OK, my WAG concrete/steel numbers are about a fifth or eighth of the actual ones - within an order of magnitude, just.

Still, the last sentence of the abstract is a bit of hint: “The total greenhouse gas emissions from CANDU nuclear plants, per unit of electricity ultimately produced, are very small in comparison with emissions from most other types of power plants.”

Last para of the conclusion: “Over one hundred times as much CO2 is avoided by deployment of the CANDU fuel cycle in place of coal plants in Canada than is released by CANDU construction, the fuel production process, and decommissioning. The electrical energy output per unit of CO2 released overwhelms that from the direct use of fossil fuel for electrical energy.”

Posted By: renewablejohnBut the point still remains Nuclear power is only low in CO2 if you ignore the embodied CO2 in the build and processing of fuel.

I only read the first couple of pages and skipped down the rest very quickly but that report you linked did seem to include both those yet still came to the conclusion that nuclear was a relatively low carbon energy source.

And you originally cited just the steel and concrete which does seem to get “paid back” (vs an equivalent-output coal plant) in a relatively small number of months.

You could quite easily argue the same point with coal in an IGCC plant where the CO2 is captured and utilised in a closed loop Sabatier process producing synthetic gas.

Not sure. Coal in, must have carbon out somewhere. Where, if it's not COâ‚‚ into the atmosphere?

Posted By: SteamyTeaThis thread is about grid stability, not COâ‚‚,

Sorry, yes, rose to rj's bait though the original point was yours.

This is the main reason for not having enough storage:
<blockquote><cite>Posted By: Mikel</cite> Snygappa, yes, a small store capable of 3 kW power output would be useful. Difficult to justify the expense for now</blockquote>

LiFeYPo4 batteries can be used but charging and discharging is a bit more complex then using lead acid batteries. LiFeYPo4 has a longer life then lead acid but cost for installing and replacing them every 5 years is much higher then having a backup powerplant. Until we have a cheap way to store energy the current state will persist.
This is the reason I have been looking at other ways to generate power. As ST said we could have a high base load but then for peak power could have a micro/mini power at city level using current tech which can be switched on when needed. This way the energy (any form i.e. heat from idle steam genset/electric) waste can be reduced or even eliminated.

<blockquote><cite>Posted By: renewablejohn</cite> As for your comment on the inability to quickly turn on or off nuclear that is not a problem for any steam generating plant whether its nuclear,coal,gas,biomass or solar so long as you have sufficient steam accumulator capacity. The technology has been around for a very long time with the first plant built in Berlin back in the 1930's. Now with modern insulation steam accumulators can work for days rather than hours while retaining efficiencies similar to the best pumped storage.</blockquote>
So do the powerplants shutdown their generators when the demand is low?

All,

There is some discussion of storage here..

http://www.renewableenergyworld.com/rea/news/article/2014/08/the-next-big-challenge-for-energy-storage


Hope that works, if not you'll have to google it up.

Cheers

Thanks for that Ed. Mike/ST: Interesting read.

Has anyone come across Ultrabattery? Apparently it has better life cycles then the simple lead acid battery.

Right, have managed to look at the grid data again and work out just how much it fluctuates.
Standard Deviation is a measure of fluctuation, 1 Standard Deviation covers 68% of all the data, 2 SDs 95% and 3 SDs 99%.
So if we want to stabilise the grid with some storage we need to decide how much storage is needed. This will be based on the largest SD, or fluctuation.
Looking at half hour segments of demand data from Jan 2010 to Jan 2014 the largest SD is 6,948 MW and happens between 11:30 AM and 12:00 PM (noon). This does not mean that there is a sudden jump of nearly 7 GW at lunch time, just that it peaks at this time. Part of the reason for this is that demand is higher during the day. The smallest SD (3,588 MW) is between 4:30 AM and 5:00 AM (those storage heaters have fully charged by then even though there may be another couple of hours left of E7).
So how much storage is needed to cover this fluctuation?
If 6,948 MW is 1 SD and will smooth out 68% of the fluctuation, then doubling this will smooth out 95%. I think that, allowing for seasonal variations, getting 95% 'smoothness' is pretty good. There are always weird times when there are large fluctuations, Royal Weddings and Football matches being the notable ones, but these are known well in advance and can be catered for.
Therefore by installing enough storage to cover double the fluctuation will get us close. That will be storage capable of delivering 7,000 MW for half an hour, times 2. This works out at 7 GWh of storage.
It would be wrong to think that every household is capable of having this kind of storage (just like it is to think that every house can have PV panels), but let us assume that 25% of houses are suitable, that is about 7.5 million houses.
7 GWh / 7.5m = 0.933 kWh/house. We can call that 1 kWh of storage.
This is quite achievable (someone could design and build this in a week).
But, and this is the hard bit, peaks are not followed by troughs of equal amount that would give enough time to recharge the storage. The longest period of continuous discharge is 3.5 hours (15:00pm and 18:30pm, kids coming home and supper on table). The total discharge is 879 MWh. Luckily this is followed by 5 hours of lower usage, 1,420 MWh in total, so plenty of time to recharge and have some to spare.
Let us assume that we want to take full advantage of this 1,420 MWh, that would be 2 kWh of storage per house. This would allow plenty for losses in charging, not stress batteries if that was the route chosen and be affordable when you consider that 7.5 million units would be made (though supply chain economics would push the price of batteries up if that was the storage medium of choice).

Controlling this sort of power at the micro level is a little tricky. The normal way to monitor grid stability is with a combination of voltage and frequency monitoring. These become useless with a stable grid. What would need to be monitored is current (the real power). Now I have no idea how this is done reliably and quickly, but I know it is done with PV systems to divert energy from the modules to a load without exporting it to the national grid, I will let others work on that one.

So by adding 2 kWh of storage to 7.5 million homes we can stabilise the grid at 36,085 MW so that it only has a 5% demand fluctuation. Makes my first guess of 5 kWh way out, but out in the safer direction, 5 kWh in all homes would give us total stability, but 3 kWh in 10 million suitable homes would just about achieve that too.

So what would be a suitable home?
One that is in a high housing density area, has room for something this hopefully washing machine sized (is there room for one more wheely bin) and has relatively modern and robust local grid.

As always, I may have made a mistake in my arithmetic.

Can it be done cheaper than upgrading the grid and fitting smart meters? I think it can.

It also has the advantage that it does not have to be done quickly, or change peoples behaviour. As long as a relatively small area is targeted, say 50 houses at a time, then the benefits would start right away by reducing the need to strengthen that part of the grid/sub grid.
One downside is that it would encourage the large generation companies to just put in the cheapest short term generation, which is gas at the moment. So it may need a 20 to 30 year implementation, rather than be thought of as a quick, cheap fix.

The charge/discharge cycles would mainly be partial. There are also more half hour blocks below (charging times) than there are above (discharging times). Not sure how much difference this would make to longevity (it is a 27 to 21 ratio).
Also, the St Dev I worked out was for the full period, 2010 to 2014, and though closely correlated to demand, I don't think it is necessarily a true correlation. More a case of the baseload being higher in the winter than the summer, and the SD being worked out on the full range (summer low to winter max).
If I get time I may investigate this area more.

Posted By: Shaha big disadvantage of replacing the battery bank every few years.

Yes, why I am not sold on chemical storage yet.

Some of you may know that I have Economy 7 heating.
A while back I fitted some additional timers to stop my heating coming on at 11 pm for an hour, then off for an hour and then on again until 7 am (or until no more energy can be stored).
This caused the house and water to me nice and warm at about 3 am, but I really get up before 5 am, so I had at least a couple of hours of 'unused heat'. This caused problems later in the day as the stores had discharged though legitimate usage and standing losses.
By time shifting the 'on' time until 5 am and only using the last couple of hours I have found that I can store sufficient energy for the day and reduce my standing losses.
But I thought is was about time I actually checked how well it fitted in with grid demand. So I have plotted the last week. I have not turned on the space heating get, just use a small 1 kW fan heater), so the majority of the E7 is for water heating with occasional usage of the washing machine (bigger blue spikes on the 4th and 6th).
It seems to me that if I shifted the on time back by half an hour then my peak will match the minimum demand a bit closer, but I will have another half hour of standing losses. Have done this now so shall see what it is like next week.

Had a quick look at the change in frequency with respect to the demand and during the times I am interested in, not worth worrying about. The trend is basically flat. This causes a problem for simple over power grid sensing.
After a bit more tinkering I have worked out the grid intensity between midnight and 7 am. Quite a slope, but as I am interested in the bottom end I can feel quite pleased that my personal usage is very low intensity.
By looking at grid intensity to see if there is any real environmental benefits (I am only using about 1 10 millionths of the minimum grid demand), it is clear that my personal usage is in the bottom half of the CO2 scale.
Basically any storage system connected to the grid (as it is today), needs to be time based rather than grid sensing. This makes control very easy. Just turn it on at 4 am and off at 5:30 am.

Anyway, enough of that, here is the picture. First one is my usage against time, second the 'flat' frequency and demand slope and the third the CO2 intensity between midnight and 7 am (and below 35 MW, which it all was).

Whoops yes, thanks,

Thanks Steamy who sent me his numbers for estimated intensity against demand. Actually he sent me lots of numbers - I think he used just the ones from overnight but, not being sure of the details, I used the ones for when demand was less than 34 GW. My first graph is similar to his last but with a few more data points.

intensity = 0.03126 * demand - 0.5456
R² = 0.671

However, I then multiplied demand by intensity to get total emissions, second graph.

emissions = 1.3436 * demand - 28.43
R² = 0.817

Ie, total emissions are more linearly related to demand than intensity is related to demand. Further, the marginal emissions for an extra kWh, even when the grid is at relatively low power levels, is still quite high: 1.34 kg/kWh.

Hi Nick, you are multi tasking as well, being on the GBF and Ebuild forums?????, I dont seem to be able to whisper comments to you on the Ebuild site!!!!. Also if you look at new comments on a thread you have to wade through the thread where the GBF sends you to the place where new comments start!!!! (or am I a thick builder that does not get on with technology?) I didnt hear from Jeremy regarding a meet at his house, it would be good to catch up with others on these forums. It look like I will be able to start building in Devon this spring so watch out I will be asking lots of questions soon.

Regards John