Solar Curtailment in Thailand: Too Much Solar for the Grid

Thailand keeps setting electricity records. The country’s demand peak in 2025 hit 34,620.4 megawatts at 8.48 pm on 24 April (Nation Thailand). Look at that timestamp again. It’s night. Every solar panel in the country was producing nothing at the exact moment the grid strained hardest.

That mismatch is the whole story behind solar curtailment — the deliberate throttling of clean power that a grid can’t absorb. It sounds absurd. Perfectly good electricity, switched off. But it’s happening in California, in China, in Germany, and it’s coming for Thailand as rooftop and utility-scale arrays multiply. Here’s why excess solar sometimes can’t be used, and what’s actually being done about it.

TL;DR: Solar curtailment means switching off working panels because the grid can’t use their output. California’s operator curtailed 3.4 million MWh in 2024, and solar was 93% of it (U.S. Energy Information Administration)(U.S. Energy Information Administration). Thailand’s risk is structural: its demand peaks after dark, so midday surplus has nowhere to go without storage.

What Is Solar Curtailment, and Why Does It Happen?

Curtailment is a grid operator ordering generators to produce less than they physically can. California’s grid operator curtailed 3.4 million megawatthours of utility-scale wind and solar output in 2024, a 29% jump over the previous year (U.S. Energy Information Administration)(U.S. Energy Information Administration). Solar accounted for 93% of it (U.S. Energy Information Administration). The cause isn’t broken equipment. It’s arithmetic.

Electricity grids must balance supply and demand second by second. Push in more power than customers draw, and frequency rises, equipment trips, and the system risks collapse. When midday sun floods a network that already has coal, gas, and hydro plants running, something has to give. Solar gives, because it’s the cheapest thing to switch off.

There are two flavours worth separating. Economic curtailment happens when power is technically usable but nobody will pay for it — prices go negative, so generation gets dialled back. Grid-constraint curtailment happens when transmission lines physically cannot carry the electrons from where they’re made to where they’re needed. Thailand faces both, in different provinces, for different reasons.

The distinction matters because the fixes differ. Economic curtailment is solved with contracts, markets, and storage. Grid-constraint curtailment needs copper in the ground.

Why Does Thailand Peak After Dark?

Thailand’s demand curve is unusual, and it’s the single biggest reason curtailment looms. The 2025 peak of 34,620.4 MW landed at 8.48 pm (Nation Thailand). The all-time record, 36,792.1 MW, was set at 10.24 pm on 2 May 2024 (Nation Thailand). The March 2025 peak of 33,658.3 MW followed the same nocturnal pattern (Nation Thailand).

The pattern nobody talks about: Thailand’s three most recent demand records were all set between 8 pm and 11 pm — hours when solar output is exactly zero. A country whose grid strains at night has no natural home for a midday solar surplus.

Why so late? Air conditioning. Concrete and asphalt hold heat long after sunset, so Thai households run cooling hardest in the evening. Add returning commuters, cooking, water heating, and increasingly EV charging, and the load stacks up after the sun has gone.

Compare that to a solar generation curve, which arcs from roughly 7 am, tops out near noon, and collapses by 6 pm. The two curves barely overlap at their extremes. Solar shaves the afternoon shoulder nicely — it just isn’t there when the system needs it most.

That’s not an argument against solar power. It’s an argument for pairing it with something that can move energy across a few hours.

How Much Solar Does Thailand Actually Have?

Thailand’s cumulative installed PV capacity reached 9,942 MWp (IEA-PVPS). That splits into 6,334 MWp of ground-mounted plants, 3,310 MWp of rooftop systems, and 281 MWp of floating solar (IEA-PVPS)(IEA-PVPS)(IEA-PVPS). Roughly a third of the fleet now sits on rooftops — distributed across millions of connection points the grid operator cannot individually dispatch.

Our breakdown of Thailand’s rooftop solar programme covers who can join the current buyback quota.

That rooftop share is what changes the problem. A utility-scale farm can be told to throttle back. Ten thousand houses with 5 kW inverters cannot — not without smart inverter standards and communication infrastructure that Thailand is still building out.

The trajectory adds pressure. Under a progressive scenario modelled by the International Energy Agency, variable renewables reach a 15% share of Thai generation by 2030 (International Energy Agency). That share is where curtailment stops being theoretical in most power systems.

So is Thailand already curtailing at scale? Not publicly, not yet, and that’s an important honesty check. There’s no published national curtailment statistic the way California publishes CAISO data. What exists is the structural setup that produces curtailment everywhere else it’s appeared.

The Real Bottleneck Isn’t Panels — It’s Gas Contracts

Here’s the part that surprises people. Thailand’s curtailment risk is written into fuel contracts, not into physics. Thai gas supply agreements carry minimum-take obligations of 65% of capacity during off-peak hours, according to the IEA’s power system flexibility study (International Energy Agency).

Minimum-take means the buyer pays for the gas whether or not it burns it. So the economically rational move is to burn it — which means gas plants keep running through the middle of the day, occupying grid space that solar could otherwise fill. When consumption is too low to absorb both the contractual minimum and the renewables, the renewables get curtailed.

The counterintuitive bit: Thailand’s first big curtailment events are more likely to be contractual than physical. The wires can carry the power. The paperwork says a gas turbine has first claim on the space.

The upside is that contracts are easier to renegotiate than transmission corridors are to build. Agora Energiewende puts the overall economic benefit of a more flexible Thai power system at about 3.48 billion USD over 20 years (Agora Energiewende). That’s the prize for fixing minimum-take terms, plant cycling limits, and dispatch rules — before spending a satang on new cable.

EGAT has acknowledged the issue directly, saying it is updating Power Purchase Agreements to manage renewable curtailment with clear rules and fair compensation. Clear rules matter enormously to project developers. Unpriced curtailment risk raises the cost of capital for every solar project in the country.

What Is Thailand Doing About Excess Solar?

The headline answer is energy storage, and the gap between plan and reality is wide. Thailand’s Power Development Plan 2024 targets 10,485 MW / 26,010 MWh of battery storage by 2037 (Energy-Storage.News). EGAT’s operational grid-scale battery storage today amounts to a 16MW system in Chaiyaphum and a 21MW system in Lopburi (Energy-Storage.News)(Energy-Storage.News).

Do the division: those two flagship batteries add up to about 37 MW against a 10,485 MW target. Thailand has built roughly a third of one percent of the battery storage its own plan says it needs by 2037.

Batteries aren’t the only lever. Pumped-storage hydropower shifts bulk energy across hours by pumping water uphill at midday and releasing it at night — a good match for a country whose peak lands at 10 pm. EGAT is also expanding hydro-floating solar, with plans for over 2,725 MW across nine major dams (Enlit Asia (EGAT interview)). Siting solar at existing hydro nodes is quietly clever: the grid connection already exists, and the dam’s turbines can smooth the solar output on site.

Demand-side measures round it out. Time-of-use tariffs that reward midday consumption, EV charging shifted to daylight hours, and industrial cooling pre-loaded before the evening — these move demand to the sun rather than moving the sun to demand.

The honest summary? The plan is coherent. The build rate isn’t there yet.

What Does Curtailment Mean for Your Rooftop System?

For homeowners, curtailment shows up as a slow erosion of export value rather than a dramatic shutoff. Thailand’s residential net billing round buys surplus rooftop output at 2.20 THB/kWh (Green Energy Thailand canonical Thai facts), with the national round capped at 500 MW on a first-come, first-served basis (Green Energy Thailand canonical Thai facts). Once that quota fills, exporting stops being a guaranteed option.

That reframes the design question. If export is capped, low-value, or uncertain, the kilowatt-hour you consume yourself is worth roughly twice the one you sell. System sizing should follow your daytime load, not your roof area.

Three practical implications:

• Size to self-consumption. A smaller array you fully use beats a larger one you export at 2.20 THB/kWh.
• Consider battery storage. Shifting a few midday kilowatt-hours into the evening captures the marginal retail rate instead of the buyback rate.
• Check export rules before you sign. Some commercial and industrial connections in saturated areas require zero-export or limited-export controllers.

Does this mean rooftop solar is a bad deal? No. It means the economics now favour self-use over export, which is a different optimisation than the one installers pitched five years ago. Related: on-grid solar system.

Frequently Asked Questions

Is Thailand currently curtailing solar power?

There’s no published national curtailment figure for Thailand comparable to California’s, where 3.4 million MWh was curtailed in 2024 (U.S. Energy Information Administration). What’s documented is the structural setup — night-peaking demand and 65% off-peak gas minimum-take obligations (International Energy Agency) — that produces curtailment in other systems.

Does curtailment affect residential rooftop solar?

Not directly at present. Residential systems under the 500 MW net billing round export at 2.20 THB/kWh (Green Energy Thailand canonical Thai facts)(Green Energy Thailand canonical Thai facts). The practical effect is quota scarcity and low export value rather than forced shutdowns. Commercial rooftops in saturated grid areas more often face export limits.

How does battery storage reduce curtailment?

Storage absorbs midday surplus and releases it during Thailand’s evening peak, which hit 34,620.4 MW at 8.48 pm in April 2025 (Nation Thailand). That’s the exact time-shift curtailment demands. Thailand’s PDP 2024 targets 10,485 MW of battery storage by 2037 to do this at national scale (Energy-Storage.News).

Why don’t grid operators just build more transmission lines?

Transmission helps with location-based constraints but not with timing ones. If the whole country has surplus at noon and deficit at 9 pm, more wire moves the problem sideways. That’s why the IEA’s flexibility work values contract reform and storage at roughly 3.48 billion USD in benefits (Agora Energiewende).

Will curtailment make solar a worse investment in Thailand?

For self-consumption-focused systems, no. For export-dependent ones, the risk is real. Rooftop capacity has already reached 3,310 MWp (IEA-PVPS), and the more distributed generation competes for the same midday window, the more the value shifts toward energy you use on site.

The Bottom Line

Solar curtailment isn’t a sign that Thailand has too much solar. It’s a sign the grid was built for a different shape of supply.

• Thailand’s demand peaks at night — 34,620.4 MW at 8.48 pm in April 2025 (Nation Thailand) — while solar peaks at noon.
• Curtailment elsewhere is overwhelmingly a solar problem: 93% of California’s 2024 curtailment (U.S. Energy Information Administration).
• The near-term Thai constraint is contractual, with 65% off-peak gas minimum-take obligations crowding out midday renewables (International Energy Agency).
• The fix is energy storage plus flexible dispatch, worth an estimated 3.48 billion USD over 20 years (Agora Energiewende) — but operational batteries are still a rounding error against the 10,485 MW target (Energy-Storage.News).

For homeowners the takeaway is simpler. Design for what you use, not for what you can sell. That advice holds whether or not curtailment ever makes the evening news.