Introduction

ArdaSol is the project name for my solar energy and Arduino based monitoring system. This description shows how the system is built and how it works. The energy production of a photovoltaic plant is monitored and also the consumption or feeding to grid of the energy. Data acquisition during a solar day and publishing on the internet is also a function of this system.

System overview

This block diagram shows my solar plant with the ArdaSol Energy Monitoring System.

On the roof of my house, there is a photovoltaic plant of 3 kWp power. It produces electrical energy, direct voltage and current (DC power). The power is fed to an inverter, the energy will be converted to alternating current (AC Power) and fed to the grid. The grid voltage is 230V. The solar energy will be consumed by ourselves or fed to the public grid. Two official energy meters c1 and c2 measures the energy flows:

·         Solar Energy Produced (c2)
In Italy I get paid for this, for the next 20 years, its 23 Eurocent per kWh

·         Solar Energy fed to grid (c1)
The surplus solar energy, not used by myself, is fed to public grid, for this a also get paid, but it’s a market price, about 7 Eurocent per kWh

·         Energy consumed from grid (c1)
When the solar power is absent, the energy for our house is delivered from grid. ENEL (Italian Energy Production Company) sends an invoice for the consumed energy, I have to pay overall (energy- and network costs) 25 Eurocent per kWh.

The ArdaSol Energy Monitoring System has 3 devices:

·         ArdaSol Display
The master of the system, collects the data from the two other ArdaSol devices, shows the data on the display, stores it on a SD card and sends it to a server in the internet

·         ArdaSol Energy Monitor
Measures the consumption of the energy, shows energy values on local display and delivers it on request to the ArdaSol display

·         ArdaSol Remote PVI Interface
The photovoltaic inverter (PVI) has a RS485 interface, this is connected to ArdaSol Remote, which interacts as a gateway to ArdaSol display. It converts the request, coming with a radio signal to the PVI and vice versa

How does ArdaSol work?

The master of ArdaSol is the Display.

I
it gets the energy data from the photovoltaic inverter (PVI) by the Remote interface and the consumed energy from the Energy Monitor. This data acquisition is done every 20 seconds and data is stored on an SD card for future analysis.
The Xively cloud data service will receive also the data from the display, it is sent by an http request to the server. 
You can have a look to the data:  https://xively.com/feeds/70230/
An infrared sensor in front of the display detects a person in front of it. The data will then display in the following manner:

Display no sequence                     Shows

1                                                            Ambient temperature and Time

2                                                            Instant Solar Power

3                                                            Consumed Power

4                                                            Peak Power value in day

5                                                            Solar Energy produced in the day

6                                                            Energy consumed

7                                                            Total Solar Energy produced in a year

8                                                            Total Energy consumed in a year

9                                                            Average Solar Energy produced in a day

10                                                        Average Energy consumed in a day

11                                                        Weekday and date

Display examples:

The consumed Energy will be measured by the ArdaSol Energy Monitor

It gets the energy consumption by a current and a voltage sensor, calculates the real power, displays it locally and if requested by the ArdaSol Display, sends the values back. The solar energy data will be transmitted from the display to the Energy Monitor. Analogue LED-Bar graphs showing the solar- and consumed power values.

Here some display examples:

The Interface between Photovoltaic Inverter (PVI) and ArdaSol Display is the ArdaSol Remote

Wireless communication between ArdaSol Display and Remote Interface is done by an XBEE module. The data stream is converted to half duplex RS485 interface to the PVI.

ArdaSol Display description

An Arduino Mega board controls the display functions. An XBEE wireless module is connected on a serial port and communicates to ArdaSol Energy Monitor and ArdaSol Remote interface. The 32 x 16 dot matrix display is connected with 4 wires on the digital outputs of the mega. The SD card on the WiFi shield stores the acquired data from the solar plant and from the energy monitor in a formatted csv-file. Part of the data is also sent to the XIVELY cloud service. Data is displayed only, when a person stays in front of it, due to an infrared sensor on the front panel of the display. A TMP36 sensor is connected to an analogue input of the Arduino and measures the ambient temperature.

ArdaSol Energy Monitor description

The Energy Monitor is controlled by an Arduino Uno board. A current transformer is used to measure alternating current and a voltage transformer to measure alternating voltage. Resistor networks adapt the signals to Arduino analogue input levels. Now the real power used can be calculated, showed on 4-digit and LED bar graph displays. On request by the ArdaSol Display, the Energy Monitors answers with the energy data. For showing the solar energy production, yellow LED bar graph indicates the amount of power produced. The data will be received from the ArdaSol Display. Wireless radio communication is done by an XBEE module.

ArdaSol Remote Interface description

Power One / Aurora photovoltaic inverters are able to communicate over a half duplex RS485 interface to an external unit. ArdaSol Remote Interface sends the data, received from the XBEE module to the PVI and also sends back the answer data of PVI. ArdaSol works in a transparent mode, this means that data is handled 1:1 in both directions.

ArdaSol Software

The Arduino software for the three devices is public available on github: https://github.com/hpieren/ArdaSol

ArdaSol Schematics

ArdaSol Display

ArdaSol Energy Monitor

ArdaSol Remote Interface

Conclusion

This project made to me very much pleasure and fun. I learned a lot and would like to thank all the people, who made her know how public, most issues I could resolve with the help of the Arduino Forum http://forum.arduino.cc/

Special thanks to:

·         PVI Communication Doc. on http://stephanos.io/archives/96

·         CRC16 Calculation Algorithm and Aurora communication definitions:
Curtis J. Blank curt@curtronics.com

·         Arduino demo program for Holtek HT1632 LED driver chip
Nov, 2008 by Bill Westfield ("WestfW")Copyrighted and distributed under the terms of the Berkeley license (copy freely, but include this notice of original author.) Dec 2010, FlorinC - adapted for 3216 display

·       Open Energy for the emon library http://openenergymonitor.org/emon

Italy, January 2014
Heinz Pieren
heinz.pieren@semprevacanze.it