I too need help with loss of battery storage.

Welcome to the forum Lnd S,

It does not sound like things are working correctly... But the first question is "how do you know" the state of charge is going from 100% to 60% overnight.

Let me start with a few basics... Tools to start with. A DC current clamp DMM (digital multimeter). You use the DC Current Clamp to measure current in your system. How much current is coming from the charge controller in middle of day, how much current is your AC inverter + DC loads drawing at night. How well are your batteries sharing current (one open cell or wire connection can kill 1/5th of your battery bank capacity).

https://www.amazon.com/gp/product/B019CY4FB4 ($105 -- pretty nice AC/DC current clamp DMM with other features)
https://www.amazon.com/gp/product/B07546L9RT ($46 -- "good enough" for our needs)

And you should also have some sort of specific gravity tool, if you have Flooded Cell Lead Acid batteries (vs AGM or other sealed type battery). Always remember to rinse your hydrometer with distilled water before putting away:

https://www.solar-electric.com/search/?q=hydrometer (standard float type)
https://www.amazon.com/s?k=refractometer+acid&i=tools (refractometer/optical specific gravity meter--Random search results)

A Kill-a-Watt meter is handy for measuring your 120 VAC loads and understanding their energy usage (plug one appliance into meter at a time, and see how many Watt*Hours or kWH per day the appliances use).

https://www.amazon.com/s?k=kill+a+watt+meter

The above are just suggested starting points for your search about tools. Feel free to ask questions.

The above are basic tools you should learn how to use (or your handyman needs to maintain your system).

Before we get too deep into debugging a new system (that does not have a history of "working" for your needs), let's look at the design.

I am going to make some (many) guesses here, and please feel free to correct me when I am wrong.

• 10x 6 volts @ 390 AH L-16 flooded cell lead acid battery bank configured in 2x series (12 volt bus) by 5 parallel strings (5x390AH= 1,950) AH battery bank
• 8x 100 Watt Vmp~18 volts x Imp~5.6 Amp panels (x series by y parallel connections?)
• 60 amp pure sine wave Controller... Not sure what this is. 60 amp MPPT solar charge controller?
• 3,000 Watt 12 volt (TSW/PSW or MSW?) 120 VAC inverter (brand/model/link to inverter?)
• Location--Don't know... Start with San Francisco SFO airport (decent amount of sun on average)
• LED lights -- 4x 13 Watt lamps * 5 hours a night = 260 Watts of lighting overnight
• Chest Freezer/Refrigerator conversion -- Assume 350 Watt*Hours every 24 hours (per day).
• AC Inverter -- Assume 55 Watts * 24 hours per day = 1,320 WH per day

The "heart" of your system is the Battery Bank. So I like to start there and see how it is configured/what is "ideal" for your needs. For a typical cabin/off grid home, we like to see 2 days of storage (no sun; 1-3 days storage typical range of options) and 50% maximum discharge (for longer battery life). So, typically, we would like see the battery bank 4x your daily loads (or you use 1/4 of your battery capacity) in normal usage.

• 1,950 AH * 12 volts * 0.85 AC inverter eff * 1/2 days storage * 0.50 maximum discharge = 4,972.4 WH per day "ideal" energy usage per day

Your (guesstimated) system usage is:

• 260 WH lighting + 350 WH refrigerator * 1,320 WH AC inverter "tare losses" = 1,930 WH per day estimated AC loads

Or you are using about 1/8 (or ~12.5%) of your battery capacity... Seeing it go down to 60% by the next morning indicates your loads are much higher, or your charging was incomplete, or wiring issues, or your State of Charge estimates are wrong, or your battery bank is "bad"...

For the battery bank, review this website for proper bank wiring of parallel battery strings (lots of detailed information in their technical section):

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

Next, there are two solar panel calculations we need to make. One is based on the size of your battery bank (larger battery bank, needs more charging current). And the second is based on the amount of sun vs loads for your locations.

First, solar + charging: Generally, we suggest around 5% to 13% rate of charge for solar charging... 5% works OK for weekend/summer cabin charging. 10%+ is recommended for full time off grid (>9 months of system usage):

• 1,950 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 Rate of Charge = 1,836 Watt array minimum
• 1,950 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 Rate of Charge = 3,672 Watt array nominal
• 1,950 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 Rate of Charge = 4,774 Watt array "cost effective" maximum

Your present 800 Watt array, based on the size of your battery bank is way too small (as I understand your system).

Based on loading (my guesses), your battery bank is ~2x larger than you need--A 1/2 size battery bank should work fine and be easier to charge/maintain.

Also, I would suggest that a 1,950 AH @ 12 volt battery bank is too large of AH capacity for easy wiring/charging/operation (very heavy copper cabling required). Roughly, I would suggest that any battery bank >~800 AH should go up to the next sizes--Rewiring your battery bank would be 4 x 6 volt batteries in series (24 volt bus) by (2x parallel strings of 390 AH = ) 720 AH battery bank (you would have 2x L-16 batteries we cannot use--unless you buy 2x more batteries for a 3rd string). Generally, 1 string of batteries are ideal, and I would suggest that you avoid more than 2-3 parallel strings for "typical" configurations.

Next, there is sizing the solar array based on your loads and location. Picking San Francisco, fixed array, 800 Watt array, you would get:
http://solarelectricityhandbook.com/solar-irradiance.html

San Francisco
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 52° angle from vertical :
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.77	4.26	5.46	6.07	6.21	6.07
Jul	Aug	Sep	Oct	Nov	Dec
5.49	5.34	5.40	5.05	4.19	3.69

An 800 watt array would (on average) produce:

• 800 Watt * 0.52 off grid AC system eff * 6.07 hours of sun (June) = 2,525 WH per day

Now, you would only use somehthing like 50% to 65% of your solar power system for base loads (loads that you need to run everyday, like LEDs and Refrigerator--Washing machine, well pumping, etc. only done on sunny days)... So, 1,930 WH of daily AC base loads, would require roughly:

• 1,930 WH per day load * 1/0.52 off grid system eff * 1/0.50 max base load uses * 1/6.07 hours of sun = 1,223 Watt array "recommended for June"....
  

Of course, if you are up there in winter and using solar power, you would probably pick 4.26 hours of February sun and use a genset at times during the winter... Or even look at using Decemeber at 3.69 hours of sun (use very little genset)... These are your choices.

But so far, your basic system design is not really "balanced". You have a way to large battery bank (need about 1/2 size), may want to look at 24 volt battery bank (smaller wiring, fewer 24 based charge controllers). Your solar array is probably way to small for your present battery bank and AC loads. And look at a 1,500 Watt or so AC inverter (12 or 24 volt). The 3,000 Watt AC inverter is very large for your present needs (as I guess them), and that makes the Tare Losses for the inverter the major load on your system (and not your loads--Not a great starting point).

Assuming that this is one of the best months for energy production--You should, at least, sort of OK right now (during sunny weather). And your battery bank discharge behaviour is not making a lot of sense. So--You may be having some other issues and you need, at least the proper tools (DC Current Clamp DMM, hydrometer) to figure out what is happening.

Anyway, making lots of guesses here to shorten the discussion and hopefully focus on what needs to happen next.

The battery battery bank is something you have to pay attention to. It is the one thing that can be damaged or ruined if they are not properly charged/maintained. So checking the charging battery voltages during the day to get an idea what is happening (you may start at 12.2 volts before sunrise, charge to 14.75 volts (slowly rising voltage or "bulk charging"--maximum current from solar controller) and then hold 14.75 volts for 2-6 hours of "absorb charging" (deeply discharged flooded cell battery, need closer to 4-6 hours of "absorb" charging). After that, the charge controller may fall to roughly 13.6 volts "float charge" (until sun goes down/your loads exceed panel power capacity).

Some light reading:

Deep Cycle Battery FAQ
http://lib.store.yahoo.net/lib/wind-sun/Pump-Inverter.pdf

-Bill

Meters are, at best, only guesses at battery state of charge. Some are better than others, and others are worse. Some meters also need to be programmed with the battery bank type/capacity for them to have a better estimate of capacity... Others just monitor the battery bus voltage and time (under charge/discharge/etc.).

And don't feel bad about asking questions and learning more. The math is usually not too bad--And I try to write the equations like a simple sentence (read right to left).

I try to break things into pieces... Like sizing the battery bank for your loads. Then sizing your solar array based on A) battery bank size, and based on your loads and hours of sun per day.

Even if you are not doing the work, you will learn a lot just from the math and discussions and you can help your installer better understand your needs and the system.

Watts is a rate of energy flow (like gallons per minute at 100 PSI)
Amps is a rate of current flow (like gallons per minute)
Watt*Hours is an amount like 100 allons pumped at 100 PSI.
Amp*Hours is an amount like 100 gallons pumps

Watts and Watt*hours are "complete units".

Amps and Amp*Hours are not complete units... We also need the voltage to figure out Watts and Watt*Hours (WH).

Sort of like pumping water... If I pump water from a bucket up 5 feet in the air, that is little pressure and energy needed to move the water.

If I have to pump the water a 1,000 feet up a mountain, it takes a whole lot more energy to move it up the mountain.

Amps * Volts = Watts
Amps * Volts * Time (hours) = Watt*Hours
Watts * Time (hours) = Watt*Hours

The math around here does not really get much more complicated than that.

-Bill

Thank you Photowhit,

Not that bad of tare losses at (1.5ampsx24hours= 36 Amp*Hours) -- But still a lot for the overall systems loads (maybe somewhere around 250-350 Watts for a converted chest freezer per day--Vs (36 Watts * 24 hours per day = ) 864 Watt*Hours per day Tare losses...
36 AH per day * 12 volt battery bus = 432 Watt*Hours per day Tare losses
 
Still 2x or slightly more energy to run that AC inverter vs the chest refrigerator (again, lots of guesses).

If the power usage is "this simple", then using a 1,500 Watt inverter (with closer to 20 Watt Tare) that has "search mode" (generally 8 Watts or much less in "auto-standby") could really save a lot of Tare Losses... Of course that is at the expense of a much more expensive AC inverter with search mode...

-Bill

PS: Corrections: I am not doing very good at math the last couple of days.... Sorry. -Bill

Oh boy... I am not paying attention at all... 12 volt, not 24 volt system, so you are correct at 432 WH.

My excuse .... Well, probably should not say more.

-Bill

LnDS,

I am really concern that I (we) can give you technically correct answers, and you will still not have a "working towards you needs" system.

I have made a lot of guesses (where the system is installed, off grid, available generator/unity power, your power needs, what equipment you have, etc.).

Without some more answers and what you are looking for from the system (full time off grid or summer only, you have a clear of shade southern exposure vs bottom of a valley/trees/chimney & vent stacks on roof--all possibly shading panels somewhere around 9am-3pm, etc.).

We really do not know if the system is working the best it can--Or if there are other problems that need to be addressed.

At this time (assuming you are in the northern hemisphere)--You have some of the best "hours of sun" per day at this time of year (unless you are on the coast and have a problem with Marine Layer 4 days out of 6). When you head into fall and winter, your harvest will probably be a lot less (again, depending on where your system is installed, local trees/valleys/etc. shading your property). The closer you get to the North/South Poles, the greater the changes in available solar energy between summer & winter.

-Bill

Thank you Linda.

The piano heater--That is probably a very significant load---Guessing at ~37 Watts:

• 37 Watts * 24 hours per day = 888 WH per day

Or possibly 2-3x the load of your chest refrigerator... 

Using PV Watts to estimate your energy harvest @ Fort Bragg, south facing, ~45 degree tilt (roughly best year round harvest). Use these numbers for your Solar Array "hours of sun" energy production equations:
https://pvwatts.nrel.gov/pvwatts.php

Month	Solar Radiation ( kWh / m2 / day )
January	4.00
February	3.94
March	4.85
April	5.86
May	5.88
June	5.93
July	5.62
August	5.45
September	5.59
October	5.10
November	4.18
December	3.23
Annual	4.97`

That "extra 37 Watts", if 24 hours per day (no timer), that is a very significant load.

Heaters (and Air Conditioning, etc.) can be very energy intensive. Putting on timer (run at night/damp weather) can help--But when you get into winter, it is cold and damp all the time.

Generally, water pumping for household use, it not much energy... Depending on what your source is (deep well, surface water into holding tank, etc.)--Lots of details to work out. Running a genset 1-2x a week to run a "large well" pump to cistern, then use a 12 or 24 volt DC RV Pump for house pressure (and some sort of pressure/holding tank to reduce pump cycling). --- Lots of options.

You really need to measure your loads (Kill-a-Watt type meter for 120 VAC loads), a DC AH/WH meter for 12 VDC loads (or use a DC Current Clamp to at least understand the current being used and estimate number of hours per day, if not 24 hours per day operations).

Here is a sample link for a DC Watt*Hour meter (for smaller DC loads). I know nothing about the meter or supplier:

https://www.amazon.com/bayite-6-5-100V-Voltmeter-Multimeter-Amperage/dp/B013PKYAV6

Things like heavily insulating the room and making it water tight (Tyvac house wrap or similar), shading on windows to prevent direct light on piano, and avoid large temperature swings. Some of this may be easy, or it may be difficult--Depending on if you are going to remodel the house/room and construction methods.

I would highly suggest getting your solar array to a total of ~1,836 Watts minimum (with 2nd controller) for 5% rate of charge.

What you "really need", need to total up your loads (both minimum/base loads every day, and possibly seasonal loads).

What 1,500 Watt brand/model of AC inverter do you have that you can reinstall?

Again, just an first pass, I would suggest (with your present 1,950 AH battery bank)--5% to 10% rate of charge:
And based on, lets say (note: DC loads are technically more efficient because it does not use the AC inverter--But treat everything the same (as AC loads) for now (keep math simple):

888 WH = heater per day (120 VAC)
350 WH = chest refrigerator (120 VAC)
325 WH = 13w * 5 LED * 5 hours LED (AC or DC)
96 WH = 8 Amps * 12 volts * 1 hour water pumping (AC or DC)
================================================
1,659 WH base per day (call it AC loads on inverter)

Your battery bank can handle upwards of  4,972.4 WH per day very easily (2 days of no-sun, 50% maximum discharge).

And lets say you have other variable loads (running clothes washer, fan on hot/cold days and wood stove), TV, Laptop Computer, etc. of ~1,659 WH per day (i.e., 2x your base loads).

Total of 3,318 WH per day design for December @ 3.23 Hours of sun per day (long term average--Some days more, somrse days less).

• 3,318 WH per day (50% of that are every day base loads) * 1/0.52 off AC system eff * 1/3.23 Hours of sun per day = 1,975 WH "break even for December" Array...

Again, my suggestion (not my money, this is yours) is something around 1,836 to 1,975 Watt array is very easy to defend as needed for your system. (no change to battery bank, 2nd charge controller, more solar panels, need to define genset and AC battery charger).

If costs are a big hit for you... Changing to a 24 volt battery bank, can save money (only 1x mppt charge controller required). And, drop 2 batteries (8 total) for 24 volt bank (slightly less storage). Or add 2x batteries for 12 bank total (4x series by 3 parallel strings)...

And if you have a genset+AC Battery charger--You need to get the batteries to 100% State of Charge and equalized (check specific gravity, if cells are >0.030 sg units between "high and low cell", equalization is generally required to bring the bank back into balance (controlled overcharge, to bring all cells to near equal SG readings).

If the battery bank is not getting fully charged (>90% state of charge at least 1-2x per week, avoid going below 50% state of charge -- Using a hydrometer to measure your cells), need to get them back up--"Deficit Charging" -- charging less than full charge every few days, but slowly going lower and lower SoC -- A good way to kill a battery bank).

Your system is not what I would have suggested--But you have what you have--At this point, getting more solar panels (and mppt charge controller) on the battery bank is the first place to start. You want to "save your bank" -- That is a lot of $$$ to die an early death.

Going with the 1,500 Watt AC inverter should be a better fit for you needs (depending on brand/model of inverter). So I would go back to it until you get the rest of your system debugged/increased array wattage/verify that all is working correctly.

After that (and that is a lot), then can look at what to do next.

-Bill

In general, larger diameter wire than needed is not going to hurt anything except in some "corner cases".

For 1,500 Watt inverter, I would suggest:

• 1,500 watt inverter * 1/0.85 inverter eff * 1.25 NEC continuous current wire/breaker derating * 1/10.5 DC cutoff voltage for inverter = 210 Amp branch circuit wiring and fusing/breaker rating.

Your installer should have an NEC (national electric code) book for actual current/AWG calculations, but a good rough guide starting point would be:

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

Or somewhere between 3/0 AWG and 250 kcmill (depending on insulation, ambient temperatures, conduit fill, etc.). NEC with the NEC derating is a pretty conservative cable rating.

If you need to put two cables in parallel, and 1/2 current in each, you could use something like 3 and 1 AWG... However, running cables in parallel is not recommended if it can be avoided.

For the battery interconnects, I would suggest ~2 AWG or heavier cabling. Ideally, with parallel battery banks, each bank should have a fuse/breaker per string of batteries. I.e., 2 AWG cabling from battery string to battery bus would be ~105 Amp fuse/breaker. BlueSea makes some very nice/small terminal fuse holders for this type connections (links to holders only, still need to order fuses):

https://www.bluesea.com/products/2151/Dual_MRBF_Terminal_Fuse_Block_-_30_to_300A
https://www.bluesea.com/products/5191/MRBF_Terminal_Fuse_Block_-_30_to_300A

I would be surprised if more than just professional installers fuse/breaker parallel battery connections (suggested for 3 or more parallel strings of batteries).

There is also looking at wiring drop--Longer wire runs to inverters means higher voltage drop. You can use a simple Voltage Drop Calculator, and play with AWG vs one way wire run in feet vs Voltage drop. For example:
https://www.calculator.net/voltage-drop-calculator.html?material=copper&wiresize=0.2028&voltage=12&phase=dc&noofconductor=1&distance=5&distanceunit=feet&amperes=210&x=74&y=15

Example:
210 Amps by 5 feet on 3/0 cable will have:

Voltage drop: 0.13
Voltage drop percentage: 1.08%
Voltage at the end: 11.87

I suggest for a 12 volt system, you have a maximum of 0.50 volts drop--So, 0.13 drop is fine.

I guess this is your Tiger Claw inverter:

https://www.amazon.com/Tiger-1500W-Power-Inverter-DC-AC/dp/B008JGE8LE

Do you have an installation manual? Generally that is where you start for the connection requirements.

Anyway--If the inverter meets your requirements for loading--And the input wiring is correctly done--That side is OK.

Will it "fix" an 800 Watt array on a 1,950 @ 12 volt battery bank... I would still highly suggest increasing your solar array size.

However, without using  a Kill-a-Watt meter to measure each of your 24 hour 120 VAC loads--It would be pure guesswork on my part to say yea or nea for this configuration.

Before you toss a bunch of money at the present system... Measuring and logging battery specific gravity (for each cell ~once per month, then pilot cell for other readings), and understanding your loads/solar harvest--Then you can make some more informed decisions on how to proceed.

-Bill