measuring available power

Hi all
I am doing a project of switching in between power sources using a micro controller, but now I first need to determine available power from Grid tie,Generator and also PV Solar ,I believe the method would be more the same for all of the them, whats the easiest way to measure available power from these sources?

If you anyone knows how to use the small reference cell method for measuring from PV Solar please enlighten me

Surely the generator power output is written on it somewhere - likewise the solar panel... depending on light level which you could measure with an LDR. The grid tie power will be limited by the property's main fuse rating



I have a similar Project but limited to photovoltaic and battery. I can tell how much potential the photovoltaic has by measuring the voltage and amps. If the voltage is low and the amps is low, there is no power there. If the voltage is middle and the amps are high, the potential power is being used and there is no additional potential to tap. If the voltage is high and the amps low, there is more potential power than currently being used. About the same works for the battery.
"Power available" can be interpreted many ways. Is the power "available" from the Generator measured in amps and Volts, or how full the fuel tank is? If the tank is empty, there isn't much more power "available", regardless of how many Volts/amps it is currently kicking.
Please be a bit more specific in what you Need to measure.

The generator's power will be at it's full rating until the fuel runs out. The remaining fuel tells you the energy available



I received the following private message. Please respond to Posts directly and not via private message. This keeps the thread together and will allow others to possibly benefit from the discussion or to contribute as well.

"u said I must be more specific on what i need help on, like i said on my post i need help on determining the power produced by one of these source continuously using micro-controller, like i need to know at any point power each sources producing. its either by measuring short circuit current and voltage the determine power by using arduino or raspberry pi , like a very simple method"

Actually, in your post you referred to "easiest way to measure available power". "Available" power and "producing" are not necessarily the same thing. That's why comments were made concerning fuel in the Generator tank...

To measure power, you Need two measurements. Volts and Amps. P = I * E. Power (im Watts) = I (Amps) * E (in Volts). In my Project, I used an Adafruit INA219 breakout board with an off-board 0.001 Ohm (0.01?) shunt resistor. The breakout is easy to use because it communicates via I2C.

As to using the "small reference cell method", this is a methodology to estimate how much photovoltaic power may be produced. A photovoltaic cell may produce, for example, 1.5 Volts in full sunlight and if it is not attached to any (much) load. When the sun is shining less powerful, it may only produce 0.5 Volts. Using the reference cell, one reads the voltage from a small cell and calculates how strong the sun is. You could then make estimates of how much a large photovoltaic Array will be able to produce. If you have a 5KW Peak Array but are only currently getting 50% sun then you might expect 2.5 KW.

On my Project the solar Panels are used to Charge batteries. The solar Panel produces up to 18V with no load but the charger will pull it down in order to Charge the batteries. If I detect, for example 16V coming off the photovoltaic, then a) there is sun available and b) not all of it is being used to Charge the batteries. If I also detect that only a couple amps are flowing then a) the batteries are being trickle charged and b) more power is available than I am using. Therefore, my Project will start looking for things to do with that unused solar power (turn on the pump and fill a water Reservoir, check the temp in the heater to see if the power can be converted to stored heat, etc, etc, etc)

Basically you can not measure available power, only actual power.

You can only guess what the available power migh be. In the same way as you can not measure the potential top speed of a car, you can only measure what speed it is doing. You might be able to guess the top speed by looking at the engine capacity and the rpm but it is only a guess.

You can only guess what the available power migh be.

And any guess about the surplus output from a Solar Panel can vanish in a second if a cloud covers the sun.


Thank you guys atleast now I know how to go about it, I appreciate the help.