An insurer may deposit and maintain on deposit with the director of finance through the commissioner funds and eligible securities in amount exceeding its required deposit under this part by not more than $100,000 for the purpose of absorbing fluctuations in the value of securities held in its required deposit, and to facilitate the exchange and substitution of such required securities. During the solvency of the insurer, any such excess deposit, or any part thereof, shall be released to it upon its request. During the insolvency of the insurer, such excess deposit shall be released only as provided in § 431:7-309.