What is not required to be replaced as an entire set? (a)-coil springs (b)-friction discs (c)-steel discs (d)-planetaries

The ivanpah solar thermal power plant cost $2.2 billion to build. the gross plant electric output is 392 mw, and the net output is 377 mw. the planned capacity factor was 27.4%, but the actual capacity factor in 2016 was 20.5%. at best the plant thermal efficiency appears to be 18%. in addition, for the daily startup process, the solar plant also burned 1.3x10^12 btu of natural gas in 2016. the cost of natural gas in 2016 was about $2.5 per million btu. assuming a levelized annual fixed charge rate of 7%, determine (a) the capital cost (c/kwh) and (b) the fuel cost (e/k wh) for the electricity in 2016.