Rooftop Solar in Vietnam: Questions to Ask an Installer

Rooftop solar in Vietnam no longer comes with a guaranteed high price for the power you sell back, so the contract you sign matters more than ever. Before you accept any quote, get clear answers on six things: your roof, the inverter, the warranties, the grid connection, who buys your extra power, and how the payback is worked out. This guide gives you the questions to ask.

Why the old rules no longer apply

From 2017, the government offered 20-year fixed prices for new solar projects. One large farm in Ninh Thuan was paid 9.35 US cents per kWh. That scheme set off a building boom. Total solar capacity reached about 16,500 MW by 2020, far above the official target of 850 MW.

The last tariff round for solar ended in 2020. As of May 2022, reporters found that the government had not yet issued a replacement price. Government checks found that some rooftop panels in the south were connected after the deadline, and projects finished after it could not sell their power. So do not trust any installer who quotes you the old tariff as if it still applies. Ask for the rule in writing and the date it was checked.

Sources: Al Jazeera, "After renewables push, Vietnam has too much energy to handle" (May 18, 2022), https://www.aljazeera.com/economy/2022/5/18/after-renewables-push-vietnam-has-too-much-energy-to-handle.

Questions about your roof

A good install starts with the roof, not the panels. Ask who will visit the site and what they will check. A quote made from a satellite photo alone is a guess.

• How old is my roof, and will it last as long as the panels?
• Has someone checked that the structure can carry the extra weight, and the wind load in typhoon season?
• How much shade will fall on the panels at different times of day?
• Who fixes the roof if a leak starts near a mounting point?

Ask for a drawing that shows where each panel will sit. Keep it with your contract.

Questions about the inverter

The inverter turns the panels' direct current into the power your building uses. It is often the first part to fail. Ask for the brand and model by name, and read the spec sheet before you sign.

• What is the inverter's rated size compared with the panel total?
• Is it built for hot, humid weather, and what is its dust and water rating?
• Can I see its output on a phone or computer, and who has the login?
• If it fails, who replaces it, how fast, and who pays for the labor?

Questions about warranties

There are usually several separate warranties. The panel maker covers the panel itself and how much power it still makes after many years. The inverter maker covers the inverter. The installer covers the work. Ask for each one on paper, and compare the years against the spec sheets that come with the equipment.

Also ask what happens if the installer closes its business. A warranty is only useful if someone is still there to honor it. Ask whether the maker's warranty stays valid when a different company does the repair.

Questions about the grid link

Grid limits are a real issue. In 2022, some operators in the south lost a large share of their output because the power lines could not carry all the solar power at peak times. One supermarket manager told reporters he lost about 40 percent of output when panels had to be switched off for several days each month.

• Will my system be connected to the grid, or only supply my own building?
• Who applies to the power company, and who pays any fees?
• Will the power company buy my extra power, and at what price and on what terms?
• Could my panels be switched off by the grid operator, and how often?

If you do not plan to sell power, ask about a design that only covers your own use. It is simpler, and you do not depend on a buyer.

Sources: Al Jazeera, May 18, 2022 (link above).

Questions about payback

Payback is the time it takes for your power savings to cover the cost. Ask the installer to show the math, step by step, not just a final number.

• What price per kWh did you assume for my power bill, and where did it come from?
• How much power do you expect per year, and on what weather data?
• Does the estimate include the cost of cleaning, repairs and a new inverter?
• What if I sell no extra power at all? Show me that case.

Build the case on power you use yourself. It is the safest number because it does not depend on a future government price. Treat any promise of fast, guaranteed returns with caution.

Before you sign

Ask three installers for quotes and put the answers side by side. Ask each for two past customers you can call. Check that the quote names every part, lists every warranty, and states what happens if the grid rules change.

This is general information, not financial or legal advice. Check current rules with the power company before you commit.