42 • ROCK products • March 2018 www.rockproducts.com
Charleston Stone
Tarble recalls diesel prices as low as $1.50/gal. and as high
as $3.75/gal. Electricity prices, however, tend to be relatively
stable. Converting from diesel to electricity provides Charles-
ton Stone a more stable expense ledger, which enables them
to plan and invest with less risk.
A comparison of energy costs for the diesel crusher to the
new electric crusher must consider a range of possible diesel
prices. The new electric crusher had just been installed in
August 2017, as this case study was being written, and was
beginning to operate at full capacity before mid-month –
which may be enough time to begin seeing the long-term
operating cost.
Charleston Stone purchases electricity on a "Large Power
– Peak Sharing" rate schedule that provides CMEC with the
ability to interrupt much of their power in times of peak
system demand. This gives them a $.07/kWh rate for energy
and an $8.00/kW rate for all demand above a base level that
they cannot exceed during periods of curtailment.
16
Basing a projection on the first month of operation of the
new crusher injects considerable uncertainty. Presumably,
Charleston Stone will learn to operate the crusher more
efficiently as time goes on, so the projection of energy sav-
ings shown in Figure 8 is probably conservative. Demand
FIGURE 7: Diesel price volatility.
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