Who this is for
- Homeowners about to ask installers for quotes
- Owners who have a quote and cannot tell whether it is fair
- People building a new house who want to provide for solar now
Have to hand
- Twelve months of electricity bills, or at least the highest and lowest months
- A list of the appliances you want to run, with their wattage
- An idea of your roof: its area, direction and any shade
You will finish with
- A first estimate of panels, inverter and battery size
- A solar BOQ that every installer prices the same way
- A checklist for comparing quotes and for acceptance
Start with your bills and your loads
Find out how much electricity you really use, and when, because that decides the size of everything else.
The size of the house does not decide the size of the solar system. What you use does. Two houses of the same size can have bills that differ several times over, depending on air conditioners, water pumps and habits.
- 1
Collect twelve months of bills
Write down the units (kWh) used each month. Note the highest and lowest. The highest, usually in summer when the ACs run, sets the peak you need to cover. The lowest shows your base use.
- 2
Work out your daily use
Divide a month’s units by 30. A month of 600 units is about 20 units a day.
- 3
Decide what share to cover
You can aim to cover all of your highest month, or most of your average. A smaller system costs less and still cuts the bill. A bigger one costs more and covers the summer peak.
- 4
Make a load list for any backup
If you want power during outages, list what must keep running: lights, fans, fridge, router, TV, a pump. Write the wattage of each and the hours you need it. Heavy loads such as ACs and irons need a much bigger battery and inverter and are usually left on the grid.
| Appliance | Watts | Number | Hours in an outage | Watt-hours |
|---|---|---|---|---|
| LED lights | ||||
| Ceiling or DC fans | ||||
| Refrigerator | ||||
| Router and TV | ||||
| Water pump | ||||
| Total power at once, and total energy |
On-grid, hybrid or off-grid
Choose the system type that solves the problem you actually have.
| Type | How it works | Best when | Keep in mind |
|---|---|---|---|
| On-grid (grid-tied) | Panels feed the house and the grid through an inverter, with no batteries | The main aim is to cut the bill and the grid is fairly reliable | It shuts down when the grid is off, for safety, so it does not give backup |
| Hybrid | Panels, batteries and the grid work together; batteries cover outages | Outages are long or frequent and you want backup for chosen loads | Batteries add cost and wear out, and need a hybrid inverter |
| Off-grid | Panels and batteries only, with no grid connection | There is no grid, or a remote site | Must be sized for every load you need, including cloudy days |
Net metering
With net metering, power you export to the grid is credited against what you import. It needs an application to your distribution company and an approved installation. The rules, the rates paid for exported units and the licensing can change, so check the current policy with NEPRA and your distribution company before you size a system around exporting. Do not rely on a figure quoted by an installer or printed in an old article.
Calculate the system size
Turn your units into panels, inverter and battery, with the arithmetic shown.
These calculations give you a sound first estimate to compare with an installer’s numbers. They are not a design: the installer must confirm them for your roof, shade and equipment.
Solar sizing calculator
A first estimate to take into the conversation with installers, not a design. Use the units from your highest-use month on your electricity bill, and ask each installer to show their own numbers against these.
Panels
Battery backup (hybrid system only)
The arithmetic behind the calculator
- 1
Daily energy to produce
Daily units = monthly units ÷ 30, multiplied by the share you want solar to cover.
- 2
Array size in kW
Array kW = daily units ÷ (peak sun hours × system efficiency). Peak sun hours are the equivalent hours of full sun per day on the panels, which depend on your location and the roof’s direction and tilt. System efficiency covers losses in heat, dust, wiring and the inverter, and is commonly in the range of 70 to 80 per cent.
- 3
Number of panels
Panels = array kW × 1,000 ÷ the wattage of one panel, rounded up.
- 4
Roof area
Each panel takes roughly 2.5 to 3 square metres including the gaps to walk and to avoid shading. Check the total fits on the roof you have without shade.
- 5
Inverter
The inverter’s rating is usually close to the array size, commonly between 0.8 and 1.2 times it, and for a hybrid system it must also handle the backup loads’ peak, including starting surges.
- 6
Battery
Battery capacity = energy the backup loads need ÷ (usable depth of discharge × inverter efficiency). Lithium batteries are commonly used to about 80 per cent of capacity; lead-acid to about 50 per cent, so a lead-acid bank must be much bigger for the same usable energy.
- Daily use = 600 ÷ 30 = 20 units a day.
- Aim to cover 100%: 20 units.
- Assume 4.5 peak sun hours and 75% system efficiency: 4.5 × 0.75 = 3.375 units per kW per day.
- Array = 20 ÷ 3.375 = 5.93 kW.
- With 550 W panels: 5,930 ÷ 550 = 10.8, so 11 panels (6.05 kW installed).
- Roof area at about 3 m² per panel: about 33 m² (roughly 355 sq ft).
- Backup of 1,500 W for 4 hours = 6 kWh. Lithium at 80% usable and 90% inverter efficiency: 6 ÷ (0.8 × 0.9) = 8.3 kWh of battery.
Write a solar BOQ
Make a list of every item, so each installer prices the same system.
If you ask three installers for “a 6 kW system”, you get three different systems, with different panels, inverters, structure and cable, at three prices you cannot compare. A solar BOQ fixes the items first, so only price and service differ.
| Item | What to specify |
|---|---|
| Panels | Brand, model, wattage, number, type (such as mono-crystalline), tier and product warranty and performance warranty |
| Inverter | Brand, model, rated power, type (on-grid, hybrid), number of inputs and warranty |
| Batteries (hybrid and off-grid) | Brand, chemistry, capacity in kWh, usable capacity, cycles, warranty and the battery management system |
| Mounting structure | Material (such as galvanised steel or aluminium), height, tilt, wind rating and coating, and how it is fixed to the roof |
| DC and AC cables | Type, cross-section, length, conduit and UV protection |
| Protection | DC and AC breakers, isolators, surge protection and fuses, rated for the system |
| Earthing and lightning protection | Earth electrode, resistance reading and bonding of frames |
| Monitoring | App or device for output readings |
| Net metering | Who prepares the application, the bi-directional meter and the cost, if you want it |
| Installation, testing and commissioning | Labour, test results and a handover |
| Warranty and service | Written terms, who services, response time and spare parts |
Solar BOQ, before asking for quotes
0 of 8 doneCompare installer quotes
Check each quote for the specification, the missing items and the claims that cannot be true.
- 1
Put quotes in one table
List panels, inverter, batteries, structure, cables, protection, earthing, net metering, warranty and total for each installer.
- 2
Check models, not just brands
Ask for the exact model number of panels, inverter and batteries, and check each model’s data sheet from the manufacturer’s site.
- 3
Check the arithmetic
Panels × wattage should equal the array size. Compare the inverter size with the array and with the backup loads.
- 4
Check the structure and the cable
Cheap quotes often save on the mounting structure and the cable. Ask for the material, coating and thickness. A structure that rusts or moves in a storm is a bigger risk than the panels.
- 5
Ask about warranty in practice
Who honours the warranty: the installer or the manufacturer? Is there a local service centre? What happens if the installer closes?
- 6
Ask about generation
Ask the expected yearly output in kWh and the assumptions behind it. Compare with your own estimate. A claim far above yours should be justified.
- 7
Check what is excluded
Net metering costs, civil work, extra cable runs, a new distribution board, meter changes and roof repairs are common extras.
Acceptance on completion
Before you pay the final instalment
0 of 10 donePlanning for solar in a new house
Provide for solar in the design now, so it is cheap to add later.
Solar provisions in a new build
0 of 8 doneQuestions people ask
How many panels do I need?
It depends on your units, your sun hours and the panel wattage. Use the calculator in this guide, then ask installers to show their numbers.
Is a hybrid system worth it?
If outages are frequent and long and you want to run lights, fans, a fridge and the internet through them, yes. If the grid is mostly reliable, an on-grid system gives more savings per rupee. Batteries add cost and wear out, so size them for what you need.
Can solar run my air conditioner?
Yes in daylight, within the limits of the array and inverter, and with the grid as backup. Running an AC from batteries for hours needs a very large battery bank.
How long do solar panels last?
Panels are typically warranted for a long period with a stated decline in output; check the manufacturer’s product and performance warranty. Inverters and batteries have shorter lives and shorter warranties.
What maintenance does solar need?
Cleaning the panels of dust, checking the structure and cables and watching the monitored output. A fall in output is the first sign of a problem.
Should I buy from the cheapest installer?
Compare the whole specification, the warranty and the service, not the total. A low price on the same list is good; a low price on a different list usually means thinner structure, cable or support.
This guide is general guidance for building in Pakistan, last checked October 2026. Your approved drawings, your engineer's specification, the building regulations of your development authority and the law in force today take priority over anything written here. Fees, taxes and bylaws change: confirm current figures with the body that sets them.
Describe your home and your power needs, get a solar BOQ prepared, and have verified installers price the same list.
Start your project, freeKeep going
- Before you hireHow to budget a house build and use a BOQ
- While it is being builtWaterproofing a house: roofs, bathrooms, walls and damp
- The whole journeyHow to build a house in Pakistan, from plot to handover
Shorter reads on parts of this: solar BOQ and sizing a home system.