Abstract
Greenhouses in high latitudes consume vast amounts of energy for heating and supplemental lighting. Light emitting diodes (LEDs) have been suggested as having great potential for reducing greenhouse energy use, as they are extremely efficient at converting electricity to light. However, LEDs emit very little heat, which must be compensated by the greenhouse heating system. Thus, it is unclear how much energy can be saved by LEDs when the need for extra heating is taken into account. This study presents a first analysis of the energy demands for greenhouses transitioning from high-pressure sodium (HPS) to LED lighting, providing a quantification of the total energy savings achieved by LEDs. Model simulations using GreenLight, an open source greenhouse model, were used to examine a wide range of climates, from subtropical China to arctic Sweden, and multiple settings for indoor temperature, lamp intensity, lighting duration, and insulation. In most cases, the total energy saving by transition to LEDs was 10–25%. This value was linearly correlated with the fraction of energy used for lighting before the transition, which was 40–80%. In all scenarios, LEDs reduced the energy demand for lighting but increased the demand for heating. Since energy for lighting and heating is often derived from different origins, the benefits of a transition to LEDs depend on the environmental and financial costs of the available energy sources. The framework provided here can be used to select lighting installations that make optimal use of available energy resources in the most efficient and sustainable manner.
Highlights
Greenhouse horticulture in high latitudes requires vast amount of energy input
In cases where a transition from high-pressure sodium (HPS) lamps to Light emitting diodes (LEDs) does not alter the heating demand, the expected energy savings realized by transitioning to a more efficient lamp were influenced by two factors: the efficiency of the new lamp and the fraction that lighting takes up out of the total greenhouse energy demands (Fig. 5)
In a greenhouse where the energy input was only used for lighting, the energy savings of the lighting system was equivalent to the total energy savings
Summary
Greenhouse horticulture in high latitudes requires vast amount of energy input. In northern latitudes, heated glasshouses consume energy at a rate of 1100–1900 MJ m− 2 year− 1 [1]. With an estimated 40,000 ha of vegetable glasshouses worldwide [2], and at least that much area for ornamental production [3], greenhouses consume more than 880 peta joule (PJ) of energy every year. In the Netherlands, the greenhouse in dustry consumes 113 PJ of energy per year [4], resulting in 5.7 megatons of CO2 emissions, nearly 25% above the targets set for the sector by the government [5]. Greenhouse energy use is increasing, due to wider and more intense use of heating and supplemental lighting [1]. Heating is used to maintain indoor temperatures that are favorable for the crop year-round, while supplemental lighting is used either for daylength control, in order to regulate plant developmental processes such as flowering, or as assimilation lighting to increase crop growth [6]
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