## 3 Findings for Each of the Three Layers
### Technologies Layer
#### 3.3.3 Resource-Side Flexibility  
While generators and large resources can be described in terms of three main technical aspects, such as ramp magnitude, ramp frequency, and response time, smaller demand resources might need to be characterized using more details.  
Based on individual technical parameters, the eligibility of the system types can be evaluated for smart energy product and service applications. The energy resources described in this section can be assigned following the categories of controllability, shown in Figure 4 at the beginning of this section. Regarding the characteristics of resources, Table 3 provides an overview of some these for individual systems.  
The availability and activation duration of all the investigated systems is somehow limited either by technical parameters or by the needs or influence of customers. In terms of power supply or demand, most systems range within typical power connection values of households in Europe (~17 kW). Depending on system configurations, EVs or PV systems may exceed this value significantly, which may lead to increasing needs for grid investments (e.g., transformers, power lines, etc.). It was shown that the investigated systems at the residential level provide a different potential for flexibility  
Figure 4: Prosumer residual load in terms of controllability (adapted from [57]).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Resource Type** & **Availability** & **Reaction Time** & **Duration** \\ \hline PV System & \begin{tabular}{c} Depends on weather and \\ time of day \\ \end{tabular} & seconds & \begin{tabular}{c} Depends on weather and \\ time of the day \\ \end{tabular} \\ \hline Heat pumps & \begin{tabular}{c} Fully available until \\ temperature criterion of \\ household is met \\ \end{tabular} & seconds & \begin{tabular}{c} Fully available until \\ temperature criterion of \\ household is met \\ \end{tabular} \\ \hline White goods and & \begin{tabular}{c} Customer dependent \\ appliances \\ \end{tabular} & seconds & \begin{tabular}{c} Process dependent \\ (non-interruptible) \\ \end{tabular} \\ \hline Wet appliances & Customer dependent & seconds & \begin{tabular}{c} Appliance dependent \\ \end{tabular} \\ \hline Thermal storages & \begin{tabular}{c} Fully available until \\ temperature criterion is met \\ \end{tabular} & seconds & \begin{tabular}{c} Limited by maximum \\ battery capacity \\ \end{tabular} \\ \hline Battery electric & \begin{tabular}{c} Customer dependent \\ vehicles (EV) \\ \end{tabular} & \begin{tabular}{c} seconds \\ \end{tabular} & \begin{tabular}{c} Limited by maximum \\ battery capacity and \\ customer \\ \end{tabular} \\ \hline Fuel cell electric & \begin{tabular}{c} Customer dependent \\ vehicles (FCEV) \\ \end{tabular} & \
\begin{tabular}{c} seconds \\ \end{tabular} &
\begin{tabular}{c} Limited by tank capacity, \\ contrary to EV, tank fills \\ as fast as 4 min \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 3: Characteristics of resources in terms of flexibilityapplications. Whilst existing systems--such as PV systems, heat pumps, or appliances--provide limited controllability (except for downward regulation), the introduction of stationary battery energy storage systems in particular can enable full flexibility for local optimization or ancillary services.