The Government has committed to Net Zero GHG emissions by 2050, but is already off-track to meet its 2020 renewable electricity target(CCC), whereby households account for 40% of emissions. In tandem, households and businesses face increasing energy bills as we electrify transport and heat, with costs of £40bn by 2050 where unmitigated with flexible energy assets. Renewable energy(RE) is constrained by with an inflexible grid unable to handle variable supply, with costly new curtailment measures (£500m) introduced from over-supply during Covid-19\. Finally, figures from Birmingham University, IET and IEA calculate that there will be 30-60m tonnes of waste EV batteries globally by 2040; alarming in regions such as the US, EU and Australia where typical recycling rates are presently 5%. These factors create strong drivers for adoption of domestic Battery Energy Storage Systems (BESS) that i)reduce business and household energy bills by storing solar and low cost electricity ii)support the grid providing extra revenues and system savings iii)utilise second-hand EV batteries and no/negative cost. However, existing BESS have payback periods of ~7yrs, high CAPEX ~£5,000-£7,000, and with battery lifespan/replacement being a key cost concern. Powervault has surveyed its historic pipeline of leads who did not buy BESS: 55% objected on cost, and a further 24% on warrantied-lifetime payback. In turn, uptake in the UK has been low compared to international markets where incentives are available(Germany, Japan, Australia, USA). To meet this need Powervault plans to develop an innovative mass-market BESS solution using second-life EV batteries(SLBESS) and capitalise on closing a resource loop. This project constitutes technical and business model innovation, providing a system that is cashflow positive for customers from day 1 due to i)no upfront cost ii)improved battery lifespan and warranty duration iii)integration of grid services to generate revenue. This innovation addresses the key competition theme: decarbonising energy, business and industry. A zero upfront cost SLBESS solution provides a pathway to mass-market residential energy flexibility, which is critically needed for decarbonising at least cost (BEIS, Element Energy, Imperial College). Other themes the innovation addresses are improving the energy efficiency of our homes and other buildings (by helping homes import electricity at more efficient times as they switch to electric heat and transport) and accelerating the shift to low carbon transport (by reducing grid constraints and recycling costs for EV manufacturers, lowering price).