P^3

To integrate renewable energy into the existing electrical grid; cost effective, scale-able energy storage technologies are required. Currently, the most cost effective bulk energy storage technology available is pumped hydroelectric storage. But traditional pumped storage projects require years of site investigations, feasibility studies, detailed design, equipment selection, and contract negotiations before construction can begin. Each site requires a unique design that is both expensive and time consuming to produce. The size of the electro-mechanical equipment required for a typical project requires industrial and logistical infrastructure that is in short supply in the United States. This requires global supply chains and creates logistical challenges when transporting mega loads of more than 300 tons from factories oversees to remote project locations in the US.

In addition to the need for energy storage there is a growing need around the world for clean water. In developed nations, like the US, existing infrastructure is at end of life and new financing strategies are required to fund re-development. Many people in developing nations still lack access to safe drinking water which is a major public health concern. Worldwide over 2 Billion people lack access to safe water source in their home.

To help solve these problems Rebalance Energy is developing a scaleable pumped-storage system, the Patriot Power Pack (P^3), that can be integrated into existing domestic water systems. The technology will utilize a small pump turbine, a waste water settling tank, and an air-over-water accumulator that can be installed between a commercial or residential customer and the interconnection to a municipal wastewater system or septic drain field. The pump-turbine generator unit and accumulator bottles will be buried in a standard utility vault with the settling tank buried adjacent to the vault. In areas where clean water is unavailable or cost prohibitive, a reverse osmosis filtration system can also be included to recycle the “gray” water and, in conjunction with a small water treatment plant, produce potable water.

A residential P^3 unit will have a rated capacity of 3 kW with 36 kWh of energy storage – enough storage to power a typical US home for 24 hours without taking any electricity off the grid. A network of 100,000 P^3 units within a utility’s balancing area would have a rated capacity of 300 MW with 7,200 MWh of energy storage. That is enough reserve capacity and energy storage to integrate over 2,000 MW of renewable generation. Based on conceptual cost estimates completed by Rebalance Energy, the total cost of each system including installation could be approximately $7,000 ($2,333 per kW). The total operating costs could be approximately $355 per kW per year.

After completing the detailed design of the P^3 turbine-generator, treatment tank, and accumulator; the equipment design would be standardized – eliminating the need for front-end engineering prior to deployment as part of a new residential development. If the system is installed at an existing residence, a civil engineer may be required to design the excavations and interconnection of the technology into the existing wastewater system. The design of the switch gear, protection, and controls for the P^3 would be optimized to conform to the net metering interconnection requirements of most US utilities. Where the local net metering requirements cannot be met with the standard design support from the utility’s distribution engineers may be required. The limited need for front-end engineering will reduce the time required to commission an array of P^3 systems when compared with a conventional pumped-storage project. Where a 300 MW closed-loop pumped storage project with new reservoirs and transmission could take 80 to 120 months to design, permit, and construct; Rebalance Energy estimates that a P^3 array could be constructed within 1 to 3 months as part of new residential developments. If the system is installed at existing residences the time to design and construct could be between 3 and 6 months. This is an order of magnitude less than the time to commission a conventional pumped-storage hydropower project in the US.

Rebalance Energy recently completed a 100 W proof-of-concept system that includes many of the critical components that will be required for the commercial system. The system utilizes an off-the-shelf booster pump and accumulator running at 100 PSI along with a custom built Turgo turbine for energy extraction. The proof-of-concept system will allow us to better understand the water quality requirements for the turbine prior to scaling up to a commercial system. For the commercial system, Rebalance intends to design and fabricate a custom pump-turbine with a 2,000 PSI positive displacement pump directly coupled to a Turgo turbine and motor/generator. Here is a video of the proof-of-concept:

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