Four tools on one page: how many panels fit on the slope and how they are laid out, how far they have to stay from an obstacle, how much space you leave between rows so they are not shaded at the winter solstice, and how healthy an already installed array is — from the production read off the meter.
The number of panels depends on the usable slope area, the panel dimensions and the installation clearances.
Usable slope area
From the gross slope area the margins are subtracted (from the ridge, eaves and side edges) required by the mounting system and the fire regulations. What remains is the area on which panels can actually be laid out.
Panel orientation
Panels can be mounted vertically (portrait) or horizontally (landscape). The orientation changes how many rows and columns fit — often one of the options uses the area better.
How many panels fit
For each dimension, how many panels fit is calculated, taking the gap between them into account. The total number = columns × rows × the number of slopes used.
Power and production
Installed power (kWp) = number of panels × the power of one panel. The guideline annual production = kWp × the specific yield of the area (kWh/kWp/year). The values are estimates — the actual yield depends on orientation, shading and tilt.
Change the values — the visualisation and results update instantly.
Roof
PV panel
The margin of 0.3 m is below the 1.6 m minimum that P 118/1-2025 requires for the building selected in the checker below. The simulation carries on with your value — but the resulting layout does not pass the fire safety check.
Slope preview
A guideline geometric and energy estimate, with no role as a design. The actual layout takes into account the mounting system, obstacles (chimneys, dormers, roof windows), shading and the fire-prevention regulations. The electrical sizing (inverter, protective devices, cable) is done in the PV calculator.
A roof layout check, with the text of the standard next to every verdict.
The simulator above fills the roof with panels. The fire safety standard says that part of the roof has to stay empty: for the firefighters, for smoke extraction, to stop the fire spreading. The two articles that count, 2.4.18.4 and 2.4.18.5, apply to different buildings and never add up — a house of ground floor plus one does not get the 1 m perimeter of the blocks of flats, and a block of flats does not get the two access routes of the house.
The starting values are exactly the trap people fall into most often: 1.20 m from the edge of the roof covering looks comfortable, but with a 0.60 m eaves overhang the panel sits 0.60 m from the load-bearing wall, and letter a) for houses measures from the wall, not from the eaves. Change the eaves and watch what happens to the first finding.
Type of building
Everything starts here: the choice decides WHICH article applies. The form shows only the fields of the applicable article; the requirements of the other stay visible below, marked “not applicable”.
Art. 2.4.18.4 applies. The requirements of Art. 2.4.18.5 are out of scope.
Letter a) begins with “pentru fiecare pantă a acoperişului cu mai mult de două ape” — for each pitch of a roof with more than two slopes. The qualifier belongs to the ROOF — a pitch does not have slopes. Below that threshold letter a) simply does not apply; asking for it anyway means inventing a requirement.
Roof with more than two slopes: letter a) is evaluated.
Geometry of the slope
It is the direct reference of Art. 2.4.18.5 lit. a), for blocks of flats and industrial buildings. On a house, letter a) measures from the external load-bearing wall, not from here — and if the roof has more than two slopes, the eaves field appears below, and from it we work out the real distance to the wall.
Art. 2.4.18.4 lit. a) requires the clear space from the external load-bearing walls. The panel is closer to the wall than to the eaves by exactly this value. With no eaves declared the check stays UNDETERMINED — not compliant: assuming zero eaves would produce a false green.
That gives: 0.60 m from the load-bearing wall.
The metre from the ridge is required by both letters of the article for houses — by a) and by b) alike.
Declared elements
“None” and “I do not know” are not the same thing. The first takes the provision out of the discussion, the second leaves the check undone — and it shows as such in the summary. The fields start undeclared on purpose.
Valleys and dormers
Here there is no “none” option: letter b) requires them, and their absence is a breach, not an exception.
Result of the check
Obligations breached: 1
Checks not made (data not declared): 2
The layout does not pass. Move the panels or change the geometry before you order the mounting structure — at the approval stage it costs a great deal more.
On top of that, 2 checks were left undone — the list of breaches above is not complete.
Distance from the external load-bearing wall
Measured: 0.60 mRequired: at least 1.00 m
pentru fiecare pantă a acoperişului cu mai mult de două ape se asigură un spaţiu liber de minimum 1 m de la pereții portanți exteriori, minimum 1 m de la coamă şi minimum 50 cm pe fiecare parte a unei dolii sau lucarne;Quotations from the standard stay in Romanian in every language of the application.
Distance from a valley or a dormer
The value was not declared, so the check could not be made.
Required: at least 0.50 m
pentru fiecare pantă a acoperişului cu mai mult de două ape se asigură un spaţiu liber de minimum 1 m de la pereții portanți exteriori, minimum 1 m de la coamă şi minimum 50 cm pe fiecare parte a unei dolii sau lucarne;Quotations from the standard stay in Romanian in every language of the application.
Access routes on the slope
The value was not declared, so the check could not be made.
Required: at least 2
pentru fiecare pantă a acoperişului pe care se amplasează module fotovoltaice, se asigură două spaţii de acces de minimum 1 m lăţime şi minimum 1 m de la coamă.Quotations from the standard stay in Romanian in every language of the application.
Distance from the ridge
Measured: 1.20 mRequired: at least 1.00 m
pentru fiecare pantă a acoperişului pe care se amplasează module fotovoltaice, se asigură două spaţii de acces de minimum 1 m lăţime şi minimum 1 m de la coamă.Quotations from the standard stay in Romanian in every language of the application.
Requirements that do not follow from geometry
The rest of subchapter 2.4.18 is not measured with a tape: they are conditions of material, of building form and of firefighting access, declared by the designer. We list them so that they do not vanish from the report just because they cannot be mechanised.
The roof covering as an element of the roof — resistance to external fire
Gradul de protecţie pentru învelitorile acoperişului depinde de conformarea acestora şi de distanţa până la contur. Dispozitivele fotovoltaice (celule, module, panouri cu un singur tip de module etc.) situate pe acoperiş, trebuie să fie considerate componente ale acestuia şi, ca atare, trebuie să reziste la aprinderea şi/sau propagarea incendiului provenit de la o sursă externă.Quotations from the standard stay in Romanian in every language of the application.
Safety of the fire crews
La construcţiile pe care se amplasează sisteme/ dispozitive fotovoltaice, se recomandă îndeplinirea condiţiilor de siguranţă ale echipelor de intervenţie care să asigure:
a) accesul și evacuarea la/de pe acoperiş (şarpantă sau terasă);
b) trasee facile de acces la zonele de acoperiş;
c) marcarea şi etichetarea distinctă şi vizibilă a întregului sistem fotovoltaic; (întreruptorul general - care trebuie amplasat într-o zonă accesibilă a clădirii, toate conductele, cablurile, invertoarele, tablourile și cutiile circuitului de curent alternativ, precum şi bateriile și acumulatorii), cu materiale reflectorizante, rezistente la intemperii şi reciclabile;
d) prevederea unui întreruptor de sarcină, uşor acţionabil;
e) echiparea sistemului fotovoltaic cu dispozitiv de detectare a arcelor electrice.Quotations from the standard stay in Romanian in every language of the application.
Firefighting: the fire is treated as one on electrical equipment
Incendiile la dispozitivele fotovoltaice (celule, module, panouri cu un singur tip de module etc.) amplasate independent sau dispuse pe acoperiş sau pe închiderile perimetrale ale construcţiilor, se vor trata de către echipele de intervenţie (pompieri) ca incendii la echipamente electrice.Quotations from the standard stay in Romanian in every language of the application.
Façades and roofs to which photovoltaic devices are applied
(1) Faţadele și acoperișurile pe care se aplică dispozitive fotovoltaice, vor avea:
a) termoizolaţia și/sau sistemele compozite de izolare termică (sisteme compacte în condiții de utilizare finală) faţadei incombustibilă, indiferent de destinaţie şi/sau de regimul de înălţime al clădirii;
b) ancorări şi asamblări incombustibile, indiferent de destinaţie şi/sau de regimul de înălţime al clădirii;
c) legături de echipotenţializare şi legare la pământ, în conformitate cu normativele de specialitate;
d) pe acoperiș, stratul pe care se aplică:
- trebuie să îndeplinească performanța la foc exterior prevăzută în Tabelul 2 și Tabelul 3 pentru sistemele de învelitoare (panouri/sisteme de învelitoare ale acoperişurilor în pantă c u încărcări suplimentare provenite din dispozitive fotovoltaice );
sau
- în cazul dispunerii panourilor fotovoltaice peste un planșeu tip terasă, stratul component exterior al acoperişurilor cu rol de asigurare a etanşeităţii construcţiei faţă de intemperii (de cele mai multe ori hidroizolația), să îndeplinească performanța la foc exterior prevăzută în Tabelul 2 și Tabelul 3 pentru sistemele de învelitoare (panouri/sisteme de învelitoare ale acoperişurilor în pantă c u încărcări suplimentare provenite din fotovoltaice ) conform încadrării în nivel de stabilitate la incendiu a construcției.
e) pe fațade, stratul pe care se aplică trebuie să îndeplinească performanța la foc de minimum EI 30.
(2) Atunci când panourile fotovoltaice sunt integrate în sistemele de pereți cortină sau tâmplărie exterioară (fiind parte funcțională a anvelopei clădirii), se aplică dispozițiile Art. 2.4.18.8. alin. (1) lit. a), b) și c) și se vor lua una dintre următoarele măsuri:
între panourile fotovoltaice care sunt integrate în sistemele de pereți cortină sau tâmplărie exterioară, la fiecare nivel, pentru întârzierea propagării incendiilor între nivelurile construcţiei prin exteriorul închiderii perimetrale (pe faţade), se prevăd una din măsurile prezentate la Art. 2.3.6.1.2. ÷ Art. 2.3.6.1.6.;
se prevăd cortine (rezistente la foc EI sau etanșe la foc E prevăzute cu ansamblu de sprinklere), cu aceeași rezistență cu a elementului prevăzut pentru întârzierea propagării incendiilor între nivelurile construcţiei prin exteriorul închiderii perimetrale (aceeași rezistență precum a elementelor prevăzute la Art. 2.3.6.1.2. ÷ Art. 2.3.6.1.6. pentru diferitele tipuri, înălțimi și utilizări ale construcțiilor);
se prevăd sisteme active de stingere a incendiilor (perdea de apă) amplasate în interiorul clădirii, la o distanță de maxim 30 cm de închiderea perimetrală.Quotations from the standard stay in Romanian in every language of the application.
Technical rooms for the equipment of the panels
Încăperile tehnice pentru echipamentele panourilor fotovoltaice se vor realiza cu pereţii şi planşeele minimum REI 180, respectiv REI 90 clasa de reacţie la foc A1, iar golurile de comunicare din pereţi se prevăd cu uşi rezistente la foc și etanșe la fum EI 2 90-C3S 200. Ele vor avea asigurată ventilare conform standardelor de specialitate.Quotations from the standard stay in Romanian in every language of the application.
Suitability of the devices for use on a roof or a façade
Dispozitivele fotovoltaice (celule, module, panouri cu un singur tip de module) amplasate pe acoperişurile sau faţadele construcţiilor vor fi adecvate acestei utilizări.Quotations from the standard stay in Romanian in every language of the application.
Art. 2.4.18.6 is a recommendation, not an obligation
The text says “se recomandă îndeplinirea condiţiilor de siguranţă ale echipelor de intervenţie” — it is recommended that the safety conditions for the fire crews be met. Marking the system, the access routes on the roof, the easily operated switch-disconnector and the arc fault detector are, through P118, recommendations. You do them because they are good, not because the article demands them — and in a design report you do not present them as an obligation.
Isolation on the direct current side does have a mandatory basis, only in a different standard: I7-2011, Art. 7.11.23, in the chapter on photovoltaic systems.
Pe zona de tensiune continuă a invertorului PV se va prevedea un separator de sarcină.I7-2011, Art. 7.11.23
How the standard is cited
The year in the designation is 2025; “2024” is the working label left on the covers in circulation. The exact day it came into force is not fixed by any primary source — secondary sources give 8, 9 or 10 May 2025 — so what is cited is the rule from the order, not a calendar day.
The check covers the provisions of subchapter 2.4.18 that can be worked out from the declared geometry. It does not stand in for a fire safety scenario, it does not cover the rest of the standard and it is no substitute for the attested checking engineer.
A simple rule for site work, worked out for the worst day of the year.
Shading is what ruins an array of panels fastest, because the cells are wired in series: shade even half a cell and the result is as if half the row were in shadow. When surveying the site you measure the tallest obstacles around it, and the practical rule for distance is worked out for the winter solstice, when the sun is at its lowest.
Lmin = 2 × H
H = how far the obstacle rises above the module plane, not its total height above ground.
The level at which the modules sit. Only how far the obstacle rises above them matters.
The distance is sufficient
At the winter solstice the shadow should not reach the modules. Check the time window all the same: no shading is recommended between 08:00 and 17:00, with at least 6 unshaded hours a day.
1.Find how far the obstacle rises above the module plane
formula:H = H₁ − H₂
with your numbers:4.00 − 1.00
gives: H = 3.00 m
H₁ is the height of the obstacle measured from the ground, and H₂ the level at which the module plane sits. Only the difference between them counts: the part of the obstacle below the modules cannot cast a shadow on them.
2.Apply the minimum distance rule
formula:Lmin = 2 × H
with your numbers:2 × 3.00
gives: Lmin = 6.00 m
The rule is worked out for the winter solstice, when the sun is at its lowest — if it holds then, it holds all year.
3.Compare it with the actual distance on site
formula:d ≥ Lmin
with your numbers:6.00 m ≥ 6.00 m
gives: The distance is sufficient
Orientation and tilt
Losses — the orders of magnitude
The 2 × H rule is a rough approximation: it answers to a sun seen at about 26.5°, an angle that at Romanian latitudes is never reached at the winter solstice. The next section works the distance out from the actual latitude and hour and gives, for the same data, an appreciably larger result. Use the rule here as an order of magnitude out on site, and the calculation below when you design.
The rule Lmin = 2 × H, the recommended time window and the orders of magnitude of the losses come from lessons 2 and 4 of the specialist course “Instalator sisteme fotovoltaice solare”. They are not provisions of I7-2011 — the standard covers the electrical side (ch. 7.11), which is dealt with on the string sizing page.
On a flat roof or on the ground, the spacing between rows is a design decision, not an installation one.
A row of modules casts shade on the row behind it. The course recommends that the spacing between rows keep the rows out of shade between 09:00 and 15:00 at the winter solstice — that is when the sun is at its lowest and the shadow at its longest. Self-shading is listed explicitly under design mistakes, not under site accidents.
Lmin = (sin a / tan ψ + cos a) × L
The side that sets the height of the row — on a module laid landscape it is the short side.
The course recommends that there be no shading between 09:00 and 15:00. 09:00 is the most severe case in that window.
The elevation tells you how high the sun is; the profile angle tells you how long the shadow is measured perpendicular to the rows, in the direction in which one row follows the next. In the morning the sun is well round to the east and the two differ noticeably — with the raw elevation you would end up with over 20 % more ground per row. They coincide only at midday, when the sun is exactly in the plane of south-facing rows. The profile-angle correction is the application’s own addition: the course gives the equation without distinguishing between the two angles.
The row behind falls into shade
At the chosen hour the front row shades the next one. A single shaded cell drags down the whole string, because the cells are wired in series — you do not lose in proportion to the shaded area.
1.Find how far the top edge of the module rises
formula:h = L × sin a
with your numbers:1.75 × sin(30°)
gives: 0.87 m
The symbols in the calculation breakdown: L — the module length along the slope; a — the module tilt; h — the height the top edge of the row rises to; ψ — the profile angle; g — the clear space left up to the next row.
2.Find how long its shadow is, measured perpendicular to the rows
formula:g = h / tan ψ
with your numbers:0.87 / tan(14.07°)
gives: 3.49 m
This is where the profile angle comes in, not the elevation: in the morning the sun strikes at an angle, and the shadow measured perpendicular to the rows — across from one row to the next — is shorter than the one measured along the ray.
3.Add the footprint of the module to the shadow
formula:Lmin = L × cos a + g
with your numbers:1.52 + 3.49
gives: 5.01 m
The pitch is measured from the bottom edge of one row to the bottom edge of the next row. The clear space between the rows is smaller than the pitch by exactly the footprint of the module.
The equation is the one in the course notes: Lmin = (sin a / tan β + cos a) × L, where β is the angle at which the sun is seen. The key to the symbols is not given in the text — it sits in a figure that was not transcribed — so this is our reading of it, as is the decision to use the profile angle in place of the elevation. The position of the sun is standard physics, worked out from the latitude and the solar time with the −23.45° declination of the winter solstice; the course gives “about 23°” as a guide for Greece, an indicative value somewhere between midday and 09:00. It is not a provision of the standard: I7-2011 does not regulate shading.
An indicator you use to judge the actual production, and the estimating method from the site visit.
The performance ratio compares what the installation actually produces with what an identical system with no losses at all would produce in the same place. It is the only figure that tells you whether an installation is healthy without dismantling anything: if this summer it comes out at 0.55 where last year it came out at 0.72, something has happened between the panels and the meter.
Performance ratio (PR)
From PVGIS, for the actual tilt and azimuth of your array — not the irradiation on the horizontal plane.
Quick production estimate
The site-visit method from the course: you start from the irradiation at the site, apply the module efficiency and the tilt/azimuth correction, then cut it down by the performance ratio.
The rule of thumb in the course is 10 m² for 1 kWp — a site-visit figure, which takes in the gaps and the unusable zones. The module area above is a different thing: the installed power divided by the efficiency. Today’s modules need appreciably less than 10 m²/kWp.
The manual also gives 2,800–3,600 €/kWp as an order of magnitude for a grid-connected system, without stating the source or the year. It is kept here as a reference point from the course, not as a quoted price — figures of this kind date quickly.
1.Find the specific yield
formula:Yf = E / P₀
with your numbers:5750 / 5.00
gives: 1150 kWh/kWp
E is the energy read at the meter over the period analysed (kWh), and P₀ the installed power of the system (kWp). The specific yield Yf comes out in kWh/kWp.
2.Divide by the reference yield
formula:PR = Yf / Yr (Yr = H)
with your numbers:1150 / 1650
gives: 0.697
The reference yield is precisely the irradiation in the module plane: an ideal 1 kWp system would produce exactly as many kWh as there are kWh/m² falling on it.
3.Correct the irradiation for tilt and azimuth
formula:H_corr = H × f
with your numbers:1000 × 0.95
gives: 950.0 kWh/(m²·a)
The factor is a penalty against the optimum orientation, not a conversion from the horizontal plane to the tilted plane.
4.Find what a system with no losses would produce
formula:E_ideal = H_corr × η
with your numbers:950.0 × 0.15
gives: 142.5 kWh/(m²·a)
η is the module efficiency (0.15 means 15%), and H_corr the corrected irradiation from the previous step. E_ideal comes out per square metre of module, before any system loss.
5.Cut it down by the performance ratio
formula:E_est = E_ideal × PR
with your numbers:142.5 × 0.70
gives: 99.8 kWh/(m²·a)
6.Go from the square metre to the whole installation
formula:E_a = P₀ × H_corr × PR
with your numbers:5.00 × 950 × 0.70
gives: 3325 kWh/a
Do not multiply the production per square metre by the gross area of 10 m²/kWp: that figure takes in the gaps and the unusable zones, and the result would come out some 50 % above reality. The module area is the installed power divided by the efficiency.
The performance ratio and the estimating method come from the course notes, not from I7-2011. The standard does not regulate production, it regulates the electrical side.
How the warranty is written and how the panel actually declines — two figures that do not match.
A panel does not produce at twenty years what it produced in its first summer. Datasheets declare a larger degradation in the first year, then a constant one. The preloaded figures are those from the practical exam papers; they are meant for teaching, and a real module ages faster.
The two figures differ because warranties are written linearly, against the rated power, whereas physical degradation compounds year on year. At ten years the difference is under a tenth of a percent; at twenty-five it becomes visible, and on a warranty claim it matters which model is written into the contract. The practical exam papers give only the percentages, without saying which model to use — the 3.40 % at ten years comes from the linear model.
The manual says that “module manufacturers usually guarantee a power output of 80% even after 20, 25 years of use”, and the usual service life is around 25 years, with operation beyond 30 also possible.
Three levels, on the geometry of the roof and the shading rules from the course.
Design decisions, no calculation.
The chimney next to the panels
A chimney rises 3 m above the plane of the modules, on the south side.
Step 1: What minimum distance do you keep from it?
Which tilt you choose
A fixed system on a roof in the Brașov area, where snow builds up in winter.
Step 1: Which value do you start from for the optimum tilt?
Shade on a single cell
In the morning an aerial casts a narrow shadow across the corner of a module.
Step 1: What effect does it have on production?
You get hints if you get stuck.
How many panels fit on the slope
A slope 8 m wide × 4.5 m along the pitch. Panel of 1722 × 1134 mm mounted portrait (1.134 m horizontally, 1.722 m vertically), a 0.3 m margin at each end, a 0.02 m gap between modules, 410 Wp each.
Step 1: How many columns fit across the width?
The distance from a tree
A tree is 5 m tall, and the plane of the modules sits 1.5 m above the ground.
Step 1: How far does the tree rise above the plane of the modules?
The estimated annual production
The 4.92 kWp above, in an area with a specific yield of 1150 kWh/kWp a year.
Step 1: How much does the system produce in a year?
A single final answer.
Big roof, big modules
A slope of 10 m × 5 m, modules of 2278 × 1134 mm mounted portrait (1.134 m horizontally), 0.3 m margin, 0.02 m gap. How many modules fit in total?
A tall tree next to the house
A tree 8 m tall, plane of the modules 2 m above the ground. What minimum distance do you require from it?
The installed power of an array
18 modules of 550 Wp. What installed power does the array have, in kWp?
exercitii.panouriSolare.sources.tag
exercitii.panouriSolare.sources.title
exercitii.panouriSolare.sources.intro
exercitii.panouriSolare.sources.pvgisTitle
exercitii.panouriSolare.sources.pvgisText
exercitii.panouriSolare.sources.globalSolarAtlasTitle
exercitii.panouriSolare.sources.globalSolarAtlasText
exercitii.panouriSolare.sources.enfSolarTitle
exercitii.panouriSolare.sources.enfSolarText
exercitii.panouriSolare.sources.note
Have the number of panels? Continue with the electrical sizing of the system.
PV system calculatorComments are moderated before publication. Your email is not displayed publicly.