A key aspect in determining the feasibility of on-site solar for a given site is the anticipated solar array’s life-time return on investment (ROI). Meanwhile, the ROI for any solar array is heavily influenced by state net metering policies and the local electric utility’s solar array interconnection policies and tariffs. These considerations define the monetary value of the electricity that is produced and exported to the grid.

For solar arrays located in regions without full net metering, or arrays larger than what is allowed within the electric utility’s full net metering tariff limits, estimating the likely return on investment can be very challenging. To do so, an estimator has to determine how much of the array’s electricity will be exported to the grid and how much will be used on-site.

We decided to research this topic. Below is what we’ve found based on recent studies and resources.

Self-Consumption vs Exported Solar Electricity

Rooftop photovoltaic (PV) systems supply electricity to a building and can export excess generation to the grid. Self‑consumption (also called direct consumption) is the fraction of PV generation that is used within the building at the time it is produced. If only 30 % of PV production is self‑consumed, then 70 % of the electricity is exported to the grid[1]

Factors Influencing Self‑Consumption

Ratio of PV capacity to demand: Undersized systems (PV capacity smaller than the building’s demand) have high self‑consumption because generation seldom exceeds load. Oversized systems produce more energy than needed, so excess is exported[6]. The Dualsun example shows that small 500 W systems can self‑consume over 90 %[4], whereas a 3 kW system self‑consumes only ~30 %[7].
Load profile and daily schedule: Self‑consumption is higher when loads coincide with daylight hours. Commercial buildings open during the day achieve 50–80 % self‑consumption[10], while facilities with continuous loads (e.g., supermarkets) can reach ~100 %[12].
Demand‑side management: Using timers, smart appliances and behaviours to run energy‑hungry devices when PV is producing can raise self‑consumption to 50–60 % in homes[3][8].
Energy storage: Batteries store daytime generation for evening use, boosting self‑consumption to 65–80 % or higher[3][9].
Other factors: Orientation and shading affect generation patterns; however, the main determinant of self‑consumption is the relationship between system size and consumption[13]. Export tariffs and net‑metering policies also influence whether exporting is beneficial.

Resources for Further Study

1. Pylon Tech self‑consumption guide (renewables design) – Explains the concept of self‑consumption and provides recommended self‑consumption ranges for residential and commercial projects[1][2].

2. Dualsun – Self‑consumption and autonomy – Discusses how self‑consumption varies with PV system size, from small 0.5 kW to 3 kW installations, and presents measured data from French installations[7][5].

3. CRG Direct Solar – Maximising self‑consumption – Offers practical tips for households to increase self‑consumption through load shifting and battery storage[3].

4. European Commission policy brief – Energy self‑consumption – Summarises research on household self‑consumption across Europe, including the impact of demand‑side response and storage[9][10].

5. SMA Solar Technology – Self‑consumption potential in commercial settings – Analyses self‑consumption for different commercial load profiles (dairy farms, supermarkets, retail stores) and provides real examples showing self‑consumption ranging from 20 % to nearly 100 %[12][11].

These resources collectively illustrate how the majority of electricity from a typical residential rooftop PV system is exported to the grid unless the system is matched to the load, demand‑side measures are implemented, or storage is added.