A general figure of merit for a renewable-fossil hybrid system designed to reduce carbon dioxide emissions ("avoided carbon") is the resultant cost of one ton of carbon avoided (CCA). As before, it relies on the comparison of the hybrid system to an efficient, practical fossil fired power system, generally the baseline standard system. It is the same standard as for GREF and FCR. A particular cost parameter is obtained, based on essential information on both the costs and performance summary of both systems. As such it is a combined cost-performance parameter:

(3)

COST OF AVOIDED CARBON (CCA) ($/ton C) by hybrid system =

COST of HYBRID SYSTEM output… COST of STANDARD SYSTEM output AVOIDED CARBON (ton C/MWhe)

The parameter COST of output means here the annual system product cost, including both the annualized capital and operation costs ($/MWhe). The quantity of avoided carbon is equal to the GREF (dimensionless) times the specific fuel carbon consumption of the baseline standard system (ton/MWhe).

Equation 3 is useful in many ways. It can be used for observing functional tradeoffs and engineering optimization of system design. Also, for monitoring the CCA as a function of the number of operation hours in the year, electricity price-tariffs and other data. As well, for deriving the minimum cost of avoided carbon as a function of the number of annual operation hours and relevant variables.

Conclusions

Renewable-hybrid systems have the potential of playing a decisive role in massive supply of renewable energy in the near-term. However, the hybridization of renewable energy with fuel — fired generators has to be designed and operated properly. The issue of baseline standards is elucidated. Hybrid systems are analyzed by use of environmental parameters, the fuel consumption ratio (FCR) and a new parameter, the green energy fraction (GREF). They are numerically illustrated for several solar electricity systems. The FCR and REF establish vital metrics for environmental system evaluation by providing a summation figure for the overall fuel avoidance of the whole hybrid power system, simple or complex, for the full or part of the year. Together with the CCA (cost of carbon avoided, $/ton C) parameter, the three metrics (all defined with the same environmental reference standard), establish a unified technology — evaluation criterion, or figure of merit, enabling helpful assessments of various systems on an equal basis. This allows the comparative evaluation of renewable energy plants for upright clean (green) energy. The metrics and related equations provide useful yardsticks for project evaluation and for guidance in planning improved, cost effective, sustainable solar and other renewable-hybrids systems. They also provide generalized evaluation tools for emissions verification, which is necessary for green energy incentives management.

References

[1] Swezey, B., Bird, L. Buying green power… you really can make a difference. Solar Today, Jan/Feb 2003, pp.28-31 http//www. eere. energy. gov/greenpower/pdf/Buying_Green

[2] Geyer, M. Panel 1 Briefing materials on status of major project opportunities, Internatio Executive Conference on Expanding the Market for CSP, 19-20 June 2002, Berlin, German p.4

[3] Wholgemuth N, Missfeldt F. The Kyoto mechanism and the prospects for renewable technologies. Solar Energy 2000; 69(4):305-314

[4] Svoboda P. A.,. Solar boiler for a 100 MW integrated solar combined cycle system.

In: Faiman, D. (Ed.), Proceedings of 7th Sede Boqer Symposium on Electricity Production, 18-20 March, 1996, Blaustein Inst., Sede Boqer, Ben-Gurion University, Beer-Sheva, pp.125-128.