The ver­ti­cal farm insti­tute has been com­mis­sioned by Bet­ter Plants R&D GmbH to deter­mine the ener­gy poten­tial of using Bet­ter Plants light­ing fix­tures as part of the research and devel­op­ment com­pa­ny’s inno­va­tion check fund­ing pro­gram. FFG - Öster­re­ichis­che Forschungsförderungsgesellschaft

The glob­al radi­a­tion of the ref­er­ence city of Vien­na reach­es around 1,120 kWh/m2/a, where­by the ratio between direct and dif­fuse light is around 56.5% (direct irra­di­a­tion) and 43.5% (dif­fuse irra­di­a­tion). The annu­al dis­tri­b­u­tion of total glob­al radi­a­tion shows that the month with the high­est total solar radi­a­tion is July with 172.62 kWh/m2 (dir=68.35%, diff=31.65%). The month with the low­est total solar irra­di­a­tion is Decem­ber with 18.93 kWh/m2 (dir=72.58%, diff=27.42%).

Cal­cu­lat­ed over the whole year, this cor­re­sponds to an over­sup­ply of PAR by a fac­tor of 2 and there­fore requires no fur­ther consideration.

The inclu­sion of the avail­able day­light inte­gral (DLI) or the obser­va­tion unit of a day deserves clos­er con­sid­er­a­tion and cor­re­sponds to the great­est poten­tial for reduc­ing the elec­tric­i­ty demand for sup­ple­men­tary light­ing. If light­ing fix­tures are con­trolled in such a way that they are only acti­vat­ed when the DLI for the plant is not reached dur­ing the pho­tope­ri­od - regard­less of a poten­tial exten­sion of the pho­tope­ri­od to 16 hours - a reduc­tion in ener­gy demand of up to 31% can be expected.

From an ener­gy and eco­nom­ic point of view (syn­er­getic depen­den­cy), it can also be rec­om­mend­ed - for year-round pro­duc­tion - that the dis­in­fec­tion phase of the build­ing is sched­uled for the month with the most hours of sun­shine. In July, the mar­ket is sat­u­rat­ed with L. escu­len­tum and the solar yield (day­light and heat) is at its highest.

The ori­en­ta­tion of the build­ing (N-S, E-W) has a neg­li­gi­ble influ­ence on the ener­gy require­ment, espe­cial­ly for the green­house - com­pared to the ver­ti­cal farm or the Plant Fac­to­ry. The ori­en­ta­tion itself will only become more rel­e­vant when the pro­duc­tion site is locat­ed in an urban area and the enclosed space is inte­grat­ed into the sim­u­la­tion def­i­n­i­tion as a geo­met­ric con­text for the day­light simulation.

Deter­min­ing the crop sequence (sow­ing - har­vest shift) is one of the key deci­sions for ener­gy-effi­cient oper­a­tion of a growth vol­ume - regard­less of the build­ing typol­o­gy. The depen­dence on grow­ing con­di­tions and the enclosed space can be seen as essen­tial para­me­ters here. Mixed crop sys­tems should be tak­en into con­sid­er­a­tion when plan­ning deci­sions for year-round pro­duc­tion (avail­able light vs. grow­ing conditions).

Unsur­pris­ing­ly, the τ and U val­ue play the most impor­tant role in the build­ing enve­lope. How­ev­er, more in-depth inves­ti­ga­tions are rec­om­mend­ed in the direc­tion of translucency.

Light is not even­ly dis­trib­uted in green­hous­es. This sit­u­a­tion can be improved by increas­ing the dif­fuse light com­po­nent. To deter­mine the effect of dif­fuse light on the growth and devel­op­ment of plants, a tri­al was car­ried out with L. escu­len­tum under com­mer­cial cul­ti­va­tion from Decem­ber 2010 to Novem­ber 2011. Three types of glass were used as green­house cover:

Stan­dard glass (no dif­fuse light, 0%) and two types of dif­fuse glass that con­vert­ed part of the direct radi­a­tion into dif­fuse light (from 45% to 71%).  A more in-depth study of the depen­den­cy between yield and arti­fi­cial light­ing is rec­om­mend­ed (see below). Fur­ther poten­tial for reduc­ing the ener­gy used in plant pro­duc­tion is sus­pect­ed here.