Most nations have agreed to limit the emission of greenhouse gases within the Paris Agreement. The agreement relies on the assumption that all participating nations have accurate means of estimating carbon emissions and offsets accurately. However, global carbon emission accounting methodologies lack accuracy in approach and required carbon intensity data of utility grid electricity. From this, a need for developing a standardized accurate carbon emissions assessment methodology arises. The aim of this research is to develop an accurate carbon offset assessment methodology and determine the effect of using marginal, hourly average and annual average emission factors. The methodology is applied to a solar carport system in the Netherlands, consisting of a 465 kWp solar PV system, a 345 kWh nickel metal hydride battery and 16 DC charge points for EVs, in order to quantify the emission offset potential of the respective system components. This research presents a comprehensive literature review of existing carbon accounting methodologies based on which a new accurate methodology to calculate carbon offsets is developed. This methodology uses marginal emission factors from observed power dispatch and computes offsets on an hourly timestep. Application of marginal emission factor results in a 30 % and 23 % increase in carbon offset compared to hourly average emission factors and annual average emission factors, respectively. The carbon offset attributed to the battery system is roughly 100 kg CO2eq annually in 2019 and 1.5 -1.7 tons CO2eq in 2030. Relative to the lifecycle emissions caused by the battery system of about 200 tons CO2eq, including the battery system is not beneficial in terms of mitigating carbon emissions in solar carport applications. 99.96 % of the total offset is attributed to the solar PV system and lifecycle emissions of the solar carport can be mitigated after operation of 1.5 years when excluding the battery. Including the battery, lifecycle emissions are mitigated after 2 years and 3 months. To conclude, the results show that using marginal emission factors results in significant impact on the assessment results and are conceptually more accurate. Hence, they should be applied for carbon offset studies. Additionally, the carbon offset potential of the PV system is high while the contribution of the battery is low and installation of battery systems at solar carports is, therefore, not recommended.