The interest on a loan of RMB 30,000 per year depends on the loan interest rate and repayment method. The following are some possible situations and explanations:

1. Fixed-rate loan: If the loan interest rate is 10%, the interest for one year is 3,000 yuan (loan amount 30,000 times the interest rate 0.10).

2. Floating rate loan: If the loan interest rate floats according to a certain index, such as the base interest rate plus 2%, the specific amount of interest will change according to changes in the base interest rate.

3. Installment repayment: If the loan is repaid in 12 months, the total monthly repayment of principal and interest will be about 2,500 yuan. This is based on the monthly principal repayment of 2,500/12 = 2,083 yuan (loan amount 30,000 divided by 12 months), and then the interest calculated based on the remaining loan amount.

Summary: To determine the interest on a loan of 30,000 per year, you need to consider factors such as the loan interest rate, repayment method, and loan term. The above are just some examples and do not represent specific loan interest rates and repayment methods. It is recommended to check with a bank or other lending institution for the exact amount of interest.

Extended information: In China, loan interest rates are affected by central bank policies and internal decisions of commercial banks. Loan interest rates are often related to the borrower's credit profile, loan type and market changes. Banks usually determine specific loan interest rates based on the borrower's credit score and repayment ability.