Solar curtailment — and how to avoid it

Watch the solar curtailment explainer

Why prices go negative, what curtailment really means, and how Jousto’s “use it first” approach works across three EMS layers.

Want to see how the market moves in real time? Use our tracker: NEM spot energy price tracker.

What is solar curtailment?

Solar curtailment is when your system reduces export (and sometimes generation) because exporting has become constrained or low value. In a negative-price window, exporting may be worth little — and on some plans, it can be actively undesirable.

Curtailment: instead of exporting freely, your export is reduced or limited when conditions make export low value.

Why it’s happening more

• Rooftop solar has grown rapidly.
• Midday demand can be low while solar supply is high.
• Network constraints can limit exports locally.
• Negative prices are more common in high-solar periods.

The takeaway: it’s not that solar is bad — it’s that we need smarter ways to use and route excess energy.

Why prices go negative (the “sun tax” story)

In the NEM, prices are set in short intervals and reflect supply vs demand. When solar supply surges and demand isn’t there to absorb it, the price can fall sharply — sometimes below zero. That’s why “dumping” solar to the grid isn’t always a win anymore.

What this means for solar owners

• Export can be low value at midday.
• Negative prices create new incentives.
• The best outcome is using energy on-site or routing value to where it’s needed.

Jousto ethos: use the energy first — treat curtailment as a last resort.

Negative price windows typically occur in high-solar, low-demand periods.

Use the energy first — don’t dump it by default

If the market is paying very little (or negative) for export, the highest-value move is often to use the energy locally: charge a battery, run flexible loads, heat water, or pre-condition HVAC. This is how you reduce curtailment — by reducing the need to export during the worst windows.

Priority order: use solar locally first, then store it — export comes last.

Typical “use it first” targets

• Battery charging in the solar window.
• Hot water and heat pumps (when applicable).
• EV charging.
• HVAC pre-cooling / pre-heating within safe comfort setpoints.
• Other discretionary loads that can shift.

Every site is different — that’s why we design around your actual load profile and tariff.

Three ways to handle excess solar

Jousto EMS is built around the same principle at every layer: monitor the system, automate safely, and optimise behaviour over time. Higher levels add more market awareness and smarter dispatch — but we always start with practical fundamentals.

Level 1: smart timing makes more solar useful on-site and reduces low-value export.

Level 2: peer-to-peer trading can route value to another region/buyer (where supported).

Level 3: Ampaura AI can control inverter/battery behaviour, including curtailment + arbitrage when appropriate.

Where most people should start

Level 1 is often the biggest and simplest win: shift consumption into the solar window and store what you can. Level 2 adds value transfer. Level 3 is for maximum optimisation once the fundamentals are solid.

Note: Features depend on your retailer plan, tariff, metering configuration, and compatible hardware.

Curtailment is a last resort

Continually turning generation up/down isn’t always ideal, and “wasting energy” feels wrong. That’s why Jousto’s default strategy is to reduce the need for curtailment — then curtail only when it’s the most sensible option for your system and your plan.

Our preference is to design systems that reduce curtailment — and only use it when it’s genuinely the best option.

What we optimise for

• Higher self-consumption of solar.
• Better battery utilisation.
• Less exposure to negative price windows.
• Stable, sensible control — not aggressive switching.

Jousto EMS is included with solar + battery (for now)

At present, Jousto EMS (including our solar curtailment and optimisation features where applicable) is offered as part of a solar + battery system purchased from Jousto. We’re not supplying EMS as a standalone product at this stage.

Solar + battery + Jousto EMS (included) — designed as a complete system.

Why we do it this way

Because curtailment and optimisation depend on the whole system working together: metering, inverter/battery compatibility, safety rules, and on-site loads. We prefer to design and support the complete outcome.

Next step: book a design session and we’ll map your curtailment risk and best options.

Book a free 30-minute energy design session

We’ll review your current setup (or planned solar + battery design), your tariff, and your exposure to negative price windows — then recommend the most sensible path: use it first, trade value where possible, and only curtail when it makes sense.