I installed solar panels on my home, why am I getting only a partial credit?

On your 2019 ta return, you may see only a partial use of your solar credit because the solar credit is a non-refundable credit. It can only be used to reduce your tax liability to zero. Any excess cannot be refunded to you but is carried forward to future years.

how many future years?

And I'm so confused.  I was told I could use the tax credits to pay down my loan, so does that mean that next year I'll get the rest of my tax credit since it was substantial? Or do I get the credit over several years, I'm trying to figure out what the solar people told me I could do

No, you won't necessarily receive the rest of the credit next year. Same as this year the credit will only reduce your tax liability. Any unused credit, you will carry it forward to the following year.