Performance of terrestrial photovoltaics is generally measured by the output power under standard test conditions (STC) of 100 mW/cm² irradiance, with AM1.5G spectrum at 25 °C. Comparisons restricted to these test conditions disadvantage some photovoltaic technologies compared to crystalline silicon. Such technologies often give improved performance at more realistic operating temperatures and at the lower irradiances and larger insolation angles experienced throughout the day in a real installation. To account for these effects, various schemes have been suggested that evaluate photovoltaic performance according to their annual energy output in a typical installation. We present estimates of the annual energy output of some organic and dye-sensitised photovoltaic devices based on current-voltage-temperature, spectral response, and angular-reflectance measurements. Results show that the gap between energy conversion by organic and crystalline silicon devices is narrower than the gap in power output at STC. Using an energy-based rating scheme is a relevant and practical method of performance evaluation which accounts for some inherent advantages of organic photovoltaics.