From the wiki of private chains in parity
Parity also includes Proof of Authority Chains which do not require mining.
Is it possible to raise more ether in an existing POA chain?
Lets suppose I started a private chain with one account. Now that account used up its ether. Now there is no way to mine ether, since mining POA does not require mining. How do I raise more ether?
As said by @rphmeier on gitter channel:
currently there isn't support, but we are planning to add a feature where a contract can perform non-canonical state transition by issuing events the contract could be operated by an administrator or require majority signatures from validators as a barrier to issue events a sophisticated contract could have linked credentials for the validators themselves so they don't have to use their own keys, and impose limits on the magnitude of changes that can be made over time
