A simple runtime formula
For planning, use battery Wh × efficiency ÷ load watts. With an 85% efficiency assumption, 2,000Wh becomes about 1,700 usable watt-hours. That gives roughly 17 hours at a steady 100W load, 8.5 hours at 200W, or 3.4 hours at 500W.
Why actual runtime differs
Inverter losses, standby consumption, temperature, battery condition and loads that cycle or surge all affect the result. Appliances such as refrigerators do not normally draw their rated running power every minute.
Capacity is only half the decision
Check continuous AC output and surge capability as well as battery capacity. A large battery does not help if the inverter cannot start the appliance you intend to use.
Solar can extend runtime
Solar input can replace some energy during daylight, but panel rating isnt the same as energy actually delivered. Weather, panel angle, temperature and the station input limits matter. Verify voltage, current and maximum solar-input specifications before connecting panels.