PPA Mechanics

M&V Under a Solar PPA

M&V is how the provider measures what they generated and what they invoice you for. The metering, performance ratio guarantees and dispute mechanisms matter enormously over a 20-year contract.

The role of M&V in a PPA

The provider invoices you for kilowatt-hours generated. You need confidence that the meter reading is accurate, the methodology is sound, and any disputes have a defined resolution path.

The three metering points

• Generation meter — counts every kWh the inverter produces. This is what you pay for.
• Import meter — your existing supply meter, measures what you draw from grid.
• Export meter — what your site sends back to grid (for SEG payments).

P50 vs P90 generation forecasts

Before signing, the provider runs site-specific yield modelling. P50 is the median expected annual yield; P90 is the 90% confidence lower bound. Banks lend against P90; providers contract on P50.

Why this matters: if year-1 generation falls between P90 and P50 (i.e., below median but within forecast band), the provider has no obligation to compensate. The performance ratio guarantee only triggers below P99.

What to negotiate

• Independent metering — meter not owned/serviced by the same SPV.
• Read-out access — you can pull data directly, not via a portal the provider controls.
• Annual yield re-baselining — methodology specified for adjusting expectations as long-term irradiation data refines.
• Dispute mechanism — escalation path with independent assessor, capped at £15-25k per dispute.