reactors. The opaque situation around Iran is the obvious example. Israel prompted Iran, and Iran will prompt Saudi Arabia. I don’t believe there was a Chinese wall between India’s civilian and military programs. Pakistan’s decisions were prompted by India’s behaviour. They were probably facilitated by North Korea whose behaviour was influenced by Japan and South Korea.

I suspect Tom Blees is of the generation that experienced this message – and why he too would have liked some international control. If, when, we get to IFRs perhaps this problem disappears.

Kind regards