Small (rooftop) PV systems - up to some dozens of kW - are sold like consumer products. Often, after commissioning there is no regular professional maintenance and service. Technical support is called in an event-based manner only, for example if the plant owner notices malfunction of the PV inverter (e.g. no power export at sunny days).

All generation facilities connecting to the networks have to meet technical standards. In most countries, compliance of the PV system's inverter is confirmed by the manufacturer (type tests) and can be assumed at the beginning of the plant's life. The absence of a professional and technically competent site manager during the following years has various consequences:

• The systems may be modified by the plant owner, for example when a defective PV-inverter is replaced by another model. In such a case, the original compliance verification during commissioning becomes obsolete. If the changes are not communicated to the network operator, nobody will be aware of the new configuration.
• In the course of the power system transformation, requirements evolve and, once in a while, adjustment of plant settings may be necessary. Without technical staff, there is no addressee for implementing changes.
• Most manufacturers of PV-inverters offer online access to the devices to their clients. They use the same interface for remote maintenance, e.g. firmware updates. Of course, this is beneficial for system security. However, there is a chance that settings are changed without notice of the plant owner or network operator. Additionally, the connectivity implies potential risks related to cyber security. These are not managed professionally.

Repetitive compliance monitoring during the technical life of the generation facility helps to mitigate some of the issues. However, without on site technical support this is difficult to organise and requires involvement of external staff.

These aspects are relevant in any power system with large numbers of small scale vRES systems.

It is from the beginning. Initially, the cumulative capacity of small PV systems is limited and seems irrelevant from a power system's perspective. But with current PV prices, in large parts of the world, growth may be fast, for example, if the regulative framework allows netmetering. Be aware that the initially few, early PV plants are part of the system for the next 20 years.

Planning ('Know what is out there')
An easily accessible register of all vRES plants, including the smallest ones, helps to identify them in case of need.
Reservation: be realistic - data quality will be limited and may become successively worse for older installations, as a consequence of untraced changes. There is little you can do about that. Consequently, it does not make sense to gather very detailed data. Keep it lean.

Operation ('Check what is out there')
Repetitively monitor existance and examine the compliance of small systems over project life. This may be impractical for all plants. Nevertheless, checking samples provides an impression of the status of the plant population. It may help to identify problems with specific products / series.
Reservation: do it reasonably and share the burden. Comprehensive and frequent compliance testing without socialisation of costs will kill this vRES segment. Small plants simply do not earn sufficient profits to pay for repetitive testing.