from where can I get clear sky,overcast sky,partially overcast sky data for chennaii,delhi,ahmedabad(Indian cities)/yearly data?

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There's a lot of solar data for India available on the Web, but you have to decide what kind of solar data you're looking? Historical year time-series, "typical year" time-series, average daily values by month, etc.?

Please look at this Unmet Hours Post for weather data information.