My old dump was 24 volt 50 watt light bulbs strung together this way you could add up the watts and get the right amount for your mill, trouble though i had a spike with an extra gust of wind (130k) and blew them leaving my mill unloaded!! i thought there had to be a more reliable way so i used high tensile fence wire wrapped it around a broom stick till i was dizzy then put it around the light tube it only touches the glass and the ends stick out for connection this has had between 15 and 40 amps continusly and just gets hot enough to take the zinc coating off but i have never seen red hot.
The dump should always be able to handle max power.
When i add my new mill to the system i will change the wire to number 8 (thicker wire) and i have no pv yet but when i have them i will add up all the combined power my system can make and build/buy a hot water element, so my dump is temporary at the moment but the fence wire is good!!