670 watts is about 2.75 amps so it should be fine depending on what else you are running at the same time. Check your sites supply and be aware of what else you are running. If its on overnight, well a fridge uses about 0.5 amps, a water heater 2.75 amps a domestic kettle a whopping 8.3 amps ... so unless you have a generous supply dont whack one of these on at the same time. Some sites give only 5 amps, some 10 or 16. Continental sites are supposed to be really stingy, but I have no personal experience of this. I have found the camping and caravanning club information sheet on electricity (downloadable free from their website) useful in this respect. It gives examples of appliances and their ratings.