This section presents results from metrics that are considered a priority when assessing the potential for rooftop spaces. It contains three sections: Installation, Financing and Environmental (and Social) Benefits.
The Installation section presents the selected area of the rooftop for installing solar PV panels, with annual production and annual consumption in kWh per single or multiple buildings per year.The Financing section presents the following relevant output metrics and considered models:
The Environmental (and social) benefits section presents fundamental indicators of the prospective positive impact that rooftop system installations may have on the environment (and society). Outputs in this section include: the estimated CO2, CO2e, PM and NOx emissions avoided; their equivalent carbon emissions that may be offset in terms of tropical trees planted and passenger cars taken off the streets; and jobs created resulting from PV installations.
Access tiers (scale 1–5)
Categories that define the electricity services available to household consumers in a location. The term was established by the World Bank’s Energy Sector Management Assistance Programme (ESMAP) and later adopted as a metric by the Sustainable Energy for All initiative (SEforAll). For more information see the Multi-Tier Access Framework.
Air pollutants avoided
Estimates of air pollutants (NOx [nitrogen oxides]; PM2.5 [particulate matter with a diameter of less than 2.5 micrometres]), and emissions avoided per year when sourcing electricity from rooftop solar PV rather than from alternatives (combustion processes), all of which are of great concern to human health.
(Total) annual consumption (kWh)
Amount of electricity used by selected household(s) per year.
Annual production (kWh)
Estimated electricity generated by the rooftop solar PV installation in one calendar year.
Financing model where the building owners or estate promoter intends to buy the system. Another model is the ‘lease model’, where the private or public investor intends to buy the system with a view to selling the electricity to neighbouring consumers, to the grid or (on off-grid sites) for storage.
Cars not driven
Equivalent number of passenger cars taken off the streets for one year when electricity is generated by a rooftop solar PV installation. A typical passenger vehicle emits about 4.6 metric tonnes (4,600 kg) of carbon dioxide per year (EPA, 2019). It has been used in SolarCity as an indicator only.
Equity internal rate of return (EIRR)
Measures the efficiency, quality or yield of the equity investment.
Greenhouse gases (GHGs) avoided (kg)
Estimates of greenhouse gases (CO2 [carbon dioxide]; CO2e [carbon dioxide equivalent]) emissions avoided per year when sourcing electricity from the rooftop solar PV system instead of alternatives (combustion processes). CO2e is a metric measure used to compare the emissions of various greenhouse gases (CO2, CH4 [methane], N2O [nitrous oxide], HFCs [hydrofluorocarbons], PFCs [perfluorocarbons], and SF6 [sulphur hexafluoride]) based on their 100-year global warming potential.
Cost of the solar PV system with or without a solar storage system. Estimates include shipment, taxes and installation.
Financing model where the private or public investor buys the solar PV system for a community and homeowners do not bear the cost of investing in the system. The investor will pay the annual rent to the homeowners and profit from: (i) selling part of the electricity to the consumers for their self-consumption; (ii) selling the excess electricity to the grid or storing it at a benchmark tariff; and/or (iii) claiming subsidies.
Length of time required to recoup the equity investment used to set up the rooftop solar PV system with or without storage.
PV capacity (kWp)
Total peak electrical capacity of the solar PV panels installed.
PV surface (m2)
Area of the rooftop surface covered with solar PV panels.
Revenue of electricity consumption
Revenue from the electricity consumption savings provided by the rooftop solar PV system compared to equivalent consumption from the grid.
Revenue of electricity in storage
Revenue of the electricity saved in storage for other consumption under the off-grid scenario.
Revenue of electricity sold to the grid
Revenue from selling the remaining electricity back to the grid under the on-grid scenario.
Revenue of generation and installation subsidies
Revenue from a subsidy scheme offered for installing rooftop PV systems. This includes generation and installation subsidies.
Self-consumption is defined as the ratio of the energy use from on-site generation to the total energy generated.
Measures cumulative revenue without a bank loan. This definition does not consider the time value of money.
Equivalent number of trees planted in a tropical environment to electricity generated by a rooftop solar PV system.
The initial investment, starting capital or advance payment before other payments, deductions or returns.