SOLID STATE HYDROGEN vs. NATURAL GAS •••••

Renewable Solid Hydrogen Energy Storage and Power Generation Project

Natural Gas can, of course, be used as a fuel for both reciprocating engines and for gas turbines.  Its main advantage over liquid fuels is that it produces less emissions, especially NOx.  When burned in an engine or gas turbine, the overall efficiency of the energy conversion process should be ~32-34% (for a gas turbine) and perhaps as high as 38-40% for a recip. engine - assuming that the turbine and engine are rated at ~5MW electrical output.  Hydrogen is a cleaner burn than natural gas as the emission is water vapor with the by-product of electrolysis being oxygen.

However, comparing these efficiencies with the round-trip efficiency of the hydrogen storage and power generation system is not really comparing like with like.  One of the main drivers for the surge in interest in large-scale energy storage technologies, especially by the utilities and energy companies, is to enable the capture of low cost renewable energy that's produced during periods of low grid demand (and therefore correspondingly low wholesale electric rates) and storing it so it can be released during periods of peak demand (and high wholesale pricing) - and thereby displacing fossil generation plants that are used to meet peak power demands.

As an example, if the effective cost of the renewable energy that's produced during overnight hours is very low, then the round-trip efficiency doesn't greatly impact the cost of the electricity that's ultimately generated.

For example, consider wind energy that could be sold to the grid at 1:00 am at a wholesale price of 1 c/kWh.  If the hydrogen storage to electricity system's round trip efficiency is 40% (assuming an electrolyzer efficiency of 75%, storage system eff'y of 95% and a fuel cell eff'y of 60%), then the effective cost of the energy that is sold would be 1.0 cent divided by 0.4 (representing the 40% round trip efficiency), giving a 'cost' of 2.5 cents/kWh - plus an amount for capital cost recovery and maintenance.  This energy can be sold at rates above 10 cents/kWh during periods of peak demand. However, a natural gas fired recip. engine that is operating at 40% is still burning high cost Natural Gas that is today costing ~$12/mmbtu (prices have been fluctuating).  What this means is that the cost of the power produced by the recip engine would cost approximately 12 cents/kWh just for the fuel alone, plus capital cost and maintenance.

Natural Gas recips. and turbines are frequently used by utilities to provide peak load support, but they can't capture and store (and effectively 'time-shift') renewable energy.   The system proposed by HES allows them to do that efficiently and effectively.  Even for peaking applications, utilities have become cautious of natural gas-fired units because of the increasingly unpredictable costs associated with the natural gas fuel, their associated emissions, the cost of running fuel lines to often remote substations, and the current move toward green technology solutions.