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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.

How does it work? PhiSaver monitors up to 14 sub-circuits and provides highly reliable operation without batteries or maintenance. A mobile-phone-sized data collector is installed in your switchboard, and connects via WiFi. Excerpt from Forum: 'IoTaWatt is an open source hardware/software project to build a low cost multi-channel electric power monitoring system. It works standalone or integrated with other open-source web server software like Emoncms 47 from the good people at openenergymonitor.org 47 or influxDB 23.

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.

Available solutions

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

Literature review

An analysis of commercially available energy monitoring devices has recently been published in [1]. 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.

Market analysis

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.

Product	Sensors[2]	Parameters[3]	Frequency	Risolution	Channels	Storage	Cost
Sense[4]	CT	P,E	4 MHz	2	Cloud	$ 299
Aeotec[5]	CT	P,E	1 min?	1	Cloud	$ 80
TED[6]	VT, CT, RC	V, I, P, PA, PR, VRMS, IRMS, cosφ, E	1 s	1 W	32	Local, Cloud	$ 299
Neurio[7]	CT	P,E	10 Hz - 1 Hz	1 W	1	Cloud	$ 179
Efergy[8]	CT	P,E	10 s	1	Cloud	€ 99
Ecoisme[9]	CT	P,E	?	?	6	Cloud, API	$ 200
CURB[10]	CT	V, I, P, PA, PR, VRMS, IRMS, cosφ	8 KHz	1 W	18	Local, Cloud, API	$ 399
Smappee[11]	CT, VT	V, I, P, PA, PR, VRMS, IRMS, cosφ, IARM	> 1 KHz	1 W	3	Cloud	€ 199
Net2Grid[12]	Meter	V,I,P,E	10 s	?	1	Local, API	?
emonTx[13]	CT, VT, Pulse	V, I, P, E, VRMS, IRMS, T	1 s - 1 min	10 bit / 10 W	4	Gateway, Cloud	£ 60
emonPi[14]	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[15]	CT, VT	V, I, P, E, VRMS, IRMS	16 KHz, 2 KHz	12 bit / 1 W	32	Local, DashBox	$ 300 - $ 500
GridSpy[16]	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[17]	CT	V,I,P	7.68 KHz	16 bit / 10 W	42	Cloud, LTE	$ 50 / month
BlueLine[18]	Pulse	P	1	Cloud	$ 179
Episensor[19]	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[20] 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.

Sense

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

It is an energy monitor that focuses on measurement accuracy and interfacing with the Z-Wave gateway. The user is responsible for saving consumption and must recognise which equipment is active and how much it is affecting overall consumption. It is characterized by wireless technology, and for being suitable for outdoor use, the range of the wireless signal declared is 150m. Power is taken from the switchboard. The idea here is that the electrical panel can be located outside, so it may be necessary for the metering system to be waterproof. The proposed system has a degree of protection of IP 43. The system uses the Z-Wave Plus protocol [21], a domotics protocol, and uses AES-128 encryption. The sampling interval is not clearly defined, the impression is that it is very low, in the order of ten minutes, and therefore not suitable for the application of the project. It is distributed in the UK by Vesternet and can also be purchased on Amazon. It can be supplied with a clamp for measuring the current in different numbers and with different ranges.

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.

Neurio

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.

Efergy

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.

Ecosisme

It is a very recent system, created by an English startup and financed by indiegogo. Production started at the end of 2017 and the first devices are expected to be delivered by the end of the year for campaign subscribers. On the site you can pre-order the system whose delivery is scheduled for the first quarter of 2018. This is a Non Intrusive Load Monitoring, which therefore allows not only the measurement of electrical consumption but also the detection of significant loads, starting from 100W. The system is able to show the consumption history and generate specific alarms through messages for smartphones. The system consists of a single unit of measurement and transmission, which also uses a CT split core sensor to be connected to the domestic electric panel. The information collected is sent online and is accessible via the app or via the website. In the project description it is said that the system is open so that APIs will be disseminated to access the data directly, it is not clear whether directly from the measuring device or (more likely) from the cloud. An interface for the IFTTT system will be realized. The system has a spectrum analyzer in addition to the consumption analyzer, this allows the recognition of the electrical signature of the device. They claim to be able to distinguish even the brand of the switched on device. It requires a WiFi connection for data transfer over the network. System training requires user interaction, which must interoperate by turning the device on and off to be recognized. The data transmission is secure and certified and uses the TLS 1.2 protocol. The system requires a continuous connection to the network as the processing required for the recognition of electrical devices cannot be entirely conducted on the client side. Currently it is possible to pre-order the household measuring system for 200€. In addition to the metering system, the order also includes access to cloud services. The specifications of the measuring system are not particularly informative, the maximum current being measured being 100A with a guaranteed accuracy of 99%. The system is obviously certified.

CURB

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.

Smappee

It is a platform for energy monitoring and non-intrusive load monitoring. The system, like the most modern systems available on the market, works by means of a metering unit connected to the power supply outside the electric panel, and by one or more current clamps to be connected to a phase inside the electric panel. The measurement of CT sensors, always split-core, is collected by the metering unit that connects to the WiFi network using the home router. The data is sent to the cloud and, as in similar cases, access is granted via an app for iOS and Android or via the browser. In addition to measuring consumption, the system also promises to recognize the active equipment, but no information is provided about the performance, the accuracy of the measurement, the sampling frequency, or neither on the system used to achieve the identification of the loads. There is no open and accessible API, but it is granted access through the IFTTT platform. The system is distributed in Italy in both the consumer and prosumer types, with information about photovoltaic production. There is also a Plus version for the management of heat pumps and electric vehicles and finally a version that also monitors the consumption of gas and water.

Net2Grid

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

It is an open-hardware and open-software system for monitoring electrical consumption, temperature, pressure and humidity. It is based on the Arduino and Raspberry platforms and originally consists of 5 units to which a sixth has recently been added.

EmonPi

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.

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EmonTx

It is a remote measurement unit that can receive readings from 4 CT split core sensors and send them to an EmonPi unit, or an EmonBase compatible unit via a 433MHz radio frequency signal. Alternatively it is also possible to send readings directly to the cloud using the WiFi module ESP8266 Huzzah. Power is guaranteed by an AC/DC transformer and buffer batteries to manage any faults. The maximum data transmission rate in the cloud is 10s, while the system is able to acquire voltage and current with a much higher sampling rate, 50 current measurements and 50 voltage measurements every 20ms, thus higher than 2kHz.

EmonBase

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.

EmonTH

This is the unit of measurement for indoor environmental variables. It is powered by two AA batteries with an estimated life of 6 months. Allows the measurement of indoor temperature, outdoor temperature and temperature and humidity through DS18B20 and DHT22 sensors. Connects to the EmonPi or EmonBase via an RJ45 connector. The maximum data acquisition rate is 60s. It represents the ideal solution for reading the environmental variables in connection with the EmonPi gateway or similar.

EmonCMS

The EmonPi system is designed to send data in the cloud to a Content Management System called EmonCMS. It is an open source system for storing and ensuring access to data.

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IoTaWatt

It is a 14-channel WiFi power meter, based on the ESP8266 chipset for data transmission and the MPC3208 12-bit ADC converter for voltage and current sampling. It can be equipped with 14 CT sensors and a voltage sensor, is compatible with different types of sensors, allows logging on a local SD card and can connect in WiFi with a Gateway base such as EmonPi and EmonBase. It can connect directly via WiFi to post data to CMS. It allows the reading of 35-40 channels per second, so the maximum sampling frequency is theoretically 40Hz, but the logging on the SD card takes place every 5s. It's CE certified like the other Emon class devices, it has an on board clock with backup. At present, it exports data via WiFi to EmonCMS or influxDB; in the future, it will be possible to use MQTT for data transmission. IoTaWatt is a less developed system than closed commercial solutions and is also less developed than other systems in the Open Energy Monitor group, such as EmonPi or EmonTx. However, it represents the platform with the greatest potential and that has the most up-to-date hardware. It has extremely interesting features, such as the ability to connect directly to a gateway in WiFi, or to a cloud system, and not necessarily to the EmonPi system. It is therefore extremely open when connected to a Gateway developed in the project. The development of the MQTT system for the posting of the measurements is foreseen, and also this is a reference standard for the aggregator developed in the project. Its specifications are totally open hardware and the software is likewise open, and has a good developer base. It does not have a unit for reading the environmental parameters.

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[1] 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
[2] CT: Current Transformer, VT: Voltage Transformer; RC: Rogowski Coil
[3] 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
[4]https://sense.com
[5]https://aeotec.com/z-wave-home-energy-measure
[6]http://www.theenergydetective.com
[7]https://www.neur.io
[8]http://efergy.com/it/
[9]https://ecoisme.com
[10]http://energycurb.com
[11]https://www.smappee.com/eu_it/home
[12]https://www.net2grid.com
[13]https://guide.openenergymonitor.org/setup/emontx/
[14]https://guide.openenergymonitor.org/setup/
[15]http://www.brultech.com/greeneye/
[16]https://gridspy.com/devices.html
[17]http://verdigris.co
[18]https://www.bluelineinnovations.com
[19]http://episensor.com/products/zem-30-zem-30i-wireless-single-phase-electricity-monitor/
[20]https://openenergymonitor.org
[21]https://it.wikipedia.org/wiki/Z-Wave