Depending on how long you can have the batteries store the energy, you could theoretically hook up enough battery storage to charge the jump drive and then use conventional power generators to charge the battery during the jump.
I suspect that the reduced fuel consumption would more than cover the extra fusion plants you would need.
In CT, the formula (in LBB5.80) is that you need to spend 2 EP per parsec per 100 tons of starship in order to jump ... and you have a time limit of 2 combat turns to achieve that result.
Thus ... a 100 ton starship with a power plant generating 2 EP per combat turn requires 2 combat turns to generate the 4 EP needed to jump 2 parsecs at the end of 2 combat turns, which will also consume 20 tons of fuel.
One way to rationalize a reduction in fuel consumption needed to jump would be to stipulate that the "within 2 combat rounds" limit on power build up gets ... moved ... to perhaps 3+ combat rounds. In other words, the
longer prep time is needed for more fuel efficient jumps.
Using the example from above (and sticking to LBB5.80 for the moment, because that's what I know), a 100 ton starship capable of J2 will have 1 ton of jump capacitors in its jump drive that can store up to 36 EP before a catastrophic failure. If a J2 needs the jump capacitors to be "pre-heated" with 4 EP in preparation to jump before the power plant goes into "overdrive" to generate the necessary power spike in order to jump, that means that there is 32 EP of "headroom" available for the power spike needed in order to jump.
Let's call what the "overdrive to jump" procedure does is a temporary output multiplier, which is very fuel wasteful.
If the temporary output multiplier is functionally 8:1 ... then a 4 EP output power plant would consume 20 tons of fuel in order to generate a
surplus of 32 EP in a single combat round, costing 20 tons of fuel ... therefore 2+2+32=36 EP capacity resulting in J2 at the end of the second combat round. This then yields a (combat round relevant) "instantaneous" fuel consumption of 0.625 tons per "overdrive" surplus EP needed to jump at the end of the second combat round.
The constraints around this computation are the fact that the jump capacitors need to be charged to 4 EP within 2
consecutive combat rounds. If the 4 EP can be transferred within a single combat round, then you can jump at the end of combat round 1 without needing to wait for combat round 2.
So what happens if that 2 consecutive combat rounds limit ... gets adjusted?
What if with additional technological improvements you're able to "shift" how long you can USEFULLY "pre-heat" your jump capacitors for in preparation to jump ... yielding a reduction in the power spike that your power plant needs to produce?
Using the above assumptions as a baseline to play with ... let's say that an "over tech level" J2 drive can jump after (up to) 4 combat rounds of jump capacitor "pre-heating" in preparation to jump, rather than being "limited" to just 2 combat rounds.
So now we're able to load 2+2+2+2=8 EP into the jump capacitors using "normal output" levels from the power plant. So now, instead of needing to generate a power spike of 32 EP at the end of combat round 2 in order to jump, the 100 ton starship only needs to generate a power spike of 28 EP at the end of combat round 4 in order to jump.
- 32 * 0.625 = 20 tons (100% nominal consumption rate)
- 28 * 0.625 = 17.5 tons (87.5% nominal consumption rate)
Include some "slight inefficiencies" into the jump fuel consumption (when efficient) formula and you wind up with consuming 18 tons (not 17.5) in order to produce 28 EP of power spike output, yielding a 90% of nominal "fuel efficient" consumption rate in order to jump.
So you still need to generate the same amount of power outuput in order to jump, but due to advancing technologies the drives are better able to "load balance" in a way that is more efficient and less wasteful of fuel. However, in order to achieve that outcome (improved jump fuel efficiency) there is a tradeoff ... the "windup" in preparations to jump take longer and power output needs to be "held steady" in preparation to jump for a longer duration. In a military context, where a rapid retreat via breaking off by jumping may be necessary, that requirement for additional time in preparation to jump "efficiently"
may not be an option since it could potentially expose a ship to hostile fire for "too long" before it can escape from a battle and retreat into jump space.
Note that such a tradeoff (longer "windup" before jumping in a more fuel efficient manner) can also have implications for civilian merchant operations when there is a risk of being attacked by pirates.
For most civilian merchant ship classes, they won't have much (if any!) surplus power available for maneuvering+defenses while preparing to jump. So when a civilian merchant prepares to jump, they will usually need to divert ALL of their available power plant output into the jump capacitors in preparation to jump for 2 consecutive combat rounds ... during which time, the starship IS VULNERABLE TO ATTACK.
Change that to needing 4 consecutive combat rounds in order to "jump fuel efficiently" and ... you've basically DOUBLED the duration of time the starship IS VULNERABLE TO ATTACK before it can jump ... in a normal space, ship to ship combat kind of way.
Basically, if a pirate is tailing a merchant ship that is outbound for a jump point ... the time to "move in for the kill" is when the merchant ship stops accelerating (major tell!) while keeping its power plant running at 100%. That then signals to the pirate that the merchant ship is now preparing to jump and is least likely to be able to defend itself against attack, due to the power demands needed to "warm up" the jump drive. Even getting the merchant ship to "abort" its attempt to jump by needing to divert power into defensive agility and weapons can prevent a merchant ship from escaping into the safety of jump space.
Do I need to point out that increasing the duration of that vulnerability time before jumping (fuel efficiently) could be consequential?
Remember, successful pirates are rarely interested in a "fair fight" ...
