John Laing Environmental Assets Group's net asset value per ordinary share stood at 99.0 pence at the end of September compared with 100.1p at the end of March.
JLEN said the change was primarily due to the decrease in forecast electricity prices during the period.
It said the portfolio valuation at the end of September was £375.9m compared with £327.6m at the end of March.
The group declared a further interim dividend of 1.5775p per share making total dividends declared for the six months to 30 Sep of 3.16p per ordinary share, in line with the target set out in the 2017 annual report.
Chairman Richard Morse said: 'JLEN has made steady progress in the performance and growth of the fund's portfolio throughout the six month period to 30 September.
'The board is appreciative of the continuing support of shareholders, demonstrated during the period by the successful equity raise in July.
'We were able to use the funds raised to pay down debt and fund a healthy level of acquisitions.
' We continue to deliver on our commitments to our shareholders and to that end we have paid and declared interim dividends during the period that have increased in line with inflation from last year.'
At 8:08am: (LON:JLEN) John Laing Environmental Assets Group share price was +1.13p at 105.63p