is at all possible to convert from watthours to watts?

Question

hi guys,

does anyone know if it is at all possible to convert from watthours to watts?
see i have this data which looks like:


timestamp watthour
"2004-01-01 00:30:00"; 74340
"2004-01-01 01:00:00"; 73584
"2004-01-01 01:30:00"; 74124
"2004-01-01 02:00:00"; 74124
"2004-01-01 02:30:00"; 73944
"2004-01-01 03:00:00"; 74196
"2004-01-01 03:30:00"; 73692
"2004-01-01 04:00:00"; 74376
"2004-01-01 04:30:00"; 73656
"2004-01-01 05:00:00"; 72720
"2004-01-01 05:30:00"; 72828
"2004-01-01 06:00:00"; 75888


etc for a couple of years

and i need to calculate 2 things:
1) the maximum demand in a billing period, which is given by
a charge per day of 30.00¢ per kw

2)find the maximum demand recorded in a particular month and calculate a cost using $22.91 per kW

Will i be able to work out these with this kind of data?
cheers.
vanessa

Answer 1

Yes. Your numbers appear to be the watt-hours registered by the meter in each half-hour interval. If you accumulated 74340 watt-hours in a half hour, then the "demand" was 74340 watt-hours per half-hour x 2 half-hours per hour = 148660 watts.

To make life easier, cut and paste it into a spreadsheet program and then add another column that divides all the numbers by 1000 to convert from watts-hours to kilowatt-hours (kWh). Then multiple the kWh values by two. Label this new column "demand", and the units will be kW.

I don't understand your item # 1. It sounds like you need to find the highest kW value in the day and then multiply by $.30.

For item # 2 you need to find the highest demand (kW) over the month. You'll probably want to use the MAX function to find the highest value over the month.

Good luck.

Answer 2

Well watt hours do not really convert to watts - unless you want to say something like 1 watt hour is equal to having 3600 watts on for 1 second.

A 60 watt bulb for example, tells us how much power it will take when switched on. If you have it on for 1 hour, it will have used 60 watt hours. If you have it switched on for 1000 hours, it will have used 60 KWH.

It is meaningless to say 60 watts = 60 watt hours or 60 KWH KWHours - and effectively wrong too.

The good news is, you do not need to do that providing you know what data you have. The data shown is a bit misleading unless it is for a Heavy industry factory. It seems that they are using nominally 73KWH per 30 mins - in other words 146 KWH.

If you add all the figures together over 24 hours for each day you are evaluating - andf then pick the day where the consumption was highest. If for example, the factory runs 24 hours a day like this, then you might expect a figure along the lines of 13.824 MWH. If you found this was the most expensive day, then at a cost of 30c per KWH, you would be looking at $4147.20 per day

As for item 2, pick the month with the highest total, and again multiply the KWH by the price. I am VERY confused at the price of $22.91 per KWH though.


So yes, you *could* work this out, but this data has extremely unsuual values - unless you are running a BIG industrial factory AND pay a couple of hundred times more for electricity than most people ( $22.91 per kWH ????? )

Mark

Answer 3

The short answer is No.

This is because a kWh is based on time. Measuring a Watt is an instantaneous measurement. Besides, utility companies charge per kWh not per Watt.

1 kWh is like running 10 - 100 Watt light bulbs for 1 hour. An equivalent is 20 - 100 Watt light bulb for half an hour. Same kWh (1). The difference is, if you took an instantaneous Watt measurement, you would get 1000W usage for the first, and 2000W usage for the second.

Answer 4

Nah, it's totally impossible, you're screwed.