Gardeners Corner Global Energy Policy

An interesting read and loosely connected
The Role of Synthetic Fuel In World War II Germany

 

HVDC (High Voltage DC) may help

Wikipedia says:

"The advantage of HVDC is the ability to transmit large amounts of power over long distances with lower capital costs and with lower losses than AC. Depending on voltage level and construction details, losses are quoted as about 3% per 1,000 km. High-voltage direct current transmission allows efficient use of energy sources, remote from load centres."

High-voltage direct current - Wikipedia, the free encyclopedia

and

"As of 1980, the longest cost-effective distance for DC electricity was determined to be 7,000 km (4,300 mi). For AC it was 4,000 km (2,500 mi), though all transmission lines in use today are substantially shorter."

Electric power transmission - Wikipedia, the free encyclopedia

 

The trouble with DC is it is so much harder to convert the voltage efficiently. AC you can, because an alternating electrical current creates a proportional alternating magnetic field, and that magnetic field will induce a proportional matching current in a conductor. That's how transformers work. There are losses at at the transformers through heat, noise, and the resistance of the materials, but they are generally quite efficient.

To convert the voltage of DC, to convert down is easy, but not without losses. No matter how you do it, you have to voluntarily throw some of the energy away in what is called a 'potential divider', effectively two loads in series, one being the consumer, and the other being a regulator which in effect adjusts its resistance to track demand. Or the more efficient switched mode regulators which require a huge capacitor (I have no idea how you'd get one big enough for the sort of demand we have) and the regulator then switches off the supply completely when the capacitor is fully charged, and switches it on as it starts to discharge, thus maintaining a regular voltage. You still have to voluntarily throw some of the power away though because if you don't absorb the spike of the regulator switching on, everything connected gets wiped out.

Stepping DC voltage up is even more of a nightmare, and totally impractical in high demand situations.

AC is the most efficient means of transmitting electricity. Apart from being far easy to change the voltage with minimal loss, it has other advantages. Firstly, almost all means of generating the power boil down to a what is effectively an electric motor in reverse. Whether the power comes from a little wind turbine or a nuclear power plant, the thing that converts the energy (wind, heat, moving water) is just like a big car alternator. It outputs AC. So its easier to work with that than it is to convert it at source. Another often overlooked advantage of AC over DC is it is less fussy about the condition of its wires and connectors. At the point where two different metals meet, you will get corrosion. That's a fact of life. For DC, that means lots of resistance and lots of energy lost through heat as it tries to pass through the rubbish conductor. AC still has to get through it, but it can cheat a bit. A changing potential difference (voltage - as you get with AC when it meets resistance) causes whatever is on the other side of the resistance (ie the corroded contact) to polarising proportionally. Then when the AC flips the other way, it polarises the the thing on the other side of the resistance the other way. So in effect, some of the power gets across the bad connection by inductance, while the rest makes its way through just by normal conductivity. I.e. AC gets across the bad connection with less loss than DC would.

The trouble is, this last advantage of AC is also a disadvantage. The gap of air between the live and neutral overhead cables is effectively a very deliberate bad connection, and AC will try to cross it. DC would too. For DC to get across it has to ionise the air between the two cables sufficiently to turn the air into plasma. That would take a colossal voltage. Far higher than is typically used in electricity transmission. To get AC across the gap, you just need an alternating magnetic field, which it has because that's what happens when you put alternating current through a conductor. The gap is wide enough such that not much gets across, but some does, and so for every mile of overhead cables, there is some loss of power through inductance.

The solution is is simple but expensive. You just need to widen the gap between the cables along their full length.

 

Thats a lot of info there Dave Very interesting, so we'd just need to modify the existing grid to make this a possibility.

Another thing I was wondering about was using sunlight to make potential energy, something that could be transported independantly of the grid.

Can seawater be split into hydrogen & oxygen, or does it get messy with all the minerals in it?

 

Ziggy - I think that the electrolysis of seawater into oxygen and hydrogen would be very easy. It uses a massive amount of energy but you will get most of that back (nothing is 100% efficient) when you recombine them. But transporting hydrogen (the useful bit) in large quantities would be pretty dangerous and pretty expensive as you either have to pipe it (expensive to build) or liquify it (also expensive).

Much has been talked about using hydrogen to power cars. But I see that as very difficult. One reason, that they tend not to mention, is that the hydrogen atom is the smallest atom there is. And as a result it can slip through the tiniest of gaps and escape. If you fill a balloon with hydrogen, it just escapes through the fabric of the balloon itself. Development is done in laboratories where they can have very expensive and highly engineered joints and seals. Can you imagine your local garage meeting the same standards with just a hammer.

I seriously believe that we have to be practical and use nuclear power - the French have done it and are laughing at us.

 

Hi Peter, I had pictured liquifieing it, the same way we currently import gas from the middle east, but didn't know about the size of the Atom.

Maybe we ought to be not looking at solar pv then, but a biofuel that will grow in a hot climate, just using solar pv to process it.

 

biofuel takes land away from producing food crops (in the main ... unless you grow it where food could never be grown).

Just another one of the difficult-choices that will have to be made.

 

Combined with Bromide.

 

There was a news article a while ago on the BBC website about hemp as biofuel. There'd been some big study apparently.

It was found that hemp would grown in land that was not much good for anything else, so it wasn't taking land away from food production. It improved the soil structure, thus making the land useful later, required no irrigation, with the hemp being very, very drought tolerant, and the hemp had 4 times the yield of bioethanol that you get from oilseed rape.

Funnily enough the article didn't stick around for too long, and I've not been able to find it again since. It seems we don't need a fuel source with no strings attached. We're better off raping the planet safe in the knowledge that there'd probably enough left to see us out.

 

Lazydog picked up on that one earler,

Learn The Truth About Hemp

Sorry LD, I meant to go back & have a look but forgot. Brilliant There's our crop then

 

Nuclear is the way for me, cheap and cheerful, Non reliant on foreign neigbours to cut us off

I slept alongside one for many years, and for those years I was never further than 250' from it, my Rad badge was low
I have a normal and healthy family, my bits still work, and now aged 65 I am still OK apart from general abuse of my body with food fats and alcohol
I do not glow in the dark, so I am advised

Once we are free from generating companies from abroad, and are self sufficient and cheap, Then the reality of electric powered transport would be available and we can chuck the Middle East into touch to ransom prices of fuel

Electric trolley busses or trams again, no diesel or petrol required, and please please no more energy saving bulbs, just like home used to be with gas lamps in the sitting room, and you could go blind trying to read

Jack McH

 

Sorry to LD, I must have missed your post.

 

Ziggy - I couldn't remember the details of hydrogen so had to look it up. It needs to be 70C colder than liquid oxygen to liquify and it also needs to be at a pressure above 13 atmospheres. At atmospheric pressure you can't liquify it. The technology is available as NASA uses it as a rocket fuel - but I suspect its pretty expensive.

Leakage of 1% per day is even worse than the effect of inflation on my savings. :D

 

Jack we've got horse drawn and electric trams here still, also got a steam railway.

Whatever happened to horses and carts though, they'd be a devil in rush hour. I've been saying for years that's what we'll end up going back to.

 

In parts of our area horse drawn vehicles are still commonplace. When I used to work up in county durham, about a year ago, I used to regularly be temporarily held up on the way home in rush hour by one or more horse and carts, and in my own neighbourhood, we have several. I think its great. They're easy enough to overtake when you have to so they don't cause any bother, and lets face it, some people could do with being slowed down a bit on the roads.

As for steam power, this is a point that I feel quite strongly about. It just seems logical to me. Steam engines of old, as fascinating as they are, we know now to be a bit of an environmental nightmare. However that doesn't mean we should turn our back on the technology of the past.

Consider an old steam engine. A massive water tank and boiler made of cast iron. Think of the weight of that. And then burning enough coal to produce enough steam from cold water to power an engine that is going to have to move probably a couple of hundred tonnes in all. Then you simply vent that steam. Its an open circuit for the water. Understandable given the era they were designed, but crazy nowadays.

Now consider what it actually is trying to achieve. Its used the fact that water tries to expand into a gaseous form as soon as it reaches 100'C, and the result pressure can do stuff. Reduce it down to that and consider that a car uses water (with an additive) to prevent the engine overheating, and that water is in a closed circuit (if it wasn't you'd have to carry so much weight in water your car would be a nightmare to drive because of the weight of water, and even more of a nightmare to fuel), and something becomes pretty clear. Using more or less any solid fuel to heat a relatively small quantity of water, you can achieve the power of a steam engine. Then instead of venting the steam, you condense and cool it, and put it back into the circuit. Do that and what you get is a steam engine that has to pull a tiny fraction of the weight of the old engines, and can run off any flammable waste. Great, Edinburgh to London on a few households worth of rubbish.

Ok, I couldn't build this. I couldn't even do the maths. But that's because I'm not an engineer. I've almost certainly overlooked all sorts, but I'm pretty sure there are plenty of engineers who could make it work.