Why Is Forced Cooling Often Useful in Solar Applications?
Forced cooling is often useful in solar applications because solar transformers usually operate outdoors, often in hot ambient conditions, and their loading profile can be highly site-specific. Manufacturers for solar step-up transformers explicitly call out the need to design around higher ambient temperature ranges, while Eaton notes solar/energy-storage transformers are often customized around loading profile, temperature profile, site altitude, and required system life.
In that context, forced cooling gives the transformer more heat-rejection capacity than natural cooling alone. Eaton's substation-transformer literature shows that fluid-filled units above certain ratings are offered with natural-air / forced-air cooling options, and Hitachi Energy specifically lists upgrades from ONAN to ONAF when more cooling is needed.
The practical reason is simple: lower operating temperature helps protect insulation life and maintain reliability. Hitachi Energy's transformer monitoring material says cooling control helps avoid insulation degradation, so in solar plants forced cooling is especially valuable when daytime heat, enclosure exposure, and peak generation periods push transformer temperature upward.
