In order to segregate Energy and Non Energy charges you have the following options depending on what you need to do in the subsequent processes (e.g clearing, reporting).
1. You can use different amount statistic groups in the schema. This will tag each charge with a amount statistic group and you can use the amount statistic group in reporting (BW or ABAP)
2. You can use summarization subtransaction (FI-CA posting area R410 - transaction FQC0). In standard all billing subtransactions are posted on the SAME FICA subtransaction (0020 for debit and 0010 for credit). Using Posting area R410 you can actually assign the billing subtransactions (the ones you define in the schema) to different FI-CA subtransactions. In your case you can have a separate set of FI-CA subtransactions call Non-Energy (0030 and 0040 for example). When you post the invoice to FICA you will actually see the 2 BP items for each invoice, one item for all energy charges and one item for all non energy charges. You can then use this in clearing or other subsequent FICA processes (for example you can apply different dunning procedures, interest clearing algos, etc).
Hope this helps.
Daniel