SolarCity Simulator
Overview
The SolarCity is a web-based simulator application created to help households, businesses and municipal authorities evaluate their prospects for generating electricity using rooftop-mounted solar photovoltaic (PV) systems.
For homes and businesses, the simulator provides the means to calculate likely savings from rooftop solar PV compared to other power sources and based on a cash flow financing model.
For municipal authorities, the simulator supports assessments of different policy incentives – such as generation or capital subsidies – on each city’s rooftop solar PV market.
The SolarCity simulator combines ultra-high-resolution three-dimensional building footprints with solar irradiation data, computed at one metre (m) grid cells. It is one of a series of web applications developed by the International Renewable Energy Agency (IRENA) as part of the Global Atlas for Renewable Energy.
Reach out to IRENA to develop and promote your own SolarCity Simulator.
FAQs
SolarCity is a web application provided by IRENA to enable households, businesses and municipal authorities to evaluate the prospects for electricity generation using rooftop-mounted solar PV installations.
The methodology of the SolarCity simulator can be deployed worldwide, including in locations where solar potential is high but not yet fully evaluated. The first implementations of the simulator were in the districts of Kasese in Uganda and Chongli in Zhangjiakou, China. SolarCity is one of a series of web applications developed by IRENA as part of the Global Atlas for Renewable Energy.
The solar irradiation simulation for SolarCity is very accurate. To correctly estimate the effects of shading, rooftops are captured in three dimensions, with the respective tilt and azimuths of each rooftop section determined before the shading simulations are applied (see methodology).
The calculations have been made using a base resolution of one metre – the same as the source imagery.
We estimated the amount of energy (in kWh) that can be produced from sunlight based on the size of the system (in kW) per year. In this case, the user can use any conversion efficiency that corresponds to the technology of interest to calculate the yield.
The combined uncertainty in the models used to perform these calculations (irradiation and performance) is estimated to be typically around 5% when fed with accurate input data. However, as this is the first implementation with rooftop attributes that have been calculated from satellite-sourced imagery at 1 m resolution, the precise uncertainty estimate will be updated after the release of the platform.
No. The PV performance modelled in the SolarCity simulator, although calculated on an hourly time stamp over a typical meteorological year, has been aggregated to provide annual average results to simplify the calculations and visuals.
Yes. The option to configure storage has been included in the simulator to allow users to assess how to live off the grid and be energy self-sufficient when excess solar energy cannot be fed into the electricity grid.
The general architecture of the SolarCity simulator contains a module for empirical and business assessments of net metering, feed-in tariffs and storage capabilities.
For investment and operating costs, the default values are obtained from either IRENA’s Costing Database or IRENA’s focal points in the country; users can edit these values.
The current version of the SolarCity simulator has been built for demonstration in Kasese, Uganda and Zhangjiakou, China. With careful consideration on a case by case basis, IRENA may work with its Members to develop versions of the simulator for selected cities in their countries. For more information, please contact IRENA’s Resource Assessment unit at: GlobalAtlasServices@irena.org.
On a case by case basis, IRENA may decide to use the capabilities of SolarCity to conduct specific studies requested by its Members. The outcome of such studies could be in the form of a published report and may not include interactive software online. Please contact IRENA for more information at: GlobalAtlasServices@irena.org.
You may download the SolarCity methodology report here.
User Guidance
The Setting section presents the capacity of solar PV panels that can be accommodated on a single (or multiple) rooftop(s) as well as the self-consumption of a single (or multiple) building(s).
The Set Input tab allows users to adjust some of the parameters of the analysis. This window comprises two sets of parameters: non-alterable and alterable.
The non-alterable parameters – such as the PV capacity, surface area, number of buildings and annual consumption – are precalculated by the SolarCity simulator based on the user’s chosen configuration and area of interest. The annual consumption figure responds to user interaction via the consumption subsection of the tuner.
Alterable parameters, such as storage capacity, PV efficiency, system cost, interest rate, loan, loan period, emission factors, average consumption, tariffs, tax credits and subsidies can be adjusted as required. The SolarCity simulator recalculates the outputs of the ‘Financing’ and ‘Environmental (and Social) Benefits’ sections of the ‘Output’ panel.
For instance, by inputting values for subsidies or income tax credits, the SolarCity simulator can assess the economic feasibility of rooftop solar PV systems. This assessment is based on a simplified model that assumes a solar programme aiming at full utilisation of all suitable rooftop spaces.
Note that the output metrics comprise the direct accounting cost of the subsidy or income tax credits to the municipal or central authorities and the prospective value created by these interventions. This first approximation does not estimate the indirect costs of implementing the schemes or measure the positive and negative externalities that may arise from their implementation.
All outputs from the SolarCity model can be downloaded by clicking on the ‘Get report’ icon in the ‘Results’ section.
Glossary
The amount of electricity used by selected household(s) per year.
The amount of electricity used on average per household per year.
Price to be paid to a consumer per kWh of electricity fed into the grid (on-grid) or saved in the storage system (off-grid) if there is any surplus power generated from the rooftop solar PV system. The default values are obtained from the local authorities in the city but can be edited by users. CO2 emission per kWh (kg) An estimation of the carbon dioxide emissions per kWh of electricity generated from combustion systems, considering the carbon footprint of solar photovoltaic panels.
An estimation of the equivalent carbon dioxide emissions in other forms (greenhouse gasses) per kWh of electricity generated from combustion systems considering the carbon footprint of solar photovoltaic panels.
An estimation of the equivalent carbon dioxide emissions in other forms (greenhouse gasses) per kWh of electricity generated from combustion systems considering the carbon footprint of solar photovoltaic panels.
Parameter used to estimate the equivalent carbon savings achieved by a PV installation in terms of passenger vehicles taken off the road. The default value for a passenger vehicle is set to 4,600 kg, assuming an average gasoline vehicle has a fuel economy of 9.35 kilometres per litre and drives 18,500 km per year (EPA, 2019). This is used in SolarCity as a basic indicator only.
Parameter used to estimate the equivalent carbon savings of an installation in terms of number of mature trees planted in a tropical environment. The default value is set to 22.68 kg, assuming an average tropical tree (Egbuche Christian, 2018).
The initial investment, starting capital or advance payment percentage of the total investment before other payments, deductions or returns.
Price to be paid by a consumer per kWh of electricity consumed from the utility. The default values are obtained from the local authorities in the city, but can be edited by users.
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.
Direct accounting costs from central government or from provincial or municipal authorities of implementing an incentive such as a generation subsidy. The default values are obtained from the local authorities in the city, but can be edited by users.
Tax payable by cooperatives, limited liability companies and trusts in the city. The default values are obtained from the local authorities in the city.
The percentage of the tax payable that can be waived from the liability. This can be edited by users.
The subsidy that is given to building owners to reduce the initial investment required to install the rooftop solar PV system. The default value is zero but can be edited by users.
The sum of money that is borrowed and is expected to be paid back with interest over a specific period.
The period over which the loan is to be repaid.
An estimation of the nitrogen oxides emissions per kWh of electricity generated from combustion systems.
The number of buildings being actively assessed; a promoter can assess multiple buildings simultaneously.
All costs that are related to daily operation, including the replacement of minor components.
Most solar panels come with a warranty of 20–25 years (covering their ‘useful’ lifetime). Over the expected lifetime, most panels continue to operate at low efficiency. In most cases, solar panels lose about 1% of their efficiency over each year of operation.
An estimation of the particulate matter emissions with a diameter of less than 2.5 micrometres per kWh of electricity generated from combustion systems.
Total peak electrical capacity of solar PV panels installed.
Cost of the solar PV system, including shipment, taxes and installation. This is obtained from local authorities in the city.
The ratio of useful electrical energy produced to the amount of solar energy incident on the cell under standardised testing conditions.
Under the lease model, a private or public investor will pay an annual rent to the building owner(s) and benefit from the returns derived from the solar PV system.
Salvage cost is the estimated residual value of a rooftop solar PV system at the end of its useful lifetime.
Self-consumption is defined as the ratio of the energy use from on-site generation to the total energy generated.
The total amount of energy that a solar battery can store. This can be edited by users.
Cost of the storage system, including shipment, taxes and installation. This is obtained from local authorities in the city.
Area of the rooftop surface covered with solar PV panels.
Results
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:
- Total investment required with total annual revenue for building owners or promoters;
- Policy costs (generation and installation subsidies, and tax credits), total value created, and the resulting coverage of electricity for end-use and reduction of alternative sources;
- Financial indicators to guide private and public investments, such as equity internal rate of return (EIRR), payback to equity; Understanding of the broad economic, social and environmental benefits of interventions introduced to the market, for municipal authorities;
- Financial payment options to help indigent people address concerns regarding significant upfront investments and illustrate revenue through dynamic graphs.
- Relevant output metrics are calculated based on two optional financing models:
- A ‘buy financing model’, wherein the building or estate owner intends to buy the solar PV system for personal or localised consumption without the intention of selling electricity;
- A ‘lease financing model’, wherein a private or public investor intends to buy the solar PV system for a community by leasing a rooftop from a building owner. The investor will pay the annual rent to the building owners and in return gain a profit from: selling part of the electricity to the consumers for their consumption; subsidies or tax credits; selling the remaining electricity to the grid at a benchmark tariff (on-grid); or storing electricity for other forms of consumption at a benchmark tariff (off-grid).
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.
Glossary
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.
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.
Amount of electricity used by selected household(s) per year.
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.
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.
Measures the efficiency, quality or yield of the equity investment.
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.
Total peak electrical capacity of the solar PV panels installed.
Area of the rooftop surface covered with solar PV panels.
Revenue from the electricity consumption savings provided by the rooftop solar PV system compared to equivalent consumption from the grid.
Revenue of the electricity saved in storage for other consumption under the off-grid scenario.
Revenue from selling the remaining electricity back to the grid under the on-grid scenario.
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.
Acknowledgements
This project is part of the International Climate Initiative (IKI). The Federal Ministry for the Environment, Nature Conservation and Nuclear Safety (BMU) supports this initiative on the basis of a decision adopted by the German Bundestag.
http://international-climate-initiative.com/en