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Hydroponic Growers
Bigger yields in smaller spaces
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Hydroponic Air Farms


4 Cents per Head of Lettuce

S
ome 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.

First, 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).

Our air pump operates at 4 watts. We run it 24 hrs. a day. So our electrical requirement will be:

4 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 pump.
$.30528 / 9 heads of lettuce = $.03392 / head.

Including 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.

This 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.

We 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.

Of 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:

One 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.

Growing 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.

Depending 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:

Lettuce 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.

Lettuce 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.

Your 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.

Whether 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!

Copyright 2000
Glenn Rice
Air Farms
New Tool Co.
Reprinted with permission.


Growing Ideas


Fabric Workshop - Hydroponics - Cryan Studio
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Fabric Workshop
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