Estimated round-trip efficiencies calculated using the difference in energy potentials. Common for hydrogen, formic acid, and methanol we use U_OER = 1.6 V_RHE and U_ORR = 0.8 V_RHE.

	Energy stored (electrolyzer)	Energy released (fuel cell)	Round trip efficiency, η
Hydrogen	U HER = −0.1 VRHE	U HOR = 0.1 VRHE	≈41%
Formic acid	U CO2→HCOOH = −0.8 VRHE	U FAOR = 0.2 VRHE	≈25%
Methanola	U CO2→CO+H2 = −0.6 VRHE	U CO→CO2 = 0.65 VRHE	≈7%
Li-batteryb			≈90%

^aHere only the cost of syngas production is considered, not the full formation of methanol.

^bTypical charge/discharge efficiency.