0

How to Size a Solar System for Your Home Step by Step

Last updated: October 2026. Prices, incentives and utility rules change often. Every rule below is dated, and all figures are estimates.

Quick answer

To size a solar system, divide your yearly electricity use (kWh, from 12 months of bills) by the yearly output of 1 kW of panels where you live (kWh per kW), then round up to whole panels. In the Gulf, 1 kW typically yields about 1,500 kWh a year, so a home using 18,000 kWh needs roughly 12 kW.

Four inputs decide your system size: your yearly kWh, the share of it you want solar to cover, how much 1 kW of panels produces at your address, and your system losses. This guide walks through each one with a worked example for a Gulf villa, then shows how the same method changes in the US and UK.

Step 1: Find your yearly electricity use

Add up the kWh (units consumed, not the amount in dollars, dirhams or riyals) from your last 12 bills. That total is your annual consumption. Divide it by 365 for a daily figure.

Use 12 months, not one. Summer air conditioning pushes Gulf bills far above winter levels, so a single month gives a wrong answer in either direction.

Example used in this guide: a villa averaging 1,500 kWh a month uses 1,500 × 12 = 18,000 kWh a year, or about 49 kWh a day (18,000 ÷ 365).

Then add what is coming. A second AC unit, an electric car or a pool pump will raise the total, and it is cheaper to size for them now than to extend the array later. Estimate each one’s yearly kWh and add it to the base figure.

Step 2: Decide how much of it solar should cover

Most homeowners aim for 70% to 100% of annual use. The right target depends on what your utility pays or credits for exported power, so check this before you pick a number.

  • Dubai: exported units are credited against your bill at your own tariff rate, credits roll over, and they cannot be cashed out (SurgePV, 2026). Sizing above 100% of your use earns you nothing extra.
  • Saudi Arabia: a draft framework published in October 2026 proposes crediting exports at SAR 0.07/kWh (about USD 0.02) for homes, far below the retail value of self-consumed power (SMM, October 2026). A system sized to your own daytime use makes more sense than one built to export.
  • UK: the Smart Export Guarantee pays roughly 4p to 15p per kWh depending on the supplier (The Green Age, 2026), again well under the price of the electricity you avoid buying.

The pattern is the same everywhere: power you use yourself is worth more than power you export. For the example villa, I will size for 100% of use and show the 70% version afterwards.

Step 3: Find what 1 kW of panels produces near you

This number is called specific yield, measured in kWh per kW per year (kWh/kWp). It folds sunshine, temperature and typical losses into one figure. A related term is peak sun hours: one peak sun hour equals 1 kWh of sunlight per square metre, so 5.5 peak sun hours means 5.5 kWh/m² arrives on a typical day.

Free tools that give you both, for your exact address:

  • NREL PVWatts (covers the US and many international locations)
  • Global Solar Atlas (World Bank, built on Solargis data; shows PV output in kWh/kWp for any point on the map)
  • PVGIS (European Commission tool, useful for Europe, Africa and Asia)

Rough reference values (installer figures, so treat them as ballpark):

Location Typical yield per 1 kW per year kW needed for 10,000 kWh/year
Dubai, UAE 1,500–1,600 kWh (after heat and dust) about 6.7 kW (at 1,500)
Southern California, US 1,200–1,400 kWh about 7.7 kW (at 1,300)
Southern England, UK about 850 kWh (a 4 kW system makes roughly 3,400 kWh) about 11.8 kW (at 850)

Sources: Dubai and California ranges from Voltflow (April 2026), an installer blog. UK figure derived from ExpertSure (2026): 3,400 kWh ÷ 4 kW = 850 kWh per kW. The last column is my own division.

For the Gulf, DEWA’s own figure is about 2,100 kWh/m² of sunlight per year on panels facing south at roughly 24° tilt (Gulf News, quoting DEWA). That works out to about 5.75 peak sun hours a day (2,100 ÷ 365). Kuwait is similar, at about 5.5 kWh/m² a day according to a study cited by the Kuwait Times.

Step 4: Calculate the system size

Two formulas give the same answer. Use the first as your main number and the second as a cross-check.

Formula A (yield method)
System size (kW) = annual kWh ÷ specific yield (kWh per kW per year)

Formula B (sun-hours method)
System size (kW) = daily kWh ÷ (peak sun hours × efficiency factor)

The efficiency factor covers everything between sunlight and your sockets: heat, dust, inverter and wiring losses. NREL’s PVWatts assumes 14% total losses by default, which is a factor of 0.86 (ESIG PVWatts reference). US installer guides typically use 0.80 to 0.87 (for example Unbound Solar). For a hot, dusty Gulf site I use a more cautious 0.75. That is my working assumption, not a published standard, so ask your installer what they model.

Worked example: Gulf villa Calculation Result
Annual use 1,500 kWh × 12 18,000 kWh
Daily use 18,000 ÷ 365 49.3 kWh
Formula A (1,500 kWh/kW assumed) 18,000 ÷ 1,500 12.0 kW
Formula B (5.5 sun hours, 0.75 factor) 49.3 ÷ (5.5 × 0.75) 12.0 kW
If you only want 70% coverage 12.0 × 0.70 8.4 kW

Both methods land on 12 kW because the 0.75 factor was chosen to match the roughly 1,500 kWh per kW that Gulf installers report. If your two numbers disagree by more than about 10%, one of your inputs is off. Recheck the yield figure first.

The same method in the UK: a home using 3,100 kWh a year (close to Ofgem’s typical figure, as quoted by EvoEnergy) needs 3,100 ÷ 850 = 3.6 kW. That is why 4 kW is the most common UK size.

Step 5: Turn kW into panels and check your roof

Number of panels = system size (kW) ÷ panel wattage (kW), rounded up.

With 550 W (0.55 kW) panels: 12 ÷ 0.55 = 21.8, so 22 panels, a 12.1 kW array that should produce about 18,150 kWh a year at 1,500 kWh per kW.

Now check the roof. A 550 W panel is typically about 2.3 m by 1.1 m, roughly 2.6 m². Twenty-two panels need about 57 m² of clear, unshaded roof, and more if you mount them on tilt frames on a flat roof, because each row needs spacing so it does not shade the next. Water tanks, parapet walls, satellite dishes and neighbouring buildings are the usual shade sources.

If the roof is too small, you have three options: use higher-wattage panels, accept a lower coverage target, or add a second roof section. In the example, 16 panels (8.8 kW) would still cover about 73% of use (8.8 × 1,500 ÷ 18,000).

Step 6: Size the inverter, then decide on a battery

The inverter converts the panels’ DC power into the AC power your home uses. Installers usually pick one slightly smaller than the array, because panels rarely hit their full rated output. PVWatts defaults to a DC-to-AC ratio of 1.1 (ESIG), so a 12.1 kW array pairs with about an 11 kW inverter (12.1 ÷ 1.1). Real inverters come in fixed sizes, and your installer will round to the nearest suitable model and match it to your single-phase or three-phase supply.

A battery is a separate calculation based on the loads you want to keep running and for how long. With net metering, most homes do not need one for savings, only for backup. If you want backup power, list the essential loads (fridge, lights, a single AC unit, Wi-Fi) and total their daily kWh before talking to installers.

Step 7: Check your local rules before you sign

Rules decide the maximum size you can connect and what exports are worth. They also change often. The table reflects what I found in October 2026, so confirm with your utility.

Country What is reported (2026) Sizing takeaway
UAE (Dubai) Shams Dubai net metering since 2015. A DEWA-accredited contractor must submit the application, and only rooftop and building-integrated systems qualify (SurgePV). Size to 100% of annual use at most.
UAE (Northern Emirates) EtihadWE’s Distributed Solar System program launched 17 September 2024. Credits reportedly expire at year end (SurgePV). Avoid building up large yearly surpluses.
Saudi Arabia A net metering scheme has run since July 2018 for systems from 1 kW to 2 MW (Enerdata). In October 2026 the regulator proposed a new net billing framework: SAR 0.07/kWh credit for homes, credits valid 12 months, systems up to 11 kW exempt from connection charges. This is a draft. Size for self-consumption. Check whether the draft became final.
Qatar Kahramaa’s BeSolar service is described as a net metering mechanism. The framework is newer and less detailed than DEWA’s (Smart Gulf Solar). Sources disagree on its details. Contact Kahramaa before designing.
Oman The Sahim scheme is built around feed-in tariffs and developer-led rooftop projects, not classic net metering (Qamar Energy report). Ask the regulator which route applies to your home.
Bahrain A net metering system managed by EWA lets owners export surplus power (PV Know-How). Confirm current limits with EWA.
Kuwait No nationwide net metering policy as of 2025 (pv magazine). A 10 kW residential pilot using net billing was reported for 2026 (SurgePV). Rules are still forming. Verify with MEW.
United States The 30% federal credit for homeowner-owned systems (Section 25D) ended on 31 December 2025. Leased and PPA systems can still access a business credit (Solar.com). Net metering terms vary by state and utility. Many older guides still assume the 30% credit. Remove it from your payback math.
United Kingdom 0% VAT on solar installations until 31 March 2027. The Smart Export Guarantee requires an MCS-certified installer (Heatable). A 3–4 kW system fits most homes.

Everywhere in the Gulf, use a licensed or accredited installer. Utilities such as DEWA refuse applications from contractors that are not on their approved list.

Gulf factors: how heat and dust change the numbers

Heat. Panels are rated at a cell temperature of 25°C, but a panel on a Gulf roof runs far hotter. Most silicon panels lose 0.3% to 0.5% of their output for every degree above 25°C. At the typical 0.4% per degree, a cell at 50°C loses about 10% (SolarQuotes). At 65°C, a panel rated at −0.41% per degree loses about 16% (Sinovoltaics). The “temperature coefficient” line on the datasheet matters here. Closer to zero is better.

Dust. A UAE University study found that panels left uncleaned for three months lost up to 13% of output compared with daily-cleaned panels. Cleaning every 15 days cut the loss to about 4% (UAEU, 2020). Plan a cleaning routine as part of the system, not an afterthought.

What to do with this. Use a yield figure that already includes heat and dust (the 1,500 kWh per kW above does), or use a lower efficiency factor like 0.75. Do not use the 0.86 default from temperate-climate tools without adjusting it.

Common sizing mistakes

  • Using one month of bills. It hides the seasonal swing. Use 12 months.
  • Confusing daylight hours with peak sun hours. A Dubai day has 10 to 12 hours of light but only about 5.5 to 6 peak sun hours.
  • Sizing above 100% of use where exports earn little or nothing. Dubai credits are not paid out in cash, and Saudi Arabia’s proposed export rate is low.
  • Ignoring future loads. An extra AC unit or an EV adds thousands of kWh a year.
  • Skipping the shade check. A shadow from a water tank at 3 pm can cost more output than a smaller array would have.
  • Trusting an old incentive. US guides written before 2026 still count a 30% credit that no longer exists for purchased systems.

FAQ

What size solar system do I need for my house?

Divide your yearly electricity use in kWh by the yearly output of 1 kW of panels in your area. A Gulf villa using 18,000 kWh needs about 12 kW at 1,500 kWh per kW. A UK home using 3,100 kWh needs about 3.6 kW at 850 kWh per kW.

How many solar panels do I need?

Divide the system size in kW by the panel wattage in kW and round up. For a 12 kW system with 550 W panels, that is 12 ÷ 0.55 = 22 panels.

How many peak sun hours does the Gulf get?

Installer figures for Dubai are about 5.5 to 6.0 a day, which matches DEWA’s reported 2,100 kWh/m² per year on well-oriented panels (about 5.75 a day). Kuwait is cited at about 5.5 kWh/m² a day.

Should I size my solar system for 100% of my bill?

Not always. Where exports are credited at the full retail rate and credits carry over, 100% of annual use is a sensible ceiling. Where exports earn little, such as the proposed Saudi rate of SAR 0.07/kWh, aim for the share of power you will use during the day.

Does heat mean I need a bigger system in the Gulf?

Heat and dust reduce each panel’s output, so use a Gulf-specific yield (around 1,500 kWh per kW per year) rather than a temperate-climate figure. Using the right yield is what sizes the system correctly. You should not add extra capacity on top.

Do I need a battery?

Not to save money under net metering. A battery is for backup power or for places where exported energy is worth little. Size it separately from the panels, based on the loads you want to keep running.

Sources

Please note: all figures in this guide are estimates for planning, not quotes or guarantees. Yields, prices, incentives and net metering rules change and differ by country, utility and even street. Get written quotes and a site survey from licensed installers before you buy. This article is general information, not financial or engineering advice.

You may like these posts

Comments