What does a seed starting shelf cost to run?
Usually a few dollars to a few tens of dollars for a whole season. The formula is short.
The formula
Total watts x hours per day x days, divided by 1,000, gives kilowatt hours (kWh). Multiply by your price per kWh. Your bill or utility website shows the price.
A season at 14 hours a day for 70 days
| Total power | kWh | At $0.10 | At $0.15 | At $0.30 |
|---|---|---|---|---|
| 20 W | 19.6 kWh | $1.96 | $2.94 | $5.88 |
| 40 W | 39.2 kWh | $3.92 | $5.88 | $11.76 |
| 80 W | 78.4 kWh | $7.84 | $11.76 | $23.52 |
| 160 W | 156.8 kWh | $15.68 | $23.52 | $47.04 |
| 240 W | 235.2 kWh | $23.52 | $35.28 | $70.56 |
14 hours is within the 14 to 16 hours most extension sources give. Seventy days is a placeholder for a season. Change both in the calculator.
Where the watts come from
Use the watts printed on the fixture, times the number of fixtures. Two 4-foot, 40 watt fixtures are 80 W. Four 2-foot, 10 watt bars are 40 W. Barrina, for example, lists a 4-foot T5 LED bar at 20 W, so two would be 40 W.
Ways to use less
- Light only the part of the shelf that holds trays.
- Use a timer so lights do not run past the hours you chose. See hours per day.
- Raise lights only as much as needed. Farther lights need more hours, as the UNH example in the distance guide shows.
Heat mats add to the bill. Check the watts on the mat as well. See the heat mat guide.
Sources
- UNH Cooperative Extension (Jonathan Ebba): Growing seedlings under lights (PDF)
- Barrina: T5 20W LED grow light 4FT 5000K (ML20), manufacturer page