The present disclosure describes use of filamentous algae to form insulating construction materials which provide thermal and noise insulation. Algae from the order Zygnematales, the Cladophorales, or the Ulotrichales can be dried and formed for use as insulating material. Algae mass can be combined into several layers, using a binder to attach the layers to each other. A composite material of algae mass and an additive can be used and form the body of insulation panels having honeycomb-shaped chambers, which are sealed by a foil that is laminated onto the body.Various plants for cultivating algae for use in construction material are disclosed. Plants utilizing gravity harvest comprise cultivation ponds located at a slope, wherein the ponds can be opened to allow algae and water to flow downhill through a collector grill. Plants utilizing net harvest, overflow harvest or rake harvest are described. Carbon dioxide injection concepts utilizing direct and indirect injection of carbon dioxide into algae cultivation ponds are disclosed. An algae harvesting machine is disclosed. Control concepts for controlling the growth of algae in an algae cultivation plant are described.
