No, you could not claim the energy saving improvements for both an energy credit and a home office repair expense. That would be double-dipping the tax benefits.
You should compare which deduction or credit will give you the most benefit to decide which tax benefit to use.
Also, consider whether the total cost of the improvements was needed in order to claim the maximum energy credit. Suppose the total cost of the improvement was $5000 and $3000 of cost would have given you the maximum energy credit. It would be reasonable to claim the remaining $2000 as a home office repair expense (assuming it qualifies under that category). That way you would not be double-dipping, but claiming the total cost in two different areas of your return.