Load resistor selection question

[ZooT]

A while back I posted a thread about bulding a simple shunt regulator for a smallish solar and/or wind dump controller.

I was told by our friend Flux

2N3055 is limited to about 60W per device, with practical heat sinking, but if you choose a suitable series resistor you can dump 240W as the dissipation in the transistor is 25% with half volts across the resistor.

Now for the question:

Is there an example formaula that I could plug values into to determine the proper resistor value to obtain "half volts" across the resistor?

Thanks much in advance for any help given

[SparWeb]

R=V/I  

Aren't you looking for Ohm's law?

A few years ago, I discovered for myself that I did not understand this deceptively simple formula.  I learned a lot from "All About Circuits", too.

[ZooT]

So I've been banging my head against a wall over something "so" simple?