Researching options for new off-grid system

jmsol

New Member
Joined
Mar 27, 2022
Messages
4
Hey!
After a few weeks of researching, I've just found this forum and I'm hoping you guys can help me with your experience.

My plan is to take my country home off-grid. I'd like to have the capacity to power these items during longer days with full sun.
  • Lighting
  • Charging computers, phones, tool batteries, etc.
  • Fans
  • Energy efficient fridge and freezer.

I'm considering 12v or 24v, whichever works best in the final setup. The panel(s) will be very close (within 2 meters) to the batteries and charge controller, etc.

Option 1:
  • 395w panel(s)
  • Renogy Rover 40 Amp Mppt
  • 100ah LifePo4 battery (possibly 2 batteries)
  • Inverter 2000w
  • LifePo4 battery charger

Option 2:
  • 395w panel(s)
  • Mpp Solar mppt 24v 3000w
  • 2 x 100ah LifePo4 batteries

(Both options need to be able to operate with a generator.)


I'm trying to choose suitable panels, I've found these and I'm wondering if they are compatible with 12v or 24v system.

Trina Solar Vertex S (mono)
Peak Power Watts-PMAX (Wp) 395
Power Tolerance-PMAX (W) 0/+5
Maximum Power Voltage-VMPP (V) 34.0
Maximum Power Current-IMPP (A) 11.62
Open Circuit Voltage-VOC (V) 41.0
Short Circuit Current-ISC (A) 12.21
Module Efficiency η m (%) 20.5
Maximum Power-PMAX (Wp) 298
Maximum Power Voltage-VMPP (V) 31.9
Maximum Power Current-IMPP (A) 9.32
Open Circuit Voltage-VOC (V) 38.6
Short Circuit Current-ISC (A) 9.84

I was originally considering purchasing four Renogy 100w panels but then I came across this 395w panel, which was much less expensive. Can anyone suggest why it's so much cheaper?

Which system option would be most value for the cost?
Thank you in advance for all input, I'm very new to all of this!
 

OffGridInTheCity

Photon Sorcerer
Joined
May 23, 2021
Messages
844
Location
Southern Oregon
A few more details would be helpful - e.g. how many panels (for example) which will inform better advice on battery size. Also, do you want to power things thru the winter? or just summer? You can use PVWatts to get power estimates for your location weather - https://pvwatts.nrel.gov/pvwatts.php

So I'd go 24v and 395w panels - e.g. for a fixed / home installation and the list of things you want to run 24/7 is large enough - its a better fit. It's really helpful to figure out what power you actually need by measuring things OR... plan a small/complete system but leave room to double / quadruple over time as you see how it works

Just speculation - with the list above - you could use on the order of 8kwh/24hr period kind of range of power. You can pin this down buy using killowatt meters (or other power measurement) on your equipment and see what it averages. If it is 8kwh/day, in stormy/multi-day-cloud-rainy/short-day winter months you'll need on the order of 10-15 x 395w panels and a 5kwh battery (4-6 x 100ah) to average 8kwh/day.
 
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MichaelK

Photon Sorcerer
Joined
Mar 21, 2020
Messages
2,131
If this is for a home, then forget about 12V completely. If your application doesn't have wheels on it, then 12V is just too limiting. Your needs might be met by either a 24V system, or a 48V system, with me leaning towards recommending 48V (I myself have). As the voltage of everything goes up, limitations concerning the transmission of the power over longer distances goes way down. With a 48V system, you may run high-voltage solar for hundreds of feet with little power loss if you are using the most modern electronics.

Based on the loads you listed above, I'd guestimate you'll need about 4.0kWh (4000Wh) of power per day. Easy to accomplish that. Here is what I just cut and pasted for another user with about the same needs.

8 250W grid-tie panels, 30V each. Wire them in 4S2P Grid-tie panels are far cheaper per watt than 12V panels designed for the automotive market.
Epever 6420AN charge controller ~270$ on ebay can transform raw solar power from up to 200V down to battery voltage.
8 6V Trojan L-16 batteries, wired in series for 48V
Schneider SW4048 sine-wave inverter, 1700$ (hard-wired directly into the main electrical panel)
main electrical panel for the inverter, ~350$ (this has the breakers and switches for binding the batteries, inverter, and charge controller together. Schneider Electric 865-1016 Conext SW DC Breaker Panel - RES Supply 411$
wires, breakers, spit, and other stuff, another 500-750$

I built my own rotating solar arrays out of schedule 40 pipe and unistruts. Two could easily handle 8 large grid-tie panels. I wire my panels four in series to make 120VDC, which I transmit ~130' from the array position to the controller. With 10 gauge solar wire, voltage drop at 120VDC is less than 2%. By rotating an array East to West over the course of the day, I was able to make 5.0kWh of power from one array in the first week of February.

If you bought the 395W panels, six of those might be all you need and you might be able to fit them all on just one array frame. Wire them as 3S2P. I would dissuade you from buying anything Renogy. I've been dissappointed in the quality of the things I bought from them.
 

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jmsol

New Member
Joined
Mar 27, 2022
Messages
4
A few more details would be helpful - e.g. how many panels (for example) which will inform better advice on battery size. Also, do you want to power things thru the winter? or just summer? You can use PVWatts to get power estimates for your location weather - https://pvwatts.nrel.gov/pvwatts.php

So I'd go 24v and 395w panels - e.g. for a fixed / home installation and the list of things you want to run 24/7 is large enough - its a better fit. It's really helpful to figure out what power you actually need by measuring things OR... plan a small/complete system but leave room to double / quadruple over time as you see how it works

Just speculation - with the list above - you could use on the order of 8kwh/24hr period kind of range of power. You can pin this down buy using killowatt meters (or other power measurement) on your equipment and see what it averages. If it is 8kwh/day, in stormy/multi-day-cloud-rainy/short-day winter months you'll need on the order of 10-15 x 395w panels and a 5kwh battery (4-6 x 100ah) to average 8kwh/day.
If this is for a home, then forget about 12V completely. If your application doesn't have wheels on it, then 12V is just too limiting. Your needs might be met by either a 24V system, or a 48V system, with me leaning towards recommending 48V (I myself have). As the voltage of everything goes up, limitations concerning the transmission of the power over longer distances goes way down. With a 48V system, you may run high-voltage solar for hundreds of feet with little power loss if you are using the most modern electronics.

Based on the loads you listed above, I'd guestimate you'll need about 4.0kWh (4000Wh) of power per day. Easy to accomplish that. Here is what I just cut and pasted for another user with about the same needs.

8 250W grid-tie panels, 30V each. Wire them in 4S2P Grid-tie panels are far cheaper per watt than 12V panels designed for the automotive market.
Epever 6420AN charge controller ~270$ on ebay can transform raw solar power from up to 200V down to battery voltage.
8 6V Trojan L-16 batteries, wired in series for 48V
Schneider SW4048 sine-wave inverter, 1700$ (hard-wired directly into the main electrical panel)
main electrical panel for the inverter, ~350$ (this has the breakers and switches for binding the batteries, inverter, and charge controller together. Schneider Electric 865-1016 Conext SW DC Breaker Panel - RES Supply 411$
wires, breakers, spit, and other stuff, another 500-750$

I built my own rotating solar arrays out of schedule 40 pipe and unistruts. Two could easily handle 8 large grid-tie panels. I wire my panels four in series to make 120VDC, which I transmit ~130' from the array position to the controller. With 10 gauge solar wire, voltage drop at 120VDC is less than 2%. By rotating an array East to West over the course of the day, I was able to make 5.0kWh of power from one array in the first week of February.

If you bought the 395W panels, six of those might be all you need and you might be able to fit them all on just one array frame. Wire them as 3S2P. I would dissuade you from buying anything Renogy. I've been dissappointed in the quality of the things I bought from them.
Hey, thanks for the responses!
I think I've got to add some things to clarify a bit. My country home is more of a cabin than a modern house. The items I'll be running off the solar power will not be standard home items, it will be more like some LED lights in the evening, charging phones or laptops and a small table fan. I won't be running heavy draw appliances like coffee machines or vacuum cleaners, etc. Just an efficient fridge and/or freezer. Whatever I can run, if possible, on a 800w system preferably with two panels..

Also, I failed to mention that I'm in Sweden. The summer days are quite long and I've calculated for 5-6hrs of southern sun per day from March to October. I won't be depending on this system much in the winter season. At times when we aren't receiving much sun, we will use a generator to charge batteries. I have seen examples of other systems similar to the setup I mentioned, and they appeared sufficient for our needs. So I'm hoping to build something like the smaller systems I've seen. But I'm open for any suggestions and tips.

If this is for a home, then forget about 12V completely. If your application doesn't have wheels on it, then 12V is just too limiting. Your needs might be met by either a 24V system, or a 48V system, with me leaning towards recommending 48V (I myself have). As the voltage of everything goes up, limitations concerning the transmission of the power over longer distances goes way down. With a 48V system, you may run high-voltage solar for hundreds of feet with little power loss if you are using the most modern electronics.
The panel will be installed on the outer wall of the house where charge controller/batteries will be directly on the inside, at most 2 m apart, so longer cables will not be required. Still leaning towards a 24v system.
8 250W grid-tie panels, 30V each. Wire them in 4S2P Grid-tie panels are far cheaper per watt than 12V panels designed for the automotive market.
This system will not be connected to the grid. Is the Trina Solar Vertex S a grid-tie panel only or can It be used completely off-grid?
Epever 6420AN charge controller ~270$ on ebay can transform raw solar power from up to 200V down to battery voltage.
8 6V Trojan L-16 batteries, wired in series for 48V
Epever 6420AN looks interesting, but I prefer the faster charging time of Lithium batteries. One 24v 100ah or two 12v 100ah in series.

Thanks again!
 
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