By means of a case study, we examine the effect of size on the estimated weight and cost of an advanced wind energy conversion system, the diffuser-augmented wind turbine (DAWT) concept. Preliminary designs are described for three DAWT sizes (ratings) in each of three construction approaches: all-aluminum, ferrocement, and a hybrid fiberglass reinforced plastics (FRP) diffuser shell on an aluminum frame. Common design criteria are employed in designs for these three materials. Installed cost estimates are generated by professional industrial estimators. Excluding the foundation, it is concluded that for geometrically similar DAWTs the weight-to-power ratio varies approximately as the rotor diameter to the one third power, over a 4 to 1 change in rotor diameter, 2.7–11 m (9–36 ft). Futhermore, because the total direct production cost of these various DAWT units and designs proves to change by about D1.5, the cost-to-power ratio is approximately proportional to D−.5 and the cost/weight ratio varies as D−1/6. Therefore, for the investigated DAWT unit ratings between 5 and 200 kW, the larger units appear increasingly to become more efficient structures with apparently lower specific costs (dollars per kW) for each of three candidate construction approaches.