Note page 25 excerpted from Washington State ELCCA Guidelines, which documents the acceptable criteria for using one of the previously-studied alternatives as the High-Performance Building (HPB) alternative.
According to the criteria, the HPB alternative may use ANY previously studied alternative, PROVIDED that it meets the energy savings goal of the LEED scorecard.  IF the previously studied alternative will meet the energy goal only with a some modification (e.g. the addition of heat recovery and/or demand ventilation) THEN the MODIFIED ALTERNATIVE may be used as the HPB.  However a modified alternative is still another alternative, and so must be analyzed equivalent to the others.
Note that the HPB alternative does not necessarily need to be based on the 'Renewable' alternative.  But 'waste heat recovery' can qualify many of the systems we design as renewable alternatives (see Table 4.3 the ELCCA Guidelines, at the top of page 25), and this feature will help significantly in attaining the LEED energy goal.
So what is the 'energy goal' referred to by LEED as the benchmark criteria?
The energy goal is defined per ASHRAE 90.1-2004 Appendix G as the energy savings required of the HPB over the Baseline Building (BLB):
LEED 2.1 EAc1:
 1 Point        New Buildings  10.5%      Existing Buildings & Renovations   3.5%
 2 Points     New Buildings  14%            Existing Buildings & Renovations   7%
 3 Points     New Buildings  17.5%      Existing Buildings & Renovations   10.5%
 4 Points     New Buildings  21%            Existing Buildings & Renovations   14%
 5 Points     New Buildings  24.5%      Existing Buildings & Renovations   17.5%
 6 Points     New Buildings  28%            Existing Buildings & Renovations   21%
 7 Points     New Buildings  31.5%      Existing Buildings & Renovations   24.5%
 8 Points     New Buildings  35%            Existing Buildings & Renovations   28%
 9 Points     New Buildings  38.5%      Existing Buildings & Renovations   31.5%
10 Points    New Buildings  42%            Existing Buildings & Renovations   35%
Attaining LEED Silver requires 33-38 points on the LEED Scorecard; the ELCCA Guidelines further stipulate that no less than four points shall be earned from the 'Energy Optimization' portion of the scorecard for the HPB alternative.
So, the bottom line is that the HPB alternative is required to show improved savings of 21% for new construction, and 14% for existing buildings and renovations over the BLB.