May 7, 20197 yr Hi, I'm busy with a fun little project to make a little display of available solar power to put in the house to try to encourage running the high draw stuff when there is spare solar power. I used a little ESP8266 board and some led strips driven over i2c. For me the ESP8266 runs a program that listens to MQTT events from my monitoring and drives the display based on the worked out numbers. So on the right you see the current power usage in the house. (Geyser was on so we are full scale) On the left the idea is to show the "available" solar power - at that time it was just a few watts. I might refine to use colours to show more info. But a challenge is that if there is no load there is no power from the panels. So I want to show an estimate of the available power. The first part of making that estimate is the weather - yr.no has an API which should allow me to get an estimate of cloudiness. The second part would be the solar insolation at the address on the date. Those two with a fudge-factor should provide an estimate of what is available. Has anyone looked at this before - can anyone point me at a public API or dataset that can work our insolation for a lat/long and date? My idea was to mash together the insolation and the weather and come up with a "factor". I can make this available on a public API. User would query the API and multiply the factor by their system size and a fudge factor that gets the estimate to be approximately right for their results.
May 7, 20197 yr Mount a small LDR or photo transistor in the same orientation as your solar panels. Feed that to an A/D input with a suitable pull-up to 5V or whatever you need. Now you have a simple but effective "potential PV power" indicator after a quick calibration to match its output with what your panels are doing at max load.
May 7, 20197 yr Author 8 hours ago, The Bulldog said: Mount a small LDR or photo transistor in the same orientation as your solar panels. Feed that to an A/D input with a suitable pull-up to 5V or whatever you need. Now you have a simple but effective "potential PV power" indicator after a quick calibration to match its output with what your panels are doing at max load. To be fair, that is a lot simpler...
May 7, 20197 yr The most accurate way is to buy a very small PV panel with a defined Wp and the same crystaline technology like the one that you are using for your main PV array. 10W panel is more than enough. Place the panel at the same direction and angle (important), like your production panels are. Then attach a big resistor that will cause this small panel to work near it's maximum power point aka MPP. The truth is, that MPP does move just a little, regardless of insolation/ Therefore a resistor is a sufficient load simulator and MPPT controller is not needed. Next, you just measure the Volts x Amps with an Arduino. This will give you a maximum available power at the moment, which can be just multiplied, in order to predict main PV array's potential. Similar approach is sometimes used in the solar trackers:
May 8, 20197 yr 7 hours ago, Youda said: The most accurate way is to buy a very small PV panel with a defined Wp and the same crystaline technology like the one that you are using for your main PV array. 10W panel is more than enough. Place the panel at the same direction and angle (important), like your production panels are. Then attach a big resistor that will cause this small panel to work near it's maximum power point aka MPP. The truth is, that MPP does move just a little, regardless of insolation/ Therefore a resistor is a sufficient load simulator and MPPT controller is not needed. Next, you just measure the Volts x Amps with an Arduino. This will give you a maximum available power at the moment, which can be just multiplied, in order to predict main PV array's potential. Similar approach is sometimes used in the solar trackers: Just keep in mind that that a 36 cell (10W) panel's efficiency is generally much lower than a 72 cell panels
May 8, 20197 yr @Elbow , I have done something similar and it has been running for quite a while now. I used one of those small solar LED lights that almost always only last three months. While I was at it I also added a Temp sensor and a LDR for fun. I am currently measuring the voltage output from the small panel. As the max output volts is 5 v I could have used it directly but decided to use a Voltage divider just for in case. It tracks the output quite well but I still want to put a small fan on it and measure the current output to check if it will make a difference. The LDR is not that accurate as it does not measure the radiation. Then there is an App running in NODE RED that is very accurate in forecasting what Solar you should get but will need to tweak the settings to match up it with your array.https://flows.nodered.org/node/node-red-contrib-solar-power-forecast Edited May 8, 20197 yr by PaulF007
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