CO₂ Offsets Generated from an Aquabank™ facility

The production process flow diagram of an Aquabank™ facility is shown below.

In this process, the product is the electricity to meet the peak-demand in the power grid.  There are two major inputs, raw water from the upper reservoir and electric energy from the regional power supply grid. All other inputs (such as lubricating fluid, hydraulic oil, etc.) are relatively small and negligible.  The raw water is almost fully recycled, and the electricity input is for pumping water back to the upper reservoir, usually during mid-night to absorb excessive electric energy in the power supply grid. Aquabank™ is expected to generate for 6 hours and pump for 7.9 hours a day; thus the daily electricity generation is 6,000 MWh and electricity consumption for pumping is 7,625 MWh.

As a new facility, the embodied energy input and GHG emissions related to the facility construction and maintenance have to be taken into account in the life cycle assessment of emissions. A preliminary analysis based on economic input-output model (see Note 2 below Table 1) shows the CO₂ (eq.) emissions from the construction and maintenance of one Aquabank^TM facility are around 8.6 kg per MWh of peak power generation; that is, the annually distributed amount of emissions from the facility is around 18,576 tonnes, assuming its full generation capacity is utilized.

How Aquabank™ operates

• An Aquabank™ system effectively reduces the need for fossil fuel peaking plants. By generating clean peaking power for 6 hours daily at full capacity of 1,000 MW, it avoids 6,000 MWh equivalent of CO₂ emissions produced by fossil fuel plants during peak demand period

• An Aquabank™ system consumes excess baseload or intermittent electricity for pumping water back to the original source. At an operating efficiency of 78%, it requires 7.9 hours of pumping daily, therefore consuming 7,625 MWh. The equivalent CO₂ emissions produced by baseload units or intermittent units, such as nuclear or wind energy is significantly less than a fossil fuel peaking plant.

• Net number resulted from the above processes demonstrates significant CO₂ benefits an Aquabank™ system is able to achieve

Table 1 Summary of CO₂ (eq.) Offset from Aquabank^TM under Two Scenarios

Project Location	Current Peaking Units	Emissions Rate from Current Peaking Units(kg/MWh)	Annual Avoided Emissions from Current Peaking Units      (tonnes)	Baseload Power Supplier	Emissions Rate from Baseload Supplier  (kg/MWh)	Annual CO2 Emissions for Water Pumping    (tonnes)	Emissions Rate for AquabankTM Facility Construction & Maintenance    (kg/MWh)	Annual CO2 Emissions from AquabankTM Facility    (tonnes)	Net Annual Avoided CO2 Emissions   (tonnes)
NEPOOL	Natural gas and oil	464*	1,002,240	Nuclear	30.5*	83,520	8.6**	18,576	900,144
Ontario	Natural gas	540*	1,166,400	Nuclear	1.8*	5,040	8.6**	18,576	1,142,784

Note:

1)  *   These emissions rates are from available literature, subject to change with more detailed data available.

2)  ** This result is based on the cost estimate of the Aquabank^TM system and running of Economic Input-Output Life Cycle Assessment (EIO-LCA), US 2002 Benchmark model [Internet], Carnegie Mellon University Green Design Institute. Available from:<http://www.eiolca.net> Accessed 22 November, 2009. The result is subject to change with the progress of the Aquabank^TM projects.

Table 2 Greater Benefits Achieved Assuming Baseload Electricity for Pumping is Excessive