Solar Power Cost Calculator - SPCC

The Solar Power Cost Calculator (SPPC) is a web application intended to help investors assess the end cost of electricity generated by a solar system. Using a series of inputs that characterise the system it produces a final figure in €/kWh, the same units used by grid operators to charge households and consumers in general. With this result the investor is furnished with a direct comparison to the cost of tapping electricity from the grid. This application is conceived for Photo-Voltaics (PV) but can also be used for other technologies that have similar cost structures.

SPPC is open source, released under the EUPL v1.1 license; the code is publicly available at GitHub. This post is presently using SPCC v1.1.

The application is pre-set with generic values for demonstration. Use zero (0) to exclude non mandatory costs from the calculation (e.g. Financing, Storage). Click on an input descriptor to see further details on its function. The calculation implements the mathematical formulas laid out in The Price of Solar Power post.

To leave a suggestion or report a bug please use the comment box, or better still file an issue at GitHub.

1. System characteristics
Installed capacity		kWp
The installed capacity of the system in Watt (W - sometimes called Watt-peak, Wp). This is the maximum power output the system can generate under optimal conditions.
Expected generation		Wh/Wp/a
The expected amount of energy generated yearly in Watt-hour per Watt-peak per year (Wh/Wp/a). This figure is a function of the sunlight the system receives each year, dependent on latitude and orientation. The JRC produces a series of maps for Europe with maximum generation values that can be a good starting point to obtain this information.
Efficiency decay		%/a
The efficiency with which solar panels harvest energy decays with time, in part due to the impact of sunlight itself. Although not linear, nor constant, a figure of 0.5 percent per year (%/a) is a sensible option (i.e. a system that generated 1000 Wh this year will generate 995 Wh next year).
Expected lifetime		years
The number of years the system is supposed to last. Various indicators can be used to determine expected system lifetime, like the point where efficiency drops below 80% of initial characteristics. However, the most sensible option is to match this figure to the panels warranty period.
2. Investment costs
Panels		€/kWp
The cost of the solar panels composing the system in euros per kWp (€/kWp). If only the bulk cost is known, including inverter and installation, insert the full value here and leave zero on the following two fields.
Inverter		€/kWp
The cost of the inverter linking the system to the grid (or storage system) in euros per kWp (€/kWp). If only the bulk cost is known, including panels and inverter, leave zero in this field and use only the Panels cost field.
Assembly and Installation		€/kWp
The cost of system installation (usually also including paperwork and other procedures) in euros per kWp (€/kWp). If only the bulk cost is known, including panels and installation, leave zero in this field and use only the Panels cost field.
3. Maintenance
Inverter lifetime		years
The lifetime of a solar panel is usually measured in decades, but the inverter is unlikely to last as long. To calculate full costs the replacement of the inverter must accounted for. Again, warranty may be the best indicator.
Other costs		€/a
Other costs that may arrive, in euros per year (€/a). Cleaning can be a necessity after long periods without rain, or in places frequented by birds. If insurance is required it can also be included in this field.
4. Financing
Percentage financed		%
In case the system needs to be financed, this extra cost must be taken into account. Here goes the percentage of the initial investment financed by a third party. As an example if the initial investment is 1000 € and financing is 800 € the value to insert is 80%.
Time		years
The time span in years that it will take to pay back the financing.
Interest		%/a
The interested paid back to the financier as percentage per year (%/a).
5. Storage
Cost		€
If the system is being installed off-the-grid, linked instead to a storage system, its costs must be included in the calculation. Beyond batteries this value must include controller(s) or any other additional hardware costs.
Lifetime		years
The storage harware should have a lifetime inferior to that of the panels themselves, thus replacements must be accounted for. Warranty is once more the best indicator.
Effiency		%
Any storage system has losses, meaning that the amount of energy it feeds back is always somewhat inferior to that used to charge it. This value is the percentage of the energy return relative to the energy charged. For instance, if a system is charged with 1000 Wh and returns back 900 Wh this value is 90%.
Share of energy stored		%
Not all the energy generated by the solar panels needs to be stored, part of is consumed immediately by household appliances. An off-the-grid system should be dimensioned in order to minimise the usage of the storage system, so that it is needed mainly during summer, making the extra energy generated during the day available to the night; during the winter months ideally the storage system should not be needed. This field is thus the percentage of the total energy generated throughout the year that needs to be stored.