Pay back time, energy

Costs and energy pay-back times of present PV systems at an armual production rate of lOMW were calculated to be 55()/W ( 83/kWh) and 5.7 years for poly-Si and 79/W ( ll9/kWh) and 6.4 years for a-Si PV systems, respectively. These cases correspond to the present level of PV technology. 

PV high cost, and long energy pay back time (EPT). 

In addition to the cost effectiveness of silicon ribbons, energy payback time (i.e. the time needed to produce the amount of energy that was consumed during the manufacturing of a solar system) is drastically reduced. In a recent life-cycle analysis of crystalline silicon wafer based PV systems, it was demonstrated that the energy pay-back times can be reduced by half (based on cut multi-crystalline wafers), by the use of RGS ribbons for systems in central Europe [97]. 

Laboratory efficiencies of 16.7% and module efficiencies of 10.9% have been reported. The theoretical conversion efficiency is considered to be 28%, however, more recently a more conservative estimate of 17.5% has been proposed. The drawbacks to CdTe systems include the toxicity and low abundance of the materials, temperature-dependent efficiencies and only an average light tolerance. Nonetheless, CdTe solar cells have entered the market. The leading manufacturers of CdTe modules are First Solar in the USA, with a capacity of over 1 GWp yr , and Calyxo GmbH, a Q-cells subsidiary, in Germany, who have a 25 MWpyr and a 6 MWp yr capacity facility and boast an energy-pay-back time of approximately 1.5 years for their systems. 

Assuming Vc = 300 (m ), the electric power density averaged over this volume is 0.4 10 Wjm ) the corresponding pay-back time (derived from Fig. 13 of K. H. Schmitter s lecture) ranges from 5.5 to 8 years. Thus the pay-back time in this case turns out to be typically one-third of that evaluated for a NUWMAC type reactor in the above mentioned Schmitter s lecture, whose conclusions would exclude from the energy game any fusion approach except, possibly, the inertial one. 

Thin film solar cells in general require a minimum of material and energy input. This is an important fact in view of availability of materials and pay-back time of solar generators. Thin film technology provides means for large scale production and the feasibility to realize integrated photovoltaic generators by the same production process. 

Measurement. The need for cost-effective pollution prevention, efficiency improvements, and emissions meastmement has created a need for new types of integrated control and meastirement systems. One of the best methods to improve environmental performance initially is to maximize efficiency through optimization in their manufacturing and energy processes. Many cement kilns now use continuous NOx measurement at the kiln exit to feed back information to the process control to optimize combustion. Capital costs are usually small, especially if PEM/ optimization software systems can be included at the time of a control system u rade. The increased operator awareness of the plant is a benefit, and fuel savings, qualify control, and maintenance planning can quickly pay back initial costs. 

If the gas is then allowed to expand back to its initial volume under the same conditions, the same amount of work will be regained. For the process to be reversible, it must occur very slowly, in fact, infinitely slowly for true reversibility. But infinitely slow processes last an infinitely long time If we wish to have the process occur at a finite rate (as in a real engine), we must sacrifice efficiency. More work (than shown in Eq. lOE) is needed to compress the gas, and less is regained during its expansion. The difference represents the irreversibility of the process, or the price we pay, in terms of energy, to secure a desired rate of operation. 

---