# Effects of Adding Batteries in Household Installations: Savings, Efficiency and Emissions
## 1 Introduction  
Most of electrical appliances used in private homes nowadays operate with AC supply, mainly due to its availability. However, there are others that need to be powered with DC, such as certain facilities located in remote places, ships or campervans and also appliances such as fridge-freezers, extractor hoods, microwave ovens or coffee machines. From the point of view of their internal architectures, most home appliances need to be supplied with DC. For instance, televisions, routers or other electronic devices. The presence of this type of domestic equipment increases with the progress of technology, involving losses due to the need of AC/DC conversion [1; 2; 3; 4; 5; 6]. The consumption of electricity by household appliances has an increasing trend. First, electric cookers have been gradually substituting gas ones. Second, for heating and cooling, heat pumps are also increasing their share percentage. Moreover, the growing dependency on phones, tablets and any other kind of battery charging devices gives rise to a proliferation of plug-load devices. Moreover, resident preferences such as large screens, high resolution ones or the need for Internet connectivity creates a large electricity demand of commonly connected devices [7; 8; 9; 10]. The most efficient AC appliances on the market are expensive. The prices of AC devices are lower than the prices of their equivalent DC models, mainly due to the mass production of household appliances for AC uses. However, if both possibilities were evaluated under the same conditions, the prices of DC appliances could be similar to the prices of their AC versions--or even lower. In fact, due to their simplicity, DC electrical appliances need a lower quantity of components for their construction, making their cycle of life longer and having lower probability of failure [11; 12; 13; 14; 15; 16]. Climate change is a fact. There is evidence that since industrial revolution, the climatic trends of our planet differ from the natural behavior previously produced on the Earth, such as shrinking ice sheets, global temperature and sea level rising or extreme events, among others [17]. In the Roadmap 2050 [18], the European Union (EU) has established some goals with the aim of reducing up to an 80% the greenhouse gas emissions by 2050, with respect to 1990. This requires emissions' reduction to take place in all sectors. Residential and commercial buildings consume a 40% of the total energy needs in the EU [19], being energy efficiency the key to achieve its objectives. Regarding household savings, the efficiency of each appliance is important to reduce the total demand, entailing a lower need of energy production and a reduction of emissions [20, 21]. Furthermore, a large amount of household energy demand happens during peak hours, i.e., those when the electric price is higher, so the reduction in energy consumption leads to lower electricity costs [22, 23, 24]. Most electrical appliances such as smartphones--and nowadays, hybrid and electric vehicles--have a battery integrated that has had a huge importance in the development of the batteries. In this way, the advancement of technology has led to the optimization of batteries that involves a reduction of costs and an improvement of their properties. In turn, the fact of using a battery as a power source for electrical appliances provides security of supply against power outages for a certain period of time (depending on the level of charge at the moment when the fault occurs and the total capacity of the battery) [25, 26, 27]. The installation of a battery makes it possible to accumulate energy in the most suitable periods and to supply this stored energy throughout the rest of the day, allowing one to optimize consumption and to reduce, in turn, the electricity bill. In [28] a mathematical model was developed to find optimal schedules for an energy management system used in a home where energy prices and generation from renewable sources are time-varying, integrating storage devices and electric vehicles.