Green gas for the grid

By Paul Whitehead

September 7, 2009 - Renewable biogas could replace a significant amount of natural gas in Europe's gas grids. But turning raw biogas into grid quality biomethane is expensive. All sorts of barriers remain to get decentralized biogas production into a grid designed for natural gas from just a few sources.

No amount of wind power or nuclear power can help Europe diversify its energy sourcing if countries like the UK, Germany and Italy continue to depend on natural gas for heating. In Britain, western Europe's biggest gas market, 80% of homes are heated by gas -- and with indigenous supplies from the North Sea fast depleting, there is an increased reliance on imported gas.

Most existing European Union-wide renewable energy initiatives have focused on the electricity market, boosting the use of wind power and co-firing of biomass in coal-fired power plants, and more recently attention has shifted to biofuels or electric vehicles as a means of cutting reliance on oil in the transport sector. The role that renewable heat could play has been largely overlooked.

The EU's target for renewable energy source to meet 20% of all energy consumption by 2020 only sets a specific target for renewables in transport (10%), not heat or power, but as heat typically accounts for a third of all energy use, individual national targets -- ranging from 10% in Malta to 49% in Sweden -- will be hard to meet without some contribution from renewable heating.

But renewable heating requires large capital investments and changes in consumer behavior. Solar water heating is starting to take off as a relatively low-cost renewable technology for households but, even so, has a payback period of at least 30 years, according to data from the UK's Energy Saving Trust. As it works best in sunnier weather and on those homes with a south-facing roof it is not an option for many of Europe's city-dwellers who live in apartment blocks. Neither are ground source heat pumps, which extract heat from the ground and use heat exchangers to heat water. These only work in very large gardens or in other properties, like farms, with lots of outdoor space.

Wood chip and wood pellet fired boilers -- including CHP -- are another renewable heat alternative, especially for households already connected to a district heating grid. But for households with gas-fired heating, wood chip or wood-pellet boilers need more space, as well as sufficient storage space for the fuel pellets or chips.

The attraction of biogas is that if it is upgraded to grid quality methane, it could be injected into existing gas infrastructure alongside natural gas, allowing consumers to source a percentage of their heating fuel from renewable sources without even noticing it.

They would continue to run their existing boilers, gas fires and cookers without any need for new infrastructure at the consumer end. But considerable investments would be needed to produce the biogas in the first place and then to "upgrade" it to grid quality, and current regulatory frameworks do not provide adequate support to make that happen on a large scale. That was the consensus that emerged at a London Greenpower conference on biogas in July.

Biogas is a renewable, organic gas produced by anaerobic digestion or gasification of organic waste. Its production is already quite common in the waste-water industry, where it is a bi-product of digestion treatments designed to remove pathogens. Anaerobic digestion is also increasingly popular in agriculture as a treatment for animal manure, chicken litter and agricultural waste to produce energy and fertilizers. And biogas can also be produced from the organic component of municipal waste that is increasingly being diverted from landfill following introduction of the EU landfill directive in 2002.

But raw biogas is unsuitable for injection into the gas grid as its composition is typically only 60% methane, with carbon dioxide making up most of the rest (around 38% of the total) and other gases including nitrogen and oxygen accounting for the remainder.

To get grid quality gas, raw biogas has to be converted to biomethane, by removing the CO2 and some of the other impurities in an upgrading plant. Biomethane typically has a methane content of around 98%.

Could supply half of UK households

Biomethane production in Europe remains relatively limited. Sweden has pioneered the technology but uses biomethane in compressed form – like compressed natural gas – as a transport fuel for cars and buses. Germany and the Netherlands both boast a handful of biomethane production facilities that produce gas for grid injection. And while there is plenty of opportunity for expansion in both countries, the use of district heating makes biomass-fired CHP a more viable alternative than in the UK.

So far the UK has no grid connected biomethane production – despite hundreds of mainly agricultural biogas and sewage gas production facilities. But biogas could heat half of the UK's homes by 2020, given the right sort of government support, Janine Freeman, head of the sustainable gas group at UK national power and gas grid operator National Grid told the conference. Freeman said this would provide a much more affordable alternative than some of the other technologies being considered to deliver renewable heating -- like heat pumps and wood-fired boilers.

National Grid has set out two scenarios for biomethane production to 2020. Under its baseline scenario, biogas derived from sewage, agriculture and waste as well as Miscanthus grass planted specifically for the purpose would produce 5.6 Bcm of grid quality biomethane. This works out at little more than 5% of UK gas demand, typically around 95 Bcm/year. But that's still enough to meet 14% of residential gas demand. Under its most optimistic scenario, given optimal support and incentives, National Grid believes biomethane production could meet 18.4 Bcm in 2020, enough to satisfy a fifth of total gas demand, or half of residential demand (see table: UK biomethane potential).

Not only would biomethane help the UK meet its renewable energy target and bolster security of supply, it also could change the way the grid operates by creating new entry points for gas at different points on the network.

"Renewable gas ticks all the boxes. It's more affordable than many other renewables, and it offers a unique solution because it uses existing gas infrastructure. There is no need for consumer action or for consumers to install new infrastructure," Freeman said. Her presentation set out that 1 MWh of biomethane would cost between £50-100 ($81-162) to produce and inject, which she said was in the same "ball park" as other renewable technologies currently supported by the UK government.