Post-intall support, maintenance/service contracts, repairs (before taking on a service contract, for example) and performance verification - which can open up upselling of retrofit monitoring solutions, surge/lightning protection equipment, smart-energy management etc, etc. Don't put all your eggs in one basket focusing on picking up new, residential installations. Keep a close eye on the developments in battery storage technology and regulatory development.
As an example of diversification, we have been a country representative of Solarlog for over a year now, and sell/support/install/commission their monitoring & control solutions. We've now developed the capability of hosting client systems that are monitored via SolarLog (so no pressure on installer/seller to take over monitoring etc for the end client) so that the full portal features are available to all involved - customer just pays us for the annual portal fee. One of the reasons for developing this capability is that several UK-based portal operators have now left the industry, leaving the system owners somewhat up the proverbial creek without a paddle.
We set up the online portal for the end client, and configure email alerts/notifications/reports etc. We've been moving into a more O&M-focused service offering lately, and I envisage that we will need independent installers around the country that we can sub-contract required site work to if needed, whether installation or service response, or just for advice/consultancy etc.
Couple your solution/product offerings with other services such as energy assessment, LED lightning solutions, load management (increasing self-consumption) etc, etc. Look at offering other renewable technologies too, although not so easy with limited staffing resources I guess.
