There are no feature to set the value via API today.

You can set the price via the Rules, where you can use the Action called Set Property. You can for example use the rules to define different electricity prices depending on time or day. Rule actions can also be triggered via the API if needed.

I do understand this doesn't give as much flexibility as having an API method for setting an exact price from an external application. Please let me know if you still prefer the API method and I will look into supporting it when possible. Thanks!