Small Off Grid Solar Setup

Welcome to the forum JY,

It can be difficult to expand a system without replacing some major component or another... But, here is what options you have (in a smaller system).

First, the MorningStar Sunsaver is a very nice/reliable small MPPT charge controller... Depending on the Voc/Vmp ratings of your 80 Watt panels, and how cold it gets in your region (Ohio, NJ, or NY?), it is possible that 3x panels in series, the Voc-array-cold could exceed the 75 Volt maximum input voltage for the MPPT charge controller (it is close--Cold/clear winter mornings, Voc and Vmp of solar panels rise over Vxx-standard test conditions). What is your minimum temperature (winter morning)?

Next, the "cost effective" maximum array for the 15 amp Morning Star MPPT charge controller on a 12 and 24 volt battery bank:

• 15 amps * 14.5 volts charging * 1/0.77 solar panel deratings = ~282 Watt array "cost effective" max into 12 volt bank
• 15 amps * 29.0 volts charging * 1/0.77 solar panel deratings = ~565 Watt array "cost effective" max into 12 volt bank

Of course, if you go to a 24 volt battery bank, then you are looking at a new AC inverter ($$$).

And, you can keep the present panels+charge controller, or even add more panels (within reason/specifications) to the current array, and even add a second array+charge controller to your system (paralleling solar chargers is not usually an issue).

And then there is looking at your existing battery bank and charging current. 5% rate of charge can work for emergency backup, sunny weather use. 10%-13%+ rate of charge is better for full time off grid:

• 225 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.05 rate of charge = 212 Watt array minimum
• 225 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.10 rate of charge = 424 Watt array nominal
• 225 AH * 14.5 volts charging * 1/0.77 panel+controller deratings * 0.13 rate of charge = 551 Watt array "typical" cost effective maximum

If you add more batteries in parallel (12 volt bank), you should really add solar panels. Similar if you add batteries in Series--Add more solar panels to keep the "battery bank happy".

If you can give us your nearest major city, we can estimate your energy harvest by month... For example, say you have an array tilted to latitude, and you get 3 hours of sun in February, then the average harvest equation for your existing system would be:

• 160 Watt array * 0.52 off grid AC system eff * 3.0 hours of sun = 250 Watt*Hour in winterish sunny conditions

You can use this solar irradiation calculator to see your solar harvest options for your area:

http://www.solarelectricityhandbook.com/solar-irradiance.html

-Bill

You are very welcome JY,

You can use the PV Watts program to figure out hours of sun for SE Ohio... For Athens, 40 degree tilt from horizontal, and using 52% efficiency for AC off grid power (or 48% losses in PV Watts terms). Note the AC energy column is for a 1,000 Watt array (smallest array PV Watts accepts, your 0.16 kW/160 Watt array would produce 0.16x the AC Energy column):
https://pvwatts.nrel.gov/pvwatts.php

Month	Solar Radiation ( kWh / m2 / day )	AC Energy ( kWh )	Value ( $ )
January	3.30	50	6
February	3.89	52	6
March	4.38	64	8
April	5.20	69	8
May	5.32	73	9
June	5.52	71	8
July	5.65	74	9
August	5.69	74	9
September	5.49	70	8
October	4.54	63	7
November	3.83	55	6
December	2.92	43	5
Annual	4.64	758	$ 89

So, 3 hours of day for Winter is not a bad guess... You don't have a lot of sun in summer, but not bad. 

For the energy harvest math from the AC Energy column:

• 50,000 WH per month * 1/30 days per month * (160W array/1,000W array entry) = 250 Watt*Hour per day usage 

The problems with loads that are "on" when you are not there--You always have the issue of a week of dark/stormy weather and very little sun, and your battery bank "goes dead" running the loads. Some folks do run Internet and camara/security systems when nobody is there... You just need to watch the power usage... For example, say 50% discharge on your battery bank, and 5 days of "no sun" (rare, unless you get snow that "sticks" for weeks at a time on solar panels), what would be the average load:

• 225 AH * 0.50 max discharge * 1/5 days * 1/24 hours per day = 0.94 suggested max load when gone (winter)
• 0.94 Amp load * 12 volts = ~11 Watt load

"Wasted/Unused" energy harvest from a solar power system is just par for the course. Your system needs to be almost 2x larger than your "base loads"--To account for bad weather, and such. Weekend Cabin systems--Yep, you just lose the "excess harvest" from during the week.

Note that any solar power calculations that are within 10% +/- of each other, are pretty much "identical" (solar power predictions are not exact, and the amount of sun is highly variable over time/weather/etc.).

Some folks use a small array and larger battery bank to harvest "during the week" sun... But that is not really great for Lead Acid batteries... Ideally, for deep cycle FLA storage batteries, you want a 10% minimum rate of charge. And some people are happy with 5% rate of charge (large battery bank to carry power through weekend, small array to recharge during the week). But with solar panels "cheap" these days, and lasting 20 years or more--And batteries "expensive" and lasting 3-5 years (golf cart type)--More panels and fewer batteries are generally a better/more cost effective way to go--And you have enough power for those 1-2 weeks stays too.

Water usage... For a battery bank that is being used every day, refiling roughly every 1-6 months is normal, more often is too much, and less often is not enough (roughly). If you are using a lot of water, just back down on the charging voltage set point and check the water levels for the next few months (check controller's float voltage set point, if it has one). Just make sure you are not ever exposing the plates to air.

Getting 6 years from Golf Cart Batteries--You are probably not doing anything wrong.

-Bill