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3Kwh of solar power from my panels, need direction on what I can do?

Saywatman

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Sep 25, 2019
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I just inherited 38, 24v 80w panels which comes to a little over 3Kwh of power. Is this enough to live off grid with? Here is some information: our living conditions add up to between 7-8Kwh a day, it was 15Kwh a day when we had our children living with us, but since they flew the coop our electricity went down to 7-8Kwh a day. We live in Hawaii and everyone I been talking to says we generally have between 5-6 hours of usable sunlight a day. Some questions I have are: Should I run my system at 24v or 48v? And according to which system, what would be a good setup for each? Batteries, charge controller/s, inverter etc.? These panels have never been used yet and are still in the box. Where we live our main supply of water is caught on our roof and stored in a catchment of 5000 gal. There is a lot of useful information about solar on the internet and at times it can be daunting so figured maybe I would ask someone in this forum for some advice or try to steer me in the right direction. Mahalo
 
over 2kWh, you need to go on 48V or more because the wiring become very expensive due to excessive thickness required.
so you will need to build an array that use probably a mix between serial and parallel to benefit both what serial and parallel offers.
(parallel offers anti-shading while serial offers higher voltage, easier conversion, cheaper wiring).
all the details will depend from the where and how you will mount panels, the type of SCC and inverter you will choose etc...).
batteries come last, since there is no real constraint about it, the choices are almost unlimited.
for you, the easy way would be to create a scalable sytem with all-in-one MPPT boxes (you can start with a 5KWh 48V box and add a 2nd if needed). Just make sure you choose a non-grid-tie model.
7Kwh of battery is easy and cheap to find. You will be able to expand later and you can fine-tune battery charge complementing with grid if necessary, until you can totally unplug.
you got 3A per panel, so putting 3 panels in series gives you about 72V 3A and putting 12 group of 3 in parallel gives you 12x3 a =36A.
so you will get an array at 72V 36A= 2500Wh
you could even go 4 in series at 96V i think an MPP box can support up to 150V) and 9 in parallel that is 27A for even cheaper wiring.
you can charge a 7000Wh battery in 3 hours and use the remaining energy to run hungry devices (washing machine, pump to lift water on the roof)
during the day. Not sure you can afford AC running all day and night, you should consider upgrading your panels to bigger ones and you target should be 12KWh at least. New AC type with inverter is recommended in that case
That looks like a lot, but consider that most ratings are maximum ratings, so you hardly get that all the time. A clouded/rainy day can drag you way down under 50%.
You would also install solar tube/panel to produce hot water, so you can store 100-200 liter in an isolated tank that you can then use later, even if you need to heat up again with electricity, the energy spared is huge. (washing machine, dish washer all heat their own water)
 
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Aloha Nosys70, thank you for the information. We will not have AC due to our trade winds and we’re up around 1000’ elevation. Part of the 7Kwh is with an old refrigerator that runs on 6.5 amps. And a chest freezer that runs on 2.5 amps. These are going to be replaced by newer models that are more efficient: 1.5 amps each. I’m glad you responded because I didn’t know you could connect the panels for that high of a voltage. I really thought I could only go as high as 48v. My whole setup is going to be part of my car port (garage). I do not have grid power where I’m at so there will be no grid power to tie into. I was also thinking of using a dc water pump vs an ac pump due to the high amp draw (?). I have two ph6 Paloma water heater’s also to be added in later. We have a propane dryer and stove also. Can you recommend some “all-in-one MPPT boxes? Mahalo. Saywatman
 
there is a popular one on this forum, just look the page of Will ("DIYSolar Blueprints") on top of that page
 
The battery bank will be a lower voltage than the panel array...ex: you don't need a 24v panel for a 24v battery, you can wire the panels to whatever voltage you'd like (up to the charge controller's max), and use any voltage battery you'd like (must be below the panel array total voltage).

24v 80w sounds like they could be veeeery old panels? 20-30 years maybe? If so, run some output tests on them before going through the trouble of mounting to weed out any bad ones and get a better idea how much they still put out. They should be ok, but better safe than sorry. Also, check the labels on the back to see what their highest string voltage is.
 
I just inherited 38, 24v 80w panels which comes to a little over 3Kwh of power. Is this enough to live off grid with? Here is some information: our living conditions add up to between 7-8Kwh a day, it was 15Kwh a day when we had our children living with us, but since they flew the coop our electricity went down to 7-8Kwh a day. We live in Hawaii and everyone I been talking to says we generally have between 5-6 hours of usable sunlight a day. Some questions I have are: Should I run my system at 24v or 48v? And according to which system, what would be a good setup for each? Batteries, charge controller/s, inverter etc.? These panels have never been used yet and are still in the box. Where we live our main supply of water is caught on our roof and stored in a catchment of 5000 gal. There is a lot of useful information about solar on the internet and at times it can be daunting so figured maybe I would ask someone in this forum for some advice or try to steer me in the right direction. Mahalo
UGH!

NOT KWh!
You have 3040KW of output wattage...

depending on the sun hours in your area you have 18,240KWh of PV... assuming 6hours of sunlight.
 
over 2kWh, you need to go on 48V or more because the wiring become very expensive due to excessive thickness required.
so you will need to build an array that use probably a mix between serial and parallel to benefit both what serial and parallel offers.
(parallel offers anti-shading while serial offers higher voltage, easier conversion, cheaper wiring).
all the details will depend from the where and how you will mount panels, the type of SCC and inverter you will choose etc...).
batteries come last, since there is no real constraint about it, the choices are almost unlimited.
for you, the easy way would be to create a scalable sytem with all-in-one MPPT boxes (you can start with a 5KWh 48V box and add a 2nd if needed). Just make sure you choose a non-grid-tie model.
7Kwh of battery is easy and cheap to find. You will be able to expand later and you can fine-tune battery charge complementing with grid if necessary, until you can totally unplug.
you got 3A per panel, so putting 3 panels in series gives you about 72V 3A and putting 12 group of 3 in parallel gives you 12x3 a =36A.
so you will get an array at 72V 36A= 2500Wh
you could even go 4 in series at 96V i think an MPP box can support up to 150V) and 9 in parallel that is 27A for even cheaper wiring.
you can charge a 7000Wh battery in 3 hours and use the remaining energy to run hungry devices (washing machine, pump to lift water on the roof)
during the day. Not sure you can afford AC running all day and night, you should consider upgrading your panels to bigger ones and you target should be 12KWh at least. New AC type with inverter is recommended in that case
That looks like a lot, but consider that most ratings are maximum ratings, so you hardly get that all the time. A clouded/rainy day can drag you way down under 50%.
You would also install solar tube/panel to produce hot water, so you can store 100-200 liter in an isolated tank that you can then use later, even if you need to heat up again with electricity, the energy spared is huge. (washing machine, dish washer all heat their own water)
Also, mixing up KW output with KWh ...
 
The battery bank will be a lower voltage than the panel array...ex: you don't need a 24v panel for a 24v battery, you can wire the panels to whatever voltage you'd like (up to the charge controller's max), and use any voltage battery you'd like (must be below the panel array total voltage).

24v 80w sounds like they could be veeeery old panels? 20-30 years maybe? If so, run some output tests on them before going through the trouble of mounting to weed out any bad ones and get a better idea how much they still put out. They should be ok, but better safe than sorry. Also, check the labels on the back to see what their highest string voltage is.
Aloha SolaRat, the panels are made by: bpsolar, Apollo, model: bp980L. Peak power (pmax): 80w, minimum (pmax): 75w, Voltage(vmp): 32.3v, Current (imp): 2.4A, Open circuit voltage (VOC): 45.2, Short circuit current (Isc): 3.01A, they are still in their own boxes. Thank you for the advice.
 
Aloha SolaRat, the panels are made by: bpsolar, Apollo, model: bp980L. Peak power (pmax): 80w, minimum (pmax): 75w, Voltage(vmp): 32.3v, Current (imp): 2.4A, Open circuit voltage (VOC): 45.2, Short circuit current (Isc): 3.01A, they are still in their own boxes. Thank you for the advice.

Here's an old datasheet for them. Looks like they have a max series connection of 600v. Only 8.6% efficiency, so older, but should work...

With an OCV of 45.2, look for a charge controller with at least a 100v input (for 2 in series), but preferably much higher to allow more panels in series.
 
Here's an old datasheet for them. Looks like they have a max series connection of 600v. Only 8.6% efficiency, so older, but should work...

With an OCV of 45.2, look for a charge controller with at least a 100v input (for 2 in series), but preferably much higher to allow more panels in series.
Since they were free, I figure I would use them until I can get better panels later. Thank you for the information.
 
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