I've been offered a free dead 2200va ups. Death is the standard reason of battery failure. So I figure this is a good starting point for an inverter etc. And it will cover 95% of our power requirements, but we do have spikes of 3-6kw. As this is going to be mainly used for timeshifting our power usage until solar panels are fitted, I'm not too concerned about the lower than ideal output power, I'll just use it as proof of concept. However I need to deal with the spikes. Is there any simple way of switching back to grid, and bypassing the ups in an overload situation? I was thinking at something like 1500w, I can do it with an SSR and an esp8266 but I fear it won't respond anywhere near quick enough.