Rooftop Solar PV: Size and Savings
How many solar panels a Saudi roof needs and what they save: a grid-connected system sized from your consumption, from your roof or from a size you choose, in 31 cities, the production month by month (NREL PVWatts), the bill under the SEC tariff and SERA net billing, the row spacing on the roof, the contracted-load check and the payback.
A grid-connected rooftop system for a Saudi home, villa or small building. Choose the city (the typical year of its weather station, hour by hour) and the way the panels face, then size the system three ways: from your consumption and the share of it you want to cover, from the roof you have, or from a size you type in. The production is NREL's PVWatts Version 5: the Perez sky model, the reflection off the glass, the Fuentes cell temperature, the system losses and the inverter, month by month. The money is the SEC consumption tariff with its 6,000 kWh step and the net billing of the SERA small-scale solar PV framework, a kWh used in the building saving the tariff and a kWh exported earning 7 halalas for a residential consumer, shown between all used on site and all exported, because only your load decides where it falls. The page draws the rows on your roof with the gap that keeps them out of each other's shade at noon on 21 December, checks the inverter against your contracted load, and gives the payback when you enter a price.
Location and the way the panels face
Your consumption and your bill
The roof and the panels
The clear flat area: leave out the stair, the water tanks and the AC units.
From the panel's datasheet; the default is a 580 W panel of 2.278 × 1.134 m (LONGi LR5-72HTH-580M).
The checks
The panels on the roof
Month by month
The typical year's production (PVWatts Version 5, AC), split at the share used on site you entered; the line is your consumption.
The bill month by month
| Month | Production kWh | Consumption kWh | Used on site kWh | Exported kWh | Before SAR | After SAR | Saving SAR | If all used SAR | If all exported SAR |
|---|
Consumption charges in SAR without VAT and the meter fee; "after" takes off the export credit and can go below zero: a credit carried forward.
The roof in 3D
Yield at every tilt and direction
The PVWatts chain month by month, and the row geometry
The PVWatts chain, per kWp
| Month | Transmitted E_tr kWh/m² | Mean T_cell − 25 K | DC before losses kWh | DC after losses kWh | Clipped kWh | AC kWh | Inverter efficiency % |
|---|
Row geometry
| Quantity | Value |
|---|
Export
Questions engineers ask
How many solar panels do I need for my house?
Enter your consumption (one monthly figure, the bill in riyals, or the twelve months from your bills) and the share of it you want the panels to produce. In Riyadh a south-facing array tilted 20° produces about 1,855 kWh per kWp a year with the default 580 W panel and the PVWatts default losses, so a villa using 57,300 kWh a year that wants half of it needs about 15.4 kWp: 27 panels of 580 W. The page stops at what the roof holds and what the contracted load allows, and says which one stopped it.
How much will solar panels save on my SEC bill?
A kWh the building uses at the moment the panels produce it is a kWh not bought: 18 halalas for a home up to 6,000 kWh a month and 30 above, so the summer months of a large villa save the most. A kWh exported to the grid is credited at 7 halalas for a residential consumer and carried to the next bill. How much is used on site depends on when the building draws power, which the page cannot know, so it shows the saving at the share you enter and between all exported and all used. The figures exclude VAT and the meter fee.
Can I sell my solar electricity to SEC?
Under the SERA Regulatory Framework for Small-Scale Solar PV Systems (ERD-TA-012) a system of 1 kW to 2 MW works in parallel with the grid on a bidirectional meter, and the energy it exports is recorded as a financial balance carried to the next bill: net billing, not a sale. Annex 3 sets the credit at 7 halalas per kWh for residential consumers and leaves the other categories to an ECRA resolution, so for a shop or a school enter the price you are given. The system may not exceed the contracted load.
Which way should the panels face, and at what tilt?
South, tilted a little below the latitude: in Riyadh the most is about 1,865 kWh per kWp a year at 26° facing 175°, and a flat array gives about 9 % less. Facing due east or west at 20° costs about 11 to 13 %. The map under the results shows the yield for every tilt from 0 to 40° and every direction from east to west, with your choice and the best marked.
How far apart should the rows of panels be?
Far enough that no row shades the next at solar noon on 21 December, when the noon sun is lowest: the gap is the height of the row's top edge divided by the tangent of the sun's altitude. In Riyadh the noon sun on 21 December is 41.8° high, so a row of 2.278 m panels tilted 20° rises 0.78 m and needs a 0.87 m gap: a row every 3.01 m. The page draws the rows that fit on your roof at that spacing.
What is the contracted load and where do I find it?
It is the capacity of your supply, set by the main breaker: the SEC bill prints the breaker's amperes. On a three-phase 230/400 V supply a 100 A breaker is 69 kVA and a 150 A breaker 104 kVA. The Framework does not allow the solar system to exceed it; the page compares the inverter's AC rating with it and says whether the array's DC rating is within it too.
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Electrical
An electrical package a utility reviewer, a contractor and a commissioning team can all work from.
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