Answer
Solar self-consumption rate is the share of PV generation used on site. Without storage, divide solar used on site by total PV generation and multiply by 100. Self-sufficiency divides by site consumption instead. Use the same period and meter boundaries, and track battery losses and charging source separately.
A production total tells you how much electricity the PV system generated. It does not tell you how much the building used, how much it imported later, or whether a battery improved the result. This calculation guide separates those questions before assigning a percentage.
Last updated: November 2026.
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Self-consumption and self-sufficiency answer different questions
| Metric | Question | Denominator |
|---|---|---|
| Solar self-consumption | What share of generated PV energy is used on site? | PV generation |
| Solar self-sufficiency | What share of site demand is supplied by solar? | Site consumption |
| Annual generation-to-load ratio | How large is annual generation relative to annual consumption? | Site consumption, without matching timing |
The IEA PVPS methodology report (T1-28:2016) distinguishes self-consumption from self-sufficiency. It is useful for that conceptual distinction; it is not a current tariff directory.
“Solar fraction” can refer to a demand-coverage measure in some reports. Ask for the equation and system boundary instead of assuming that every software label means the same thing. Here, self-sufficiency means the fraction of electrical site load supplied by PV, not independence from the grid during outages.
A small system can use nearly all its output on site while supplying only a small share of a large building’s demand. A larger system may cover more demand but export more surplus, reducing its self-consumption percentage. Compare the energy amounts alongside both ratios.
Formula for a system without storage
Use kilowatt-hours measured at compatible boundaries over the same period. In a simple PV-and-grid system with no battery or other generator:
S = PV energy used directly on site
G = PV generation
X = exported PV energy
I = imported grid energy
L = total site consumption
G = S + X
L = S + I
Self-consumption (%) = 100 × S / G
Self-sufficiency (%) = 100 × S / LIf the metering arrangement supports these balances, calculate S = G − X and L = S + I. Do not use grid imports as total consumption: imports exclude the solar already used behind the meter. Nor should exported energy be counted as energy physically supplied to the building just because it earns a bill credit.
Worked example using annual meter totals
These are hypothetical quantities, not a named customer case or a measured SurgePV project:
| Quantity | Energy |
|---|---|
| PV generation | 6,760 kWh |
| Exported PV energy | 3,650 kWh |
| Grid imports | 2,840 kWh |
| Direct onsite solar use | 6,760 − 3,650 = 3,110 kWh |
| Total site consumption | 3,110 + 2,840 = 5,950 kWh |
Self-consumption is 3,110 ÷ 6,760 × 100 = 46.0%. Self-sufficiency is 3,110 ÷ 5,950 × 100 = 52.3%. The two percentages describe different shares of the same 3,110 kWh.
- Annual example: self-consumption46%
- Annual example: self-sufficiency52.3%
- Interval example: self-consumption50%
- Interval example: self-sufficiency40%
Source: arithmetic from the two worked examples in this post, checked November 2026.
Key Takeaway: Pick the Denominator First
Self-consumption asks how much of the solar output you used. Self-sufficiency asks how much of your demand solar covered. State which one a report uses before comparing percentages across tools or proposals.
Annual measured flows give an annual balance for the stated system. Annual generation and annual load alone cannot give one: without exports, imports or time-matched data, the overlap remains unknown.
Estimate the overlap from time-matched profiles
For a simplified interval model without storage, calculate the solar/load overlap separately in every interval, then sum the energy flows. Do not apply the minimum function to the annual totals.
For each interval t:
S[t] = min(G[t], L[t])
X[t] = G[t] − S[t]
I[t] = L[t] − S[t]
Period self-consumption = 100 × sum(S[t]) / sum(G[t])
Period self-sufficiency = 100 × sum(S[t]) / sum(L[t])This is an interval-net model. Shorter intervals can reveal changes hidden by coarse averages; solar and load can switch within a half-hour interval. If measured import and export flows are available, reconcile those records rather than assuming the minimum of coarse interval totals equals physical direct use.
A three-interval illustration
Each row below represents a half-hour and contains energy in kWh, not instantaneous power in kW.
| Interval | PV generation | Site load | Direct solar | Export | Import |
|---|---|---|---|---|---|
| 1 | 1 | 2 | 1 | 0 | 1 |
| 2 | 3 | 1 | 1 | 2 | 0 |
| 3 | 0 | 2 | 0 | 0 | 2 |
| Total | 4 | 5 | 2 | 2 | 3 |
The modeled self-consumption is 50%, and self-sufficiency is 40%. Taking the minimum of period totals would wrongly assign 4 kWh to direct use; the modeled time overlap is only 2 kWh.
If the source file instead contains interval-average power, convert it to energy. For example, 2 kW averaged over 30 minutes = 1 kWh. A single instantaneous power reading does not tell you the energy consumed during the whole interval.
Check the data before trusting a percentage
The Australian Government’s solar monitoring guidance distinguishes monitoring data and electricity-bill information. An export payment on a bill does not show all the savings from solar used directly.
Before calculation, check:
- Production, load, import and export records cover the same dates and complete intervals.
- Timestamps use the same time zone and account for daylight-saving changes, duplicate times and gaps.
- Power and energy units are identified; import/export signs are consistent.
- Generation is measured at the stated boundary, rather than mixing modeled DC module output with measured AC exports.
- Site load includes behind-the-meter consumption and any excluded loads are documented.
- Missing values remain missing until an estimation method is recorded; they are not silently converted to zero.
- The meter topology, other generation and any battery are identified.
For incoming load data, see consumption profile import. A calculated negative direct-use value or a ratio above 100% is a reason to investigate boundaries and data, not to clip the result and call it verified.
Pro Tip: Reconcile Before You Report
Before quoting a percentage, check that generation equals direct use plus exports and that consumption equals direct use plus imports. If either balance fails by more than your meter tolerance, fix the data first.
If generation is zero, self-consumption is undefined. If load is zero, self-sufficiency is undefined. Report those results as unavailable and explain the denominator, rather than inventing a percentage.
See generation and financial modeling on your own numbers
Load your production and consumption inputs and compare system sizes on one project.
Book a DemoChecking cost first? See the SurgePV pricing page.
Batteries require an energy ledger
Storage can move solar to a later time, but energy entering a battery is not identical to energy delivered to site loads. The Australian Government’s battery overview explains storage capacity and charging/discharging power as distinct quantities. Neither capacity alone nor an assumed percentage tells you what outcome is achievable.
Consider this hypothetical energy ledger at consistent AC boundaries, with solar-only charging, no battery export and unchanged stored energy between the start and end of the period:
| Energy flow | Quantity |
|---|---|
| PV generation | 12 kWh |
| Direct PV to site loads | 4 kWh |
| PV charging the battery | 6 kWh |
| PV export | 2 kWh |
| Battery discharge to site loads | 5 kWh |
| Storage-path losses | 1 kWh |
| Site consumption | 9 kWh |
| Grid imports | 0 kWh |
The PV balance is 12 = 4 + 6 + 2. The storage balance is 6 = 5 + 1. Useful PV energy delivered to loads is 4 + 5 = 9 kWh, or 75% of generation. It supplies 100% of the stated 9 kWh load.
But generation minus exports is 10 kWh, or 83.3% of generation. That counts the energy absorbed by the storage path, including its loss; it is not the same useful-load metric. State which convention the calculator uses.
Real systems also need beginning and ending stored energy, auxiliary consumption and the source of charging energy. Grid-charged discharge cannot automatically be labeled solar self-sufficiency. DC-coupled systems need boundaries appropriate to their actual topology. Do not combine production-side and load-side figures without identifying losses between them.
Test improvements without promising an outcome
Compare a measured or documented base case with an alternative using the same weather, production and load basis. Flexible loads may be moved to periods with available surplus, provided the timing suits the household or business and equipment constraints.
Do not assign every home a fixed daytime window or an automatic improvement from EV charging. Check when the vehicle is present, the surplus available, charging limits and the energy it needs. Heating and cooling schedules must also respect comfort and equipment requirements.
For storage, model usable energy, charging and discharge limits, losses, reserve settings and dispatch. Retain grid imports and useful energy delivered, not just the self-consumption headline. Buying a larger battery solely to increase a percentage does not prove economic value.
Keep physical ratios separate from bill savings
Bill credits do not change when electricity physically enters or leaves the site. Actual import and export prices, timing and usable credit rules determine financial value. A higher self-consumption ratio may also result from a smaller system, with less total useful generation.
Use the net-metering savings inputs guide for the bill comparison and the state and country source directory to locate relevant authorities. This article supplies a calculation framework, not a current policy or country-benchmark table.
Solar professionals can evaluate the generation and financial workflow using their own load and production records. A demonstration can help assess which inputs and reports suit the project. No particular battery gain or customer savings is promised here.
Methodology and limitations
SurgePV publishes this guide as a solar software provider. The examples are arithmetic illustrations with explicit system boundaries, not first-hand customer measurements or country averages. The IEA PVPS source informs terminology; government monitoring and battery guidance inform the data questions. No tariff rates, national benchmark percentages or guaranteed payback are claimed. The IEA PVPS report was re-read in November 2026. The Australian Government pages were cited from the September 2026 review.
Frequently Asked Questions
How do you calculate solar self-consumption?
For a system without storage, divide PV energy used on site by total PV generation over the same period, then multiply by 100. PV generation minus exported PV energy gives onsite use only when the measurement boundaries and energy flows support that balance.
What is the difference between self-consumption and self-sufficiency?
Self-consumption divides onsite solar use by PV generation, while self-sufficiency divides solar energy supplied to site loads by total site consumption. The same onsite solar amount gives different percentages because the denominators differ.
Does matching annual solar generation to consumption mean 100% self-sufficiency?
No. Equal annual totals do not show whether generation and consumption coincide. The site can export during sunny periods and import at other times, so the timing of both profiles matters.
Can I use generation minus exports when a battery is installed?
Not as a complete measure of useful solar energy delivered to loads. Battery losses, changes in stored energy, grid charging and battery exports change the balance. Record those flows and define whether the metric counts energy entering storage or energy delivered from it.
What is a good self-consumption percentage?
There is no universal target for every building or country. Judge the result alongside production, consumption, grid imports, export terms, equipment costs and operating constraints. A higher percentage alone does not make a better investment.
What should a calculator report when solar generation is zero?
The self-consumption ratio is undefined when its generation denominator is zero. Show it as unavailable rather than dividing by zero or claiming 100%. Other metrics need their own denominator checks.
How do I calculate self-consumption from interval data?
Calculate the overlap in every interval as the smaller of generation and load, then sum those values over the period and divide by total generation. Do not apply the minimum function to annual totals, because that overstates direct use.
Where this fits
This article is part of SurgePV's Solar Design hub, which works through the topic from first principles to the decisions a project team actually has to make.
