RadChart is an image generated by the server and as such can be exported as image only. You can use RadChart.Save() method to save the chart to an image or a memory stream. Then you can use it in any custom scenario. You may as well find this KB article helpful as it demonstrates how to export RadChart to PDF.
We do not have a framework that exports charts to excel charts as such and for the time being only images/PDFs can be used out of the box (with RadChart). What you can try is to get the data from the code-behind, together with chart properties and build excel charts yourself. Should you succeed in this task and post it as a code library project we will gladly award your efforts with Telerik points.
All the best,
the Telerik team
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