Abstract: Among other things, an online interface is provided in which a property owner enters information defining a specification of an intended energy system to be installed for the property owner. The specification is in sufficient detail to enable each of two or more different installers to provide commercial offers of an energy system that conforms to the specification. An online interface may be provided in which a property owner is presented with a guided sequence of interactive steps in which the property owner is prompted to enter information associated with energy systems that may be relevant to the property owner, the content of at least one of the later steps being dependent on the information entered by the user in a prior step. A selection of energy systems based on technical feasibility and suitability as determined from information provided by the property owner may be presented through the interface.