12v 200watt U type heating element with bolt on terminals,these can be used for gently heating water in most hot water cylinders and water tanks and would be great for use in environments where there is no mains electricity for warming water such as in caravans and boats and other off grid environments,they can be run direct from a 12v leisure battery or even directly from a solar panel providing its evenly matched,ie an 18v200 watt solar panel or close to it,ampage draw on these is around 16amps per hour at 12 volts so that gives you an idea how long your battery will last before its going to need recharging,ie if its an 80 ah battery it should last around 5 hours if its fully charged,the ideal scenario would be to run one from a large leisure battery connected to a large solar panel/ pv array or a wind turbine and connect a cheap normally closed thermostat directly to your tank in the positive or negative feed to the element so the element only comes on below a certain temperature like 75c ,one could also be used to prevent water from freezing with a normally open thermostat so that the element will only start heating once a certain temperature like 5c is reached, these have a 1 inch bsp fitting and measure approx 20cm,the heating rod thickness is approx 10mm,they can be fitted using a 1 inch bulkhead fitting if you can gain access inside the water tank if not as in the case of a standard hot water cylinder then a 1 inch essex flange can be used, to give some idea of power output it takes a 100 watt element approximately an hour to raise the water temperature of a 100 litre tank by 1 degree,hopefully this should help you work out if this element is going to be powerful enough for your needs,its worth remembering as well that im most cases where warm or hot water is required the element isnt going to have to bring the temperature up from 0 degrees, the water in insulated hot water cylinders in a reasonably warm indoor environment sits at between 10 and 15degrees c in winter and 18 to 25 degrees c in summer on average, for baths and showers around 40 degrees c is usually hot enough for most people and slightly less is usually fine for most handwashing requirements for all but the dirtiest of hands ! Therefore the temperature in the tank only needs to be raised by around 15 to 30 degrees on average depending on the time of year,installation is much more straightforward than installing an evacuated tube type of solar water heater , theres no additional pipework to be installed and no insulation to add and generally with the decreasing cost of large pv panels setup costs are much less too for this method of solar water heating, they can also be used as a dump load for small wind turbines and for warming other liquids such as waste vegetable oil used in the making of biodiesel as well as for brewing beer and wine, if your looking for a more powerful water heater we have many more dc water heating elements arriving with us over the next few weeks and now have a dedicated dc water heater elements section in our ebay store, price for these heaters includes p&p throughout the uk, thanks for looking