1) Bye-law 171 explicitly states that if a member wants to install a solar energy system, it is binding on the society to provide space on the terrace, subject to availability.

2While the terrace is a common area, Bye-law 171 acts as a "legitimate diversion" from the usual restrictions on individual use of common areas for the specific purpose of renewable energy.

3) : Since you have provided technical details for structural and electrical safety and the society has not pointed out any specific technical deficiencies, a blanket "final" rejection without evaluation is arbitrary

4)File a formal complaint with registrar under the Co-operative Societies Act regarding the MC’s failure to implement Bye-law 171. You can use the Sahkar Samvad portal for online grievance redressal.

5)You can approach a Consumer Disputes Redressal Forumbecause the society provides services (maintenance) in exchange for fees, and refusing a legitimate facility permitted by law can be considered a "deficiency in service".

6)  You can specifically claim compensation for "mental agony" and financial loss (e.g., cost of the expert you engaged) in this forum.

Under the Maharashtra Co-operative Societies Act and the Model Bye-laws, a housing society cannot arbitrarily block green energy initiatives without valid, documented technical grounds.

The by law 171 is a mandatory provision. The society has a statutory obligation to facilitate the installation. The society can impose reasonable conditions viz., ensuring no damage to the roof slab, maintaining access for water tank cleaning, but they cannot use these as a pretext for an outright ban. By declining to accept your request or evaluate your submission, the society (MC) has violated the law in this regard.

The Supreme Court and various State Commissions have held that a member of a Co-operative Housing Society is a "consumer" and the society is a "service provider.".

By Preventing a member from exercising his rights under the bye-laws (especially regarding amenities/infrastructure like solar) constitutes a deficiency.  The consumer redressal commission can award compensation for mental agony and harassment besides passing an order directing the MC to permit you install the desired solar panel as per the conditions, no doubt the entire process will be time consuming. 

At the same time you can even plan to exhaust the remedy available before the Dy. Registrar of cooperative societies for relief and remedy. 

Under Section 23 and Section 91 of the Maharashtra Co-operative Societies Act, the Registrar has the power to intervene when a society acts against its own bye-laws. You should file a formal complaint under Bye-law 174, citing the violation of Bye-law 171. The DR can issue a mandatory direction to the society to grant permission if they find the rejection was arbitrary.

Before that you can send a legal notice through a lawyer by  Registered Post to the Chairman/Secretary stating that you have complied with Bye-law 171, that the society failed to appoint an expert or hold an SGM as requested. You may give  them 7 to 14 days to provide a technical reason for rejection, failing which you will initiate legal proceedings at their personal cost.

Consult an advocate in the local and proceed as suggested 

Yes you can approach consumer court as the terrace is common area and not the sole property of MC.