More on the R Factor

I have gotten average data from EIA and an article by Papatheodoru:

Energy-----R------Eff (%)----Eff/R----Cost
Source--------------------------------------$/W

Coal-----------5.9-----70----------12-------1.25
Nuclear------7.5-----90-----------12-------2.10
Hydro---------3.7-----35----------9.5------1.54
Biomass-----6.3-----50--------- 7.9------1.80
Geotherm.---6.4----80----------13-------2.20
Solar-----------1.3----20----------15-------5.00
Wind-----------2.0----25----------13-------1.18
Avg.----12.8

So R is essentially a function of efficiency. As an estimate:
-------------------------R = Eff/13

note: R converts MW to GWh or kW to 1000kWh