Warehouse rooftop solar: is the North or the South more profitable?

Warehouse owners usually start by asking how many kWp fit on a roof of a given size. The question that really decides returns is different: how much electricity the warehouse uses during the day. Self-consumption rooftop solar only saves money when the power generated is used immediately; surplus fed into the grid is limited under current regulations and is not valued in this article.

Example inputs

Take a 10,000 m² warehouse roof with 70% of the area usable for panels at a density of about 0.2 kWp/m², giving a system of about 1,400 kWp. Specific yield by region: Hanoi about 912 kWh/kWp/year, Ho Chi Minh City about 1,426 kWh/kWp/year. Generation follows the solar curve from 6:00 a.m. to 6:00 p.m. Self-consumed electricity is valued at the industrial tariff for 22 kV to below 110 kV (Decision 1279/QĐ-BCT); generation overlapping the 5:30–6:00 p.m. peak period is valued at the peak rate, Monday to Saturday.

Output: the South is over 56% higher

With the same 1,400 kWp, the system in Hanoi generates about 1.28 million kWh/year and the one in Ho Chi Minh City about 2.0 million kWh/year. On output alone, the southern project looks far better.

Small warehouse: savings only about 5% higher

For a typical warehouse with a daytime load of about 150 kW (lighting, forklift charging, offices), the Hanoi system self-consumes about 46% of its output, saving about VND 1.08 billion/year. In Ho Chi Minh City, only about 31% of output can be used, saving about VND 1.14 billion/year. Output is over 56% higher but savings are only about 5% higher, because most of the extra electricity is generated when the warehouse does not need it.

Large-load warehouse: the gap widens

For a warehouse with a daytime load of about 400 kW, such as a cold store or a warehouse with conveyors, the Hanoi system self-consumes about 96% of output, saving about VND 2.25 billion/year; in Ho Chi Minh City it uses about 72%, saving about VND 2.64 billion/year, roughly 17% more. The South's sunshine advantage turns into money only when the load is large enough to absorb it.

Installing less can be more effective

Back to the Hanoi warehouse with a 150 kW load: if only 600 kWp is installed (30% of the roof), savings are about VND 0.90 billion/year, about 83% of the savings of the 1,400 kWp system with less than half the panels. Per kWp invested, the 600 kWp system saves about VND 1.49 million/kWp/year, nearly double the roughly VND 0.77 million/kWp/year of the 1,400 kWp system. At the same unit investment cost, the smaller system pays back nearly twice as fast.

What to fix before choosing capacity

Three pieces of data are needed before choosing capacity: an hourly load profile for at least one typical month, the tariff group and voltage level currently purchased, and plans for load growth over the next few years (cold storage, EV charging, automation). Remaining roof space can be reserved for the period of higher load, or combined with battery storage to shift surplus to peak hours. The numbers in this article are preliminary estimates for comparing options; readers can enter their own roof area, region and daytime load into the warehouse rooftop solar calculator.