overages for power usage
kaze0010 at umn.edu
Fri Sep 21 17:25:54 UTC 2018
This isn't a data center specific answer but it may help explain upstream
cost drivers that may factor into rates seen. For commercial and industrial
customers, utilities will often measure and bill power demand in kW
separate from energy in kWh. Energy may only be $0.04/kWh but demand
charges can be tens of dollars per peak kW during a bill cycle (averaged
over 15 minute intervals).
The demand fees are a result of grid capacity requirements...the utilities
need to maintain enough readily available generation capacity (turbines,
storage, etc.) at all times to handle the peak loads, even if those loads
are only seen once a year. If demand ever exceeds capacity, then brownouts
and blackouts are on the plate.
Assuming a $10/kW demand charge, a customer consuming 5000 kWh energy and
drawing a 15 min peak average of 40 kW would pay $200 for energy + $400 for
demand, for a monthly electric cost of $600. If the same customer could do
load leveling to get those peaks down to 10 kW, they'd pay a $100 demand
charge instead of $400, for a monthly electric cost of $300.
With perfectly constant loads, 5000 kWh consumed over a 30 day month (720
hours) translates to 6.94 kW. 20 amp 240v circuits can each supply up to
3.84 kW continuous using the 80% loading rules. At 208v, that drops to
3.328 kW continuous.
Said another way, with level loads, approximately 5000 kWh per month could
be pulled through two 20 amp circuits running close to their capacity
Here is an example rate sheet for Xcel Energy in the US state of Colorado:
On Thu, Sep 20, 2018, 21:11 Alan Hannan <alan at routingloop.com> wrote:
> What kind of typical overage costs have you seen when a customer/you use
> more than you've committed to?
> I'm especially interested in datacenter power situations, where maybe you
> sign up for 5kw or 500kw and use more than that in a given month. Is it
> billed at the same rate? Is it billed at a higher rate? What's the %
> increase of the higher rate versus the regular rate?
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