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In Northern Europe the production of ornamental pot plants in greenhouses requires use of supplemental light, as light is a restricting climatic factor for growth from late autumn until early spring. By participating in demand response programs such as real-time pricing, growers can schedule electricity consumption in hours where electricity prices are low, thus achieving savings in their electricity expenses. In this context we present a novel software system for dynamic control of supplemental lighting in greenhouses that aims at decreasing the electricity costs and energy consumption without loss in productivity. The software uses weather forecasts and electricity prices together with a photosynthesis model to compute energy and costefficient supplemental light plans, which fulfills the productivity goal defined by the grower. Experiments with different light control strategies revealed that electricity savings about 25% was possible without noticeable reductions in plant flowering and production time. KEYWORD: Energy Management System; Demand Response; Smart Grid; Demand Side Management; Climate control; Supplemental Light; Photosynthesis; Weather Forecast; Electricity Cost; Decision Support; Energy Saving. International Conference on Industrial Technology and Management Science (ITMS 2015) © 2015. The authors Published by Atlantis Press 199 large parts of the expenses ascribed to production. A key example of this is protected cultivation of plants. In Denmark, year-round protected cultivation of plants requires a high-energy use for supplemental light in order to maintain both high plant quality and a well-planned plant production. Light is the energy source for plant photosynthesis and growth and when light levels are low, plants are unable to take advantage of environmental factors associated with protected cultivation such as higher temperatures and higher CO2 concentrations. A number of approaches to climate control systems based on mathematical models (Seki, et al., 2005), more complex dynamic responses (Gauthier & Guay, 1990) and simulation models (Jones, 1998) has been developed, but often failed due to their complexity and crop specificity, while validated microclimate models linked to both transpiration and CO2 use has been more successful (Korner, 2003). A dynamic climate control system based on a model system for leaf photosynthesis resulted in the development of an energy-minimizing and daylightdependent control system called IntelliGrow for production of ornamental pot plants using dynamic management of CO2 and temperature (Hansen & Hogh-Schmidt, 1996) (Aaslyng, et al., 2003). The basic principle of IntelliGrow is that it regulates temperature and CO2 concentration according to the actual photosynthetic photon flux density (PPFD) thus utilizing the free energy generated by the sun and allowing the setpoints of temperature and CO2 to increase considerably, compared to standard climate control under high light conditions, and, contrarily, reduce heating during low light periods thus generating a much more dynamic range of climates compared to a traditional climate management. However, whereas the implementation of the research efforts resulted in a steady decline in the use of energy for heating purposes in Denmark of up to 38% since 1996, the energy used for supplemental light have only increased during the last 10 years (Dansk Gartneri, 2011). The Danish greenhouse industry utilized 257.7 GWh of electricity or 0.83% of the total national electricity consumption in 2012 and it is estimated that 75% of this is used on supplemental light 1 . The increase in energy prices has put many growers out of business since 2010, and the remaining growers need to solve the problem of reducing their energy consumption while preserving their plant-production level and quality to stay in business. The introduction of a variable price structure in the Nordic countries renders supplemental light control strategies in greenhouses, which do not take the fluctuating price of electricity into account, very expensive. Therefore, there is a need for control 1 Sources: The Danish Energy Association and The Danish Energy Agency strategies that utilize the fluctuating price pattern to optimize the cost of using supplemental light. Furthermore, the creation of such energy and costefficient light control strategies needs to consider the natural plasticity in plants to irregular light periods especially under low light intensities, as plant photosynthetic carbon gain is mainly linked to the daily light integral (DLI), whereas plant growth rate and development is a function of temperature and the interrelation between temperature, CO2 and light integration (Liu & Heins, 2002) (Moccaldi & Runkle, 2007) (Oh, et al., 2009). In contrast, the distribution of the light intensities during the photoperiod, and light interruptions during the dark period, compared across treatments with the same DLI have only marginal effects on plant carbon gain in different plants species (Langton, et al., 2003) (Markvart, et al., 2009) (Kjaer, et al., 2011). However, changing the light patterns may have complex effects on the photoperiodic-dependent plant responses such as leaf development, stem elongation, and flower initiation (Thomas & VincePrue, 1996). Furthermore, differences in light patterns may interfere with the critical day length controlling flowering induction in short-day (SD) plants, but also the time to flower in long-day (LD) and day-neutral plants (Runkle, et al., 1998) (Karlsson & Werner, 2002) (Mattson & Erwin, 2005) (Rohwer & Heins, 2007) (Currey & Erwin, 2010). Therefore some plant types may be nonsuitable for production in the irregular light environments. Despite significant disturbances of circadian light-regulated processes in plants by changing light conditions (Resco, et al., 2009) (Kjaer & Ottosen, 2011), campanula plants were only marginally affected in growth and development by changing light (Kjaer, et al., 2011). This suggests that the development of induced flowers in campanula depends more on the duration of light than on the distribution of light. Realizing that parts of plant production are able to cope with irregular light environments makes protected cultivation an ideal candidate for participation in demand response programs. In order to enable effective participation of greenhouses in a variable price electricity market, we have developed a software system which allows for integration of DR strategies at the consumer side. We have exemplified this by implementing a strategy which imports electricity prices and, combined with the use of weather forecasts, computes energy and costefficient strategies for the use of supplemental light. The software interfaces with a greenhouse ECC to effectuate the supplemental light strategies in the greenhouse. A dynamic supplemental light control is novel as most research has focused on light and temperature integration using constant conditions (e.g. (Runkle, et al., 1998)).

Integrating Commercial Greenhouses in the Smart Grid with Demand Response based Control of Supplemental Lighting