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Solar Panel and Battery Calculation: Method and Examples

Huawei Team7 min read
Huawei LUNA2000-S1 battery, used in the worked solar panel and battery calculation

The four sums behind a solar panel and battery calculation, worked on three real loads with Huawei SUN2000 and LUNA2000 figures, and the calculator.

Sizing a solar system is arithmetic, and it is short. Four sums take you from a list of appliances to an inverter size, a battery capacity and a number of panels. This guide writes the sums out, runs them on three real loads, and checks each result against the figures in the Huawei SUN2000 and LUNA2000 records. The sizing calculator runs exactly these sums; the point of doing them once by hand is to know what the result means.

Products mentioned in this article

The four sums

  1. Daily energy (kWh) = watts × hours for each appliance, added together.
  2. Peak load (W) = every appliance running, plus the starting surge of the largest motor. An air conditioner compressor draws about three times its running power for a moment.
  3. Battery (kWh) = daily energy × hours of backup ÷ 24. With no grid at all, the battery covers the full day.
  4. Array (kWp) = daily energy ÷ (sun hours × performance ratio). The calculator uses a ratio of 0.8, and 0.75 for an off-grid system. Panels = array ÷ the wattage of one panel, rounded up.

Sun hours are the one figure that changes by country: 5.7 for the UAE, 5.8 for Saudi Arabia, 5.4 for Iraq, 3.7 for France.

Example 1: an apartment, in the UAE and in France

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) and 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 + 2,400 W compressor surge = 4,850 W
  • Battery for a night (8 h): 13.8 × 8 ÷ 24 = 4.6 kWh
  • Array in the UAE: 13.8 ÷ (5.7 × 0.8) = 3.0 kWp → 6 panels of 550 W
  • Array in France: 13.8 ÷ (3.7 × 0.8) = 4.7 kWp → 9 panels of 550 W

The inverter has to cover 4,850 W. The SUN2000-5K-LB0 states 5,000 W rated AC power, single-phase, with two MPPT inputs of 16 A and a 600 V maximum DC voltage. The finished kit is the apartment system with overnight backup.

Example 2: a family house in Saudi Arabia

Two air conditioners, a fridge, lights and Wi-Fi, a television, a washing machine and a 2,000 W kitchen appliance for an hour.

  • Daily energy: 19.2 + 1.2 + 1.6 + 0.6 + 0.8 + 2.0 = 25.4 kWh
  • Peak: 5,650 W running + 2,400 W surge = 8,050 W
  • Battery for an evening (4 h): 25.4 × 4 ÷ 24 = 4.2 kWh; for a night: 8.5 kWh
  • Array: 25.4 ÷ (5.8 × 0.8) = 5.5 kWp → 10 panels of 550 W (11 in the UAE, at 5.7 sun hours)

On the Huawei catalogue the evening need is met by the LUNA2000-7-S1 (6.9 kWh usable) and the night by the LUNA2000-17-S1 (16.9 kWh usable), which is what the house system with overnight backup lists. The peak of 8,050 W is above the 6 kW top of the single-phase SUN2000-LB0 range, so the kit states a 9 kW inverter line; on a three-phase supply the SUN2000-10K-MAP0 states 10,000 W rated power and an 11,000 VA maximum.

Example 3: a villa, and the limit most calculations miss

Four air conditioners, a fridge, a freezer, two lighting circuits, two televisions, a washing machine, a pump and a kitchen: 49.5 kWh a day and a peak of 11,700 W.

  • Battery for an evening: 49.5 × 4 ÷ 24 = 8.3 kWh; for a night: 16.5 kWh
  • Array in the UAE: 49.5 ÷ (5.7 × 0.8) = 10.9 kWp → 20 panels of 550 W, about 52 m² of roof

The kits list the LUNA2000-15-S0 for the evening and the LUNA2000-21-S1 for the night. Here the kWh figure is not the whole answer. A battery also has a power limit, and the records state it:

BatteryUsable energyMaximum power
LUNA2000-5-S05 kWh2.5 kW (3.5 kW for 10 seconds)
LUNA2000-15-S015 kWh5.0 kW (7.0 kW for 10 seconds)
LUNA2000-7-S16.9 kWh3.5 kW
LUNA2000-17-S116.9 kWh10.5 kW
LUNA2000-21-S120.7 kWh10.5 kW

The villa's 11,700 W peak is above the 10.5 kW of the largest LUNA2000-S1. During a power cut at night the battery alone cannot run all four air conditioners at the moment one of them starts; in daylight the panels add their share. Read the power row on the LUNA2000-S1 datasheet before you decide how many circuits go on the backup side.

Checks the sums do not make for you

  • String voltage. The panels in one string must stay inside the inverter's DC window. The SUN2000-LB0 states a 600 V maximum and a 40–560 V MPPT range; the SUN2000-MAP0 states 1,100 V and 160–1,000 V. The LB0 datasheet and the MAP0 datasheet carry the full rows.
  • Array size per inverter. The SUN2000-10K-MAP0 record recommends at most 18,000 Wp of panels; the SUN2000-10KTL-M1 recommends 15,000 Wp.
  • Battery voltage. A LUNA2000 works at 350–560 V on a single-phase inverter and 600–980 V on a three-phase one; the inverter's battery row must state the same window. To see two units' rows next to each other, use the comparison page.

Run it on your own list

Open the calculator, pick the preset closest to your site and correct it: the number of air conditioners, the backup hours, grid or off-grid. The result names the Huawei units that fit and states a size where no unit does. Every ready-made system opens there with its list already entered. The price on each product page is the price you pay, and orders are collected from our store in Dubai or Riyadh.

Frequently Asked Questions

How do I calculate the solar panels and battery I need?

Add up watts × hours for every appliance to get the daily energy in kWh. The battery is that figure × the hours you want covered ÷ 24. The array in kWp is the daily energy ÷ (sun hours × 0.8), and the number of panels is the array divided by the wattage of one panel, rounded up. The calculator on this site runs the same sums from your appliance list.

What sun hours figure should I use?

The calculator uses 5.7 for the UAE and Oman, 5.8 for Saudi Arabia, 5.6 for Qatar, Kuwait and Bahrain, 5.4 for Iraq and 3.7 for France. Where it holds no figure for a country it uses 5.0 and says on the result that the value was assumed.

Is battery capacity in kWh enough to choose a battery?

No. The battery's power in kW decides what can run at the same moment. The LUNA2000-5-S0 record states 5 kWh usable and 2.5 kW maximum output; the LUNA2000-21-S1 states 20.7 kWh and 10.5 kW maximum system power. Check the kW row against the load you want running during a cut.

Why does the same home need more panels in France than in the UAE?

Because the array is divided by the sun hours. The apartment load of 13.8 kWh a day needs 3.0 kWp at 5.7 sun hours and 4.7 kWp at 3.7, which is six 550 W panels in the UAE and nine in France.
  • #solar panel and battery calculation
  • #solar battery calculator
  • #solar system sizing
  • #LUNA2000 sizing
  • #SUN2000 hybrid
  • #sun hours
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