Temperature and photovolatic monitoring


I'm monitoring temperatures in my home office and the power of a little solar installation with a 55W panel and an old 12V car battery. From this battery I charge my mobile phone by a small DC/DC converter and my model plane batteries via a Lipo charger. I also use the 12V for running the EmonTX modules, so most of the measuring system is powered by the sun.

The values collected by two EmonTX modules, the one measuring power uses an ACS712 current sensor and a voltage divider to measure voltage and current flowing into the battery. I've also here a self developed EmonTX based measuring node that will use two current sensors to measure both, the charging current and the load current. It will be installed when the 868MHz RF module arrives from the shop. I also have a 250W module on my garden house that is connected to a inverter, this is the next step, I will measure, DC voltage/current and AC voltage/current, but I have to solve the RF problem first, because this is about 30m away from my house and I think I don't get a signal from that position.

All values come together in a RaspberryPI, the database is stored external on an old PC running a LAMP server. Data is also exported to Emoncms Website.

Short description of the temperatures: One Sensor is hanging under the desk, one is hanging out of the window (East side of the house, sun can directly shine onto the sensor at about 14:00). The other two sensors are glued to the window with a piece of tape, one inside and one outside. The window also has got a hand-driven shutter. If it is down, the temperature of the window drops down some degrees in summer or rises in winter. This can also be seen in the graph.

So enjoy the monitoring:

http://www.emoncms.org/jb79/Temp You have to choose day or week to show values, I'm not sure what's the problem with it-


TrystanLea's picture

Re: Temperature and photovolatic monitoring

Thats really nice dashboard and data, thanks for sharing. Not sure either why it does not show as default, will have to look into that.

jb79's picture

Re: Temperature and photovolatic monitoring

Today I got my RFM12B modules, so I was able to finish the new measurement system that could monitor the solar cell and the load. You can find the first revision of the dashboard here: http://www.emoncms.org/jb79/Solar1

I'll try to develop the dashboard (other dials or such a thing) when I have got some values in the feeds, so in maybe one or two weeks it will look better.

Is there a possibility to display Wh instead of kWh in the dials or does it mean that I have to modify all the input calculation? It would be useful in this case because the energy generated from the 55W panel is about 0.1-0.2kWh per day, it would be better if the dial could show values between 0.1 and 0.2.


I've attached a picture of the pcb I designed for this modified version of the EmonTX. It can monitor solar current, load current, battery voltage and temperature sensors (maybe used in the future). All unused ports of the processor are connected to pins so it is easy to add new functions. For this reason there is also some space on the pcb where components could be added.

I also had a small problem tomorrow, no new measurements arrived. I had to do the install procedure for the PI's RFM module again, now measurements arrive like before.

Second bug fixed: Temperature inside/outside on the window were interchanged, fixed 14.07. 2:31

jb79's picture

Re: Temperature and photovolatic monitoring

@TrystanLea: I've just found out why the diagrams don't show the actual values per default.

I used multigraph and didn't tick "floating time". Now it works. I think it might be a good idea to set this point to enabed per default for new multigraphs in the next version of emoncms.

jb79's picture

Re: Temperature and photovolatic monitoring

After installing a Atmega328 with the groupRelay script from jeelabs into the kitchen I'm able to receive the values of the 250W solar panel mounted onto the roof of my gardenhouse.

It can be found here: http://www.emoncms.org/jb79/Solar2

As there is no transformer for voltage monitoring I use will use 230V for calculation of AC power but first I have to install the CT sensor later this day.

jb79's picture

Re: Temperature and photovolatic monitoring

Latest Update: I modified the system in the gardenhouse. Now there is a DS18B20 temperature sensor mounted on the grid power inverter.

The system in the gardenhouse monitors the solar voltage and if it gets over about 24V (under that voltage there is not much power so the inverter won't really work) it also checks the temperature of the inverter. If the temperature rizes over 35°C a fan is switched on to cool the inverter until it's temperature drops below 30°C. This also helps to run the EmonTX for a longer time because the fan also took some power of the solar cell before this modification. Now if the voltage is under 24V there is only the EmonTX running, and it can do the shutdown at 12V (sending DC and AC current measurements of 0 to the raspberry) correct. Before there have sometimes been trouble when the voltage drops to fast because of bad weather or something else.

jb79's picture

Re: Temperature and photovolatic monitoring

Today I added another custom EmonTX to measure temperatures in my installation room and to check if there is water on the floor there. I programmed the processor and everything is working fine until I installed it in the room because I didn't get any data even if the led is blinking all 5 seconds. When it's connected to the programmer  (CP2102 USB to RS232 interface) everything is running but if the circuit is connected to a battery or another powersupply it doesn't work.

The powersupply of the circuit consists of a LM7805 and a MCP1702, I use this combination for most of my tests because I often use LIPOs with 4 cells => up to 16,8V for testing, that's too much for the MCP1702.

The solution was very simple: I added a 1µF capacitor at the IN pin of the MCP1702, after that everything is working fine, the 100nF capacitors in my circuit seems to be too small.

The new EmonTX will measure the temperatures of my 800l boiler that is used for hot water in the house and for the heating. The heat-source for the boiler is my heatpump and a 10m² thermal solar cell on the roof of the house. In summer it can reach up to 80°C during the day. I will install 3 or 4 sensors from the top to the bottom. At the moment there is only one sensor measuring the room temperature.

The second sensor connected consists of two litte pcbs connected by two wires. I installed them on the floor so that they get wet when there is water on the floor. There is a 47k pull-up resistor to 3,3V. If the wires get connected by water the pin goes to 0 and I get an email (by the event module of emonCMS).

The "flood sensor" and the new temperature can be found on the overview dashboard: http://emoncms.org/jb79/Main

jb79's picture

Re: Temperature and photovolatic monitoring

And today the flood sensor passed its first test, when the water pump in the installation room failed to pump away the water from the decalcifying plant. The only problem was that the notification email doesn't work this time, so I saw it when the water allready covered the complete room (it was about 60l of water on the floor).

I think I have to check what's going wrong with the event module and it's configuration. If I test it by pressing the "test" button it seems to work.

jb79's picture

Re: Temperature and photovolatic monitoring

Some days ago the next step was taken by putting another (custom built) EmonTX into service. Now I can monitor 4 temperatures on my 800l water boiler. As they are in the same room I also connected the temperature sensor for the installation room and the flood sensor to this EmonTX.

So there are 4 EmonTX in my house at the moment and another one in the gardenhouse with the solar cell.

The boiler and the inside/outside temperatures can be found on http://emoncms.org/jb79/Boiler

jb79's picture

Re: Temperature and photovolatic monitoring

A week ago I corrected the software for the temperature measurement (sometimes I get no values from the sensors, that looks ugly in the graph): http://openenergymonitor.org/emon/node/3228

I also took a picture of my modified emonTx clone in the wild: no case, the little power that is needed is stolen from the 12V power supply of my decalcifying plant next to it. To get a clean supply a LM7805 takes down the 12V to 5V, so that the 3,3V regulator can't get to high voltages if the voltage goes over 13V some time.

With this emonTX I measure 6 temperatures temperature in this room, temperature of the 10m² solar system coming down from the roof and 4 temperatures of the 800l boiler. Another "sensor" consists of two little pcbs, each having soldered 2 wires on it. If a water drop touches both of them a pin of the arduino pins is pulled down near 0, normally a 47k resistor does a pull up to 3,3V. I can connect a lot of such sensors simple in parallel if needed.


jb79's picture

Re: Temperature and photovolatic monitoring

Latest updates:

I've installed a EmonTX Clone with a LDR and a DS18B20 in my garage some weeks ago. The temperature never gets lower than about 1°C, even if it's about -5°C outside. The walls are 10cm concete and there is no insulation, there is also no heat source because the way to the garage is not finished yet, so I can't drive my car inside.

The LDR measures the light in the garage, the sensor value can be 0-1024 (0 is very dark), during the day it get's up to about 990. When the electic door is opened a small lamp is switched on, I can also measure that (reading it all 30 seconds).


The latest update is my 12V battery storage. I removed the old car battery because it was very weak and replaced it with a brand new 230Ah/12V lead-battery. It can take some time till the 55kWp solar cell will charge it. The small 12V/32Ah battery is still ok and switched in parallel, giving me a total capacity of more than 260Ah (20h discharge) and more than 280Ah at 100h discharge.

I plan to install another Raspberry PI (with harddisk) in some weeks that should be powered by this battery. Later that year I'll maybe install an autmatic charger that will keep the battery above a certain level if the charge by the solar cell is lower than the power consumtion  (normally in winter). If the raspberry takes about 10W at maximum, it can run about 14 days without solar charge.

phermansson's picture

Re: Temperature and photovolatic monitoring

Thnaks for sharing that nice system! I wonder, how do you create the temperature graphs in http://www.emoncms.org/jb79/Temp?

jb79's picture

Re: Temperature and photovolatic monitoring

Latest development:

A few days ago I swiched off my first raspberry (logged to local database on my homeserver and emoncms.org). Before that I allready installed a second raspberry with the harddisk option (2,5" 24/7 type), that's directly fed from the 12V/230Ah battery. It's power consumtion is about 114Wh per day, so about 4,75W. This 4,75W are used for: raspberry, harddisk, SATA to USB adapter, a dc/dc converter for this system and an EmonTX with 7805.

The solar panel that's feeding into the battery creates an average of 6,7W, so abou 2W more than the power consumtion of the measurement system.

I've also checked the average from the begin, that's only 4,2W since July 12th 2013, but May and June seem to be two month with a lot of energy to load into the battery, so I hope I can get this up to 4,75W or more over the complete year. The average of this week for example was 6,9W.


Last week was a good week for hot water generation too, my heatpump had nothing to do since April 17th, all energy (hot water and house heating) was done by the sun, even with low outdoor temperatures in the night (down between 0 and 10°C) => http://www.emoncms.org/jb79/Boiler

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