Is green energy supposed to mean cheaper energy?

johntheexpat

Burning it, how quaint

It is almost perfect for fuel cell based CHP (combined heat and power) which would give you an almost 100% return on your energy.  I read recently that Worcester Bosch are working on a home CHP unit and IIRC it gives 9KW of heat for every KW of electricity.

IronGiant

I confess

I think the problem for local generation would be pressurising it if you wanted to keep it in liquid form, which would be an efficient way of storing it, but unfeasible (I assume).

IronGiant

Wow!

EarthRod

Er... the hydrogen combustion engine ignites the fuel (hydrogen) just like the petrol engine in a car. There are quite a few about, in fact Mazda has developed a form of wankle engine which ignites hydrogen.

You are on about the hydrogen fuel cell which is very expensive, easily damaged and don't last long - yes, development is continuing but at the moment the hydrogen combustion engine is cheaper to produce and more reliable.

The hydrogen ignition engine works well in cold conditions. The fuel cell has a tendency to solidify at temperatures below zero!

johntheexpat

But fuel cells run at almost 100% efficiency while engines waste most of their energy.

EarthRod

Come on now John, that's impossible. Except in theory of course - then anything is possible!

In the laboratory, on average, fuel cell efficiency lies at about 60%. The highest efficiency rating achieved for a fuel cell is about 80% (direct carbon type), 70% for the complete working fuel cell system.

See here:

Fuel cell - Wikipedia, the free encyclopedia

In real world applications, fuel cell efficiency averages about 40 - 60%. If the wasted heat energy is diverted for other purposes the efficiency can be increased to about 80%, but then that applies to any energy source and not just fuel cells.

However, having said that, hydrogen fuel cell technology looks good for future power plants. Interesting stuff.

johntheexpat

I did mean overall efficiency, sorry for any mis-understanding.  But if the fuel cell unit is placed in the house, with no losses through having to vent it (since the by products are water) then what is the reason for inefficiency?  The 60% you quote is presumably the best achievable result for electricity generation, but within the home environment there is no reason to waste any of the heat produced, thus making the thing way more efficent.  If you keep the unit within the four walls of the house, then surely all the energy generated, both heat and electricity, will remain within the house thus pushing the efficiency right up?

johntheexpat

Micro CHP - Worcester Energy Homes

Now there will be losses with this system, because being based on natural gas, the by products (CO2 and water and thus potentially CO) have to be vented to the outside world and that will carry heat away with it.  On a hydrogen based fuel cell CHP, the by product is water which has no toxicity problem and thus doesn't need the inefficient step of venting.

EarthRod

Good posts John - thanks.

Micro-CHP systems info here:

Micro combined heat and power - Wikipedia, the free encyclopedia

Stirling engine info here:

Stirling engine - Wikipedia, the free encyclopedia

OK. It really does look good for the future (in other words not so bleak as some like to paint it). All this 'stuff' being re-developed and utilised to cut down on heat wastage.

johntheexpat

It does rather take one's eye off the main point though.

It's all very well having incredibly efficient energy sources in the home, but which is greener?  A modern house that uses an old, 50% efficient boiler giving out say 5 KW of heat to keep the place warm, or an old house which uses a 12KW state of the art Micro CHP unit to keep it to the same level of comfort?

Insulation, insulation, insulation.  It is the only real "green" policy.  

FWIW, I'm very much opposed to supplements on my electricity bill to support the feed in tariff for solar power.  I am also very much against tax breaks for wind power. (I have no objection to wind farms as such, I just don't believe I should pay for them).  What I do support with a fair degree of fanatacism eek: ) is helping to pay for  subsidised loft insulation and the like and low energy lights.  Why?  Because they reduce consumption and reduced consumption leads directly to reduced levels of imported energy which is good for the balance of trade figures, which is good for the whole country (ie ME!)