Here is something that you may want to consider. Estimating 6 amps, 240 volts, $0.30 per KWH, assuming a roughly resistive load for calculation simplicity, you will pay about $0.12 per minute while the pump runs. So I am presuming 1440 watts while the pump runs.
While the pump will draw a little less current when the CSV is applying major restriction, the pump is pumping 3 GPM rather than 15 GPM. Now if you pump $500 gallons at 15 GPM, that would cost you $4.00. If you pump another 500 gallons at 3 GPM, that would cost you $20 in electricity. The total would be $24. Yes, that sounds high to me too. So
maybe I made an error or two. If I presume the power consumption drops to 80% during the 3 GPM time, then the $20 figure becomes $16.
If I presume that 500 gallons would be pumped at 15 GPM and 500 at 13 GPM, then I compute $4+$4.63 for 8.62 total.
Now is it reasonable to presume that you would pump as many gallons at 3 GPM as at 15 GPM with a CSV? Got a better prediction? I am presuming fairly low flow toilets and no irrigation.
I took great simplifications in calculations.
If somebody has less simple but
more accurate figures to substitute in, then I would be glad to try those numbers in my spreadsheet. Such as how many amps the pump would be expected to draw while pumping against 35 PSI at 15 GPM vs pumping 3 GPM at whatever pressure would be probable. Also consider that 1000 gallons per month per person is a fairly modest use and would be rather low use for 2 people.
http://www.csgnetwork.com/waterusagecalc.html is a calculator.
Bermuda power rates bill the fuel costs as a separate line item. With low oil prices right now, the $0.30 per KWH is probably a little high.
http://www.gb-power.com/en/home/residentialservices/billing /fuelasurchargecalculation/default.aspx then add $0.1195 to $0.1495 per incremental KWH.
http://www.bahamaselectricity.com/rates.cfm