What is biogas anyway?

You had to ask!  

Well, yes it is. As Culhane's Biogas song goes, "It's the same gas as the gas we pass!".

Seriously though, biogas is a mixture of methane (CH4) 60 to 70%, carbon dioxide (CO2) 30 to 40% and sniffable amounts of H2S (that makes it safe because you know if there is a leak, right?).  It can be dropped in in place of so called "natural gas" but has less heat content per unit volume.  But that doesn't make much of a difference in any practical sense for the home user since it is free (once you have paid for the digester).

It can be made from almost any organic foodstuff that animals would eat and from the resultant poo that animals make when they are done eating.  The ideal way to make biogas in our opinion is from food scraps -- the wasted parts of plants and animals that you don't eat and that you would throw away anyway.

But to Solar CITIES Biogas is something else:

Biogas is solar energy.  More precisely it is STORED SOLAR ENERGY. 

In effect, biogas is a solar battery.  But it is  far more reliable, durable and usable than any other form of stored sunshine because biogas "never loses its charge".  It can be kept in storage until needed for... well, for millions if not billions of years. Try to do that with a battery!

Plants and animals, of course, are also forms of stored solar energy, but they don't last.  They grow for a while, storing sunshine along the way, but then they die, and when they decay most of that energy is lost to entropy pretty quickly.  But when we turn those dead animal and plant parts, with the help of living microbes, into biomethane, and we store that biologically derived methane, that energy is held in place in a stable form until we need it.  And since methane is lighter than air, unlike batteries it is really easy to transport.

Of course biogas is a gas so it takes up a lot of volume (remember Avogadro's number? 22.4 liters per mole, and a mole of methane is only 16 grams so even without the CO2 content, which is 44 grams per mole and makes up roughly 35%, it's a lot of space for something so light).  But it doesn't have to be transported in big baloons (although we do carry it around like that sometimes), it can easily be piped.  Just like so-called "natural gas".

And yes, it can be compressed (again just like CNG) but we generally don't do that at the home scale because you have to remove the CO2 first and it is still fairly expensive to do that relative to the economies of scale.  So we tend to use biogas as a local way to store the solar energy in organic chemical bonds and use it where we generate it.

Because biogas stores sunshine so well we believe it is the best solar solution.  We capture it whenever the sun shines (even on cloudy days) because plants use the sunshine to grow.  Then we create comfortable conditions for the archaea and the bacteria to turn dead parts of  plants and the animals that feed on them into useful energy that is available 24/7, 365 days a year.

So that is the bottom line -- BIOGAS IS SOLAR ENERGY.  And that is why we are so interested in it in Solar CITIES.


Is it really the same as "fart gas"?