The amount of solar photovoltaics (PV) that can be connected to the grid is a question which, especially for distributed solar, is characterized by a strong information unbalance between, on the one side, the grid operators and on the other side those wanting to feed in electricity. Herein, how the grid impact of PV can be assessed by analyzing inverter voltage measurements that today are available from millions of online PV inverters is demonstrated. In the case where grid capacity is limited by voltage, online PV inverters are shown to provide a valuable complement to distribution system operators estimation of grid capacity. Using 25 million voltage samples from a thousand PV systems, a hosting capacity map is produced for 20 of 21 regions of Sweden. The map shows the amount of PV that typically can be installed without causing voltage rise that would lead to inverter cutoff and loss of production. By monitoring and following the voltage impact from solar PV over time, local saturation effects can be detected and the timing of grid investments better planned. The information could also enhance regulators in their role to monitor grid operators and assure the right level of grid investments.