refrigerator

catweasel

I have 4 -300 watt panels  4 -120 amp calcium batteries and a 3,000 watt victron inverter

In my mind , since i leave the refrigerator plugged in and it cycles normal turning the compressor on and off , seems to me that this alone will act as my "controller" in other words , i cannot imagine overcharging the batteries .  convince me otherwise 

softdown

Use an Energy Star chest freezer with an external temperature controller for max energy savings.

Photowhit

catweasel said:

I have 4 -300 watt panels  4 -120 amp calcium batteries and a 3,000 watt victron inverter

In my mind , since i leave the refrigerator plugged in and it cycles normal turning the compressor on and off , seems to me that this alone will act as my "controller" in other words , i cannot imagine overcharging the batteries .  convince me otherwise 

Well, a lot's wrong...

Sounds like you are inverting the energy from DC from the batteries to AC... Your solar panels are likely 35 volt VMP. It shouldn't take long for the voltage to spike and your inverter to quit running. If they don't your not charging enough for the load... so the batteries are diing the slow death of under charging because you are never reaching the absorb absorb stage of charging... So pick your battery death.

I'm not aware of Calcium batteries, perhaps lead calcium AGM?

Please let us know what you have, system wise, a 24 volt battery bank or 12 or 48? What is the VMP of the solar panels.

Basically the charge controller will keep your batteries healthy. If your inverter isn't having issues, it's likely not completely charging the batteries, because in most cases you would have runawy voltage and your inverter would shut down.

706jim

Get a charge controller

BB.

Welcome to the forum CW,

I would like to start with some math. Using our rule of thumbs for designing an off grid system for a cabin and/or very energy efficient home. The first is that a good use of a battery bank is to size it for 2 days of storage and 50% maximum discharge (for flooded cell lead acid batteries):

• 4 x 120 AH * 12 volt batteries * 0.85 AC inverter eff (if used) * 1/2 days of storage * 0.50 max planned discharge = 1,224 Watt*Hours per day

A typical full size energy star refrigerator (USA) is around 1,000 to 1,500 WH per day (since I do not have the actual WH per day for your fridge--I will use the above number to continue).

Next, there are two calculations we make for sizing the solar array. The first is based on the size of the battery bank. 5% to 10%-13%+ rate of charge (larger battery bank, larger solar array for charging). And second is based on your daily loads and location (hours of sun per day).

First, rate of charge. 5% can work for a weekend/sunny weather seasonal seasons/emergency backup system. 10%-13%+ rate of charge for full time off grid system is better:

• 4 * 120 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 452 Watt array minimum
• 4 * 120 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 904 Watt array nominal
• 4 * 120 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 1,175 Watt "typical cost effective" maximum

And sizing the array based on load and hours of sun per day. Assuming a fixed south facing array. Somewhere around Montpellier France (guess):
http://www.solarelectricityhandbook.com/solar-irradiance.html

Montpellier
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 46° angle:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
2.86	3.69	4.55	4.82	5.20	5.61
Jul	Aug	Sep	Oct	Nov	Dec
5.99	5.72	5.07	3.43	2.86	2.42

You have to figure out what your energy needs are... If we drop the bottom three months (genset, not using solar during winter, etc.)... That leaves October at 3.43 Hours of sun per day (20 year average). Assuming 1,224 WH per day energy usage:

• 1,224 WH per day * 1/0.52 off grid AC system eff * 1/3.43 Hours of sun per day = 686 Watt array "October breakeven"

And you have a 1,200 Watt array... For "base loads" that need to run 24 hours per day, 7 days a week, you should plan on using around 50-65% of your predicted harvest--Makes up for some bad weather, less than expected harvest, reduced genset runtime... Your 1,200 Watt array in October would support:

• 1,200 Watt array * 0.52 off grid system AC eff * 3.43 hours of sun per day = 2,140 Watt*Hours per day (ave October)
• 2,140 WH per day * 0.65 base load derating = 1,391 Watt*Hours for "base loads" (based on 65% derating)

So, based on all my SWAGs above, you probably have a reasonably "balanced" system design.

Now, your other question... Why a charge controller. It is true that the battery is what controls the battery bus voltage--An FLA battery that is between 20% to 100% State of Charge and discharging/charging/resting will have a battery bus voltage of ~11.5 thru 16.0 volts.

The charge controller's there for two reasons... One is that Lead Acid Batteries need around 14.4 to 14.8 volts (nominal, room temperature) charging voltage, held for 2-6 hours or so (deeper discharge, longer absorb time)... And once the battery bank is "full", need to reduce charging voltage to ~13.6 volts or so--"Float Voltage" is used to keep the battery >~90% State of charge (make up against self discharge) and to support loads during the day (charging time). To low of float voltage, the battery will begin to discharge a bit. Too high of float/charge voltage setpoint, the battery will start to Gas (produce hydrogen and oxygen), "use water", erode the plates, oxygen forming on the positive plates corroding the plates and positive grid.

Also, "excessive" charging current/voltage (many hours) is used short term for "equalizing cells"--Controlled over charging once the battery is "full", the over charging current brings up "weak cells" and also mixes the electrolyte (some battery vendors recommend EQ once per month). 

A 1% over charge current or less, can be "OK" (not cause much in the way of issues). However, a 2% or larger charging current (once battery bank is full), causes the above issues (gassing, erosion, etc.), it also cause the battery bank to overheat (and worse in some cases).

Your Calcium batteries typically use the calcium to reduce water usage... Normally, I suggest that if you are needing to add water every couple to 6 months, you are probably charging OK... If you never add water, you probably need higher charging current/voltage. If you need to add a lot of water every month or less, then you are overcharging.

With Calcium batteries, they naturally use less water--So the above may not be as accurate (especially on "low water usage").

Your thoughts?

-Bill

catweasel

mon texte n'est-il pas dans la catégorie débutant? Même si les réponses sont authentiques, vous ne m'avez pas convaincu. Surtout avec permettre un comportement enfantin comme un visage malheureux

BB.

Catweasel's replay (Google Translate):

is my text not in the beginner category? Even if the answers are authentic, you have not convinced me. Especially with allowing childish behavior like an unhappy face

-Bill

softdown

Not the first foreigner with a bit of an attitude. Curious.

mike95490

catweasel said:

I have 4 -300 watt panels  4 -120 amp calcium batteries and a 3,000 watt victron inverter

In my mind , since i leave the refrigerator plugged in and it cycles normal turning the compressor on and off , seems to me that this alone will act as my "controller" in other words , i cannot imagine overcharging the batteries .  convince me otherwise 

You will be more open to learning when your have to replace batteries frequently, convince me otherwise .

mcgivor

catweasel said:

I have 4 -300 watt panels  4 -120 amp calcium batteries and a 3,000 watt victron inverter

In my mind , since i leave the refrigerator plugged in and it cycles normal turning the compressor on and off , seems to me that this alone will act as my "controller" in other words , i cannot imagine overcharging the batteries .  convince me otherwise 

The 3000W inverter itself may be using close to what the refrigerator demands are, if the inverter is on 24 hours without  search mode, it may well exceed the refrigerator demands. If the refrigerator is an inverter type search mode likely wouldn't work.

The array to battery ratio is less than optimal particularly in the winter months, most refrigerators need between 1-1.5Kwh per day , which is almost impossible to achieve with a less than 1Kw, real value, array taking into account inefficiencies and the odd cloudy day. Everything may seem to work on the surface but cronic undercharging will eventually raise it's ugly head resulting in battery failure, I convinced myself through experience. Heed the advice, most here are are offering what has been learned from failure to prevent others from doing the same, there is no offense intended.