EFFICIENCY- The key buzz word of our energy future. Every thing we do is successful or not based on efficiency. The simpilist definition of efficiency is effort out divided by effort in.
Amorphous Thin film 6 to 8%
Chrystal silicon photovoltaic arrays 12 to 15 %
Multilayer solar cells with concentrators 20 to 38%
Fluid thermo electric 14 to 20 %
Direct thermo electric (new) 30 to 40%
Printed Solar cells (new) 12 to 14%
Electrical energy converted into hydrogen gas
alkaline electrolysis (low intensity) 85-95%
PEM electrolysis (low intensity) 80-90%
PEM electrolysis (high intensity) 50-80%
Hydrogen gas compressed to 700 bar (10,000 psi)
Mechanical compressor 85%
hydride compressor 80%
Hydrogen gas converted into electricity
Standard Piston engine generator 20-25%
Hydrogen optimized piston engine gen 30-50%
Hydrogen optimized diesel engine gen 40-58%
Hydrogen fuel cell
Alkaline 40-50%
PEM ( high intensity) 35-50%
PEM ( low intensity) 50-65%
Solid oxide 35-45%
Maximum available efficiency for solar to stored hydrogen to electricity would therefore be
1 kw of solar energy falling on one square meter X 40% = 400Watts
400 Watts of electrical energy to PEM electrolyse water to hydrogen (low intensity PEM) X 85% =340 Watts
340 Watts of hydrogen compressed to 700 Bar X 85% = 289 Watts
289 Watts reconverted to electricity X 60% (low intensity PEM) = 173.4 Watts to power a house or drive a vehicle
173.4 Watts to drive a vehicle X 90% to convert to AC electricity X 90 % to convert from electricity to mechanical motion in motor X 90% to transmit rotary motion to the wheel and ground = 146.4 Watts to the ground.
Therefore a kilowatt of solar power can be turned into hydrogen and back into home power at 173.4/1000= 17.34% efficiency
A kilowatt of solar power can be turned into hydrogen and back into auto motive power at 14.64 % efficiency
The virtue is that the sun shines, on year around average, 5.5 hours per day (San Francisco bay area).
Therefore the square meter of sunshine capture area can accumulate 5,500 watt-hours per day and supply to the house X 17.34% efficiency 953.7 Watts, to be utilized when the sun is not shining (dusk to dawn).
That same square meter of sunshine capture area can supply 5,500 Watt -hrs per day X 14.64% efficiency = 805 Watt-hrs per day for an electric vehicle.
An electric vehicle requires approximately 200 Watts per mile at fifty miles per hour. Therefore 200 Watts X one hour running time = 200 Watt-hours per running hour. the 805 Watt-hours supplied by the hydrogen will propel the car for four hours per day. Assuming fifty miles per hour speed then the vehicle can travel 200 miles per day.
Not bad for one square meter of concentrated trippel junction solar cell or direct thermo electric generator both of which can operate at approximately forty percent efficiency in converting solar energy to electricity.
The limitation of course is that the 5.500 solar Watts can either power the house or business or the car, not both.
So a working installation would require at least two square meters of solar capture area.
The automotive equation can be improved if the vehicle is a battery or ultra-capasitor hybrid for two reasons.
One, regeneration, the vehicle can recapture energy every time it slows down to come to a stop and Two, if it is a deep hybrid, with a plug in battery pack capable of propelling the vehicle forty to fifty miles before the fuel cell has to kick on to recharge the batteries, then the range can extend to two hundred fifty miles. If most trips are short range the the batteries can do the work and the fuel cell becomes a backup. Also if the battery pack is sufficiently robust then the fuel cell in the vehicle can be smaller, needing only to be sufficiently powerful to provide power for cruising down the highway and recharging the battery.
This examination shows that the core requirement to the solar hydrogen power system is efficiency. If each of the components can operate at sufficient efficiency levels, then the system is functional. If any components operates at a much lower efficiency then the whole system ceases to effectively function.
So here's to high efficiency and a new secure, pollution and carbon free world powered by solar hydrogen.
John Gotthold
President- Silicon Valley Chapter of the American Hydrogen Association www.ahasvc.org
co-founder and CTO of Independent Energy Research www.ier-usa.org
In solar hydrogen energy systems the efficiency keys are
Solar energy converted to electrical energy (watts out /Solar kilowatts in)Amorphous Thin film 6 to 8%
Chrystal silicon photovoltaic arrays 12 to 15 %
Multilayer solar cells with concentrators 20 to 38%
Fluid thermo electric 14 to 20 %
Direct thermo electric (new) 30 to 40%
Printed Solar cells (new) 12 to 14%
Electrical energy converted into hydrogen gas
alkaline electrolysis (low intensity) 85-95%
PEM electrolysis (low intensity) 80-90%
PEM electrolysis (high intensity) 50-80%
Hydrogen gas compressed to 700 bar (10,000 psi)
Mechanical compressor 85%
hydride compressor 80%
Hydrogen gas converted into electricity
Standard Piston engine generator 20-25%
Hydrogen optimized piston engine gen 30-50%
Hydrogen optimized diesel engine gen 40-58%
Hydrogen fuel cell
Alkaline 40-50%
PEM ( high intensity) 35-50%
PEM ( low intensity) 50-65%
Solid oxide 35-45%
Maximum available efficiency for solar to stored hydrogen to electricity would therefore be
1 kw of solar energy falling on one square meter X 40% = 400Watts
400 Watts of electrical energy to PEM electrolyse water to hydrogen (low intensity PEM) X 85% =340 Watts
340 Watts of hydrogen compressed to 700 Bar X 85% = 289 Watts
289 Watts reconverted to electricity X 60% (low intensity PEM) = 173.4 Watts to power a house or drive a vehicle
173.4 Watts to drive a vehicle X 90% to convert to AC electricity X 90 % to convert from electricity to mechanical motion in motor X 90% to transmit rotary motion to the wheel and ground = 146.4 Watts to the ground.
Therefore a kilowatt of solar power can be turned into hydrogen and back into home power at 173.4/1000= 17.34% efficiency
A kilowatt of solar power can be turned into hydrogen and back into auto motive power at 14.64 % efficiency
The virtue is that the sun shines, on year around average, 5.5 hours per day (San Francisco bay area).
Therefore the square meter of sunshine capture area can accumulate 5,500 watt-hours per day and supply to the house X 17.34% efficiency 953.7 Watts, to be utilized when the sun is not shining (dusk to dawn).
That same square meter of sunshine capture area can supply 5,500 Watt -hrs per day X 14.64% efficiency = 805 Watt-hrs per day for an electric vehicle.
An electric vehicle requires approximately 200 Watts per mile at fifty miles per hour. Therefore 200 Watts X one hour running time = 200 Watt-hours per running hour. the 805 Watt-hours supplied by the hydrogen will propel the car for four hours per day. Assuming fifty miles per hour speed then the vehicle can travel 200 miles per day.
Not bad for one square meter of concentrated trippel junction solar cell or direct thermo electric generator both of which can operate at approximately forty percent efficiency in converting solar energy to electricity.
The limitation of course is that the 5.500 solar Watts can either power the house or business or the car, not both.
So a working installation would require at least two square meters of solar capture area.
The automotive equation can be improved if the vehicle is a battery or ultra-capasitor hybrid for two reasons.
One, regeneration, the vehicle can recapture energy every time it slows down to come to a stop and Two, if it is a deep hybrid, with a plug in battery pack capable of propelling the vehicle forty to fifty miles before the fuel cell has to kick on to recharge the batteries, then the range can extend to two hundred fifty miles. If most trips are short range the the batteries can do the work and the fuel cell becomes a backup. Also if the battery pack is sufficiently robust then the fuel cell in the vehicle can be smaller, needing only to be sufficiently powerful to provide power for cruising down the highway and recharging the battery.
This examination shows that the core requirement to the solar hydrogen power system is efficiency. If each of the components can operate at sufficient efficiency levels, then the system is functional. If any components operates at a much lower efficiency then the whole system ceases to effectively function.
So here's to high efficiency and a new secure, pollution and carbon free world powered by solar hydrogen.
John Gotthold
President- Silicon Valley Chapter of the American Hydrogen Association www.ahasvc.org
co-founder and CTO of Independent Energy Research www.ier-usa.org
Robert Michael Foster, MA
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