how to build dummy loads?

Ok... if you're dissipating 100 watts you have to get rid of 100 watts worth of heat.

You can't do this in a particularly small space. A 100 watt soldering iron gets quite hot. Heck, kids used to have these "Easy-bake oven" toys that achieved baking temperatures with a 40 watt light bulb or so.

But the key to that was a small, insulated, enclosed space. A 100 watt light bulb in a metal perforated box should do. Use a porcelain bulb socket mounted to the bottom of the box with rubber grommets. You want the box to be large enough so that the heat is mostly carried away by air currents through the holes.

"Hilux" is a Toyota brand name and carries no official meaning, so I don't know exactly what your requirements are, but the above should give you at least a starting idea.

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edit - added:

Hey, I completely missed where you said "lights will only get broken." Well, they do have the advantage of being cheap.

Any other electric appliance that pulls 100 watts would do as well. You'll mostly be looking for things that heat up. A small electric iron might do it, or maybe a curling iron, or a small electric kettle or immersion heater.

The "official" way would be a power resistor. You would want a resistor of

R = E(squared) / P = 240*240*100 = 576 ohms

You don't need exactly 100 watts just to put a load on your generator, so you don't need exactly 576 ohms. There are 100 watt R's available in 560 ohms. But you really should use a somewhat higher-rated resistor than what you think you need.

A good approach would be to use four 560 ohm resistors in a series-parallel configuration. The total R is still 500 ohms, but if you use 50 watt resistors you have a capacity of 200 watts, which is more than enough margin. Those resistors are available new for US 3.26.

Just like with the light bulb, though, you'll be producing 100 watts worth of heat. So build a guard box around the thing, and put holes in the box so the heat can escape.