# Power to weight ratio of fuel cells

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#### Dusan

##### Well-Known Member
A lot of people are talking about hydrogen fuel cells for aircraft in order to get over the low specific energy of current batteries, but during my research I've discovered the fuel cell stacks are relatively heavy for the power they can deliver. The best numbers I found for specific power are around 1.5KW/Kg. Does anybody have a better source?

#### Vigilant1

##### Well-Known Member
What type of "fuel" are you planning on? Ammonia, methanol, liquid hydrogen, compressed hydrogen? The weight per watt-hour of the fuel will be at least as important as the pounds per watt of the fuel cell.

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#### Dusan

##### Well-Known Member
What is the "best" in the sense what system can get the best power to weight ratio regardless of fuel type?

#### pictsidhe

##### Well-Known Member
Just wait until you see the price of fuel cells.

#### 12notes

##### Well-Known Member
Log Member
A lot of people are talking about hydrogen fuel cells for aircraft in order to get over the low specific energy of current batteries, but during my research I've discovered the fuel cell stacks are relatively heavy for the power they can deliver. The best numbers I found for specific power are around 1.5KW/Kg. Does anybody have a better source?
50kg (110lbs) for a 75 kW (100hp) power source doesn't seem too heavy to me. If you add a 25 kg(55lb) electric motor*, it's the same installed weight of a 100hp Rotax 912ULS package (including the alternator and everything needed to run the engine) at 75 kg (165 lbs).

* - I don't have time to look up and confirm, but I seem to recall a 75kW motor was available at this weight.

#### pictsidhe

##### Well-Known Member
Now all you need is some hydrogen.

#### Noeson

##### Member

2.0 kW/kg, but that's Toyota. My understanding is it's 10 lbs/kwh for a battery system and 2 lbs/kwh for practical purposes with current tech.

One bare bones system might be a 3kwh fuel cell ($15k) with 100 lbs / 10kwh of batteries ($5k diy?) for takeoff, a pair of Roto Max motors, ($1k) and a 200 lb tank ($1k?) with 6 lbs hydrogen producing a total of 100kwh (assuming efficiency is going to be lower than Toyota). Forklift industry has an infrastructure built up already for generating/pressurizing hydrogen, same with drones:

HYSTAT™15 – Indoor | Hydrogenics

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#### WonderousMountain

##### Well-Known Member
GeoGull TryKink wing canted tail aircraft was

Originally conceived as a Solar/Hydrogen cafe
like self launch. At that time the Hydrogen part
of the system was looking at about \$5,000 for ~
2Kw lasting Maybe 2 & 1/2 adding around 1Kw
each hour. It was to fly 75mph at altitude.

It was getting costly, complicated & Optimistic.
Anyway, that's what you need to do, get the lead
out of flying.

Optimistically,
CK LuPii

#### John.Roo

##### Well-Known Member
50kg (110lbs) for a 75 kW (100hp) power source doesn't seem too heavy to me. If you add a 25 kg(55lb) electric motor*, it's the same installed weight of a 100hp Rotax 912ULS package (including the alternator and everything needed to run the engine) at 75 kg (165 lbs).

* - I don't have time to look up and confirm, but I seem to recall a 75kW motor was available at this weight.
Unfortunatelly you need much more components = final weight will be much higher.
Problem is that fuel cell is not able to react quickly to different power demand.
So typically you need battery with capacity able to give you takeoff power.
Too high discharge rate is dangerous so lets calculate with 5C (I woudl prefere 3C but.... lets says 5C). It means that 10 kWh battery will give you 50 kW for takeoff.
For horizontal flight you need 20-25 kW so you need 25-30 kW fuel cell.
Don´t look for max. power of fuel cell - you need continuous power.
Here are some spec. for 30 kW Ballard hydrogen fuel cell
10 kWh battery = +- 50 kg
60-80 kW electric motor = 15-20 kg (depend on cooling system)
Controller = 3-5 kg (depend on type and on cooling system)
+
BMS system for battery, fuel cell, hydrogen tank (designed for min. 300 Atm pressure), wiring....

And somebody mentionned price....
Definitelly is not cheap solution.
If you would like to fly with hydrogen fuel cell powered airplane start with some light one seater "motorglider" so you can use only +-5 kW fuel cell. That may could be afordable solution

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#### henryk

##### Well-Known Member
Normally is a two seat glider,

=test pilot ing. Boguslaw Mrozek (BODEK)...

-fatal test fly in BEKAS tailles Kasper glider!
(one second before crash=circa 10 m level,

and one second after=WILGA circa 50 m high !

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