Yes I know. I said (posted), "Real men use kinetic energy to kill." But on reflection I wouldn't want to call Han Solo or Jim Kirk a wuss, would you?
Beam weapons are a science fiction staple having been introduced in 'Edison's Conquest of Mars" published in 1898. Jeff Prucher's Brave New Words: The Oxford Dictionary of Science Fiction lists the first use of a 'blastor' as 1925 in N. Dyalhis' 'When a Green Star Wanes' in Weird Tales 6/2. That blastor and Edison's ray weapons fired disintegrator beams that could give a Type II Phaser a run for its money. Eventually blasters evolved into the familiar 'Pyew pyew pyew!' weapons we know today. That is to say they worked basically like modern firearms. They would wound or kill on a good shot or miss completely if you were wearing white armor. They are often portrayed as hurling relatively slow moving pulses of light but otherwise not much distinguishes your DL-44 blaster pistol from say a Mauser.
One of the things I noticed about energy weapons in many many SF RPGs is their high ammo capacity. It's not unusual for the crazy things to have double or more the capacity of an equivalent slug thrower. As one who never liked tracking ammo I've considered other ways of portraying this than tally marks on your equipment sheet.
Let's say that an energy weapon for most purposes does not run out of power in a fight (or three considering what my players would get into.) Instead the rate of fire causes other technical problems. Perhaps it's heat build up or maybe the weapon has to charge a capacitor from a very efficient battery. When the capacitor runs down the rate of fire will drop. You choose the brand of unobtainium that works best for you. I'm going with the term 'heat' but it could be anything else you can come up with (static cling, rattling like crazy etc).
You need to establish a heat rating for each weapon. When you roll for damage rolling that number generates a heat point. When your weapon generates that much heat it shuts down until it cools off (or recharges etc). So if you wanted to call all the Classic Traveller firearms blasters you might say that auto pistols and revolvers generate a heat point on every die of 1-2 in a damage roll. Rifles and long arms have bigger, better capacitors or heat emitters and generate heat on a die that comes up 1 and the lowly body pistol on a 1-3 on its 2D of damage. Note that you'd have to roll for damage on every shot, even the ones you missed because the Universe doesn't take pity on your lousy aim. The number of of heat points a weapon can have before shutting down and how fast it loses heat can be a function of tech level or the grade of materials available. Maybe pistols shut down after 3 points and dissipate one point a turn while rifles have double the number. Automatic fire could double the chance for heat or automatically generate one point per die as options.
Another option (with more of a d20 feel to it) is to have weapons do a set number of dice (3dX works well.) All weapons generate heat on a roll of one or two but the more powerful weapons use larger dice reducing the chance of heat. A pistol does 3d6 and tends to pick up a point a turn. Weapons shut down after generating six points and dissipate two points a turn. The fun part comes from detailing special attacks like double tapping or wide beams that build up heat very fast, double, triple or more in exchange for a better chance to hit or more damage. Does the player risk having an inoperative weapon for a turn or more to toast the monstrous alien beast charging him? What about a miss?