Rooftop Performance and Electricity
What Happens to Solar Electricity You Do Not Use?
Follow self-consumption, grid export and the value of an exported unit.
A real system shows a symptom related to “What Happens to Solar Electricity You Do Not Use?”, and you need to find the cause before replacing parts or changing settings.
Trace solar electricity through on-site loads, batteries, grid export or curtailment, then separate physical energy flow from policy-dependent billing credit.
- Select or check first
- Use it on site. Flexible loads that operate while solar is available can increase self-consumption, if running them then is safe, useful and permitted.
- Controlling assumption
- Irradiance, weather, module construction, wiring, orientation and measurement boundary match the case being discussed.
- Top risk
- Do not assume another state's rule applies. Capacity eligibility, meter type, application sequence, accounting period, credit rate, carry-forward, settlement and technical settings can differ by jurisdiction and can change.
- Proof
- Curtail it. A zero-export control, grid instruction, inverter limit or full battery may cause the inverter to reduce production instead of sending surplus outward.
Start with the basics Optional foundation before “What Happens to Solar Electricity You Do Not Use?”
Solar-energy basics
These terms separate what sunlight supplies, what a photovoltaic system converts and what a meter finally records.
- Power and energy
- Power is the instantaneous rate of using or producing energy, measured in watts. Energy accumulates over time and is commonly measured in watt-hours or kilowatt-hours.
- Irradiance
- Irradiance is solar power arriving per unit area, usually expressed in watts per square metre. It is an input condition, not the same thing as electrical output.
- Voltage and current
- Voltage is electrical potential difference; current is the rate of electric charge flow. Their product gives electrical power for a DC operating point.
- Cell, module and string
- A cell is one photovoltaic device, a module connects many cells, and a string connects modules in series. A limitation at one level can affect the others through the wiring.
- Rated versus real output
- Nameplate values come from defined test conditions. Real output changes with sunlight, temperature, angle, shading, wiring, conversion losses and ageing.
How to use this article: Before using a number, identify whether it describes sunlight, DC module output, inverter output or billed energy, and record the time and weather boundary.
On this page
Solar electricity is not automatically saved for later. At each moment, the inverter supplies the connected electrical system according to available sunlight, equipment limits and control settings. Energy can serve loads on the premises, charge compatible storage, flow through an approved meter to the grid, or be curtailed. Which path is available—and how it appears on the bill—depends on the physical design and the current metering agreement.
What happens at one instant
Consider a grid-connected system without a battery. If the building is using more power than the PV system is producing, all available solar power is consumed on site and the grid supplies the balance. If generation and load are equal, net exchange at the meter is approximately zero. If generation exceeds the coincident load, the surplus can flow outward—provided the interconnection and inverter settings permit export.
Instantaneous power balance without storage
self-use = min(Psolar, Pload); export = max(Psolar − Pload, 0); import = max(Pload − Psolar, 0)
This simplified balance assumes one connection point, no battery, no generator, negligible losses and permission to export. Real meters integrate energy over time and may record import and export in separate registers.
- Psolar
- available AC solar power behind the meter
- Pload
- simultaneous site load at the same electrical boundary
- import/export
- net power direction at the utility connection
With 5 kW solar and 3 kW load, about 3 kW is self-used and 2 kW is available for export. One hour at those steady values would correspond to about 3 kWh self-used and 2 kWh exported.
Diagram description
Yellow arrows carry solar generation toward the home's appliances and meter. A bidirectional meter stands between the house and utility network. A green arrow points from the premises toward the grid for export, while a blue arrow points from the grid toward the premises for import.
Once exported, the electrical energy joins the distribution network. It is not held in a personal grid account as identifiable electricity waiting to return. The account is a billing record. Nearby network demand may consume the energy physically, while the meter data and applicable rules determine the financial offset or credit.
Four possible destinations for a surplus
- Use it on site.Flexible loads that operate while solar is available can increase self-consumption, if running them then is safe, useful and permitted.
- Store it.A compatible battery system can absorb some surplus within its power, energy, state-of-charge, temperature and control limits, with conversion losses.
- Export it.An approved grid-connected system can record outward energy through the required metering and settle it under local rules.
- Curtail it.A zero-export control, grid instruction, inverter limit or full battery may cause the inverter to reduce production instead of sending surplus outward.
Net metering, net billing and gross metering
India's National Portal for Rooftop Solar describes several arrangements. Under net metering, on-site generation serves the consumer and a bidirectional meter records import and export; the billing-period method offsets eligible energy according to the applicable rules. Under net billing, surplus export is generally purchased at a predetermined tariff instead of being carried forward in the same way. Under gross metering, the rooftop plant's generation is separately delivered to the grid and paid at an approved rate.
| Arrangement | How energy is commonly recorded | What must be checked |
|---|---|---|
| Net metering | Import and export are recorded and offset over the specified accounting period | Eligibility, capacity limit, carry-forward, settlement, fixed charges and year-end treatment |
| Net billing | Import is billed and eligible surplus export receives a defined purchase credit | Export rate, billing period, taxes, adjustments and whether credits can roll forward |
| Gross metering | Generation for sale and consumer import are separately metered | Approved generation tariff, contract term, meter boundary and auxiliary consumption |
| Zero export | Controls attempt to keep outward flow at or below the permitted limit | Response time, meter placement, failure mode, commissioning test and residual tolerance |
Diagram description
Solar modules feed a lit home with refrigerator, washing machine, television and air conditioner. The remaining yellow flow reaches a bidirectional meter, then a green arrow continues to transmission towers. Separate labels identify lower grid imports, surplus export and a possible credit.
Why one self-used unit and one exported unit can have different values
A self-used kWh can avoid an import that would otherwise have been billed. Its value therefore depends on which energy charge, slab or time band is actually avoided; it may not avoid fixed charges. An exported kWh receives the credit specified by the applicable arrangement. If the export credit is lower than the avoided marginal import charge, increasing useful daytime consumption can be more valuable than exporting—but only when that consumption represents a real need rather than waste.
Separate energy value by destination
Value = Σ(self-used kWhₜ × avoided import rateₜ) + Σ(exported kWhₜ × export creditₜ)
The rates can depend on slabs, time periods and settlement rules. This expression omits fixed costs, taxes, battery losses, degradation and operating expenses, which belong in a full financial model.
- self-used kWhₜ
- solar energy coincident with eligible site load in interval t
- avoided import rateₜ
- marginal import energy charge actually avoided in that interval
- exported kWhₜ
- eligible outward energy recorded in interval t
- export creditₜ
- credit assigned by the approved arrangement
If 100 kWh is self-used and 40 kWh is exported, calculate the two terms separately. A project should not price all 140 kWh at the headline retail rate unless the tariff explicitly produces that result.
Diagram description
The left panel states that directly used solar offsets a grid purchase and can reduce the bill. The right panel states that exported energy is settled under applicable rules and commonly receives a lower value. A central home and meter illustrate the two paths, while a footer says local regulations control.
Can a battery make every surplus unit more valuable?
A battery can shift some midday energy to a later load or provide configured backup, but it does not create free value. Charging and discharging lose energy; usable capacity declines over life; power limits can leave some surplus unstored; and equipment, installation and replacement have costs.
Evaluate the value difference between charging and the next-best destination, then subtract conversion loss, degradation cost and operating constraints. A low export credit alone does not prove that storage has a good payback.
What changes during a grid outage
A normal grid-following rooftop inverter is designed to stop energizing the grid when required grid conditions are absent. Anti-islanding protection reduces danger to utility workers and equipment. Solar panels being in sunlight therefore does not mean ordinary sockets stay powered during an outage. Backup operation requires a system specifically designed, isolated, controlled and approved for that mode, commonly with compatible storage and protected backup circuits.
Evidence to collect before changing the system
- 1. Export interval data.Collect synchronized generation, load, import and export readings instead of relying only on monthly totals.
- 2. Read the agreement.Confirm the exact metering arrangement, approved capacity, accounting period, export rate and settlement rules.
- 3. Identify curtailment.Separate low solar resource from inverter limits, grid outages, export caps, battery limits and zero-export control.
- 4. Map flexible loads.Move only useful, controllable demand that can operate safely during the solar window.
- 5. Model alternatives.Compare export, load shifting, storage and generation changes with the same interval data and conservative assumptions.
To reconstruct the rupee impact rather than guessing from units, use From Electricity Units to a Real Solar Bill. To understand how shade and temperature can change the available energy before it reaches any destination, read Why Shade and Heat Reduce Solar Output.
One-minute questions
Questions to answer before you apply this lesson
What should I select or check first for What Happens to Solar Electricity You Do Not Use?
Use it on site. Flexible loads that operate while solar is available can increase self-consumption, if running them then is safe, useful and permitted.
Which assumption can change the conclusion?
Irradiance, weather, module construction, wiring, orientation and measurement boundary match the case being discussed.
What can go wrong if I copy the example directly?
Do not assume another state's rule applies. Capacity eligibility, meter type, application sequence, accounting period, credit rate, carry-forward, settlement and technical settings can differ by jurisdiction and can change.
How do I verify the result in the real system?
Curtail it. A zero-export control, grid instruction, inverter limit or full battery may cause the inverter to reduce production instead of sending surplus outward.
Sources and further reading
- FAQ: Grid Connected Solar Rooftop SystemNational Portal for Rooftop Solar, Ministry of New and Renewable Energy, Government of India · 2026-10-12Reviewed for the portal's descriptions of self-consumption, bidirectional metering, net metering, net billing, gross metering and the persistence of some fixed charges.
- RegulationsDelhi Electricity Regulatory Commission · 2026-10-12Reviewed to confirm that net-metering rules and amendments are jurisdiction-specific and dated; the article deliberately gives no universal capacity or credit rate.
- Draft Model Regulation for Grid Interactive Distributed Renewable Energy SourcesForum of Regulators via the National Portal for Rooftop Solar · 2026-10-12Reviewed for example technical provisions covering metering arrangements, safe operation, anti-islanding and prevention of grid backfeed during loss of supply.
- Solar Integration: Inverters and Grid Services BasicsU.S. Department of Energy · 2026-10-12Reviewed for the general behavior of grid-following household inverters during significant voltage or frequency disruption.
- Solar and Resilience BasicsU.S. Department of Energy · 2026-10-12Reviewed for the distinction between ordinary grid-connected PV and a properly configured solar-plus-storage system capable of serving protected loads during an outage.