Skin
The other light instruments ask how bright it is; this one asks what it pays. Take Surveyor's climate (or drop an EPW), pick a massing, and paint PV zones onto roofs and facades. Skin walks all 8,760 hours: beam plus a Hay–Davies diffuse decomposition transposed onto each panel's tilt and azimuth, the building shading itself, a temperature derate from the same weather file, and PVWatts-shaped system losses — out comes annual kWh, specific yield in kWh/kWp, and a monthly generation profile. An orientation dial sweeps every tilt and azimuth so the lesson lands: a vertical south facade is not a roof. A carbon line talks back to Footprinter. Client-side; sign in to ask the coach about your own re-orientation idea.
Skin refuses to guess a climate — a bundled default would be a silently wrong answer for every site that isn't that city. Pick a site in Surveyor and its weather pipes over automatically, or drop a real EPW weather file here (climate.onebuilding.org and the DOE EnergyPlus set are free).
Everything runs in your browser — the weather file is parsed locally, nothing is uploaded.