New to the forum and need some help.

dd76522

I live off grid in northern Idaho, about an hour south of CDA. We've been using solar exclusively four about 4 months as its 25k a mile to get power up here. Until recently we had no internet so all of our initial solar decisions were just winging it and I made a lot of mistakes. I have two separate setups that I could really use some help refining. 

The first setup is 4 Renogy eclipse 100w 12v panels now wired in series into a Renogy commander 40. I have 3 310w Renogy 24v panels on the way right now to replace them with. the battery bank is currently 6 Interstate group 27 deep cycles that are allegedly 120AH in parallel and the inverter and controller are wired to diagonal ends of the bank. 

As for most of us money is a concern. I've got 2 Iota DLS27-40 on the way and an inexpensive inverter from amazon already here. thats all I have to work with except my own brain and now, the internet. 

my intent was to convert to 24v and wire the panels for now as a single string in series and redo the batteries as three pairs in series and then the pairs in parallel. After this evolution the next upgrade is a Midnite Classic 150 and then more panels but its going to be a minute. I estimate the daily usage at about 2kw but right now the batteries are usually at 11.8-9 when I get up in the morning. I would really like to see them no more than say 30% discharged overnight but adding more batteries is out of the question right now. 

I'm a little overwhelmed by the math right now. I've found the formula for calculating who much panel we should have but 930w will have to work for now in conjunction with the chargers and generator. 

I'm currently monitoring the energy usage with a meter on a shunt on the inverter input. It does not give me daily energy used but cumulative. Currently the RV is powered off the generator during the day while the panels and current battery charger charge the battery bank. I do have a line on T105's for a good price but it's going to have to wait for a couple of months.

Sorry for the long first post!

DConlyGuy

you have every thing now for a small 24 volt system. but your battery's are most likely 75ah . my dmc31 is 105ah and way bigger than group 27's

westbranch

Welcome.  So as not to fog your brain, the most effective in power terms is to series any panel so that it gives you ~ 2 x the voltage If you are sending the electrons a long distance, if you are close to the CC and battery bank, staying at the native battery voltage is good s the devil is in energy that is made into heat by the CC. so think on that overnight and post your decision for analysis. 
There is more and you may come up with some of the wrinkles but we will deal with them next...

BB.

Welcome to the forum "DD", I will give it a shot and see if I can help... I am going to be making some guesses here--So anything I may get wrong, please correct me/ask questions.

Your "upgraded system" will have 2s x 3p 12 volt @ 120 AH batteries for a 24 volt @ 360 AH battery bank (you are looking at other batteries--Good thing. If cost is an issue, look for 6 volt @ ~200 AH batteries (golf cart type). 4s x 2p will give you a 24 volt @ 400 AH. G.C. batteries are cheap and rugged, and not going to drain your wallet if something messes up).

And I would suggest reading this link for suggested ways to wire up your parallel battery strings for optimum current sharing (charging/discharging):

http://www.smartgauge.co.uk/batt_con.html

The recommended rate of charge for solar is typically 5% to 13% rate of charge... 5% is good for weekend/summer use... 10% plus recommended for full time off grid (9 months or more off grid per year):

• 360AH * 29 volts charging * 1/0.77 panel+charger derating * 0.05 rate of charge = 678 Watt array minimum
  
• 360AH * 29 volts charging * 1/0.77 panel+charger derating * 0.10 rate of charge = 1,356 Watt array nominal
  
• 360AH * 29 volts charging * 1/0.77 panel+charger derating * 0.13 rate of charge = 1,763 Watt array "cost effective" maximum
  

The standard amount of energy for a full time off grid system is 2 days of storage and 50% maximum discharge (rule of thumb; for various reasons seem to be optimal for most folks)--From your bank:

• 360 AH * 24 volt battery bank * 0.85 AC inverter eff * 1/2 days storage * 0.50 max discharge = 1,863 Watt*Hours of 120 VAC per day "nominal" from battery bank (no sun days).

And for a fixed array, tilted for average year round best harvest (you can tilt for best winter/best summer harvests, etc... your choice):
http://www.solarelectricityhandbook.com/solar-irradiance.html

Coeur d'Alene
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 42° angle from vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
2.12	3.30	4.37	5.04	5.24	5.53
Jul	Aug	Sep	Oct	Nov	Dec
6.07	5.88	5.11	3.71	2.33	1.88

Toss the bottom three months (assume genset use during bad weather), and basing your energy usage on 1/4 battery discharge per day:

• 1,863 Watt*Hour per day * 1/0.52 off grid AC system eff * 1/3.30 hours of sun (February break even month) = 1,086 Watt array (Feb "break even month")

You have 3x 310 Watt panels for 930 Watt array... I would suggest a larger array--Or keeping your 4x 100 watt panels and get a simple PWM charge controller (2s * 2p array of your 100 Watt panels) for the second PWM controller in parallel with your MPPT controller. You can (probably) use the extra power--especially this time of year.

Your Recology controller is probably this one(?):

https://www.renogy.com/renogy-40-amp-commander-mppt-solar-charge-controller-w-mt-50/#tab_prd-desc
https://www.renogy.com/template/files/Manuals/CTRL-CMD20-40.pdf

Your 40 Amp Commander manual says a maximum of 1,040 Watt array--If this is a good quality MPPT controller (I know nothing about it--but I am not in the solar business):

• 40 Amps * 29 volts charging * 1/0.77 panel+controller deratings = 1,506 Watts

However, because the maximum number of your 310 Watt panels you can put in series is 3 (Vmp-array~90 volts)... You can not put 4s in because it will over voltage the controller (exceed 150 VDC input for Voc-cold). And you cannot put another parallel string of 310 Watt panels because 1,860 Watts is >> Vmax input (either the manual's or my suggested "coYst effective maximim" MPPT array input).

So, if you want to put more panels on later, you will need a second (or third) charge controller, or get a larger one that is rated at 80+ amps.

Your system is relatively balanced right now--I have guessed at your power needs--So, I can be off either way--But for your present battery bank, if you are living there full time, I would suggest, eventually a larger solar array (solar panels are "cheap", battery banks are "expensive")... But that will be based on your actual power needs and $$$ available.

For your battery bank, a 10% to as much as 20%-25% genset charger can be justified... But if you use > 13% rate of charge, watch that you do not overheat the battery (particularly if you use AC charging for >~80% state of charge).

Based on your 360 AH @ 24v battery bank, we suggest a maximum solar array and maximum AC inverter output of roughly 1,000 Watts per 200 AH @ 24 volts

• 360 AH (at 24 volts) * 1,000 Watts per 200 AH at 24 volts) = 1,500 Watt maximum "full power" AC (and maximum ~3,000 Watt surge power for a few seconds).
  

That is about all I can say about your system at this time (basic first pass guesstimates).

Your thoughts?

-Bill

dd76522

DConlyGuy said:

you have every thing now for a small 24 volt system. but your battery's are most likely 75ah . my dmc31 is 105ah and way bigger than group 27's

based on the way they behave i'd be inclined to agree!

westbranch said:

Welcome.  So as not to fog your brain, the most effective in power terms is to series any panel so that it gives you ~ 2 x the voltage If you are sending the electrons a long distance, if you are close to the CC and battery bank, staying at the native battery voltage is good s the devil is in energy that is made into heat by the CC. so think on that overnight and post your decision for analysis. 
There is more and you may come up with some of the wrinkles but we will deal with them next...

The panels are mounted to the roof of a tiny shed that contains the batteries, controller and inverter, the wire run is maybe 10' tops. the panels have been in parallel up intil recently and usually running about 18v, I switched them to series the other day to see how that would affect things, they've been running around 78v and I haven't noticed any additional heat from the controller. They actually got to float pretty early yesterday which hasn't happened often lately.

BB. Bill, I really appreciate it! I got the batteries from Costco and they had Interstate GC batteries, I have to go back up to CDA next week and I think I will try and exchange the batteries for GC batteries and buy two more so I can run 4s x 2p with them. I should have the new panels and everything this week, of course it's supposed to rain forever so it may take me a bit to get the panels up as I have to add extensions to the shed roof to fit them. This solar setup is my mom's by the way. I'll make another post about mine once I have hers figured out. 

The 24v inverter I ordered her is 1500w. Renogy has been awesome so far, the tech support side. I've been pretty happy with their products. I do feel the controller is going to be a major limiting factor though and hope to replace hers around the new year. The midnite Classic 150 is what I have my eye on, hopefully that will give me the ability to expand that we need along with the the additional functionality it seems to have. 

I'll have to double check the panel angle but i'd guess it to be pretty close to 42 degrees currently. 

Ok, the plan is fix the battery problem, replace the CC with one more fitting and add another string of panels. I can do this!
Thank you gentlemen!