Michigan
State University Extension
Preserving
Food Safely - 01600534
10/13/97
Let's calculate the energy cost of drying green beans and
peaches in a dehydrator built from plans in Home And Garden
Bulletin No. 217, pages 16-20. The dehydrator can
accommodate 18 pounds of fresh product. Assume that during
the first 2 hours of drying time, all nine 75-watt light
bulbs (675 watts total) will be on. Only six light bulbs
(450 watts total) will be left on for the remaining drying
time. Calculate the energy cost at 5 cents per kilowatt-
hour.
GREEN BEANS
18 pounds = about 9 quarts
Drying time is 8 to 14 hours (average = 11 hours)
2 hours x 675 watts = 1,350 watt-hours
= 1.35 kilowatt-hours
9 hours x 450 watts = 4,050 watt-hours
4.05 kilowatt-hours
1.35 kilowatt-hours + 4.05 kilowatt-hours
kilowatt-hours = 5.40
It takes 5.40 kilowatt-hours of electricity to dry about 9
quarts of green beans. That's equivalent to 0.60 kilowatt-
hours per quart.
0.60 kilowatt-hour x 5 cents/kilowatt-hour = 3.0 cents
The energy cost of drying one quart of green beans is 3.0
cents. (This does not include the energy cost of
blanching the beans as pretreatment for drying.)
PEACHES
18 pounds = about 8 quarts
Drying time is 36 to 48 hours (average = 42 hours)
2 hours x 675 watts = 1,350 watt-hours
= 1.35 kilowatt-hours
40 hours x 450 watts = 18,000 watt-hours
= 18.00 kilowatt-hours
1.35 kilowatt-hours + 18.00 kilowatt-hours
kilowatt-hours = 19.35
It takes 19.35 kilowatt-hours of electricity to dry about
8 quarts of peaches, or 2.42 kilowatt-hours per quart.
2.42 kilowatt-hours x 5 cents/kilowatt hour = 12.1 cents
So the energy cost of drying one quart of peaches is 12.1
cents.