The tote does not use electricity.
The plants are also terrible at paying the utility bill.
In a simple pump-free indoor hydroponic system, the grow light is usually the main electrical cost. That makes the math refreshingly straightforward. You do not need an energy monitor, a spreadsheet, or a promise that your lettuce will “pay for itself.” You need three numbers from the real light you plan to use.
The formula
Find:
- The light’s actual power draw in watts
- The number of hours it runs each day
- Your electricity rate per kilowatt-hour
Then calculate:
watts ÷ 1,000 × hours per day × days per month × electricity rate = monthly cost
Example
Suppose your light draws 60 watts and runs 14 hours a day.
60 ÷ 1,000 = 0.06 kilowatts
0.06 × 14 hours = 0.84 kilowatt-hours per day
0.84 × 30 days = 25.2 kilowatt-hours per month
If your electricity costs $0.18 per kilowatt-hour:
25.2 × $0.18 = $4.54 per month
Use the rate from your own bill. Electricity prices vary by utility, location, season, and plan.
Use actual draw, not the name on the box
Grow-light listings can be confusing.
A product name may include a large number that refers to an equivalent output, model series, or marketing claim rather than the electricity it actually draws. Look for “actual power,” “power consumption,” or a wattage specification in the manual.
If the listing says “1000W equivalent” but the specifications say the fixture draws 100 watts, use 100 watts in the formula.
When the manufacturer does not disclose actual draw, that is useful information about the product too.
What about a pump?
Active hydroponic systems may use an air pump, water pump, or both. Add each device separately using the same formula.
For example:
- Grow light monthly cost
- Plus air pump monthly cost
- Plus water pump monthly cost
- Plus any fan, heater, or cooling equipment
A passive Kratky tote has no pump, so its electrical cost is mostly light. If you can use adequate natural light, the electrical cost may be lower, but a window is not automatically consistent enough for compact indoor growth.
Do not choose a light by wattage alone
Lower watts do not always mean lower cost per useful harvest.
A tiny light that leaves lettuce stretched and pale may run cheaply while producing very little. A properly sized, efficient fixture can cost slightly more to run and give the plants enough usable light to make the whole setup worthwhile.
The goal is not the smallest electric bill. It is the least wasted electricity for healthy plants.
Match the fixture to the shelf or tote footprint. Light landing on the wall, floor, or empty shelf is not growing dinner.
The timer is your cheapest employee
A basic outlet timer keeps the light schedule consistent and prevents accidental 24-hour operation.
Plants need a dark period. More hours are not endlessly better, and forgetting to turn a light off wastes electricity without fixing a weak fixture.
Choose a schedule appropriate for the crop and light, then let the timer handle it. If you change the schedule, write down the date. Otherwise it is easy to forget whether the plants improved before or after the adjustment.
Five ways to reduce wasted power
1. Keep the light close enough to be useful
Follow the manufacturer’s safe hanging-height guidance. If the light sits far above small seedlings, much of its output misses the plants.
Adjust the height as plants grow. Watch for stretching, bleaching, curling, and heat.
2. Use reflective surroundings carefully
A light-colored wall or simple reflective surface can help return stray light toward the plants. Keep materials clean, dry, secure, and away from heat or electrical hazards.
You do not need to turn a kitchen shelf into a foil cave.
3. Grow plants that fit the footprint
Lettuce, basil, bok choy, arugula, and compact greens make good use of a small lighted area. A sprawling tomato under the same fixture may shade neighbors and demand more space and intensity.
4. Fill the planting sites you intend to light
Running a full shelf light for one lonely seedling is not efficient. Start seedlings together, then move the healthy ones into the tote.
Do not overcrowd mature plants, but do use the lit footprint deliberately.
5. Clean the fixture and timer
Dust reduces light output. A failing timer can leave the light off for a day or on all night. A quick monthly check protects both plants and power use.
Compare electricity with what you actually harvest
The most useful calculation is not “Did this head of lettuce cost less than the cheapest lettuce in town?”
Your indoor garden may grow varieties you cannot buy locally, reduce spoiled clamshells, provide leaves exactly when you need them, or simply help your family eat more greens. Those benefits are real even when they do not fit a dramatic savings claim.
Still, you can measure the financial side honestly.
For one cycle, record:
- Electricity estimate
- Seeds used
- Nutrient used
- Any replacement supplies
- Harvest dates
- Purchased greens you skipped
Do not include the full cost of reusable equipment in every harvest. A light or tote used across many cycles is a longer-term cost.
After two or three cycles, you will know whether the system makes sense for your household.
A simple cost worksheet
Copy this and fill in your numbers:
- Light actual draw: _____ watts
- Daily runtime: _____ hours
- Days this month: _____
- Electricity rate: $_____ per kWh
Monthly light cost:
(watts ÷ 1,000) × hours × days × rate = $_____
Repeat for any pump or fan, then add the results.
The honest bottom line
A small pump-free hydroponic tote does not need to become a major electrical project. The light is usually the main cost, and that cost can be calculated before you buy anything.
Read the actual wattage. Use your real utility rate. Size the light for the plants. Put it on a timer.
That is much more reliable than a blanket promise that indoor lettuce is free—or a warning that every grow light will wreck the power bill.
If you want a complete beginner setup designed around one simple, small-space system, see the Indoor Mini Farm System.
