Section 12P. There shall be established and set up on the books of the commonwealth a separate fund to be known as the Department of Public Utilities Storm Trust Fund. There shall be credited to this fund all amounts collected under the third paragraph of section 18 and any income derived from the investment of amounts credited to the fund. All amounts credited to the fund shall be held in trust and shall be available for expenditure, without further appropriation, by the department of public utilities for activities of the department in investigating the preparation for and responses to storm and other emergency events by the electric companies. Any unexpended balance in the fund at the close of a fiscal year shall remain in the fund and shall be available for expenditure in the following fiscal year.