# Towards DC Energy Efficient Homes
## 5 Case Study: Scenarios Analysis and Comparison  
Even though a full comparison in terms of energy consumption and price would be the proper option, a different point of view is going to be presented here. In order to compare the scenarios on an equal basis, two hypotheses have to be stated before analyzing them:  
* The cost of the installation is the same for all scenarios. The installation may include a HESS, a classic AC distribution of power and/or a new DC one, it may contain DC/DC converters, classic sockets, DC types, etc. The tendency of the price of the full installation in all scenarios will converge due to the competitiveness, the reduction of the prices considering economies of scale and the evolution of prices of HESSs. * Energy consumption due to the different processes of conversion related to the HESS, AC/DC and DC/AC, is not considered here. In this case, the justification is that those losses are not part of the energy distribution. Instead, they are part of energy storage. This process would be critical in the future and the price of the related losses would be covered by charging the HESS during the low-price period and by discharging it during the high-price one. In fact, the low-price period corresponds to a high availability of renewables in the electrical network. Therefore, those losses are part of the energy that is going to be discarded. Note that if the scenarios also contain HESS and PV, the efficiency will be higher. Thus, there are fewer losses because no rectification is needed. For example, for a typical value of 90% in the DC/AC conversion and 80% in the AC/DC one, a house will be 16% more efficient. The values presented in Figure 12 have been taken for household devices, according to the study made by the IDAE [90]. In that study, average values of consumption by household devices, taken from Spanish homes, were assessed. The methodology used in that study was telephone and face-to-face surveys. For EVs, a consumption of 0.15 kWh/km can be considered and 12,000 km/year can be taken as a common value. Therefore, a consumption of 1800 kWh/year can be used in this case study. The results are shown for two different cases: with and without EVs, and can be seen in Table 2 and Figure 13.  
Figure 11: Block diagram of the DC distribution scenario with PV, HED, and EV. The devices identified with DC are those that internally consume that type of power and those identified with AC do not consume DC internally and therefore should not be supplied with DC. For AC/DC conversion an efficiency of 80% was considered and 90% was considered for DC/AC according to a mean value of the current devices. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Device** & **AC/DC** & **Scenario 1** & **Scenario 2** & **Scenario 3** & **Scenario 4** \\ \hline EV & DC & 1800 & 1800 & 1260 & 1260 \\ Illumination & DC & 410 & 410 & 328 & 328 \\ Fridge & AC & 655 & 655 & 655 & 721 \\ Freezer & AC & 131 & 131 & 131 & 144 \\ Washing Machine & AC & 254 & 254 & 254 & 279 \\ Dishwasher & AC & 245 & 245 & 245 & 270 \\ Clothes Dryer & AC & 71 & 71 & 71 & 78 \\ Oven & AC & 178 & 178 & 178 & 195 \\ Television & DC & 119 & 119 & 95 & 95 \\ Computer & DC & 145 & 145 & 116 & 116 \\ Standby & DC & 229 & 229 & 183 & 183 \\ Other Appliances & DC & 75 & 75 & 60 & 60 \\ \hline Total without EV & & 2512 & 2512 & 2316 & 2469 \\ Savings without EV & & - & 0 & 196 & 43 \\ Total with EV & & 4312 & 4312 & 3576 & 3729 \\ Savings with EV & & - & 0 & 736 & 583 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Efficiency comparison of the different scenarios respect to the current one, evaluating the impact of EVs on them, all units in kWh. Figure 12: Typical annual share of household device consumption. In Scenario 2, no differences were considered with respect to the first one, due to the low values in the reduction of losses in the AC/DC transformations close to sockets instead of in each DC device. This means that a small difference can be found, but it is not very meaningful.