Norms · DSTU-N B V.1.1-27:2010
DSTU-N B V.1.1-27:2010: climatic regions and Tmin for PV strings
In frost, the open-circuit voltage of panels rises. To keep a string below the inverter’s voltage limit you need the site’s lowest air temperature. In Ukraine it comes from the “Building climatology” standard.
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Edition and status
DSTU-N B V.1.1-27:2010 “Building climatology”. Status as of 14.10.2026: in force per the norms register Solispec checked on 04.10.2026.
The official text: UkrNDNC, the national standards body (the standard’s text is sold). Solispec does not host the norm texts. Look for the current edition at the official source.
Why a solar plant needs climatology
DSTU HD 60364-7-712:2022 (Annex B.1) requires UOC MAX to be calculated at the lowest ambient temperature of the installation site, Tmin:
UOC MAX = KU · UOC STC, KU = 1 + αUoc/100 · (Tmin − 25)Without Tmin or the panel’s temperature coefficient the standard says to take 1.2 · UOC STC. The colder it is, the fewer panels fit in a string. That is why Tmin needs a source rather than a “usual” −25 °C.
Climatic regions: Table 1 and Figure 1
The standard divides Ukraine into climatic regions. For regions I and II, Table 1 gives a range of the absolute minimum: −37…−40 °C and −32…−42 °C. Solispec takes the colder end, so UOC MAX comes out higher, on the safe side.
| Region | Name | Tmin in Solispec |
|---|---|---|
| I | North-west | −40 °C |
| II | South-east | −42 °C |
| IIIA | Carpathian | −38 °C |
| IIIB | Transcarpathian | −32 °C |
| IV | Southern coast of Crimea | −20 °C |
| V | Crimean mountains | −27 °C |
The engine draws the boundary between regions I and II from Figure 1 read by eye, so near it the accuracy is ±0.2–0.3° of latitude. Kyiv is in region I: Tmin = −40 °C.
An example
A hypothetical panel with UOC STC = 49.5 V and α = −0.25 %/K in Kyiv: KU = 1 + (−0.25/100) · (−40 − 25) = 1.1625, UOC MAX ≈ 57.5 V. Without data it would be 1.2 · 49.5 = 59.4 V. For an inverter limited to 1,000 V that is 17 panels per string instead of 16.
How Solispec applies it
The constructor and the string calculator first take the Tmin You entered yourself. If the field is empty, the engine finds the climatic region from the site coordinates and takes its Tmin, with the source in the report: “DSTU-N B V.1.1-27:2010, Table 1”. If no site is set, the 1.2 · UOC STC rule applies.
Terms
- Climatic region (DSTU-N B V.1.1-27)A region of Ukraine by building climatology; for PV it gives the absolute minimum air temperature used to check string voltage.
- Site minimum temperature TminThe lowest ambient air temperature at the PV site; it sets the maximum open-circuit voltage of a string, U_OC MAX.
- 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.
- PV stringA chain of panels connected in series: voltages add up, the current is shared; frost and the inverter MPPT window limit its length.
- 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.
Other norms
- DSTU HD 60364-7-712:2022: the electrics of PV systemsUkraine’s main PV electrical standard: U_OC MAX in frost, I_SC MAX, string fuses, cables under modules, SPDs and earthing.
- PUE:2026 for solar plants: what changedPUE:2026 replaced PUE:2017: scope, common earthing with the building and surge protection for a solar plant.
- DBN V.1.2-2:2006 “Loads and actions”: what matters for a solar plantThe clauses of the Ukrainian loads code a solar array needs: S₀, W₀, the factors, Changes 1 and 2, and a worked example for Kyiv.
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.