The results can be found at the bottom of Table 14, based on an electricity price of EUR 0.11/kWh and 10,000 full-load operating hours. It should be noted that the surcharge for the upgraded cross-section was already deducted from the saving, but not the set-up costs for the compensation system, since these systems cannot be supplied off the shelf at standard prices. The table (e.g. for the small motor) thus reads as follows:
A compensation system with Q = 4.7 kvar is required to reduce the loss costs per 10,000 h full-load operation by EUR 413. From here a payback period can easily be determined, if e.g. an offer exists. Increasing the cable cross-section by one standard size saves almost twice as much (EUR 751 per 10,000 h) as reactive power compensation.
It is best to combine the two – even though the overall saving will then be slightly less than the sum of the two economy measures each calculated individually. Thus, you might expect a saving of EUR 1164/10,000 h for the small motor, but in fact it is “only” EUR 1043/10,000 h. It is a general observation that the first improvement always has the greatest effect for the least cost. Each subsequent step will normally cost more and have less effect than the preceding one. In the present case, this becomes very clear, since due to the preceding setting up of the compensation system, the current had already been reduced and the difference in losses with the minimum cross-section against the cross-section upgraded by one size is correspondingly smaller. Or, looked at another way: If an over-dimensioned cross-section is already in use, the losses are already lower, and using compensation naturally does not bring about as big a reduction as if compensation were the first measure taken.
With the medium and large motors, the upgrade still saves more than compensation, but not as much as with the small motor. With this, increasing the cross-section produces a massive saving, and at EUR 29 the surcharge is minimal compared with the saving of EUR 1099 within 10,000 h – with the surcharge already deducted – which yields a payback period of just 261 h. With the medium and large motors, the differences in payback times, 2945 h or 2752 h, respectively, are less – which, however, is still remarkably short at significantly less than half a year of continuous service. In contrast, a compensation system
- of 4.7 kvar would be required for EUR 18;
- of 40.6 kvar would be required for EUR 1228;
- of 253 kvar for EUR 2820
to achieve the same payback periods as the upgrading of the cross-sections. While the former seems absurd, the other two appear to be somewhere close to reality – albeit just about so.