Hydrogen Blending into the Natural Gas Network

[NickW + 2,714]

Interesting trial. Blending 20% by volume Hydrogen into the natural gas network at Keele University (UK) 

HSE have approved project.

https://www.businessgreen.com/bg/news/3084832/hydrogen-injected-into-gas-grid-as-part-of-groundbreaking-uk-trial

20% by volume equals about 7.5% by calorific value. Hydrogen blending is one practical method of storing surplus electricity from intermittent sources. There is a potential here to displace about 5.6bn m3 of Methane from the UK grid (60Twh gross (gas)  / 30 Twh net (electricity) after burning in a CCGT. 

Would be interesting to see a comparison with other storage methodologies - Pump storage, batteries, flywheels etc. 

[footeab@yahoo.com + 2,132]

286kJ/mol... in a perfect world. 

1kWh = 3600kJ so perfect world

1kWh = 12.6 mols  = 25g H2 & 200g O2

Burning the H2 = 50% efficiency or so(assume same % as CCGT).  But, there is all of that O2.  If you had biomass, add that O2 to the mix and it will burn much hotter, much more efficiently so, slight gain there.  Lets call it 55% efficient overall. But have to drop efficiency of splitting.  Splitting is never 100%, so at best it is going to be??? 80%?  90%?  and have to separate the O2.  This makes overall H2O splitting efficiency around 45%.

Pumped Hydro Storage.  This is completely dependent on head pressure.  High head pressure can have efficiencies of 90% with the pumped portion at high head pressure likewise having an efficiency of around 70%-->80%.  Some claim a pumping efficiency of 90%... i have never seen evidence of this being true.  Overall call it 60%-->80% efficient at its maximum. 

*** Note I said HIGH head pressure ***   Most places in the world cannot achieve high head pressure due to geography constraints.  Yes, technically you could dig DOWN and create a giant bladder which RAISES a giant chunk of land...  So, lower head pressure = turbine efficiencies dropping to about +70% or a combined efficiency of ~50%+

Batteries: Technically if no AC--> DC DC--> AC conversion would be 99% efficient if using lithium, 95% if using some flow chemistry batteries which are much cheaper and use common materials.  If put batteries on a high voltage DC line, could partially*** eliminate one conversion(not really).  High Voltage Inverters are roughly 95% efficient.  The bigger they are the more efficient they are.  As an example: Lower voltage inverters you use for solar/off grid are as low as 75% efficient depending on the current throughput.  Most will claim 90% or so, but this is at low current.  If you get your inverter hot, you will kill it, so #1 thing is LOTS of ventilation and fans with thermal cut off.  So, overall: if doing grid storage at HIGH DC voltage: Efficiencies of around 90% *** depending on how long you wish to store it ***

Kinetic energy(spinning energy/extremely expensive and is used in every grid today) is about 90% efficient AC motor, but this is HIGHLY dependent on how long you are storing the energy and loses of 10% over a day would be acceptable.  Overall eff: ***80%/day***  Vacuum increases by a good margin, but the biggest factor is bearing friction losses.  Magnetic levitation has been worked on by many different people yet no one can make it work in reality.  Have to have VERY powerful magnets and cannot pull pwr out quickly.  Maybe if someone combined normal bearings and magnetic levitation so you  can pull pwr out quickly by using normal bearings and keep it humming like normal under magnetic levitation.  We would then be talking roughly ??? 95% efficient overall?

Others have talked about giant air bladders under the ocean....  Air compressors at best are ~63% efficient and then we cool the air dunking it under water???  That is going to suck another 10% out, and then we have to spin a ~gas turbine, or pumped turbine at max of 50%?  So.... 25% eff.... yea, not good. 

Chemical is possible with an intermittent supply, but would have efficiencies ranging from POOR to piss POOR.

1. So: Batteries
2. Kinetic***
3. Pumped Hydro Storage
4. Splitting water
5. Air bladders
6. Chemical

[NickW + 2,714]

21 minutes ago, footeab@yahoo.com said:

286kJ/mol... in a perfect world. 

1kWh = 3600kJ so perfect world

1kWh = 12.6 mols  = 25g H2 & 200g O2

Burning the H2 = 50% efficiency or so(assume same % as CCGT).  But, there is all of that O2.  If you had biomass, add that O2 to the mix and it will burn much hotter, much more efficiently so, slight gain there.  Lets call it 55% efficient overall. But have to drop efficiency of splitting.  Splitting is never 100%, so at best it is going to be??? 80%?  90%?  and have to separate the O2.  This makes overall H2O splitting efficiency around 45%.

Pumped Hydro Storage.  This is completely dependent on head pressure.  High head pressure can have efficiencies of 90% with the pumped portion at high head pressure likewise having an efficiency of around 70%-->80%.  Some claim a pumping efficiency of 90%... i have never seen evidence of this being true.  Overall call it 60%-->80% efficient at its maximum. 

*** Note I said HIGH head pressure ***   Most places in the world cannot achieve high head pressure due to geography constraints.  Yes, technically you could dig DOWN and create a giant bladder which RAISES a giant chunk of land...  So, lower head pressure = turbine efficiencies dropping to about +70% or a combined efficiency of ~50%+

Batteries: Technically if no AC--> DC DC--> AC conversion would be 99% efficient if using lithium, 95% if using some flow chemistry batteries which are much cheaper and use common materials.  If put batteries on a high voltage DC line, could partially*** eliminate one conversion(not really).  High Voltage Inverters are roughly 95% efficient.  The bigger they are the more efficient they are.  As an example: Lower voltage inverters you use for solar/off grid are as low as 75% efficient depending on the current throughput.  Most will claim 90% or so, but this is at low current.  If you get your inverter hot, you will kill it, so #1 thing is LOTS of ventilation and fans with thermal cut off.  So, overall: if doing grid storage at HIGH DC voltage: Efficiencies of around 90% *** depending on how long you wish to store it ***

Kinetic energy(spinning energy/extremely expensive and is used in every grid today) is about 90% efficient AC motor, but this is HIGHLY dependent on how long you are storing the energy and loses of 10% over a day would be acceptable.  Overall eff: ***80%/day***  Vacuum increases by a good margin, but the biggest factor is bearing friction losses.  Magnetic levitation has been worked on by many different people yet no one can make it work in reality.  Have to have VERY powerful magnets and cannot pull pwr out quickly.  Maybe if someone combined normal bearings and magnetic levitation so you  can pull pwr out quickly by using normal bearings and keep it humming like normal under magnetic levitation.  We would then be talking roughly ??? 95% efficient overall?

Others have talked about giant air bladders under the ocean....  Air compressors at best are ~63% efficient and then we cool the air dunking it under water???  That is going to suck another 10% out, and then we have to spin a ~gas turbine, or pumped turbine at max of 50%?  So.... 25% eff.... yea, not good. 

Chemical is possible with an intermittent supply, but would have efficiencies ranging from POOR to piss POOR.

1. So: Batteries
2. Kinetic***
3. Pumped Hydro Storage
4. Splitting water
5. Air bladders
6. Chemical

The point was that if you have  a surplus of electricity,  which will happen in the UK if we build the 30GW of wind in the North Sea then electrolysis to hydrogen is one practical option to convert that electricity to a storable form. The UK doesn't have enough suitable sites for pump storage or CAES. Batteries - in the long term maybe once vehicle fleets go EV and there is a large supply of second life batteries to use. The Ev's are also a good tool to soak up surplus electricity

The option was also explored in the event the UK went down the French route of building dozens of nuclear power stations as there would be a huge night time surplus without the same outlets as France because the UK is an Island with limited interconnections. 

Dinorwic (pump storage) built in the early 1980's is 75% efficient

https://www.withouthotair.com/c26/page_191.shtml