At Munich Zoo you can watch the courtship rituals of the banded mongoose , hear the morning song of the scarlet ibis or visit the Indian elephants , who help keep the lights on with electricity generated from their dung . They can do this because Munich Zoo has harnessed `` poo power , '' energy stored in animal waste , which can be converted into a fuel known as `` biogas . '' It works like this : The zoo has built three large containers , each capable of holding about 100 cubic meters of animal waste -- that 's around a week 's worth of dung collected from all the vegetarian animals in the zoo . Once inside the containers , it 's mixed with warm water and the bacteria in the dung is left to decompose in an oxygen-free environment for 30 days . The resulting biogas , mainly comprised of methane and carbon dioxide , rises naturally through vents in the ceiling to a corrugated hut on the roof where it 's collected in a `` big balloon , '' says park supervisor Dominik Forster . The biogas is then fed into a gas-powered engine that 's used to generate electricity . Forster says that the balloon -- which more closely resembles a small Zeppelin -- can store enough biogas to meet 5 % of the zoo 's energy needs . `` When you turn the biogas into electricity , it creates heat which we also store , '' says Forster . This is then used to warm the gorilla enclosure , `` but could be used to heat about 25 homes , '' he adds . Once the fermentation process that creates the methane is finished , the remaining solid matter , or `` digestate '' is used as an organic fertilizer for crops that will later be used as feedstock for the animals . `` We do n't waste anything , '' said Forster , who claims that his is the only zoo in Germany to generate electricity in this way . A mature elephant can eat about 100 kilograms of fruit , vegetables and pretzels a day , producing a mountain of dung and Forster says that all the zoo animals together create roughly 2,000 tons of the stuff every year . This is enough to power about 100 Munich households -- a drop in the ocean when you consider Munich 's population , which is 1.3 million , according to CIA World Factbook . The problem is that dung alone does not produce all that much energy relative to its size , says Geraint Evans , head of biofuels at the UK 's National Centre for Biorenewable Energy , Fuels and Materials . `` By the time the food has been digested by the animal , a lot of the energy in it has been used up or burped out , '' he said . `` It 's more efficient to just put the feed directly into the biogas generator . '' Even if the returns are small at this stage , Evans says this project and others similar are still worth it . `` It 's really important that we change our mindset from dependence on one source of energy to many different complementary sources , '' Evans said . `` Animal waste can create electricity , heat , fertilizer ... even clean water can be extracted from the solids to spray on crops ... So , it 's emblematic of this very holistic approach . '' In this spirit , Forster says there are now plans to install photo-voltaic solar panels on top of the animal enclosures over the coming year .
Zoo in Germany partially powered by electricity produced from animal dung . Animal waste fermented for 30 days generates `` biogas '' Energy produced enough to heat 25 homes and power 100 .