1) The Rossi QX - Chernetsky Self Generating Discharge - This concept utilizes a plasma consisting of hydrogen and specific catalytic elements along with tiny quantities of nano-particles from electrode erosion. When a pulse is applied with a high rate of change through the zone of negative resistance but not to a true arc discharge with positive resistance, a "resonant transfer plasma" like condition can be created, the input power dropped dramatically, and a series of self-generating oscillations can be monitored on an oscilloscope. These oscillations are the signature of heat, light, and electrical production via nuclear reactions and potentially ZPE extraction. If all the parameters are optimized, the oscillations can continue for extended periods of time and the COP can soar to high levels.
Positives: Precise On/Off control, High COP, High power output, High Fuel Efficiency, Direct Electrical Production Possible
Negatives: Micro-tips on the electrodes prone to damage, Sophisticated power supply and control system required.
Prediction for Future: Andrea Rossi may or may not ever be capable of partnering with a company capable of financing the mass manufacture of QX devices due to his unwillingness to share IP. However, non-commercial replications of the technology may at least prove its reality to the world.
2) Classic Nickel and Hydrogen Powder or Wire Based System - This concept can be vastly improved upon by adding optimizations such as pre-loading the fuel with atomic hydrogen via corona discharge devices (commercially available), producing atomic hydrogen and nano-particles in-situ using RFGs (radio frequency generators), producing atomic hydrogen with other methods such as internal spark discharges and/or hot filaments with low work function surfaces, and taking much greater care when testing the classic Ni-LiAlH4 combination. For example, allowing the LiAlH4 to phase change at low temperature and smothering the nickel powder can be prevented with ball milling (great care must be taken) the powder to reduce particle size, the additional of metal nano-particle additives, and slow heating ramps. Likely, pre-treating the nickel powder before hand with vacuum degassing and atomic hydrogen sources may further optimize such a system.
Positives: Potentially less electrical complexity than QX, Fuel elements few and plentiful if palladium is not used as spillover catalyst.
Negatives: No instant On/Off control, Lower likelihood of direct electrical production, Less Fuel Efficiency than QX.
Prediction for Future: More experiments in these areas are likely, especially from Alexander Parkhomov.
3) Atom Ecology Approach - This concept allows replicators to mix an abundance of different elements, apply deuterium, and very easily produce excess heat. In fact, the results seem to be fantastic for a relatively moderate amount of work. Apparently, unlike the tedious work required by Focardi and Piantelli to get nickel and hydrogen reactors to work, Russ George can produce low level gammas and excess heat reliably and very simply.
Positives: Sheer and utter simplicity. High level of success for modest effort. No complicated control system.
Negatives: No instant On/Off, Large numbers of different elements preferable, Deuterium required, Less Fuel Efficiency than QX.
Prediction for Future: Unknown.
4) Brilliant Light Power Suncell System - This technology seems similar to the QX approach except that liquid metals are used, the overall system is much larger, and a constant source of hydrogen is claimed to be required to keep the system running. Hopefully, they will attempt to test a pure plasma design (with only tiny quantities of metal vapor from electrodes) in their all quartz reactor. I expect they would learn that a constant source of hydrogen is not required due to LENR reactions.
Positives: High COP, High Output, Multiple Forms of Potential Output
Negatives: Constant denial of LENR reactions, Rube Goldberg like construction, Claim of requiring constant hydrogen source.