Green methane in the gas grid

How power-to-gas works
(Source)
erneuerbare Energien=renewable energy;  Wasser=water; Wasserstoff=hydrogen
Erdgasnetz=natural gas grid; Strom=electricity; Wärme=heat
  Mobilität=mobility; Kohlendioxid=CO₂;Katalysator=catalyser; Elektrolysator=electrolyser

One of the ways we can reduce emissions is to produce synthetic fossil fuels.  We can do this by taking "green" hydrogen, running it with carbon dioxide at pressure and temperature over a catalyst, to produce methane.  "Green' hydrogen is produced by electrolysing water using surplus electricity from renewables.

This is an energy intensive process because the bonds between hydrogen and oxygen are very strong.  But, if you use power which would any way be "curtailed" (i.e., when the grid operator says there in too much electricity being generated and fed into the grid and forces wind or solar farms to temporarily disconnect from the grid) then the cost is low.  If, in addition, you don't need to concentrate CO₂ from the atmosphere. but already have a concentrated supply, for example, from the exhaust stack of a gas power station, then the cost is negligible.  Only the capital cost of the plant is relevant.

By the way, "brown" hydrogen is produced from coal, and "blue" hydrogen from natural gas.  Neither of these is carbon-neutral, and if they are used to fuel a hydrogen economy, then the hydrogen economy isn't carbon neutral either.  Which is surely the whole point! If, however, "green" hydrogen is used, although CO₂ will be produced when it is burned, it will have already been drawn from the atmosphere to create the synthetic methane in the first place, so will not be adding to atmospheric levels of CO₂.

Two points.

First of all, in high latitudes, there will be a need for seasonal storage, and batteries will likely be too expensive for a week or two of storage, for a couple of decades yet.   Gas via legacy peaker plants will be the obvious way to fill these gaps.  And the gas grid in most developed countries (a) already exists and (b) has several weeks of storage capacity.   Synthetic natural gas won't add to carbon emissions.

Second, there will inevitable be curtailment in any renewable grid.  Yes, we will have batteries, yes, high voltage connectors between regions will be built, but just as with the fossil-fuel grid now, there will be much more capacity than we will on average use, just to ensure that when demand is high (or supply low because of the weather), there is enough power.  This will mean that output from wind and solar farms—when for example there are strong winds or sunny days or both—will often be curtailed.  If instead of being curtailed, the unneeded electricity is used to create synthetic natural gas (SNG), the cost of SNG will be lower than natural gas, despite the energy cost.

From ArsTechnica:

A Düsseldorf, Germany-based energy company called Uniper announced last week that it sent methane made from renewable hydrogen into the local natural gas pipeline.

The methanation plant in Falkenhagen that made the synthetic methane opened in May 2018, and the plant's operators began testing the process to combine renewable hydrogen with carbon dioxide from a nearby bioethanol plant.

The synthetic methane is sent into the local natural gas pipeline, where it's used along with traditional natural gas. "Today, the plant produces up to 1,400 cubic meters of synthetic methane (SNG) per day, which corresponds to approximately 14,500 kWh [kilowatt hours] of energy," a Uniper press release noted. 

Uniper's Falkenhagen-based methanation plant combines the renewable H2 from Store & Go's nearby electrolysis plant with captured CO2 from the nearby bioethanol plant, combining the two molecules to create methane (CH4), the primary ingredient in natural gas. That process also creates heat as a byproduct, which is used at a nearby veneering plant.

A big advantage of this methanation project is that it can leverage existing natural gas infrastructure, allowing vehicles, residences, and other customers to indirectly use renewable energy for fuel and heat.

The methanation plant receives renewable hydrogen (H2) from a nearby plant that has harnessed excess wind and solar power for electrolysis-based hydrogen synthesis since 2013. The renewable-hydrogen project is run with help from Store & Go, a European Union-funded research program that recently partnered with CO2-capturing startup Climeworks to build a synthetic methane plant in Troia, Italy.

[Read more here]

From pv magazine:

Vattenfall-led consortium plans 50 MW power-to-gas project in Germany.

The energy company plans to build the “HySynGas” project in the Brunsbüttel Industrial Park with ARGE Netz and MAN Energy Solutions. The consortium wants to establish a power-to-gas hub for cross-sector decarbonization in northern Germany.

ARGE Netz, MAN Energy Solutions, and Vattenfall announced a plan on Thursday to set up a large-scale power-to-gas project in an industrial park in Brunsbüttel, northern Germany. The facility will produce green hydrogen and synthetic gases (SNG) from electricity generated by nearby solar and wind plants.
It is expected that the green hydrogen will contribute to cross-sectoral decarbonization. It could be used as fuel for buses or ships, as well as in gas power plants and other industrial sectors. 

The aim of the partnership is to establish a unique power-to-gas hub for cross-sectoral decarbonization in northern Germany, Vattenfall said in a statement. The partner companies have also applied for funding from the Federal Ministry for Economic Affairs and Energy to build a related R&D laboratory.

The aim is to increase the use of renewable energy and reduce CO2 emissions in a range of sectors with green hydrogen. “The project is a central building block for a holistic energy transition and at the same time lays the foundation for the power-to-gas hub in northern Germany,” said Frense.

The consortium has already secured a number of well-known customers, such as the Volkswagen Group, various logistics firms, municipal utilities and other local companies.

According to Oliver Weinmann, managing director of Vattenfall Europe Innovation GmbH, “the technology is ready for use and the companies want to invest in the green energy future.” He said that an electrolyzer for the production of green hydrogen with at least 50 MW of capacity will be built at the industrial park, as well as facilities for the production of synthetic methane, with a capacity of at least 40 tonnes per day.

In Rotterdam, the Gigawatt Elektrolysefabriek project was also recently launched. The researchers from that project aim to start generating green hydrogen at the the gigawatt scale from 2025.

[Read more here]