One roof, two households, one decision
Two-unit duplex structures are 21.5 percent of Milwaukee's housing stock, concentrated in the older north and south side neighbourhoods. That is a far higher share than in most American cities, and it puts roughly one household in five in a position where the roof is shared with a single other party.
A duplex is the easiest of the shared-roof cases and it is still a real one. There is one other owner rather than a board or a management company, so the conversation is short, but it has to happen and it has to be written down. Cover fixings and penetrations, access for maintenance, what happens when the covering is replaced and who pays, and whose meter the array connects to. That last one is the question people forget: an array normally feeds one meter, so it offsets one household's consumption rather than the building's.
If you own both units, none of this is an obstacle, but the metering question still decides the design. If you own one and your neighbour owns the other, settle the agreement before an installer designs a layout, because a design drawn for the whole roof and then cut in half is not the same system.
Single-family detached homes are 39.1 percent of the stock, where the decision belongs to one owner and quotes are worth collecting straight away. Buildings of 20 or more units are 17.6 percent, and there the roof belongs to the building owner, so the route is a written proposal covering cost, equipment ownership, insurance and roof replacement rather than a quote for your unit.
Focus on Energy, and a deadline worth watching
Focus on Energy is Wisconsin's statewide programme, and it currently pays a cash rebate of 600 $ per kW installed, up to 2,400 $, for qualifying systems. With the federal residential credit gone for purchases, this is the main incentive still on the table for a Milwaukee household buying a system.
The rules around it are as important as the amount. Applications are due within 60 days of completion, and no later than January 31, 2027. Two deadlines, and the 60 day one is the one people miss, because it runs from completion rather than from any date you would naturally have in your calendar.
So treat the application as a deliverable with a named owner. Decide in the contract whether you or the installer files it, keep the itemised cost breakdown, and set your own reminder for 60 days from the completion date rather than relying on being reminded. A rebate missed on a technicality is not recoverable.
Because the rebate is paid per kilowatt installed but capped, it stops growing once installed capacity reaches the point where 600 $ per kW meets the 2,400 $ ceiling. Beyond that, additional capacity earns no additional rebate. That is not a reason to stop there, but it does mean the rebate should not be used to justify a larger system than your own consumption warrants.
We Energies, and why the state rule is not the whole answer
Wisconsin requires its investor-owned utilities to offer net metering under Public Service Commission rules, and excess energy sent to the grid is credited against power drawn at other times, typically at the retail rate. That is a straightforward arrangement to model and it compares well with the supply-only crediting new customers face in Illinois.
The qualification is that each utility administers its own tariff under PSC oversight. We Energies, Madison Gas and Electric, Alliant Energy Wisconsin, Wisconsin Public Service and Xcel Energy in northern Wisconsin each run their own schedule. We Energies serves Milwaukee, so the terms that matter to you are We Energies terms specifically rather than a statewide average.
Ask your installer to confirm the current We Energies net metering schedule for your rate class before the system size is fixed, and ask what happens to a credit balance over a year. Then size the array against twelve months of your own kilowatt hour totals rather than against the roof area available, because credits are applied against power you draw at other times and a system generating well beyond your consumption runs out of consumption to offset.
Output, and the credit that no longer applies
Plan on roughly 1,245 kilowatt hours a year for every kilowatt installed on a well oriented, unshaded array. That is a screening figure derived from irradiance data rather than a measurement from Milwaukee roofs, so treat it as a ceiling. On a duplex the binding constraint is often usable area on your half of the roof rather than sun, so the more useful question is how many panels fit well.
The 30 percent federal residential tax credit under Section 25D applied through December 31, 2025 and is not available for a purchased home system placed in service after that date. A purchase in Milwaukee now cannot claim it, and that is a large enough change to lengthen payback and weaken the case for adding a battery.
Much published material has not been updated, so a quote or calculator still applying the credit may be out of date rather than dishonest, but the payback figure it produces is wrong. Ask any installer to rebuild the arithmetic from what still exists: the Focus on Energy rebate, retail-rate net metering credits on your We Energies tariff, and the electricity you stop buying.
If you take a lease or a power purchase agreement rather than buying, the provider may claim the business version of the credit under Section 48E and reflect part of that value in the rate they offer. What they claim and what reaches you are separate questions, so put both to the provider and confirm with a tax advisor rather than with the sales material.