• PV-BESS
• lead-carbon battery
• energy storage
• China
• self-consumption

Growing distributed renewable energy share in electricity generation is creating challenges for the whole power system, due to its intermittent and non-programmable nature and to its level of penetration at medium and low voltages. Energy storage has the potential to solve those issues although its technical, economic and environmental impact is up for debate.
A residential PV-battery energy storage system (3kW monocrystalline PV panels and 2.5kW/14.4kWh usable lead-carbon battery capacity pack) is installed to a residential grid-connected small apartment in the Green Energy Laboratory at Shanghai Jiao Tong University, China. Daily experimental results show how the presence of energy storage reduces the midday feed-in of excess PV power and the evening peak demand providing benefits to the distribution network in terms of reduced voltage swings and peak load.
Experimental data from the real system is also used to validate a computational model built using TRNSYS software, from which annual energy flow simulations are run. For this specific domestic load, it is found that the presence of an optimally sized PV-battery system reduces the amount of energy sold to the grid by 57% and purchased from the grid by 42%, increasing self-consumption rate from 21% to 54% compared to having the same PV system but without storage.
Considering the Chinese context, an economic analysis is carried out to assess the profitability of residential PV-battery systems, using the Net Present Value as the economic indicator of an 18 years investment in which the battery pack is replaced twice (6 years life). The analysis shows that such system is not economically viable due to a combination of low electricity prices, valuable PV incentives and high technology costs. However, considering a future scenario of doubled electricity tariff, halved export tariff and falling technology costs (-66% battery & -17% PV and inverter), PV-battery investment becomes profitable and shows more resilience to future scenarios than PV-only investment.
Those results are obtained with basic operating strategy of maximizing PV energy self-consumption. Further works should focus on advanced strategies taking into account battery degradation, so as to increase battery life, and time of use tariff, so as to maximize economic benefits. Finally, policy makers have the ability to shape renewable energy and energy storage future by application of tailored electricity tariffs and incentives.