Just a couple of points
Elements arent elements, there are a range of them designed for different jobs and the cheapest one may not be the best choice,
I know several commercial breweries that use electric elements, these are mostly either sheathed (covered to spread the heat) or a low density (long for the amount of heat they produce). The reason being that the surface of a high density (short/Hot) element gets very hot, this will (not might) cause scorching, charring and darkening of the wort to some extent.
Also when choosing an element the shorter it is per kw (higher resistance) the shorter the life of the element, again shorter runs hotter - burns out sooner, they cost less but die sooner.
Elements are made of a variety of materials-
The best are Stainless Steel; a poor conductor the heat spreads out more, resistant to corrosion, doesnt add metal ions to your brew, easy to clean.
Worst would be Copper or copper alloy (brass); prone to hot spots, gets corroded in acidic wort, short life (cheapest tho).
In between are plated ones; comes down to the quality of the plating.
Elements should always be earthed, they will burn out eventually and the idea of a 240V hot pot can take on a whole new meaning. Personally I would run anything on a lead that goes near wet stuff through an earth leakage detector; you can get ones that go into power points or as part of a power board (cheap life insurance).
Just thought of a good example, look at the length of the elements in a jug and in a deep fryer, they are both in the appliance section of most supermarkets, the jug will have a short high density element, the deep fryer will have a long low density element to reduce scorching of the oil.
I think the guys from NNL could shed some light on the specifics of elements in wort kettles I hear they have had fun getting commercial sized elements made for among other things that micro that sold on EBay recently. Maybe they could shed some more light on the current thinking.
MHB
I believe we had/have one wood fired brewer on the forum - well it's an alternative to gas.
M