Open energy data from Energinet to society.
Danish data service Energi API is a free Environment API that requires no API key, is served over HTTPS and has unconfirmed CORS support.
Details from energidataservice.dk.

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Geocode an address, validate an email, track a flight or pull stock data with one account, one dashboard and one API key.
Calculate the environmental footprint created by a broad range of emission-generating activities
The Danish data service Energi API is provided by Energinet (energidataservice.dk).
Yes. The Danish data service Energi API is listed in the Environment category of the public-apis directory, which only includes APIs that are free or have a free tier. Check its documentation for rate limits and paid plans.
No. The Danish data service Energi API requires no authentication, so you can start making requests without signing up.
CORS support for the Danish data service Energi API is unknown. Test a request from the browser, and fall back to a server-side call if it is blocked.
Yes. The Danish data service Energi API is served over HTTPS, so it's safe to use in production.