Cents per Head of Lettuce
have asked how we arrived at this figure. Actually, it's a pretty
simple calculation. We can walk through it and it will serve
to demonstrate how to figure your costs for all of your growing.
Does Air Farming compare to dirt farming? Well, it does and doesn't,
but more on that later.
a few exceptions:
In these figures, we don't allow for your labor. We assume that
you're a hobbyist. Labor calculations would require a lot of
data from you, and you do enough of that at work, don't you?
But if you really have to know, you'll simply have to log your
time, assign a value to it and divide by your harvest (excluding
credits for extended life, lowered blood pressure and a better
outlook on the world).
air pump operates at 4 watts. We run it 24 hrs. a day. So our
electrical requirement will be:
watts X 24 hrs. = 96 watts / day.
A head of lettuce will take about 30 days to mature.
24 hrs. X 30 days = 720 hrs. mth.
4 watts X 720 hrs. = 2880 watt hrs. / mth.
2880 / 1000 = 2.880 kwHrs.
Using our exorbitant local (Connecticut Light & Power Co.)
rates, we multiply:
$.106 kwH X 2.880 kwHrs. = $.30528 total cost of running air
$.30528 / 9 heads of lettuce = $.03392 / head.
seed, nutrient and even water (should you have to pay for water)
another six tenths of a cent brings it to about $.04 cents per
head of lettuce.
obviously doesn't include electricity for supplemental lighting.
But we can do the same type of calculation including different
lighting configurations. Though lettuce will grow well without
a great deal of light and actually prefers cooler conditions,
the duration of the light should approximate the length of day
in early to mid spring. It's for this reason that you may need
additional lighting while growing in the winter.
plant four Air Farms under one fluorescent fixture. As lettuce
spends its whole life cycle within the reach of a fluorescent,
we can mount the fixture horizontally at a height about 8 - 10"
above the Air Farm. Planting four might be prohibitive, but you
can use a smaller fluorescent fixture to the same effect over
one Air Farm.
course, if you can get the plant some natural daylight and only
use the artificial lighting to "extend the day," you
will be able to lower these numbers. But this is how to figure
your lighting consumption:
Air Farm under a two foot fluorescent fixture:
2 20W fluorescent tubes = 40W
40W X 14 hrs X 30 days = 16800 whrs.
16800 / 1000 = 16.8 kwHrs.
16.8 kwH X $.106 = $1.78 / mth.
$1.78 / 9 heads of lettuce = $.198 / hd.
$.198 + $.04 = 24 cents per head of lettuce.
with four growers under a four foot fixture:
2 40W fluorescent tubes = 80W
80W X 14 hrs X 30 days = 33600 whrs.
33600 /1000 = 33.6 kwH
33.6 kwH X $.106 = $3.56 / mth.
$3.56 / 36 heads of lettuce = $.099 / hd.
$.099 + $.04 = 14 cents per head of lettuce.
on when and where you are pricing it, even iceberg lettuce can
cost as much as $1.29 / hd. Though iceberg is not suitable for
Air Farms, romaine and leaf lettuces are. Most hydroponic growers
grow Boston lettuce, a bibb type. Locally, we pay about $2.50
for hydroponic lettuce year round. Using our local prices, we
can calculate our Air Farm payback this way:
at $1.29 / head:
9 X $1.29 = $11.61
9 X $.24 = $2.16
$11.61 - $2.16 = $9.45 saved per month.
$64.95 typical retail / $9.45 = 6.87 months for break even.
at $2.50 / head:
9 X $2.50 = $22.50
9 X $.24 = $2.16
$22.50 - $2.16 = $20.34 saved per month.
$64.95 typical retail / $20.34 = 3.19 months for break even.
prices will depend on your local pricing and the season, but
this is how you can do the calculations. Another nice thing about
Air Farms is that your season will extend its normal range. Not
only can you have tomatoes in winter, but you can have fresh
lettuce in the heat of summer by growing them in your basement
or an air conditioned room.
you grow your lettuce completely under natural light, limited
artificial light or full artificial light, a simple trip to the
grocery will show one thing:
Hydroponically grown lettuce is cheaper!
New Tool Co.
Reprinted with permission.
Workshop - Hydroponics - Cryan Studio
© Copyright 2005-2009 Fabric Workshop
P.O. Box 204 Centerbrook, CT 06409
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