Service tax or excise on some fixed charges

There are two separate legal entities "A" and "B" separately registered under central excise as a manufacturer, and physically neighbor companies. "A" is "B" are in agreement that "A" will supply some utilities like "steam" and "nitrogen" gas i.e. excisable goods to "B". But to generate such utilities, "A" has to bear some "fixed cost" which is payable to government energy suppliers, and as per agreement "B" is ready to reimburse that fixed cost. Now if "A" is charging value as per normal costing formula, "A" is incurring loss in case of consumption is "zero" for some period, as "A" can not invoice it. - As "B" is agree to reimburse fixed cost to "A", in such case how this transaction should happen between "A" and "B" while consumption/transfer of that gas and steam is zero quantity ? - How can "A" charge Excise Duty on that "fixed amount" which is agreed to be reimbursed by "B" for such particular excisable goods ? - Can "A" raise Debit Note with Service Tax ?