Solar & PV

Cities rarely own the solar panels on their roofs — so the municipal part of rooftop solar is the map, the money and the meter. A solar-potential layer that tells an owner whether the roof is worth it; a tariff or a rental scheme that decides who is allowed to profit; and the metering and grid visibility that decide how much of it the network can absorb.

This guide reads the documented record on solar in the atlas — municipal buy-back schemes, panel rental, net metering, solar-potential maps and the small off-grid arrays that power street furniture. Where the electricity network itself is the subject, the smart grid guide carries it; the plain-language definitions of a microgrid and a smart meter sit in the glossary.

What is the city's actual instrument?

Four recur across the record, and only the last of them is about hardware.

1. The map. Helsinki's Energy and Climate Atlas computes solar radiation potential for roof and wall surfaces across roughly 80,000 buildings; Vilnius publishes an estimate for any address in the municipality. The layer is only as true as the roofs beneath it, which is why Frankfurt refreshes its differentiated roof shapes from aerial imagery every year instead of leaving a launch-day model to age.
2. The money. Cape Town pays cash, not bill credit, for exported rooftop power. Dubai's Shams net-metering scheme takes surplus back at retail rates and had reached over 725 MW across 8,430 buildings by mid-2025.
3. The way in for people without a roof. Helsinki rents individual panels on a former gasworks site by the month; Vienna sells €250 packages in more than thirty citizen solar and wind plants.
4. The array itself — and here the city is usually a customer, not an owner: Dubai's utility-scale park is built on an independent-power-producer model, Kismayo's mini-grid for returning refugees was built by a private developer.

Who gets money out of the meter?

This is the question that separates otherwise identical schemes, and the atlas has four different answers to it. Dubai credits the export at the retail tariff. Cape Town credits a regulator-approved feed-in rate and adds an incentive of its own on top, paying out in cash once a bill reaches zero — City figures to 31 January 2025 record more than R55 million earned by 1,842 sellers, of whom 1,090 were residential. Helsinki and Vienna reverse the direction of travel: the resident pays first, for a panel or a share, and is repaid in output or in a guaranteed minimum return.

Cape Town's own entry states the limit plainly, and it applies to every buy-back scheme here: a tariff only reaches people who already own a roof, an array and an account with the city. None of the schemes in this record is paired with a programme that puts panels on the roofs of people who have none — so the money moves upward unless something else intervenes.

Cape Town can do any of this only because it runs its own electricity distribution across roughly 70% of the metro. That is the unusual condition, not the tariff design. Hawaiian Electric shows the other side: 118,841 grid-connected solar systems by September 2025 and an estimated 49% of Oahu's single-family homes with rooftop solar — on a grid that cannot import power from anywhere, which is exactly why the utility fitted smart meters to see it.

The limit is the connection, not the panel

The clearest finding in this corpus is unglamorous. In Amsterdam's Buiksloterham, a block that combined rooftop solar, a geothermal well and a shared neighbourhood battery got about a quarter of the grid connection capacity it had asked for, and the project pivoted from peer-to-peer energy trading to grid flexibility. Districts that got further did so by pairing generation with storage and control rather than adding panels: Amsterdam's stadium runs a 3 MW battery built partly from used electric-car packs alongside its rooftop array, Zurich's Greencity puts 584 kWp of PV behind heat pumps and a utility contract, and Austin's federally funded pilot produced a software template for coordinating solar and storage rather than an islanding microgrid.

Solar as a power supply, not a policy

A quieter class of entry uses a small panel to put a sensor somewhere a cable cannot reach: New York's flood sensors, Melbourne's compacting litter bins, Rodgau's, Lilongwe's card-operated water kiosks. Two of them record the same failure mode, and it is worth more than most success stories here: Melbourne found that panels in shaded city-centre canyons could not keep the batteries charged, disabling compaction and fill alerts until the bins were moved to sunnier spots, and Lilongwe's entry notes that a solar dispenser losing pressure under cloud rations water by weather, with no attendant left to improvise. Off-grid power is a location decision, not a product feature.

What the evidence does not support

Three of the most-cited solar districts in this atlas cannot be checked. Fujisawa reports hitting its environmental targets, but the developer that built the town is also the only party measuring it. Yokohama's five-year national demonstration involved 34 companies and published the structure of the programme without a single outcome number. Masdar City, launched as the world's first zero-carbon city, built a fraction of its masterplan and downgraded the target to low-carbon by 2050. Nusantara's 50 MW plant supplies roughly a tenth of the new Indonesian capital's power against an 80%-renewables target for 2045, while its budget was cut sharply.

Questions readers ask

The takeaway

Solar is the rare urban technology a city can encourage without building anything. What it can build is the layer around it — the map that makes a roof legible, the tariff that decides who profits, the meter that lets the network cope. Judge a city's solar programme by those three, not by installed megawatts, and by one further question the buy-back schemes here all leave open: what happens to the household that has no roof to put a panel on.