Solar Panel and Battery Calculation, Step by Step

Sizing a solar system is arithmetic, not guesswork, and it is short arithmetic: five sums, each one line long. This article does them by hand on three real loads so that nothing is hidden, then points at the tool that does them in a second. Every Growatt figure quoted below is read from the product's own record in our catalogue.

Products mentioned in this article

Growatt 5 kWh 51.2 V Lithium Solar Battery ALP5.0L-E2

• Nominal Energy:5kWh
• Nominal Voltage:51.2V

AED 3,000

Order now — Growatt 5 kWh 51.2 V Lithium Solar Battery ALP5.0L-E2

The five sums

1. Daily energy (kWh). For each appliance: watts × how many × hours a day. Add them up.
2. Peak load (W). Add the running watts of everything, then replace the one appliance with the heaviest start by its starting power — a compressor counts about three times, a water pump three and a half.
3. Solar array (kWp). Daily energy ÷ (peak sun hours × performance ratio). The calculator uses 5.7 sun hours, the figure for the UAE, and a ratio of 0.8 — 0.75 for an off-grid system.
4. Battery (kWh). For backup: daily energy × hours of backup ÷ 24. For off-grid: one full day of energy.
5. Inverter (W). Its rated output must cover the peak load from sum 2, and its record must state a battery voltage range that holds the battery from sum 4.

Worked example 1: an apartment, four hours of backup

One air conditioner (1,200 W, 8 h), a fridge (150 W, 8 h), lights and Wi-Fi (200 W, 8 h), a television (100 W, 6 h), a washing machine (800 W, 1 h).

• Daily energy: 9.6 + 1.2 + 1.6 + 0.6 + 0.8 = 13.8 kWh.
• Peak: 2,450 W running; the air conditioner starts at 3,600 W, so 2,450 − 1,200 + 3,600 = 4,850 W.
• Array: 13.8 ÷ (5.7 × 0.8) = 3.03 kWp → six 550 W panels, about 16 m².
• Battery: 13.8 × 4 ÷ 24 = 2.3 kWh.
• Inverter: at least 4,850 W.

In the catalogue that lands on the SPH 10000TL-HU and one ALP5.0L-E2. The battery's record gives two energy figures — nominal energy 5 kWh and rated energy 4.6 kWh — and a depth of discharge of 92%; the calculator counts 90% of the nominal figure as usable, 4.5 kWh, which covers the 2.3 kWh with room to spare. This is the apartment evening-backup kit exactly.

Worked example 2: a house, eight hours of backup

Two air conditioners, a fridge, lights, a television, a washing machine and a kitchen (2,000 W, 1 h).

• Daily energy: 19.2 + 1.2 + 1.6 + 0.6 + 0.8 + 2.0 = 25.4 kWh.
• Peak: 5,650 − 1,200 + 3,600 = 8,050 W.
• Array: 25.4 ÷ 4.56 = 5.57 kWp → eleven 550 W panels, about 29 m².
• Battery: 25.4 × 8 ÷ 24 = 8.5 kWh.

The inverter is again the SPH 10000TL-HU: 10,000 W of nominal AC power against an 8,050 W peak, a recommended PV power of up to 15,000 W against a 5.57 kWp array, and a 40–60 V battery input. For the battery the calculator takes the largest single unit that is no more than twice the need, so a second night of clouds is not a crisis: the ARK 17.9L, 17.92 kWh at 51.2 V with a stated depth of discharge of 90%. The house overnight-backup kit shows the same three lines.

Worked example 3: a farm with no grid

Two water pumps (750 W, 1.5 h each), a fridge, a freezer (200 W, 8 h) and lights.

• Daily energy: 2.25 + 1.2 + 1.6 + 1.6 = 6.65 kWh.
• Peak: 2,050 W running; one pump starts at 2,625 W, so 2,050 − 750 + 2,625 = 3,925 W.
• Array, off-grid ratio: 6.65 ÷ (5.7 × 0.75) = 1.56 kWp → three 550 W panels.
• Battery: one full day, 6.65 kWh.

The inverter is the SPF 4000T DVM: 4 kW rated, a 12 kW surge rating, a maximum PV array power of 5,000 W and a 48 VDC battery input for lithium or lead-acid. The battery is the ARK 12.8L, 12.8 kWh. See it assembled on the farm off-grid kit.

If your sun is not the UAE's

Sum 3 is the one that changes with the country. The sizing engine's table holds 5.8 peak sun hours for Saudi Arabia, 5.4 for Iraq and 3.7 for France; the calculator on this site uses 5.7. To redo the array for another country, keep the daily energy and change the divisor: the house in France is 25.4 ÷ (3.7 × 0.8) = 8.58 kWp, sixteen 550 W panels instead of eleven. The battery and the inverter do not move — they depend on your appliances, not on your sky.

A note on the panel line

We distribute Growatt, and Growatt's range in our catalogue is inverters, batteries and EV chargers. The array is therefore a count of 550 W modules, not a product you can add to the cart here. If your panels are 450 W or 600 W, divide the kWp from sum 3 by your own module's watts and round up.

Let the calculator do it

The solar sizing calculator runs these five sums on your own list: pick appliances room by room, change the wattage of any of them, add a device of your own, choose on-grid, backup or off-grid and the hours of backup — or type the kWh a month from your bill. It answers with a named Growatt inverter and battery whose records fit each other. If you would rather start from a finished answer, the ready-made systems are these sums already done for twenty properties, and the Growatt hybrid inverters page lists the hybrid units it draws on for a backup system. The price on each product page is the price you pay; orders are collected from our stores in Dubai and Riyadh.