Vian141
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Joined: Sat Jan 09, 2021 3:33 pm

Calculation doesn't match up

Hi,
I am from India and thinking of starting a hydroponics farm here. For now I am in the initial stages of figuring out the cost and benefit of the system and things are not falling into place. Here are my high level calculation for lettuce production and LED electricity. For now I am ignored other cost as at this point my main consideration is to overcome the LED electricity cost.
Costing for 1 sq.ft. area:

Revenue estimation:
Spacing between plant: 4 inch
Total lettuce plant in 1 sq.ft. : 4*4 = 16
Average yield of lettuce plant: 0.5 kg/sq.ft. per cycle
Cycle time: approx 30 days
Total yield obtained: 0.5*1 = 0.5 kg
Selling price: 200 Rs/kg
Total revenue per cycle: 200*0.5 = 100 Rs.

LED cost estimation:
Wattage required for Lettuce: 40 W/sq.ft.
Watts required for 1 sq.ft. : 40*1 = 40W
Led on time: 16hrs for 30 days each (1 cycle)
Total kWh per cycle: 40*16*30/1000 = 19.2 kWh
Cost of electricity: 8 Rs./kWh
Total LED cost for 1 cycle for 1 sq.ft area = 19.2*8 = 153.6 Rs.

Total loss = 153.6-100 = 53.6 Rs
For now, I am ignoring all other cost as the LED cost are the most significant.
Is the calculation right or am I missing something here or doing something wrong?

pepperhead212
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Location: Woodbury NJ Zone 6B

Re: Calculation doesn't match up

Welcome to the forum!

I only grow hydro lettuce in my basement, but just glancing over your list, the spacing of 4" between plants seems too close, unless you are growing baby lettuce. I grow leaf lettuce, and harvest the outer leaves, and harvest from the same plants for a few months, before they begin to bolt. And I have found that 16 hours of light gives the best growth for most of these greens and herbs, so that should be good.
Dave

Vanisle_BC
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Location: Port Alberni, B.C. Canada, Zone 7 (+?)

Re: Calculation doesn't match up

@Vian, I don't grow hydroponically and haven't tried to follow through your entire calculations but:

If spacing is 4 inches, you only get 9 plants per square foot, not 16 - ??
"There are two kinds of people in the world - those who think there are two kinds of people in the world, and those who do not" - Robert Benchley

Vian141
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Re: Calculation doesn't match up

@pepperhead212. Yes for now I am thinking of baby lettuce for which I think 4 inches are sufficient
@Vanisle_BC. 16 in the sense that there will be lettuce pots at 0,4,8 and 12 inches. But I get your point that when we do consider plantation over a larger area, the average number of plants per sq.ft. comes to somewhere between 8-9 as the pots at the edges gets double counted.

My issue with the calculation is that just the LED electricity cost is more than 100% of the revenue obtained from selling Lettuce. So I am presuming there are 2 explanation for this,
1. My calculations are wrong (reason for this post) or
2. The selling price in India is less or the electricity cost is more

Vanisle_BC
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Location: Port Alberni, B.C. Canada, Zone 7 (+?)

Re: Calculation doesn't match up

It seems to me that either the project is not viable, or wrong values are being assigned to any of the variables: Yield or required KWH per unit of area; or the price that can be obtained for the product. I don't have knowledge in these areas.
"There are two kinds of people in the world - those who think there are two kinds of people in the world, and those who do not" - Robert Benchley

imafan26
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Joined: Tue Jan 01, 2013 1:32 pm
Location: hawaii, zone 12a 587 ft elev.

Re: Calculation doesn't match up

Well here is a thought. Are you growing all of this indoors, in a screen house or some kind of shade house?

If you are not growing all of this in total darkness, there will be some "free" sunlight so, your LED costs should not be that high. Actually with sun filtering shade cloths and netting to keep bugs out, LED lights are not necessary at all. Costs would be for cost of running the pumps (unless you are doing Kratky which will only need an aerator and they have even less wattage than a pump and they are water efficient. You will have to take into account the cost of the solution and cleaning of the system after each cycle, plus cost of oasis plugs, cost of seeds and seedling growing costs.

If you set up your beds right, you can use reflective material like white backgrounds and foil to reflect light. All of the light is not going to fall only on the crop. There will be spillage. If you do your calculation, don't do the calculation based on sq. ft of of production but how much watts you need to get light to the area to get the 1500-2000 lumens per sq ft. including natural light and reflectors. Lighting will be a fixed cost not a variable cost. You need to figure out not the cost of lighting a plant, but of lighting the area. Using reflective materials can reduce the cost of lighting. Again, if you are not doing this totally in the dark, there should be ambient light as well that will reduce your lighting costs. Plants in full sunlight receive about 3000-4000 lumens.

I have used a light meter for my yard. Under 50% shade cloth I was still getting up to 5000 lumens and 8000 lumens without shadecloth. ( I did it a long time ago so I forgot the season and time of day I did the test.) Under 70% shade cloth, I got 3000 lumens. Caveat: My shade cloth is only 2 ft above my orchids so it allows more light in than a 50% shade cloth at 5+ feet would let in.

It was hard to follow your calculations, but besides being fallacious to expect the light to be the only source and to only light a fixed area, it looks like your cost was based on kwh. that is a 1000 watts per hour = 1kwh. If you multiply by 16 hours = 16 kwh a day per fixture. Your electricity cost is 8rps/kwh = 16*8 = 128 rps/day (assuming 16 hour days) per fixture. How many 1000 LED fixtures do you have?
128 rps/day x no of days till harvest (30 days) = 3840 rps per LED fixture for a 30 day growing cycle. Multilpy that number by the number of fixtures and you will get your monthly cost.

I also could not understand your yield logic. If you are planting 16 plants per square foot, which would be impossible to get good yields, unless you have plants of different sizes. they would all be small. A full lettuce head needs 6-8 inches to yield a good sized head.

I'll do a calculation I know. lettuce spaced 8 inches apart in a bed 4x100 ft = approx 1200 heads in 30-45 days depending on the growing season. 1200 head after taking off the outer leaves and cleaning yields about 150 lbs of salable product. A 1000 watt LED fixture can illuminate approx a 4x5 ft growing area or about 20 sf. If this lettuce bed I described only has LED light as its only light source then it would take: 100/ 20 or 5 (1000 watt LED fixtures to light this area) If you are growing 100 sf of lettuce in this bed at your 8rp/kwh cost then for 30 days your cost would be 3840 x 5 = 19200 rps per month to produce 150 lbs of lettuce. 19200/150 = 128 rps per pound = cost of electricity to produce a pound of lettuce exclusively under grow lights. You are estimating roughly a pound = 500 gms wt per head of lettuce. I don't think with your spacing you will get that. Occasionally we did get a 1 pound lettuce, but most of them only weigh in about 170 gms or about 6 oz with 8 inch spacing. The lettuce we grew was manoa so it is a mini loose leaf variety so it does not weigh much and it sells now for about $4 lb. this is with 8 inch spacing.

You may be over estimating your cost of LED light. Even if it is a 1000 watt LED light. Is it the actual power draw of the LED light or the equivalent watts of a standard bulb? You need to calculate your electricity cost based on the actual watts used by the LED and not its equivalent wattage to a standard bulb. The LED fixture may only use 75% of the watts used by a standard bulb so you may be overestimating the cost. Your actual cost may be 25% lower (on average). It still is expensive if you also factor in that the LED costs way more than fluorescent bulbs. If you can do the hydroponics in an outdoor setting or can get some natural light in, then you should not need to spend so much on lighting.

https://hydrobuilder.com/learn/grow-roo ... Calculator

Consider growing micro greens. It is a faster harvest with even less inputs per sq ft. It has a higher price point if it is popular in your area. Do a market analysis to see if there is demand for it.
Happy gardening in Hawaii. Gardens are where people grow.

Vian141
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Joined: Sat Jan 09, 2021 3:33 pm

Re: Calculation doesn't match up

@imafan26. Thanks for such a detailed explanation. I understand that are lot of things to consider while doing the calculation. I'll start taking the parameters you mentioned in my calculation and see what result I obtain. Thanks a lot. Your post was really insightful

imafan26
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Location: hawaii, zone 12a 587 ft elev.

Re: Calculation doesn't match up

OOPS, I found an error in my calculation. a 4x100 bed = 400 sq ft not 100 to produce 150 lbs of salable lettuce. Per 100 sft yield would have been 150/4 = 37.5 lbs of lettuce per 100 sq ft. Again this is for a particular type of lettuce which is called manoa lettuce or green mignonette. It averages 8-11 inches in diameter at maturity. The rest of the calculations should still work just the yield will be 37.5 per 100 sq ft. 150 lbs would be the yield for approx 400 sq ft.
Happy gardening in Hawaii. Gardens are where people grow.

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