What does a complete list of customer requirements for off-grid residential solar systems look like?

Recently, I received a customer request from Dhaka, Bangladesh. The translated content is:

I have a residence with an average monthly electricity consumption of 1,000 kilowatt-hours. I want to supply power to my entire home with an independent solar power generation system (with a battery energy storage system), which is completely independent of the power grid (off-grid system). This system should meet all my electricity demands during the day and at night every month.

Please calculate and provide the following system design components and detailed information:

1.The required capacity of solar panels (unit: kilowatts) is based on the average daily sunshine duration

2. The total number of solar panels, including the type and size of bifacial monocrystalline silicon (for example, each panel is 650 watts)
3. The battery energy storage capacity (unit: kilowatt-hours) required to store sufficient electricity at night and on cloudy days, assuming it can maintain power supply for at least 1-2 days.
4. Inverter capacity suitable for operating average residential loads (unit: kilowatts).
5. A detailed estimate of the total system cost, including installation expenses.
6. Any assumptions regarding the daily duration of sunlight, location (assumed to be Dhaka, Bangladesh), depth of battery discharge, system loss and efficiency.
7. Optional: Recommend some reliable brands or technologies of solar panels, inverters and batteries.

In summary, the client hopes to build a completely off-grid solar power generation system for residential power supply, which does not rely on the national power grid. The average monthly electricity consumption of a residence is 1,000 kilowatt-hours (kWh), which is approximately 33 kilowatt-hours per day. The system needs to meet the electricity demand throughout the day (including at night) and also have reserve power to cope with continuous rainy days.

Based on the average sunshine duration and system efficiency in the Dhaka area, we have designed the following plan:

Solar power generation section

Effective sunshine duration: approximately 4.5 hours on average per day

System efficiency: Consider an overall efficiency of 80%

The required power generation: Approximately 41.7 kWh of electricity is needed per day to meet the demand

Required photovoltaic capacity: 41.7 ÷ 4.5 ≈ 9.3 kW. To be on the safe side, 10.5 kW is recommended

Component configuration:

A total of about 18 650W double-sided monocrystalline silicon solar panels are needed

Energy storage battery section

Objective: It can be used for 2 days when there is no sunlight

The daily electricity consumption is 33.3 kWh × 2 days = 66.6 kWh

The battery can be discharged by 90%, so the total capacity needs to be approximately 75 to 80 kWh

Recommended use: Lithium iron phosphate battery (LiFePO₄)

Inverter selection

To ensure the simultaneous operation of multiple household appliances, it is recommended to use a 10 kW off-grid inverter

Type: Pure sine wave, with MPPT controller, compatible with Battery Management System (BMS)

Budget list (in US dollars)

Recommended brand

Photovoltaic panels: LONGi, Jinko, JA Solar

Batteries: Pylontech, BYD, Tesla Powerwall

Inverters: Victron, Growatt SPF, SMA Sunny Island, Sol-Ark, Highjoule

If you want to completely break free from the constraints of the power grid, the above configuration can meet your basic living needs such as 33 kilowatt-hours of electricity per day, night lighting, air conditioning, and a refrigerator, and can also last for two days without the sun. With a budget of less than 40,000 yuan, a one-time investment ensures peace of mind for many years.

If you need drawings, supply chain recommendations or a 10-year cost-saving simulation, you can also continue to contact me.