(a) A debtor is insolvent if, at a fair valuation, the sum of the debtor's debts is greater than the sum of the debtor's assets.

(b) A debtor that is generally not paying the debtor's debts as they become due other than as a result of a bona fide dispute is presumed to be insolvent. The presumption imposes on the party against which the presumption is directed the burden of proving that the nonexistence of insolvency is more probable than its existence.

(c) Assets under this section do not include property that has been transferred, concealed, or removed with intent to hinder, delay, or defraud creditors or that has been transferred in a manner making the transfer voidable under the Uniform Voidable Transactions Act.

(d) Debts under this section do not include an obligation to the extent it is secured by a valid lien on property of the debtor not included as an asset.