The LG Chem home battery is a comprehensive solution that's perfect for existing solar systems. Because It comes with an AC inverter, it is instantly compatible with existing solar PV, allowing you to store you solar power with little to no alteration to your system.
It comes in a range of 6kWh to 18kWh. Anything above 12 kWh when paired with solar has potential for full off-grid capacity.
The Sonnen Eco is hands-down the most advanced system on the market and is also compatible with existing solar systems. The Sonnen Eco has a "smart" energy management system that allows you to have total visibility into your energy usage through a beautiful mobile app.