Glossary · DC and AC electrics
DC/AC ratio (inverter loading)
The ratio of the panels’ peak power to the inverter’s rated power; no norm sets it, it is an engineering choice.
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Definition
DC/AC is the sum of the panels’ rated power (kWp) divided by the inverter’s rated AC power. For example, 12 kWp of panels on a 10 kW inverter gives DC/AC = 1.2.
DC/AC = ΣPпанелей / PінвертораUkrainian norms do not regulate this ratio. Panels rarely produce their full rated power: sun angle, heat and soiling get in the way. So moderate inverter loading usually pays off — the inverter runs near its rating for longer and only infrequent peak hours are lost. The price is clipping of peaks on clear, cool days.
DC/AC does not replace the electrical checks. Even with a sensible ratio a string can exceed the input voltage in frost (UOC MAX), and parallel strings can exceed the input current (ISC MAX). For the grid connection a different number matters: the allowed power under the contract, which is compared with inverter power, not panel power.
How to choose the ratio in practice. A south-facing array at the optimum tilt has the highest peaks, so inverter loading leads to clipping sooner. An east-west or low-tilt array has lower, broader peaks, so a higher DC/AC loses less energy. The annual yield and payback for a chosen size can be estimated in the PV payback calculator, and the electrical input limits are checked by the string calculator. Choose the final inverter power with the allowed connection power in mind: it is often the hard limit.
How Solispec applies it
The Solispec engine computes DC/AC for each inverter and flags the extremes. These thresholds are the app’s rules, not norm requirements: above 1.3 — "will clip peaks" (warning), above 1.5 — "heavily overloaded" (error), below 0.7 — "inverter too large". Between 0.7 and 1.3 it raises nothing.
Related terms
- MPPT and the inverter voltage windowThe inverter’s maximum power point tracker; its voltage range sets the minimum and maximum number of panels in a string.
- PV stringA chain of panels connected in series: voltages add up, the current is shared; frost and the inverter MPPT window limit its length.
- Allowed connection powerThe power stated in the grid connection contract; the total power of the PV inverters may not exceed it.
- Maximum open-circuit voltage UOC MAXThe open-circuit voltage of a panel or string at the site minimum temperature; inverters, fuses and isolators are selected by it.
Solispec’s calculation is preliminary: for a design it has to be checked by an engineer. The values and clauses follow the current editions of the norms on the date of the page.