New to solar, have battery questions

SulfatedPlates · December 2013

Yes hello and thank you for taking the time to respond.

Unfortunately I was not the purchaser, but was the installer and now in charge of understanding and maintaining a new solar array; drinking from the fire hose as it were.

So we ended on 4 duracell 6v, 232amp/hr golf cart batteries, in series for 24v, An unknown "EP Solar TRACER" solar panel kit that came with 4 panels, an MPPT and the necessary MC4. 2 series 2 parallel. "1000 watt" system. On day 4 I have seen 71 volts off the panels, and I saw 28 amps at about 25.6v once I think. Seems good.

This is connected to a Samlex pure sine, 2000w. We are attempting to run 2 fridges and a full size freezer, all frost free of course. Well the damn clouds are killing us.

So here's my question: I also have 4, 12v, 105amp/hr marine batteries (and a MSW inverter == $700 mistake). Can I add these 4 pcs. 12v (in a 2 series 2 parallel obviously) to the all series 24v 4 pcs. Golf cart batteries? 8 batteries: 4 golf's in series and 2 parallels of 2 series of marine 12v..? Trying to recoup some of the $700 on the first failed attempt; obviously the MSW won't be helpful but if we could add capacity and find a home for these perfectly good batteries that would be great.

Haartilijk bedankt!

westbranch · December 2013

Re: New to solar, have battery questions

Can you add some details about the panels, specs? What is your location, Holland?

I think you are being overly optimistic to expect that small battery bank to run 3 fridge/freezers all at the same time. Each one, if new, will draw in the ballpark of 1 Kwhr per day, so 3 + Kwh per day, and that bank may have , if totally depleted 22oAh x 24 v = 5280Watts.

you don't want to go below 50% of that so 2.64Kwh available per day , then you have to recharge COMPLETELY the next day or you are into DEFICIT charging and will kill those batteries.
more later...

Cariboocoot · December 2013

Re: New to solar, have battery questions

Welcome to the forum.

You've got problems all right. Number one being the two refrigeration units plus one freezer are going to suck down over 3kW hours of power per day, and the panels can't supply that much even in sunny weather.

Adding more batteries of any type won't help without adding more panel to charge them.

What you have now is probably 220 Amp hours @ 24 Volts, which will manage about one refrigerator at 25% DOD (1.2 kW hours). It sounds like you have roughly 1000 Watts of panel which is sufficient for that much battery.

Without expanding both the battery and panel capacity by about 3X you are going to be killing those batteries in a hurry.

Is there any generator available? You should have some form of back-up charging.

The marine batteries are not going to be too helpful. They aren't really suitable for such an application long-term, they won't match the deep cycles for capacity making charging and discharging uneven, and the multiple connections can also be asking for trouble.

WNY Dave · December 2013

Re: New to solar, have battery questions

Whats the power consumption of the freezer and fridges? have you measured them with a Kill-A-Watt meter? So you know your loads. Those devices can be energy hogs.

Hopefully you have a generator (or grid hookup) as backup to charge the batteries when the clouds are around if you have your loads on drawing power from the batteries, the panels may not be able to put out enough to run the devices and charge properly.

Voltages and current sound about right for your panel array wiring into the MPPT controller for charging.
What MPPT controller is it?

SulfatedPlates · December 2013

Re: New to solar, have battery questions

Thanks for the fast response guys! I'm in Virginia. Lowes didn't have a killawatt today.. intend to get one tomorrow.
What if I reduce to one fridge and the big freezer? I guess still 2000 watts. So I really need 1 solar watt for every watt used each day? IE: 1000 watt system shouldn't be used to power more than 1000 watt per day energy usage? I was thinking If I threw 5 good 1000watt hours at the batteries every day this would be sufficient. Please tell me what I could be capable of doing with this kit, and please elaborate of why deficit charging being a problem for the batteries. Shouldnt discharge below 50% ?
The PSW cuts off at 21 volts.

I have installed this kit here: https://www.renogy-store.com/1000W-watts-1KW-solar-panel-kit-p/off-pk-4rng250d.htm

vtmaps · December 2013

Re: New to solar, have battery questions

SulfatedPlates wrote: »

Tplease elaborate of why deficit charging being a problem for the batteries. Shouldnt discharge below 50% ?
The PSW cuts off at 21 volts.

When a battery discharges the sulfuric acid in the electrolyte becomes sulfate on the plates of the battery. When you charge the battery you drive the sulfate off the plates and back into sulfuric acid in the electrolyte.

The problem is that the sulfate crystals get "hard" if they sit around too long. Then you cannot drive them back into solution. That means that the battery has irreversibly lost capacity. You must recharge the battery to 100% every week or so to prevent this "hard sulfation".

The deeper the discharge, the worse the sulfation problem becomes. Regular discharges below 50% SOC will shorten the life of the battery.

Your PSW cuts off at 21 volts... that is too low to keep your batteries from severe damage. When battery voltage goes down your inverter tries to draw more current (amps) from the battery to make up for the low voltage. This drives the battery voltage even lower and the current keeps increasing until the battery falls to 21 volts and the inverter shuts off. The inverter is shutting itself off to protect itself from the high current... it's not trying to save your batteries.

Many inverters do have an adjustable 'low voltage disconnect' which you can set to a value that does protect your batteries.

--vtMaps

Cariboocoot · December 2013

Re: New to solar, have battery questions

SulfatedPlates wrote: »

Thanks for the fast response guys! I'm in Virginia. Lowes didn't have a killawatt today.. intend to get one tomorrow.
What if I reduce to one fridge and the big freezer? I guess still 2000 watts. So I really need 1 solar watt for every watt used each day? IE: 1000 watt system shouldn't be used to power more than 1000 watt per day energy usage? I was thinking If I threw 5 good 1000watt hours at the batteries every day this would be sufficient. Please tell me what I could be capable of doing with this kit, and please elaborate of why deficit charging being a problem for the batteries. Shouldnt discharge below 50% ?
The PSW cuts off at 21 volts.

I have installed this kit here: https://www.renogy-store.com/1000W-watts-1KW-solar-panel-kit-p/off-pk-4rng250d.htm

Off-grid systems are not very efficient at all. Some may think it would be 1000 Watts * 5 hours of sun = 5kW hours of electric. But it's not. The panels will not produce their rated Watts all the time, power has to be stored in and released from batteries, and every component has its losses. The net result tends to be more like 1000 Watts * 5 hours of sun * 0.52 over-all efficiency = 2.6kW hours of electric.

How much your particular system can actually do depends on a number of things, including the exact specs of the panel, efficiency of the controller, actual capacity of the batteries, inverter efficiency and consumption, wire sizing, and most importantly how much sun really falls on the panels.

Definitely measure the loads. All of them, over several days. See how much it adds up to. It will probably be quite a bit bigger than the system you have can manage.

Deficit charging is when the batteries never get back to full charge. It may be a tiny fraction off, but the larger that fraction and the more often it happens the lower the batteries go over time. Eventually it goes 'over the edge' and the degradation becomes rapid, severe, and irreversible.

The 21 Volt cut-off of the inverter is too low. It roughly corresponds to a battery that is at 0% usable capacity. If you have been discharging to that level the batteries will have suffered damage.

If you really need to run all three refrigeration units you are going to need to invest some very serious amounts of money in a much larger system.

SulfatedPlates · December 2013

Re: New to solar, have battery questions

Unfortunately the kit purchase was a bit hasty and I didn't get a chance to do any research before the trigger was pulled - hence the 4 marine batteries and the modified sine wave that wouldn't even run the fridges to begin with.

Well I reckon I'll have more info after the killawatt is obtained. With one fridge and the big freezer running, the inverter indicates less than 160w of consumption, so I initially had high hopes.

About the discharge. We installed on Wednesday, allowed the batteries to top up, and deployed the system about 48 hours ago. Well we slowly headed right to the limit. Today was cloudy and didn't see more than 4 amps charge @ any time. I eventually pulled the plug when the sun went down (if it ever came up) @ around 22 volts. It was headed down fast like yall had previously mentioned, and clearly wasn't gonna make the night so I pulled it before it hit the limiter.

I wonder what an $1800 1000w kit is good for? I guess we'll find out. Not much apparently

Cariboocoot · December 2013

Re: New to solar, have battery questions

That's the difference between Watts and Watt hours: a refrigerator may draw "only" 160 Watts, but if it runs for 8 hours of the day that becomes 1280 Watt hours. If the solar array isn't large enough to "put back" all the power, the batteries just go down until they die.

Here's my classic example:
My refrigerator pulls 120 Watts plus start-up and a defrost cycle. It consumes 1200 Watt hours per day.
My satellite modem connection pulls only 50 Watts, but if it's on 24 hours a day it uses as much power as the refrigerator; 1200 Watt hours. So I shut it off when not in use.

New to solar, have battery questions

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