From
http://en.wikipedia.org/wiki/Energy_density
Petrol's energy density is 44.4MJ/kg = 12 kwh/kg. That generator's weight tank full of petrol is 13kg. So energy density is 0,92 kWh/kg. If we assume efficiency from tank to generator output to be 0.3 (is this reasonable?), overall efficiency would be 0,28 kWh/kg.
Teslas battery pack has 85 kWhs and weights 595 kg source
http://www.teslarati.com/tesla-model-s-weight/ so energy density is 0,14 kWh/kg.
According to this generator's effective energy density would be double compared to Tesla's battery pack?
edit: apparently generators efficiency from tank to generator output is approximately 0.2. So generator's energy density is 0.18 kWh/kg.
I will be the first to say that the generator is very close to parity with adding weight to the main pack... so close that the theoretical energy densities and inefficiencies are not accurate don't really answer the "Is there a benefit to carrying a H1000 in the Frunk?". Let's do the math by the published specs of the generator, and miles:
Honda 1000 weight, dry: 13.15 kG. Fuel capacity: 2.2 Liters. Weight of fuel: 1.6 kG. Total weight: 14.8 Kilos. But you can't carry the generator alone, you'd have to carry a UMC or similar as well. I don't know exactly how much a UMC weighs, lets just say 1.2 kilo (it's really much more than that... but this gives a round number and is more than fair). That would give us 16 Kilo weight of stuff in the frunk to be able to add range to the car when we get stuck.
Honda 1000 power output: 900 Watts, 7.5 Amps for 3.8 hours. Note that "Honda 1000" is only a name. This is NOT a 1kW generator. It can only provides 900W continuous. No knock on Honda, I have a 3000iS and absolutely love it. Any/all of these generators don't really put out the power that their marketing name would suggest.
Extrapolating from Teslas charts about charging from various outlets, we can figure that 7.5 Amps at 120V is going to put in 1.875 MPH (and this is being generous). 1.875 MPH for 3.8 hours = 7.1 Miles of range.
So... 7.1 miles of range from 16 kilos+ in the Frunk. What would 16 more kilos in the main pack give? If look at the various models:
85 (265/595) * 16 = 7.1 Break Even
85D (270/595) * 16 = 7.3 Generator loses.
P85D (253/595) * 16 = 6.8 Generator Wins!
Again, these are VERY close. But... given that it takes just under FOUR HOURS to add this range to the car... well the original question was about putting something in the Frunk for emergencies. My statement was that adding weight to the main traction pack would be better. Because there is not anything out there at the moment significantly more energy dense than the traction pack. In fact, in my challenge, I defined the word "Significantly" to mean "over 20%". The Honda 1K does not meet that 20%. Not even close.
Are there generators that would? Yes, the Honda 2K probably would. About 24Kilos with fuel, plus a couple for the UMC, puts out 13.3A for 4 hours, thus adding about 14 miles to the car. Using the 85D example from above (270/595) * 26 = 11.8. Generator wins! By 18.6%! Close enough to 20%, none of this math is all that precise, I'll declare that one a winner! This is all just fun anyway.
