Chris999

I have seen a couple of pictures where the tennant built a loose standing frame for his panels which he anchored in his lawn. The big advantage was that he could change the angle to adapt to the seasons. But I think he didn't wire it into his house system. 

Looks like we will be amending the contract.

Make an addendum, let both parties sign. 
Spell it out.
Dear Landlord,
I am writing to request an addendum to the lease agreement to clarify ownership of the backup system that I plan to install on the property. Specifically, I request that it be explicitly stated that the backup system remains my property, and that I have the right to remove it when I terminate the lease.
As the owner of the backup system, I take responsibility for ensuring that it is installed and operated in a safe and compliant manner. Additionally, I will restore the property to its original condition, including filling mounting holes in walls and changing wiring in the mains distribution board back to the original configuration, with the exception of small screw holes in the brandering used for the module purlin brackets.
I appreciate your interest in potentially purchasing my backup system, however, I am not interested in selling it at this time. Therefore, I request that this addendum be included in the lease agreement to provide clarity on ownership and removal of the system.
Thank you for your understanding and cooperation.

From a landlord's perspective, I would not want a system to be installed and removed once a year with each tenant that comes and goes. New drilling, wiring, CoC etc each time, no thanks. Would rather pursue a setup where the tenant buys his own batteries and replaces fuses, but the inverter, bypass and breakers belong to the unit.

You don't need to amend the lease, you can just add an addendum to it, signed by both parties, which supercedes whatever problematic clauses are in the lease.
It should be noted that a landlord can't simply enrich themselves at the tenants expense, i.e., take ownership of tenant property or improvements the tenant may have made. I'd imagine the clause that allows this would not be legally enforceable (IANAL).

100%; I intend to make a request to amend the contract. However I would like to see how others in this situation have set up their contracts. I'm looking for examples of such clauses that I can use in my contract and have it vetted by an attorney.  
I do not want to sell my system as it includes an SoC based inverter/battery/load controller I have been developing and testing over the past few years. The system can not be operated without this controller as the inverters built in lithium battery support is questionable/sub-optimal and all features would be lost. While I can build a new controller, machining enclosures, ordering components and a PCB for single device is cost prohibitive and I would rather wait until I complete the design for the second generation. My current priority is implementing and testing new software features while monitoring hardware reliability/robustness of the 10 units in operation.

Is it not worth discussing with landlord ahead of signing - letting them know what you have and how you have used it and if they would make exception for you in this case? Then amending the contract to reflect such