Renewable share calculation can be misleading

[smartie2076]

Currently, the renewable share is calculated both per energy vector and the whole energy system.

RES = renewable generation/total generation

For the system-wide renewable factor, energy carrier weighting is applied. For the energy vectors, all renewable generation connected to one vector (one energy carrier) is considered. The former can distort the renewable share factor per energy carrier supply:

Lets assume a sector-coupled energy system.

• Heat demand: 100 kWh(therm), no generation
• Electricity demand: 100 kWh(el), 125 kWh(el) renewable generation
• Heat completely supplied via heat pump (COP=4).

Now, with the current formula, this would result in 100% RES share for the electricity side, and 0% RES share for heat. Overall, we would have a renewable factor of generation of 100%. Should the RES of the heat sector be 0%, eventhough we supply it though renewable generation? The same principle can be applied to other sector-coupled energy systems which are stronly intertwined.

From my point of view, we should remove the single-sector perspective and instead work with energy carrier weighting from the start, resulting in 100% RES for electricity and heat. It would also be possible to introduce both values:

• Renewable factor of local generation per sector as previously done
• Renewable factor of supply, taking into consideration generation and DSO transactions and applying energy carrier weighting (for each sector and for the whole system).

[smartie2076]

The share of local renewable generation is also a KPI of WP5.3, so it adds benefit to include it as well.

[smartie2076]

I considered to include another factor, the energy demand covered from renewable sources:

Share of demand supplied by renewables (REDem)
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Describes the share of the local energy demand that is supplied from renewable sources.
For that, renewable generation is calculated from the production  of local assets and the share of energy consumption that is provided by the energy provider from renewable origin.

.. math::
        REDem &=\frac{\sum_i {E_{rgen,i} \cdot w_i + RF \cdot E_{grid}}}{\sum_j {E_{dem,j} \cdot w_j}}}

        \text{with } rgen &\text{: Renewable generation}

        i &\text{: Renewable generation assets 1,2,…}

        dem &\text{: Demand}

        j &\text{: Renewable and non-renewable generation assets 1,2,…}

        RF &\text{: Renewable factor of energy provider}

        &k &\text{: Energy provider 1,2…}

        w &\text{: Energy carrier weighting factor for output of asset i/j/k}

:Example:

An energy system is composed of a heat and electricity side. Following are the energy flows:

* 100 kWh from a local PV plant
* 0 kWh local generation for the heat side
* 100 kWh consumption from the electricity provider, who has a renewable factor of 50%
* Electricity demand of 100 kWh(el)
* Heat demand 400 kWh(therm)

This results in a system-wide renewable share of:

.. math:: RF = \frac{100 kWh(el)\cdot \frac{kWh(eleq)}{kWh(el)}+50 kWh(el)\cdot \frac{kWh(eleq)}{kWh(el)}}{100 kWh(el) \cdot \frac{kWh(eleq)}{kWh(el)}+ 400 kWh(therm) \cdot \frac{kWh(eleq)}{kWh(therm)}} = \frac{3}{10}= 30 %

This illustrates how the energy carrier weighting factor has to be considered when defining KPI for sector-coupled energy systems: The equation results in an unexpectantly low REDem of 30%, eventhough 75% of the energy provided to supply the demands is from renewable sources. This stems mainly from the problematic heat pump used to provide the heat demand using electricity. The COP distorts the energy balance here. Therefore, I decided against including such a parameter into the evaluation.

[smartie2076]

I decided to rename the KPI into

• Renewable share of local generation
• Renewable factor, oppesed to renewable share of supply, as we are not comparing to the demand.