Now that energy prices are varying as never before, you know that you have to watch them before they empty your wallet. More than that, you need a handy way to compare different offers. Whatever you are buying, your choice of best buy will often be thwarted. And why?
- The dollars-per-unit price may not use the units appropriate to your purpose.
- The units may change as you scan alternative offers.
- The vendor may make the offer too complicated for ready comparison.
So we all love commoditized products -- that is, until we become suppliers. A supplier is uneasy being lined up with other competing suppliers of comparable products. So he will be delighted to find a way to make a sale without offering the lowest price. He can join a cartel, or he can keep his prices in line with his competition.
How about mixing up the units? No problem. It's done already for him. The devilish Brits left behind a Trojan horse called the Imperial System of Units. Confusion wins.
While there are many other creative ways to confuse you, I will limit the task to putting electrical energy, natural gas and heating oil into comparable units at the user level. This is because the price and units issue is far different as you move upstream toward the power station or wellhead.
Electrical Energy. We'll use that handy sized unit, the kilowatt-hour (Kwh or kW-hr). If you've handled a 1 kW hair dryer and a 100 W light bulb, you've got your mind round the kilowatt -- a metric unit and not exclusively an electrical unit. One kWh is just enough to boil 10.8 liters (2.85 U.S. gal) of water starting from room temperature.
How to Confuse. My supplier advertises electricity 3.1 cents/kWh. This irrelevant figure is hiding in small print on the bill. Seven other items on the bill, including delivery, raise the price to 7.7 cents/kWh. This true rate -- the one to use -- is not shown on the bill. You have to divide the bottom line dollars by the kWh consumption.
Natural Gas. Not so easy. Your consumption could be shown in cubic feet (ft3), cubic meters (m3), British thermal units (BTU), therms (equal to 100,000 BTU) or megajoules (MJ) according to where you live in North America. Cubic feet and cubic meters are not even energy units, so you need the energy per unit volume, then the energy unit conversion. I have put the kWh equivalents in table 1. For natural gas, I have used a calorific value of 1,030 BTU/ft3.
My natural gas bill lists three other items after the gas price, bringing the final price to 2.35 times the posted (called the commodity) price of the gas. No price per unit of energy is shown for either the net or the gross price.
No. 2 Heating Oil. Your bill will show U.S. gallons, or liters in Canada. The price usually includes delivery, so you need only add sales tax. The Kwh equivalents of the U.S. gallon and liter are in table 1, where I have used a calorific value of 139,000 BTU/gal.
To Calculate and Compare Your Energy Costs. Using table 1, find your metered units from the first column and multiply your consumption by the figure in the second column. This gives your consumption in kWh. Divide the bottom line dollars on the bill by the metered consumption expressed in kWh.
If you go for combustion heat because it looks cheaper than electric heat, bear in mind that your process may not be suitable for combustion heat.
And, whatever the energy source, the realizable heat you can get into your product will be some percentage of the energy you bought. This figure is hard to calculate. It depends on the process, but you have to put it in your calculation. This is where you call on experience and process records.
The topic of realizable heat would take several columns, and I welcome readers' contributions on the subject.