LNG Storage

A crucial aspect of a LNG conversion is the storage of LNG in the vehicle and the refilling of the storage tank. Most LNG storage systems (typically originating from the industrial gas industry) are promoted as single line fill systems. However, a vent line must be connected to the tank at some point to relieve the pressure in tank to facilitate filling. Therefore, all systems are actually two line (fill & vent) fill systems, whether they are advertised that way or not. There are often LNG issues with single line fill systems and these issues are eliminated with a 2-line fill system.

LNG Cost

It is straightforward to put LNG in terms of Diesel Gallon Equivalent (DGE). According to the US DoE Fuel Energy Spreadsheet, LNG contains 74,720 BTU/gallon (LHV) and low sulfur diesel contains 129,488 BTU/gallon (LHV). If natural gas is selling for $4/MCF and natural gas contains 983 BTU/ft³ (LHV), the DGE price of LNG works out to

• Natural Gas Cost per BTU = (4/1000 $/ft³) / (983 BTU/ft³) = $4.069 x 10E-6 / BTU
• LNG cost = (4.069 x 10E-6 $/BTU) x (74,720 BTU/gallon) = $0.304/gallon
• LNG DGE cost = (4.069 x 10E-6 $/BTU) x (129,488 BTU/gallon) = $0.527/DGE

One MCF of natural gas contains the equivalent energy of about 7.59 gallons of low sulfur diesel (983 x 1000 / 129,488) so it's actually better than the 1 MCF = 7 gallons of diesel T Boone Pickens has been suggesting in several interviews.

Besides the commodity price for natural gas, operating and maintenance (O&M) costs of the on-site refueling equipment can substantially add to the price of LNG and extend the payback time of the conversion.