Energy Meters & Sensors
The electricity grid is going through a transition and profound change phase, linked to the growing use of renewable sources and to an increasingly distributed energy production. The grid thus becomes "smart", integrating intelligence, meaning artificial intelligence and automation, in the generation, transmission, distribution and consumption of energy. To date, the greatest changes have been recorded in energy production, large investments are being made to adapt the transmission and distribution network to the new paradigm of distributed production, but much remains to be done on the consumption front, where it would be possible to achieve great savings through mechanisms such as Demand Side Management. Every intervention on the user side, however, requires the direct involvement of the user through the precise measurement of consumption with greater accuracy and time detail. The awareness of one's role in the system and of the advantages that can be gained through more rational consumption is an essential condition for the realization of any Demand Side Management hypothesis, and has positive repercussions for the reduction of emissions as well as economic savings for the user. In the near future, an automatic system for managing domestic consumption will have to use a continuous reading of consumption, the knowledge of active household appliances, will have to be able to program the switching on and off of some devices to regulate total consumption, communicate the independent production of energy through a photovoltaic system, for example, net of any fraction accumulated in-house in a domestic battery or in the accumulator of the electric car connected to the home grid. The energy producer/consumer (prosumer) will have a continuous communication with the energy supplier, the latter can be distinguished from the distribution service operator. One can guess a great complexity of the system and the need for a constant and reliable measure of the quantity exchanged: energy.
Energy monitoring and smart meters
The solutions available for energy monitoring of household consumption are analysed hereafter. Here, a clear distinction should be made between energy monitoring devices and smart meters. The former are separate devices from the tax meter installed by the distributor, are located downstream of the latter and may be used by the consumer to monitor his consumption, since they have no effect on pricing. Generally, they can be installed in a simple way by the user, after disconnecting from the line, even if, in most cases, the assistance of a qualified technician is recommended. The commercial solutions have an extremely simple user interface, allow the storage of data locally or remotely on the cloud, and in addition to reading the history of consumption can offer additional services, such as forecasting future consumption, disaggregation and identification of loads and information on how to achieve savings. The smart-meter is the new generation fiscal and certified device that allows the electricity supplier a two-way communication with the users, allows the instant measurement of the load from remote, useful for the prediction of the same and is essential for Demand Side Management policies. This is a device owned by the energy provider, access to and use of the measured data involves privacy issues. The project objectives focus on energy monitoring devices. In the city of Cagliari, a new generation of smart meters is being installed by the distributor, and where possible, information from these devices will also be used.
Energy monitors can be divided into two main categories, called "single-point" and "multi-point". The first record the total consumption of the entire house or building, at a single point to the power supply of the system, the second measure the consumption at several points by reading different branches of the domestic system, or directly to the sockets of the system to which the most important loads are connected. The identification of consumption per user is almost immediate for multi-point systems, but they have the disadvantage of being potentially invasive for the user, requiring a more complicated installation on the electrical panel and the purchase and installation of smart plug for measurement at the socket. This type of load monitoring is called Intrusive Load Monitoring (ILM). On the other hand, the current trend is to use non-intrusive load monitoring (NILM) using single point energy monitors. Load disaggregation is achieved by processing the aggregate consumption signal using artificial intelligence algorithms, and searching for the characteristic signatures of each individual household appliance
An analysis of commercially available energy monitoring devices has recently been published in . The analysis was based on 41 devices which were compared on the basis of different parameters of comparison. Below are the main results of the comparison, which serve to give an overview of what the market offers today, before moving on to a more detailed analysis for the only devices that we have been aware of and that could actually be used for the purposes of the project.
Type of sensor used. There is a clear predominance of Current Transformers and/or Voltage Transformers. The current sensor is the most important and is always present in the analyzed systems, the measurement obtained from it can be traced back simply to the absorbed power.
CT sensor rating. The measuring range of current sensors is quite diverse. These are instantaneous currents, and 50A are more than enough for a common household. The highest values are related to use in industry or in electrical systems where the mains voltage is lower.
Parameters measured by the energy monitor. A limited number of monitoring systems offer apparent and reactive power detection, almost all current and actual power measurement, and not all systems examined detect voltage.
Sampling frequency. The sampling frequency returned by the energy monitors is extremely variable, the most frequent sampling is between 1s and 1m, higher frequencies are used for load disaggregation applications.
Measuring channels. The number of measurement channels offered by the devices is generally limited, which shows the intended use in the domestic environment with only the measurement of the aggregate load.
Type of storage. Data storage can take place either locally or remotely or on both platforms in some cases. The complexity of the device offering local storage is greater. Economical devices prefer remote storage by leveraging the user's network connection.
A survey has been carried out to identify the most suitable solutions available on the market, the attention has been limited to devices specifically designed for domestic use, and which do not require complicated installations in the electrical panel. The following table shows the most important solutions available on the market. Almost all systems are closed and rely on proprietary platforms for data storage and consultation, some offer APIs for data consultation to allow the development of custom applications. Some recent solutions offer a cloud-based NILM load disaggregation service.
|Sense||CT||P,E||4 MHz||2||Cloud||$ 299|
|Aeotec||CT||P,E||1 min?||1||Cloud||$ 80|
|TED||VT, CT, RC||V, I, P, PA, PR, VRMS, IRMS, cosφ, E||1 s||1 W||32||Local, Cloud||$ 299|
|Neurio||CT||P,E||10 Hz - 1 Hz||1 W||1||Cloud||$ 179|
|Efergy||CT||P,E||10 s||1||Cloud||€ 99|
|Ecoisme||CT||P,E||?||?||6||Cloud, API||$ 200|
|CURB||CT||V, I, P, PA, PR, VRMS, IRMS, cosφ||8 KHz||1 W||18||Local, Cloud, API||$ 399|
|Smappee||CT, VT||V, I, P, PA, PR, VRMS, IRMS, cosφ, IARM||> 1 KHz||1 W||3||Cloud||€ 199|
|Net2Grid||Meter||V,I,P,E||10 s||?||1||Local, API||?|
|emonTx||CT, VT, Pulse||V, I, P, E, VRMS, IRMS, T||1 s - 1 min||10 bit / 10 W||4||Gateway, Cloud||£ 60|
|emonPi||CT, VT, Pulse||V, I, P, E, VRMS, IRMS, T, H||1 s - 1 min||10 bit / 10 W||2||Local, Cloud||£ 155|
|IoTaWatt||CT, VT||V, I, P, E, VRMS,IRMS||40 ch/s||12 bit||14||Local, Gateway, Cloud||£ 142|
|GreenEye||CT, VT||V, I, P, E, VRMS, IRMS||16 KHz, 2 KHz||12 bit / 1 W||32||Local, DashBox||$ 300 - $ 500|
|GridSpy||CT, VT, RC, Pulse||V, I, P, PA, PR, VRMS, IRMS, cosφ, T||1 s - 1 min||16 bit / 1 W||6||Local, Cloud||$ 1600|
|Verdigris||CT||V,I,P||7.68 KHz||16 bit / 10 W||42||Cloud, LTE||$ 50 / month|
|Episensor||CT, RC||V, I, P, PA, PR, VRMS, IRMS, cosφ, E||16 KHz, 2 KHz||14 bit / 1 W||1||Cloud||$ 269|
Among all the platforms, the OpenEnergyMonitor system stands out, which is an open platform both from the hardware and software point of view, with different solutions for measuring electrical and environmental variables and with a specific Content Management System. The commercial solutions presented in the table and described in detail below have the advantage of being guaranteed and certified, which is not to be ignored when measuring a safety-relevant quantity such as electrical power. There are also, many amateur projects based mainly on the Arduino platform, but they do not offer any guarantee about the safety of installation, if not the common sense and technical skills of those who build the system and install it. They also have the disadvantage of not providing a reliable database or shared knowledge regarding the quality of the measurements obtained, the sensitivity and the calibration parameters for the sensors. The following is a description of the most important commercial solutions considered.
It is installed in the electrical cabinet of your home and provides information about electricity consumption and household activities through an app for iOS and Android. It is able to determine the switching on of individual domestic appliances and thus also determine domestic activities. It is also capable of measuring energy production from photovoltaics. Requires one or two days for training. Can not identify all devices, it needs to expand the database in order to proceed to an effective identification. It does not need any user training, it can identify common devices such as refrigerators and washing machines, it can identify new devices to which a user identification can then be assigned. Sense uses two current sensors attached to the power supply phases of the electrical panel, it does not require smart plugs or sensors attached to each branch of the panel. The solar production is detected by connecting an additional sensor to the PV system phase, which must also be connected to the same meter. For the installation of Sense, despite its simplicity, the intervention of a professional electrician is recommended. The declared sampling frequency is very high, 4 MHz is declared. On the device there is some form of intelligence that allows a characterization of the signal in real time, to reduce the amount of data to be stored. Declared consumption is below 5W but would seem to be compatible only with US voltages. The data is transferred to a proprietary platform where access for the user is guaranteed. In the legal part it is made clear that the installation can only be carried out by a professional.
Aeotec Home Energy Meter Gen5
TED PRO Home
It is perhaps one of the first systems used, in production since 2001. The system seems outdated compared to the most recent competitors, however it appears to be very open. The system works by reading from Current Transformers, both solid core and split core. A measuring component is installed inside the control cabinet and sends the measurement on the powerline, so it does not use wireless communication but powerline communication. There is, therefore, an Energy Control Center that receives readings, stores them and carries out analyses on them. The technical specifications of the equipment are not clear. The selling price in the United States is $300 and does not seem to be available in Europe. The only interesting feature is the availability of open APIs for custom applications.
In this case, too, the system consists of a reading unit that is installed in the electric panel equipped with two split-core Current Transformers. The system is compatible with any type of electrical panel, it also allows to measure the power supplied by a battery or an inverter but, above all, it appears more open than other systems because access to data is guaranteed through proprietary software, through access to the cloud neurio with specific API or can be redirected to a proprietary cloud system. The communication of readings can be done through different protocols, the system supports WiFi, ZigBee, Xbee and RS 485. In this case too, as in the previous ones, it is recommended that the installation be carried out by qualified personnel, videos are available that illustrate extremely clearly, and the system is supplied complete with all the accessories necessary for assembly. Unfortunately, the distribution of the product seems limited to the U.S. market, the power supply must be guaranteed by the electrical panel and it is expected that this has a voltage of 120V AC.
The system operates on the same principle as above. A unit of measurement to be installed in the control cabinet equipped with a CT split core, the power is taken directly from the control cabinet, coupled with an external unit for data collection, which takes measurements from the unit in the control cabinet and sends them to a cloud database. The data is presented to the user via the cloud or via a web interface or via specific apps for iOS or Android. The system looks extremely consumer friendly, but closed. The data transmission takes place in radio frequency at 433MHz with a transmission time of 10, 15 or 20 sec, the transmission range is from 40m to 70m.
The system consists of a measuring and transmitting device that must be installed inside the electrical panel of the house. It comes with a truly exaggerated number of CT, 12 30A, 4 50A and 2 100A sensors, plus a connection for voltage measurement. All current sensors are split cores. In this case, the loads are not identified by a software system that analyses the use, but by the separate measurement of all the branches of a modern electrical system. Installation by qualified personnel is clearly required, but while for other systems this is mainly a precaution, in this case it is essential due to the complexity of the installation. The measured data is also sent over the network, and can be accessed via a web service or via dedicated apps for iOS and Android. A system is for sale in the United States and is distributed through Amazon at a price of $400. Distribution in Italy does not seem to be planned.
Energy monitoring and non-intrusive load monitoring system developed in the Netherlands, the distribution method and price are not known, the product is still in the development phase and it is necessary to contact the manufacturer in order to get a quotation. The proposed architecture overlaps with that of the project. Unlike almost all other competitors, this system directly collects data from the electricity meter supplied by the operator without the need for a separate measuring device. Data is collected by the gateway and can be accessed via dedicated apps or browsers but is not sent over the network. The manufacturer points out that 'the data won't leave your home'. All applications are not done in the cloud but locally, and the gateway has enough memory to collect data and make it available. Load disaggregation is implemented with a dedicated application that uses the local data contained in the gateway. The gateway can be connected in the cloud and additional applications can be developed on the data provided. Net2Grid provides partially open APIs for access to data and above all to data processing. However, access to the data is not complete.
Open Energy Monitor
The EmonPi is a Raspberry Pi-based energy monitoring unit that is easy to install and requires a Wi-Fi or Ethernet connection. The unit can monitor two single-phase AC circuits using CT clip-on sensors; it can also measure temperature and count triggers on the energy meter. The maximum data acquisition and cloud transmission rate is 5s.
It is a Raspberry Pi equipped with the same libraries as the EmonPi but without the case and without the functionality of direct reading of electricity.
-  Haq, Anwar Ul, and Hans-Arno Jacobsen. "Prospects of Appliance-Level Load Monitoring in Off-the-Shelf Energy Monitors: A Technical Review." Energies 11.1 (2018): 189. http://www.mdpi.com/1996-1073/11/1/189
-  CT: Current Transformer, VT: Voltage Transformer; RC: Rogowski Coil
-  P: power; E: energy; V: voltage; I: current; P: apparent power; PR: reactive power; cosφ: power factor; VRMS: RMS voltage; IRMS: RMS current; T: temperature; H: humidity; IARM: current harmonics