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LEDs Reduce Tomato Growing Energy Costs

Energy Manager Today Staff

tomatoTomatoes grown around LED lights in the winter can significantly reduce greenhouse energy costs without sacrificing yield, according to a Purdue University study.

Cary Mitchell, a professor of horticulture, and doctoral student Celina Gómez experimented with light-emitting diodes, which are cooler and require far less energy than traditional high-pressure sodium lamps used in greenhouses. They got the same yield – size and number of fruit – with high-pressure sodium lamps and LED towers, but the LEDs used about 25 percent of the energy of traditional lamps.

The scientists think that the method could have other advantages because the cooler LEDs can be placed much closer and along the sides of plants, lighting not only the top, but also the understory. This means that the leaves are photosynthesizing on the lower parts of the plants, and that may be helping with the plant’s energy, Gómez said. The approach maximizes the intensity of light getting to the plant as the LEDs are so close to the plants. This can happen because they’re not hot like a high-pressure sodium lamp. If you put one of those close to the plants, you’d scorch it, Gómez added.

The heat from high-pressure sodium lamps account for about 15 percent to 25 percent of the heat needed to warm greenhouses, a technique that Mitchell describes that as an inefficient and very expensive way to heat a greenhouse.

Mitchell said the goal of his research is to reduce prices to the point where local growers could compete with the prices of tomatoes that are shipped from faraway places. Local tomatoes would be harvested vine ripe, would taste better and would boost local economies.

The average tomato is shipped about 1,500 miles from warmer climates where they’re grown to cooler climates that cannot produce the fruit cost-effectively in the winter. That journey is costly, however, because tomatoes are picked green and ripen during shipping, decreasing quality and flavor. The lengthy shipping distance also adds to the industry’s carbon footprint, according to

Energy costs drive up prices for producers who might want to grow tomatoes in greenhouses in states that have winters inhospitable to growing food. Greenhouses must be heated, and shorter, overcast days require costly lighting.

Indoor growers of an entirely different nature have were implicated in using massive amounts of energy  - with many not paying for a kWh of it – in a study released earlier this month. Awesense, a Vancouver-based company that provides sensors and software to detect energy theft, found that marijuana growers are heavy energy consumers because of the special energy-hogging lights they use to make their crops grow faster indoors. The first wave of marijuana growers just paid their bill, but then the police could easily find them, so they began tapping into either primary or secondary electricity lines. Awesense has noted that even in locales where marijuana is legal, the growers are just as likely to steal power.



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