Is there any hard limit to have number of Excel webparts on the SharePoint 2010 page?
Nothing specific to Excel web parts. There is a default maximum number of web parts per page configured in your Web.config. The setting is "WebPartLimits" if you need to modify it.
<WebPartLimits MaxZoneParts="50" PropertySize="1048576" />
With that said, however, if you run too many Excel web parts on a single page, it will load very slowly.
Just anecdotally, I have a web part page with 8 Excel web parts on it and it takes about 15 sec for them to all load. There aren't any hard limits from what I've seen. It will mostly depend on what your users deem acceptable in terms of loading time and consumption wise.