Vận hành, TOU & quản lý năng lượngOperation, TOU & energy management · BàiLesson 2/4
Peak Sun Hours and the Daily Charge–Discharge Schedule
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Solar Knowledge HubGiờ nắng đỉnh và lịch sạc xả trong ngàyPeak sun hours & daily charge-discharge schedule
Giờ nắng đỉnh (PSH) là con số then chốt để tính sản lượng, khác rõ theo vùng, không thể dùng một số chung cho cả nước.Peak sun hours (PSH) is the key figure for estimating yield, varying sharply by region, so one national average does not fit.
| VùngRegion | PSH trung bình (giờ/ngày)Avg PSH (hours/day) | Sản lượng năm tham khảoReference annual yield |
|---|---|---|
| Miền NamSouth | khoảng 4.4 – 4.8 giờabout 4.4 – 4.8 h | khoảng 1.550 – 1.700 kWh/kWpabout 1,550 – 1,700 kWh/kWp |
| Miền TrungCentral | khoảng 4.0 – 4.3 giờabout 4.0 – 4.3 h | khoảng 1.450 – 1.550 kWh/kWpabout 1,450 – 1,550 kWh/kWp |
| Miền BắcNorth | khoảng 3.3 – 3.5 giờabout 3.3 – 3.5 h | khoảng 1.150 – 1.250 kWh/kWpabout 1,150 – 1,250 kWh/kWp |
Bản gốc ghi PSH Việt Nam "trung bình 4–5 giờ": đúng cho miền Trung và Nam nhưng bỏ sót miền Bắc ~3.4 giờ. Mùa đông xuân miền Bắc nhiều mây và nồm ẩm có thể kéo PSH xuống chỉ còn khoảng 2–2.5 giờ. Không dùng số miền Nam áp cho dự án miền Bắc.The original stated Vietnam averages "4–5 hours": true for the South and Center but omits the North at ~3.4 h. Winter-spring cloud and humidity can pull northern PSH down to only about 2–2.5 h. Never use southern figures for northern projects.
Lịch "bám nắng" này tối ưu cho tự tiêu thụ tối đa với hộ gia đình. Khách doanh nghiệp có chênh lệch giá lớn nên kết hợp thêm: sạc từ lưới thấp điểm 00:00–06:00 rồi xả cao điểm 17:30–22:30 như tài liệu 05-01.This solar-tracking schedule maximises self-consumption for homes. Business customers with a large price gap should combine: charge from grid during off-peak 00:00–06:00 and discharge into peak 17:30–22:30 as in doc 05-01.
Khi tư vấn sản lượng, dùng PSH đúng vùng. Hệ ở miền Bắc cho sản lượng thấp hơn khoảng một phần ba so với cùng hệ ở miền Nam, nên kỳ vọng và bài toán hoàn vốn phải khác nhau. Hứa sản lượng kiểu miền Nam cho khách miền Bắc là cách nhanh nhất làm khách thất vọng.When advising on yield, use the correct regional PSH. A northern system produces about one-third less than the same system in the South, so expectations and payback must differ. Promising southern yields to northern customers is the fastest way to disappoint them.
The output of a solar energy system depends on the peak sun hours at the installation site and on how the battery charges and discharges throughout the day in step with the solar curve. This document explains what peak sun hours are, how they differ across Vietnam’s regions, and what a typical daily charge–discharge schedule looks like.
For: technicians estimating yield and configuring charge–discharge schedules, sales staff explaining regional output differences, newcomers who need to understand peak sun hours.
Quick summary
Peak sun hours, abbreviated PSH, is the equivalent number of hours during which sunlight reaches the standard intensity of 1000 W/m². It is not the number of hours the sun is shining, but rather the full day’s solar energy expressed as an equivalent duration at peak intensity, and it is the key figure used to calculate system yield.
PSH varies noticeably across Vietnam. The South is highest at approximately 4.4 to 4.8 hours, the Central region around 4.0 to 4.3 hours, and the North is significantly lower at around 3.3 to 3.5 hours. This regional breakdown is a point the original source often glossed over by quoting a blanket figure of 4 to 5 hours.
Over the course of a day, the battery discharges at night and in the early morning before sunlight is available, charges from the midday solar surplus, and then discharges again in the late afternoon and evening. This schedule tracks the solar curve and load demand.
What are peak sun hours
Peak sun hours is the number of hours per day that, if sunlight were held constant at the standard intensity of 1000 W/m², would deliver exactly the same total solar energy actually received across the full day. One PSH equals 1 kWh per square metre. If a location has a PSH of 4.5 hours, the total solar energy for the day is equivalent to 4.5 hours at peak intensity.
PSH must be distinguished from hours of daylight. The sun may be above the horizon for twelve or more hours, but the weak irradiance at dawn and dusk contributes very little, so PSH is always smaller than the number of daylight hours. Four factors influence PSH: weather, season of the year, geographic location, and the orientation and tilt angle of the panels.
Peak sun hours by region in Vietnam
This is the most important section and the point the original source was missing. PSH is not uniform across the country, so a single national figure cannot be applied to every region.
| Region | Average peak sun hours | Reference annual yield |
|---|---|---|
| South | approximately 4.4 to 4.8 hours | approximately 1,550 to 1,700 kWh per kWp |
| Central | approximately 4.0 to 4.3 hours | approximately 1,450 to 1,550 kWh per kWp |
| North | approximately 3.3 to 3.5 hours | approximately 1,150 to 1,250 kWh per kWp |
The North is considerably lower than the South and also fluctuates strongly by season. During the winter–spring period, heavy cloud cover and high humidity can pull PSH in the North down to around 2 to 2.5 hours. When estimating yield and payback for a northern project, regional PSH figures must be used and seasonal variation must be accounted for: the southern figures cannot simply be carried over.
The original source stated Vietnam’s average PSH as 4 to 5 hours. That range is valid for the Central and Southern regions but omits the North, which averages only about 3.4 hours. The population-weighted national average skews lower, around 3.6 to 4 hours, due to the cloudy conditions in the North.
Daily charge–discharge schedule
Throughout the day, energy flows and battery state of charge change in line with the solar curve and load demand, following the priority rule: solar generation first, then load, then battery charging, and finally the grid.
| Time window | Action |
|---|---|
| 00:00 – 06:00, night | Low load; battery discharges to supply the load; if battery is depleted, the grid supplements |
| 06:00 – 09:00, early morning | Sun begins rising; priority is to supply the load; surplus charges the battery; shortfall is drawn from the grid |
| 09:00 – 15:00, peak sun | Peak irradiance; priority is to supply the load; surplus charges the battery to full; grid import is minimised |
| 15:00 – 18:00, afternoon | Irradiance declining; priority is to supply the load; shortfall is compensated from the battery; grid import minimised |
| 18:00 – 24:00, night | No solar generation; battery discharges to supply the load; if depleted, draw from the grid |
Battery capacity and inverter power rating determine how long the battery can sustain the load, since discharge time equals stored energy divided by load power. The higher the PSH, the more energy is harvested, so the battery reaches full charge faster and accumulates more surplus for evening use.
The solar-tracking charge–discharge schedule described here targets maximum self-consumption. It differs from the time-of-use optimised schedule in document 05-01, where the battery may also charge from cheap off-peak grid power to discharge during peak tariff hours. For residential customers focused mainly on self-consumption, tracking the solar curve is the primary strategy. For commercial customers with large tariff differentials, a hybrid approach combining solar charging with off-peak grid charging makes sense.
When advising customers on expected yield, always use the PSH figure for their specific region. A system in the North will produce roughly one-third less energy than the identical system in the South, so yield expectations and payback calculations must differ accordingly. Quoting southern-level output to a northern customer is the fastest way to create disappointment.
The PSH definition as the daily irradiance integral divided by the standard reference intensity is drawn from inverter.com and SurgePV. Regional PSH and annual yield figures are based on the World Bank and ESMAP data via Global Solar Atlas: North approximately 3.3 to 3.5 hours, Central 4.0 to 4.3, South 4.4 to 4.8; seasonal variation in the North falling to 2 to 2.5 hours per Energypedia. The charge–discharge priority schedule follows Firstgreen Consulting. The northern-region correction was added based on the verification finding.