# Simulation-Supported Testing of Smart Energy Product Prototypes
## 2 Materials and Methods  
Prototypes for three conceptual HEMP designs were specifically developed for this study to serve as user interfaces for home energy management. They consisted of devices with visually appealing forms that measure energy production and consumption data from a household smart meter and display basic information to users through simple, intuitive visual feedback such as LED colouring and brightness. This feedback is updated on regular intervals to indicate how household performance changes through time and in response to users' actions. The three developed concepts (shown in Figure 1) are described below:  
1. **Bodhi**: An arrow-shaped \"energy budget\" indicator that shows users how a household's energy use compares to a predetermined daily or weekly budget through LED colouring. The relationship  
Figure 1: The three developed SEPS prototypes: CrystalLight (left), Bodhi (centre) and LightInsight (right).  
between actual and planned consumption during a given interval is determined through a budget ratio (R\({}_{\text{B}}\), unitless) defined as:  
\[\text{R}_{\text{B}}=\text{E}_{\text{cum}}/(\text{j}/\text{N})\ ^{*}\text{B}, \tag{1}\]  
where E\({}_{\text{cum}}\) (kWh) is the cumulative energy consumption in the current period (e.g., a day or a week), j is the interval number (unitless), N is the number of intervals in a period (unitless), and B is the total energy budget for a given period (kWh). An R\({}_{\text{B}}\) value between 0.95 and 1.05 indicates that users are \"on budget\" (corresponding to purple LED lighting); values greater than 1.05 correspond to an \"over budget\" state (orange lighting) while values below 0.95 indicate the household is \"under budget\" (aqua lighting).  
2. **CrystalLight**: A smart home ornament that acts like a virtual energy storage system; each day, electricity produced by a household's PV array makes its LEDs grow stronger (\"charging\" the ornament) while electricity consumption gradually dims them. The charge (C\({}_{\text{i}}\), kWh) and state of charge (SOC\({}_{\text{i}}\), unitless) for this \"battery\" at each measurement interval are calculated as:  
\[\text{C}_{\text{i}}=\text{C}_{\text{i-1}}+\text{E}_{\text{P}}-\text{E}_{\text {C}} \tag{2}\]  
and:  
\[\text{SOC}_{\text{i}}=\text{C}_{\text{i}}/\text{C}_{\text{MAX}}, \tag{3}\]  
where E\({}_{\text{P}}\) (kWh) and E\({}_{\text{C}}\) (kWh) are the produced and consumed energy during a given interval and C\({}_{\text{MAX}}\) denotes the total battery capacity (kWh). The battery's state of charge is converted into a brightness value between 0 and 100% for the prototype lights; if at any given interval C\({}_{\text{i}}\) becomes negative, it will be automatically set to zero to simulate an \"empty\" battery. Likewise, if the state of charge becomes greater than 100%, the charge will be set to C\({}_{\text{MAX}}\) to simulate a \"full\" battery.  
3. **LightInsight**: A small cylindrical dial that gives users information on the balance between a household's energy production and consumption during the day through LED lighting. Four different feedback states are possible: net energy production (green lighting), net consumption (red), transition from green to red (yellow) and transition from red to green (rainbow). These states are determined by an energy ratio (R\({}_{\text{E}}\), unitless) defined as:  
\[\text{R}_{\text{E}}=\text{E}_{\text{P}}/\text{E}_{\text{C}}, \tag{4}\]  
where E\({}_{\text{P}}\) (kWh) and E\({}_{\text{C}}\) (kWh) are the produced and consumed energy during a given interval.  
The autonomous operation of all prototypes was made possible through the use of Raspberry Pi microprocessors, where a Python script was created to periodically obtain energy data from a smart meter, calculate the required key indicator (R\({}_{\text{B}}\), SOC\({}_{\text{i}}\) or R\({}_{\text{E}}\)) and set the LED properties accordingly.