Inverters will allow you to run AC (household) appliances - e.g. Laptop or other appliance not specically designed for caravan/boat. Choose the inverter based on the highest-Watt appliance you want to run. E.g. if you want to run a 900W coffee machine, you need an at least 900W inverter.
At LUX Solar we source only high quality pure sine wave inverters. Modern electronics and appliances struggle to cope with the harmonics generated by noisy modified sine wave inverters.