Can a photovoltaic system be included in financing retroactively?

You will only get the 12k elsewhere as a regular installment loan. Do that at your bank.

It is sufficient if you look at the Income Tax Act Paragraph 4 Section 4.

(4) Operating expenses are the expenses incurred through the operation.

If you only have a loan, then it is simply not necessary business assets.
A preferential assignment to business assets is therefore not possible at all. Depending on the shareholdings, you even have the problem of possibly not being able to have it recognized as voluntary business assets.
In my opinion, an optimization of the deduction of interest on debt (100% financing) of the photovoltaic system is only possible through a separate loan. To avoid jeopardizing the interest deduction, this is also repeatedly recommended in the specialist literature for mixed-use items.

PS: To the original poster: This does not constitute legal advice. For more detailed information, you should consult your tax advisor.

If you only have one loan, it is simply not necessary business assets.
A priority allocation to business assets is therefore not possible at all. Depending on the share amounts, you even have the problem of possibly not being able to get it accepted as voluntarily assumed business assets.
In my opinion, an optimization of the interest deduction (100% financing) of the photovoltaic system is only possible through a separate loan. To avoid jeopardizing the interest deduction, this is also repeatedly recommended in the specialist literature for mixed-use items.

PS: To the original poster: This does not constitute legal advice. For more precise information, you should consult your tax advisor.

Sorry, but tell me, do you just google this together, or where do these half-truths come from?

At this point, I’m definitely out, I think the thread starter knows what to do...

Unlike you, I point out pitfalls that the original poster should clarify with their tax advisor. Your firm assertions, on the other hand, are certainly not covered by professional liability insurance. If you work at a tax advisor’s office, you should be aware that tax consulting is reserved for certain professional groups. With your statement, you are leading the original poster fully into a trap, just because it might have worked one or two times in your practice. I do not want to deny that it occasionally works, but one should be aware of the risks. And if you had taken the trouble to do some research, you would have recognized the risks as well.