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Using solar PV monitor for an off-grid installation

off-grid
solarpv
Tags: #<Tag:0x00007f16a990de10> #<Tag:0x00007f16a990dca8>

(David Bourguignon) #1

Dear all,

I am planning to use OpenEnergyMonitor SolarPV for an off-grid installation. That is, instead of monitoring the full data set:

  • Solar PV generation
  • Site-consumption
  • Solar PV generation used on-site (self-site-consumption)
  • Solar PV generation exported to the grid
  • Electricity imported from the grid

I will only have the opportunity to monitor two variables:

  • Solar PV generation (directly stored in the battery)
  • Site-consumption (that is electricity imported from the battery and used by various devices)

Do you think this off-grid scenario is compatible with the current SolarPV system and the MySolarPV app? Since I am a newcomer, I will greatly appreciate any feedback.

Thanks in advance for your help.

Best regards,

David.


(Paul) #2

Hi David,

I don’t see why it would not work. you are doing everything I am doing minus the grid connection.

you graphs would not show a negative value.

if needed once you have the data, you would be able to draw your own graphs


(stephen krywenko) #3

batteries would be a little hard to get accurate information depending on the type of battery I would think especially the absorption rate. but I guess for most part you could just do an assumption. at the beginning say for lead acid use 80% if 1kw went in then assume 800 watts will be the amount that comes out. another option would be sampling you have known number the batteries capacity the amount that goes in the amount that goes out and and the state of charge after ( based on voltage). you could set up a little math routine to calculate the actual absorption rate ( still an approximation but a very close one) that will automatically compensate as the batteries get older and absorption deteriorates.

if your using lithium batteries it probably be at ~ 92 - 95% absorption,
here is a page with info that help you out a bit
http://www.powerstream.com/LLLF.htm


(stephen krywenko) #4

for the heck here what a quick sample math routine might be. though I have not proved its viability but should be pretty close to this math routine with a few tweeks you have to map out voltage to state of charge for your type of battery )
at an idol period sample state of charge at the beginning and end of day
ie if (solar input = <0 can && consumption = < 5 watts) sample state of charge
capacity/ state of charge = capacity1 beginning of day sample
if (solar input = <0 can && consumption = < 5 watts) sample state of charge
capacity/ state of charge = capacity2 ///end of day sample -actual capacity
(solar production- consumption)/ capacity= capacity3 // production differential

capacity1+capacity3=capacity4 /// probable capacity
capacity2/capacity4 = absorption // battery absorption rate
then once you have an absorption rate you can apply to your battery capacity
now you would have to offset the original capacity by the normal brand new battery absorption rate that it was rated at ) ie lead acid 80%
(capacity+20%)* absorption= real world capacity. (it will be off by a couple percentage points but that probably compensate for stand by draw of your inverter) so now as the battery absorption capacity drops. it should calculate the real world capacity of your batteries and tell you the general health of your batteries overall

though I think you might have to invert depending on battery type if state of charge is higher then expected for lead acid


(David Bourguignon) #5

Thanks a lot to you all for your detailed answers.

I will first try monitoring only the PV production (ie. the intensity of the current in only one cable). I guess this is completely OK, even if the original monitoring system was designed with two clamps in mind.

As soon as I have started experimenting, I will let you know how it goes.


(Robert Wall) #6

I think everyone has assumed this

means that you will be measuring alternating current. If “directly stored” means a direct current, a current transformer won’t work, and you’ll need to go to a Hall effect device.


(David Bourguignon) #7

Thanks @Robert.Wall for this extra info. I confirm that I will be measuring AC.


(Alistair Ciantar) #8

Hi David, I am thinking of something similar to what you have proposed. Did you manage to get the system in operation ?

Thanks

Alistair


(David Bourguignon) #9

Unfortunately not @Alistair_Ciantar ! Best of luck in your endeavors.


(Dirk Walde) #10

Can not save the data on a local web server.