Energy distribution (and electricity generation)

[hollus]

...the energy in wood is almost entirely in the carbon content - as it is with coal
(wood's large oxygen content and most of its (small) hydrogen content has of course no energy availability)

Wood is largely hexose polymers, largely glucose, which has a lot of energy in 7 C-H bonds. Think about it next time you are burning methane.

[Tommy Cookers]

wood's hydrogen content is small (eg 6%), as I said ... (50% C, 42% O and 6% H for wood pellets)
so whether this hydrogen is in water or elsewhere it makes little difference (it's unclear whether the pellet moisture is analysed)
so I say nearly all the energy is in the carbon (as with coal - which also contains hydrogen)

please explain if this is wrong

[hollus]

It is wrong. The energy is neither in the carbon atoms nor in the hydrogen atoms, but in the bonds (in a simplistic view).
Hydrogen atoms are very light so they make up little of the total weight, but a glucose, the basic component unit of wood, has C6O6H12 as its formula, so plenty of hydrogen atoms. In it has 7C-H bonds and 5 C-C bonds. Since there is (very roughly) the same energy in a C-C bond as in a C-H bond, no, the C-H bonds are not negligible (and neither are the C-O bonds). Again, when you burn methane (CH4), all you are doing is breaking C-H bonds.
OK, it is much more complicated than this, in reality the energy comes from the difference in energy (enthalpy) in the C-C or C-H (or C-O or O-H) bonds in wood compared with the C=O and O-H bonds in CO2 and H2O, but that might serve as a first approximation. The hydrogens are not to be ignored, even if they are light.

[Richard]

the energy in wood is almost entirely in the carbon content - as it is with coal
(wood's large oxygen content and most of its (small) hydrogen content has of course no energy availability)
so wood's lower carbon content is totally misleading, there is no 'instant (carbon) saving at the point of consumption'

Yes, both release carbon. However the wood method absorbs as much carbon as it releases in the harvesting cycle (ie 20 years in this example).

The instant saving in the first year is that a year's worth of coal has not been dug out of the ground and converted to the atmosphere, and that the replacement trees have grown for a year absorbing carbon.

[Tommy Cookers]

there is no instant saving because the year 1 carbon cost of the wood burn is 117 % of the year 1 carbon cost of the coal burn
year 2 wood 114%, year 3 wood 111% etc .... so they are equal around year 5 or 6 and wood is in profit around year 10-12
Drax's wood gross figure of 120% (due to the carbon cost of wood transport etc being 7x coal's)
less 3% absorbtion annually from new growth=117% at year 1 etc

@ Hollus
call me an engineer, but wood is 50% carbon and 6% hydrogen so its CO2 emission/heat energy will be similar to coal's
we know how much carbon is there per unit of heat (for both fuels) so we know how much CO2 is emitted
and coal has significant hydrogen too, as a chemist knows

as I said, this is the RSPB's story (bird lover's society), not mine

[hollus]

TC, you asked, explicitly, to be corrected if you were wrong. And you got your wish. Coal =! wood, not even close. But good point about the 5% of H2 in most coals. One often forgets about that.

Focusing on carbon budgets: You choose to focus on the next 20 years, and there is nothing wrong with that, and in that case the CO2 budget that results is not that great. But one could also focus on the past 20 years. In that case every single carbon atom emitted to the atmosphere when the wood is burnt was in the first place stolen from the atmosphere. Neither of those two budgets tells the whole truth, but in the long term, the cycle of growing wood, burning that wood, growing it again, burning it again... has a 0 carbon budget. This is only if (a big if) one ignores fertilizer and transport costs. And not much fertilizer is spent on wood, I guess.
I don't think that burning wood for energy is a particularly brilliant idea, but it beats coal in any horizon beyond 10-15 years. In the case of coal, the carbon emitted had been buried underground for the last 100M years, and would have stayed there for another 100M years if we hadn't dug it out. Its carbon budget is 100% losses.

We are going off topic. In your original post (I know, it was moved there) you are suggesting that the world needs this much energy, and it will continue to, and that the only realistic proposition is fossil fuels (let's leave nuclear out of this for a moment). You surely must agree that at a point in the future we will start running out of fossil fuels. Maybe a close future, maybe a far future. So ignoring any climate effects, when eventually fossil fuels are so scarce and expensive as not to be able to provide... then what? What's you suggestion for, say, 200 years in the future?

[Richard]

Alas political expedience trumps technical priorities. So the driver for changing energy generation is likely to be energy self sufficiency, primarily for security but also for balance of trade.

Unfortunately the most effective solution is for people to use less energy, but that infringes on the sense of individual freedom (which is false when it comes to infrastructure) so instead we blight our environment and economy by consuming more and more energy.

[tuj]

Ok gents, I actually work in this field (electricity generation). Let's talk about the sources of power and the future:

1. Nuclear. Not getting enough attention. Very safe when done right. Low equivalent heat-rate, low O&M costs, runs for about $6-10/MWhr.

2. Coal. Depending on the type of unit, you get a heat rate around 9300 to 10,500 or even worse for some of the units built in the 1950's and 60's that are still operating. All in cost is between $11 to as much as $30/MWhr, depending on the unit, the type of coal it burns (API2, API4, Newcastle, Central App, PRB, lignite, etc...) Dirty as all hell. Even when scrubbed and the use of a baghouse and electrostatic precipitator, there is still mercury releases and particulate releases. Better would be to use IGCC technology; removes about 80% of the pollutants.

3. Natural Gas via CCGT. Good heat rates (sub-9000), good O&M, costs are on par or below coal in many places in the USA nowadays because of shale gas flooding the market. Low pollution, no particulates to worry about, nor NOx nor SOx nor mercury. Very flexible in configuration because you can run the turbines in GT mode, or combined cycle mode. Natural gas is great for the USA, probably less so for Europe having to buy LNG or Russian gas.

4. Natural gas via GT. Still good heat rates, but you have a lot of waste heat not being recovered as it would be on the CCGT. Costs are subsequently higher to strike (run) the unit.

5. Dam Hydro. Awesome power generation for super cheap, less than $2/MWhr. Lots of power potential. Bad? Hard to build.

6. Run of river Hydro. Minimal generation because of head constraints, but still super cheap.

7. Wind. Wind is the bane of my existence. It is great in theory, but in reality, it causes a TON of congestion on the grid. Congestion causes all or many prices to go up depending on what the local conditions on the grid are like. Congestion can get EXPENSIVE. To give you an idea, in Texas, where there is 11GW of wind, the wind can cause certain nodes to go to THOUSANDS of dollars/MWhr because of congestion on the grid. Wind is highly unpredictable. The ability to forecast the wind generation potential is extremely difficult and this makes scheduling generation resources very tough. The best thing is to match a GT with a wind farm; this way the GT can respond to slack in the wind and provide firm power. Another option is to use a battery, but this technology is still lagging. Wind on a per MWhr basis is still quite expensive because of O&M costs on the gearboxes of the turbines. If it wasn't for tax subsidies and renewable energy credits, wind would be unprofitable. Also wind tends to be highly non-coincident with the peak of the load.

8. Solar PV. Nice in the sense that you can site it almost anywhere that there is decent sun, and it IS coincident with peak load, so that's nice. Bad? Well it generates virtually nothing until you start to talk about acres of panels. That means lots of O&M and support equipment. So in the end, it is very expensive and contributes very little right now and is only made profitable by tax subsidies.

9. CSP (concentrated solar). Actually works (via mirrors) and can actually generate a decent amount of power, but is very difficult to site (you need a lot of sun and a big flat area). Again, only making money because of tax breaks.

10. Tidal turbines. Immature technology, doesn't generate much power. Hard to make 'dolphin-safe'. LOL.

11. Biomass. Works well in Hawaii but is harder to run than a coal unit. Most use a floating bed which is more difficult to control than a typical boiler.

There's probably something that I forgot, but that about covers most of the ways to actually generate energy. hope this helps.

[hollus]

Thanks a lot, TUJ, very nice post.
I assume that you are referring to the situation in the USA. Do you have any knowledge / opinion on the situation with wind in places like Spain and Denmark, where there are so many windmills and in many places with an almost "always on" wind, so that both countries are on their way to getting 30% of their electricity form wind? I guess that whether one can make that much electricity doesn't automatically mean that one is making it when or where it is most needed...

"the wind can cause certain nodes to go to THOUSANDS of dollars/MWhr because of congestion on the grid"
Am I correct to take that to mean that when their electricity is not needed they produce so little that the investment (the windmill) is just sitting there losing value and producing no return on investment?

[Andres125sx]

3. Natural Gas via CCGT. .....

4. Natural gas via GT. .....

You guys make me crazy with acronyms

[Andres125sx]

Thanks a lot, TUJ, very nice post.
I assume that you are referring to the situation in the USA. Do you have any knowledge / opinion on the situation with wind in places like Spain and Denmark, where there are so many windmills and in many places with an almost "always on" wind, so that both countries are on their way to getting 30% of their electricity form wind? I guess that whether one can make that much electricity doesn't automatically mean that one is making it when or where it is most needed...

"the wind can cause certain nodes to go to THOUSANDS of dollars/MWhr because of congestion on the grid"
Am I correct to take that to mean that when their electricity is not needed they produce so little that the investment (the windmill) is just sitting there losing value and producing no return on investment?

Not an expert here, but I think wind and solar energy is constantly generating its 100%, and it´s the coal plants (don´t know if nuclear too) what regulates its power according to the demand.

That´s the reason here in Spain there have been some months like april, when demand is lowest posible (no heating and no air conditioners needed), that more than 50% of energy consumed was renewable energy, they´re always at full capacity, and if demand is low, it´s the coal plants what reduce it´s generation

[autogyro]

I would suggest that the Americans update and improve their grid.

[CBeck113]

Not an expert here, but I think wind and solar energy is constantly generating its 100%, and it´s the coal plants (don´t know if nuclear too) what regulates its power according to the demand.

That´s the reason here in Spain there have been some months like april, when demand is lowest posible (no heating and no air conditioners needed), that more than 50% of energy consumed was renewable energy, they´re always at full capacity, and if demand is low, it´s the coal plants what reduce it´s generation

You have recognized the problem: "its 100%" can be 100% of the necessary energy, or 0%, depending on conditions. Therefore you need a back-up which can cover the rest, up to 100%, so why use it at all? Beyond that, the regulation of the energy in the network is very difficult, and since transformer manufacturers would need to make big changes to their products (I would call them revolutionary from the standpoint of the manufacturers, since a normal transformer is designed for an operating range of target +/-10%, which means that the energy must currently be regulated at the generation plant - which is not very fast, causing gaps in the power delivery i.e. too much or to little). BTW: I work for a transformer tier 1 supplier of regulators/on-load tap changers, so it we do find a fast and efficient way to regulate the full network, then we'll probably be rich & happy - if someone else finds it we'll probably be out of business

[Blanchimont]

If you're interested in the German energy grid, here's a nice chart about the different sources of energy and their volatility.

http://www.agora-energiewende.de/servic ... verbrauch/

At the bottom in green there are about 5 GW of power from biomass, i think these 5 GW are always present. Then on top power from hydro, wind, solar and conventional power in grey.

[tuj]

I assume that you are referring to the situation in the USA. Do you have any knowledge / opinion on the situation with wind in places like Spain and Denmark, where there are so many windmills and in many places with an almost "always on" wind, so that both countries are on their way to getting 30% of their electricity form wind? I guess that whether one can make that much electricity doesn't automatically mean that one is making it when or where it is most needed...

"the wind can cause certain nodes to go to THOUSANDS of dollars/MWhr because of congestion on the grid"
Am I correct to take that to mean that when their electricity is not needed they produce so little that the investment (the windmill) is just sitting there losing value and producing no return on investment?

Ok, so wind is never "always on". Even in coastal locations like Spain, Portugal and Denmark, while it may seem like a steady breeze, I assure you the generation is varying from 10% to 100%. The turbines actually have brakes on them so they don't overspeed. The brakes are there for another reason as well: when the wind power is too high, it pushes too much power onto the transmission system. Wind is often not located near load centers. When there is too much power on one side of the grid and equipment is at risk, price signals are used to try to rebalance the generation and protect the transmission network.

This means that the wind points get negative prices (eg. they are paying money to the grid to generate power), while units that are hundreds if not thousands of miles away get very strong positive price signals to 'turn on'. These are usually high heat rate gas turbines (GT's) that don't really want to run, but they will if prices get high enough. Thus the consumer actually loses out because of this congestion on the grid; the consumer ends up eventually paying for the 'uplift' and 'balancing' charges for out-of-merit dispatch of units.

As for suggestions that the USA should upgrade it's grid, well, #1, the USA has one of the best electrical grids in the entire world. How many 765kv lines do you have in the UK? Or look at Japan, with it's very weird mix of 50hz/60hz split grid. We have upgraded in the USA, for example, in Texas (the state with the most wind power), they build new 345kv lines to take power to the load centers. This *helps* but it isn't a total solution.

Finally, we haven't talked about regulation. Because there is no or very little storage of electricity, the load and the generation must always be in balance and equal. The difference between load and generation is called the ACE (area control error) and needs to stay within certain bounds. Therefore you can use units which ramp fast to regulate the wind units. If you look at the generation profile of a wind unit, it is not a flat line. It is very peaky and has lots of spikes. So when the wind is blowing, great, but as soon as it slacks off, something has to pick up the drop in generation, and that unit has to be able to respond fast. Which means NOT coal, because running a boiler takes 20-30 minutes to ramp up or down, so you need to run gas or diesel units to regulate the wind generation.