Carbon Balance Tool

Introduction

The Carbon Balance tool allows to estimate the saving in CO2 emissions expected for the PV installation. The basis of this calculation are so-called Life Cycle Emissions (LCE), which represent the emissions of CO2 associated to a given component or energy amount. These values include the total life cycle of a component or energy amount, including production, operation, maintenance, disposal, etc.

The reasoning behind the Carbon Balance Tool is, that the electricity produced by the PV installation will replace the same amount of electricity in the existing grid. If the carbon footprint of the PV installation per kWh is smaller than the one for the grid electricity production, there will be a net saving of Carbon Dioxide emissions. Thus, the total carbon balance for a PV installation is the difference between produced and saved CO2 Emissions, and it depends on four key factors:

The difficulty of the calculation lies in finding appropriate values for the LCE of the different contributions. Often these figures are known with little precision. Furthermore they are very specific to certain technologies or production methods. Last but not least, there can also exist controversy on how these numbers are or should be calculated, and different authors will report different values.

The PVsyst tool will propose values for the Lifecycle Emissions related to the electricity that will be replaced by the PV installation (Grid LCE). These values are based on publicly available data from several institutions (see below).

For the emissions associated to the construction of the PV installation (System LCE), no such values will be proposed for the time being. The PVsyst user will have to get those values either directly from the manufacturers or suppliers of the different components, or to resort to dedicated databases like ECOINVENT, Carbon Trust, etc. As a first guideline a few example values are For the future it is planned to include more LCE values directly into PVsyst, and which will also cover the System LCE.

As a general guideline we advise to crosscheck, if possible, the LCE values against up-do-date or more specific information from suppliers or manufacturers.

The Carbon Balance Tool is organized into three different tabs, which will be explained in the following sections. The 'Overview' Tab will always be visible, but the other two, 'Grid Energy Mix' and 'Detailed System LCE', will only show up if the corresponding choice is selected in the 'Overview'.

Overview Tab

In this Tab you have the overview of the Carbon Balance calculation. The four values that can be modified by the user are the Grid LCE, the System Lifetime, the Annual Degradation and the PV System LCE.

The System Production E_Grid is taken from the PVsyst simulation of the current Variant. The Carbon Balance values are the results from the calculation.

There are four values for the result:

• The total saving of CO2 emissions in tons of CO2 over the expected lifetime of the PV installation.
• The yearly saving of CO2 emissions in tCO2/year.
• The savings of CO2 emissions per installed power, given in tCO2/kWp
• The yearly savings of CO2 emissions per installed power, given in tCO2/kWp/year

The yearly values are averaged over the entire lifetime, taking into account the annual degradation.

For the Grid LCE there are three options to control the level of detail with which this value will be computed:

For the System LCE there are three options to control how this value will be determined:

If any of the 'Manual' options is selected, a comment field will appear, that allows to enter a text, describing the source of the value. This text will show up in the final report.