## 4 Proposed Approach: Quantitative Assessment of the Flexibility
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Market Model** & & **Strengths** & **Barriers and Weaknesses** \\ \hline \multirow{6}{*}{_Extended centralised dispatching_} & - & extension of existing markets with a & - & too limited role of DSO; \\  & - & unique buyer (TSO); & - & small interaction between TSO and \\  & - & easy implementation; & - & DSO; \\  & - & immediately feasible in sufficiently & - & minimum bid size for enabling the \\  & - & immediately feasible in sufficiently & - & participation; \\  & & robust distribution networks. & - & harmful impacts on distribution \\  & - & local dimension can reduce the & - & network operation disregarded. \\ \hline \multirow{6}{*}{_Local Ancillary Service market_} & - & local dimension can reduce the & - & the schedule should be determined \\  & - & minimum bid size; & - & at each TSO/DSO interface; \\  & - & the DSO knows its distribution & - & implementation of new small and \\  & - & networks; & - & distributed markets; \\  & - & the DSO can act as a facilitator of & - & risk of higher costs. \\  & - & the participation of DERs in the & & \\  & - & global market. & - & the schedule should be determined \\ \hline \multirow{6}{*}{_Shared balancing responsible_} & - & TSOs can foresee the demand of the & - & the schedule should be determined \\  & - & distribution systems with a very & - & at each TSO/DSO interface; \\  & - & low level of uncertainty (smaller & - & implementation of new small and \\  & - & error in the forecast of the residual & - & distributed markets (as the previous \\  & - & load demand); & - & model); \\  & - & reduced costs of balancing services; & - & the DSOs and the DERs do not offer \\  & - & DSOs gain an active role according & - & services to the TSOs; \\  & - & to the specifications of the & - & fewer flexibility options are \\  & - & European Commission [33]. & - & available for TSOs. \\ \hline \multirow{6}{*}{_Common TSO–DSO market_ (second variant)} & - & unique optimisation (possibility of & - & the computational effort for the \\  & - & identifying the least cost solution); & - & optimisation of the bid allocation \\ \cline{1-1}  & - & DSO is a buyer of flexibility in the & - & can become high due to the large \\ \cline{1-1}  & - & same market of the TSO; & - & dimension of the market; \\ \cline{1-1}  & - & TSO and DSO share the & - & it could be necessary for a third \\ \cline{1-1}  & - & responsibility for operating the & market; & party other than the DSO and TSO \\ \cline{1-1}  & - & both grid constraints are taken into & - & for supervision. \\ \cline{1-1}  & - & account in the same timeframe; & - & \\ \hline \multirow{6}{*}{_Common TSO–DSO market_ (second variant)} & - & less communication between TSO and DSO. & - & the DSO has no priority in the use \\ \cline{1-1}  & - & & and DSO. & of local resources. \\ \hline \multirow{6}{*}{_Integrated flexibility market_} & - & direct competition between & - & introduction of an independent \\  & - & regulated and non-regulated & - & market operator to guarantee \\ \cline{1-1}  & - & high liquidity due to the presence of & - & additional interaction between \\ \cline{1-1}  & - & additional buyers of flexibility; & - & the lowest costs not necessarily \\ \cline{1-1}  & - & possibility for TSO and DSO of & - & obtained; \\ \cline{1-1}  & - & reselling non-used flexibility to the & - & possible negative impacts on the \\ \cline{1-1}  & - & market at the same conditions on & - & operation of the other network; \\ \cline{1-1}  & & which it was purchased. & - & unnecessary grid costs; \\ \cline{1-1}  & - & balancing could be problematic to & the TSO. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Strengths, barriers and weaknesses of the proposed market models. * The second task aims at quantifying the availability of flexible products and the relevant costs by using local market models that optimise the DERs dispatching.