# question about utilizing excess power

Solar Expert Posts: 54
Hi everyone ,thanks in advanced for any insight you can provide.

i have 900watts in panels chargeing four rolls surritte 6 volt 440 amp hour deep cycle batteriess each wired in 12 volt series parrelle with a c60 trace controller and a m1512 1500 watt inverter with built in charger hooked to a 3500 watt generator backup.

My question is that i reach float within an hour and have sun on the panels for 4-6 hours after that and would like to use the excess power to run a water pump.

i have a 1 hp pump rated to pull 8 amps 770watts ,im thinking of hooking the pump to a timer and setting it to run for the four hours of excess another option im considering is buying another controller to use as a diversion load, any suggestions on the best system

thanks again

Re: question about utilizing excess power

Welcome to the forum Solarsquirrel!

Looking at the size of your battery bank (that is a pretty large AH battery bank for 12 volts), and a 5% to 13% rate of charge with the solar array:

880 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 829 Watt array minimum
880 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 1,657 Watt array nominal
880 AH * 14.5 volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 2,154 Watt array "cost effective" maximum

Your present 900 Watt array is about the minimum I would recommend. If you are planning on cycling the battery bank every day (off grid power, running at night, etc.), I would suggest a 10% minimum array--But that would be ~80 amp charge controller, or a pair of smaller charge controllers.

If you are cycling the battery bank--You really do not have that much extra power to run a large water pump.

A 1 HP pump, in theory, takes ~746 Watts--But in practice, probably take 1,000 to 1,300 watts or more. Add AC inverter and solar array losses, to run the pump "break even" would probably take something on the order of:

1,300 Watts * 1/0.77 panel+controller losses * 1/0.85 AC inverter losses = 1,986 Watt array (around noon)

Is your 1,500 Watt AC inverter capable of starting this pump? An induction motor can take 5 times (or more) starting current. I would worry that a 1,500 watt inverter could not start a typical 1 HP pump.

And do you really need a 1 HP pump running 4 hours per day. That is a lot of power. And many induction motor/jet pumps (if that is what you have) are not really that efficient.

If you could run a smaller pump, or possibly a pump designed for off grid use (usually much more efficient, lower power needs) that could be a big help.

Also, there are solar pumps that can connect directly to a solar array--No battery bank needed. Very good for irrigation and/or pumping to a large cistern--Then use a smaller pump for water around the home/cabin...

Lots of options--But getting larger pumps that work well with off grid solar power can get expensive (but better than building an even larger off grid solar power setup to run the "inefficient" pump).

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Banned Posts: 17,615 ✭✭✭
Re: question about utilizing excess power

You have 900 Watts of panel on four 440 Amp hour 6 Volt batteries? That's 880 Amp hours @ 12 Volts if the info is correct.
And you reach Float in under one hour?
You have far more battery than you need, then, and it aren't doing you any good because they are not being utilized fully.

You probably get about 50 Amps out of that 900 Watts on a PWM controller like the C60 (assuming the panels are 'true' 12 Volt panels and hopefully they are configured and fused properly). If the battery bank is really as described you are at the bare minimum charge rate for it: just over 5%.

If I were you I'd re-evaluate my load needs to begin with. I suspect you can drop half that battery bank. Then I'd check the health of those batteries to be sure they aren't sulphating to death. Test the SG on each and every cell looking for low readings and inconsistencies.

As for running the pump, the ideal way is with a controller that has an AUX control which can activate it when the batteries reach Absorb or Float. However, you may have trouble running a 1 HP pump from a 1.5kW 12 Volt inverter as the start-up demand can be immense - beyond the inverter's ability to handle, especially with concurrent loads. The running Watts/current is not the whole story with a water pump. I have a 1/3 HP pump which pulls slightly more power running than the listing for yours.

In short, this whole system needs a rethink and probably redesign to 24 Volts with MPPT controller and more panel if you want to get into the higher load demand: the current for 770 Watts @ 12 Volts is approximately 64 Amps - more than the controller can pass or the panels supply so you would be draining the batteries somewhat. It would be half that on 24 Volts.
• Solar Expert Posts: 3,741 ✭✭✭✭
Re: question about utilizing excess power
You have 900 Watts of panel on four 440 Amp hour 6 Volt batteries? That's 880 Amp hours @ 12 Volts if the info is correct.
And you reach Float in under one hour?
You have far more battery than you need, then, and it aren't doing you any good because they are not being utilized fully.

And not only that... the repeated shallow cycling will cause lead dioxide clumping on the positive plates of the battery.

This may be one of those situations where he needs to intentionally discharge his batteries... like run the pump when the sun is not shining.

And I totally agree that this system should be 24 volts. That means a new inverter, but he will need a new inverter anyway because his modified sine wave inverter is probably too small to start the pump, and even if it isn't too small, the modified sine wave of the M1512 will not be good for the pump.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 479 ✭✭✭✭
Re: question about utilizing excess power

I run a 1hp spa pump from my Trace DR1524. It will ****just**** start this motor.

And interestingly enough, NOT when the batteries are at my float voltage of 27.0, but when they are down a volt or so from that value.

As my 24 volt inverter has a somewhat higher surge rating than the equivalent 12 volt model, I'd think you will have difficulty starting a 1hp induction motor with the inverter at hand.
Island cottage solar system with 2500 watts of panels, 1kw facing southeast 1.3kw facing southwest 170watt ancient Arco's facing south. All panels in parallel for a 24 volt system. Trace DR1524 MSW inverter, Outback Flexmax 80 MPPT charge controller 8 Trojan L16's. Insignia 11.5 cubic foot electric fridge. My 29th year.
Re: question about utilizing excess power

It possible that running high voltage on the DC bus makes the AC output a bit higher voltage too--Which cause higher current flow and therefore hits the inverter limit.

Running a 100 foot (for example) extension cord can have enough resistance that it cuts the peak surge current down enough for the motor to start without faulting the inverter.

-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 54
Re: question about utilizing excess power

thanks for the info guys

yeah i know the battery bank is a little big but i get some shade in the winter when im not around and wanted the batteries to be topped off with a minimal running of generator

would you reccomend that i cycle these batterys more aggressivly,??
i dont use much power mostly computers ,hand tool and a freezer converted to fridge ,
the m1512 has a starting surge of 3500 watts another option is to run the generator during startup

im not sure if i= want to spend 600 bucks on a slo pump but thats seems like the most efficent route long term
what are the possibilitys of running a pump off my current array with dc current via slo pump
and using the inverter/generator via the ac submersible when light is less as a backup

thanks again
• Solar Expert Posts: 54
Re: question about utilizing excess power

thanks for the info
i went with a larger battery bank because i leave in the winter and was worried there was gonna be periods of clouds and i wouldnt be there to run a generator,

i also thought that if i was only useing minimal power the batteries would last longer
i dont use much power led lights,tools ,small fans ,washer ,small converted chest fridge

my inverter has a startup surge capacity of 3500watts and i thought maybe running the generator during startup would help

i planned to use this pump to pump water from one cistern to another higher up a hill
i know the most efficent route was a dankoff slo pump ,but the cost was a little high (might just have do it eventually)
if i go with the slo pump could i hook up another c60 and run it on diversion to power the pump after float is reached??
would you recommed i cycle my battery bank more ???i was unaware that shallow cycling is bad
i equalize every month and have a auto watering system
maybe a dual system using dc current to power a slo pump in the sunny times and having the ac pump as a backup using the generator to suppliment thanks for your insights everyone

would you reccomend running the pump off the batteries to drain down to 50% then recharging via array or genny ??
• Solar Expert Posts: 3,741 ✭✭✭✭
Re: question about utilizing excess power
yeah i know the battery bank is a little big but i get some shade in the winter when im not around and wanted the batteries to be topped off with a minimal running of generator
i went with a larger battery bank because i leave in the winter and was worried there was gonna be periods of clouds and i wouldnt be there to run a generator

The solution for cloudy days is more panels, not more battery. More battery (for any given amount of panels) means less charging current per amphour of battery capacity.

A lot depends on how much autonomy you need when you leave in the winter. If you're gone for a week at a time, you don't need panels at all, you could size the batteries to last a week and bring the battery to 100% SOC weekly with the generator. Your panels act as a battery maintainer.

On the other hand, if you are gone weeks at a time, you must count on your solar array to get the batteries to 100% regularly. That means more panel or less battery.
would you reccomend that i cycle these batterys more aggressivly?

Yes. The batteries should be used. Deep cycle batteries for backup/standby applications are designed to spend most of their lives in float. Your batteries are designed to be cycled. One way to look at batteries when you design a system is kilowatthour throughput per dollar. That is, how much did you spend on the batteries, and over their lifetimes, how many kilowatthours will move into and out of them.

Fifteen years ago batteries were cheap, gas for the generator was cheap, and solar panels were very expensive. Systems were designed with large battery banks that would lose a significant amount of capacity due to slow deficit charging. The battery bank might last a decade because it was so oversized that at half capacity it could still do the job.

Batteries are now expensive and solar panels are cheap. In the above example, if the battery started out half the size, it would work harder, be fully charged more often, and last 7 years. I would prefer to replace the battery every 7 years, than to replace twice the battery every 10 years.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Solar Expert Posts: 54
Re: question about utilizing excess power

thanks for the update vt

well i have 8 more 75watt panels that i could put up but havent because ive been reaching float within a few hours even when im using my power
when i leave for extended periods weeks to month i generally clean the fridge out and shut the inverter down so only the charge controller is operating, charging the batterys

im getting maxed out with the 60 amps on this controller (would you recommed down the line hooking the rest of these panels up and getting a different charge controller maybe an 80amp)

my power needs now are quite minimal for this bank i know but am i doing harm not cycleing them??

what would be the minimal heavy cycling to use these batteries properly (should i run the pump once a day/ or few times a week?)than recharge

any input about using a diversion controller to run a dc pump like the slow pump 1/4 hp??
Re: question about utilizing excess power

There are discussions on what is best for deep cycle batteries, but taking then down to 7turn off charge once a month (tien off change controller).

Then back to normal.

If flooded cell, get a good hydrometer and check the specific gravity daily/weekly until you know what is happening. After that log the readings once a month to make sure all is ok.

-Bill "it's a start" B.
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
• Solar Expert Posts: 54
Re: question about utilizing excess power

sounds good i got a hydrometer and will start checks the cells to make sure im not doing damage

as far as water pumping goes i think i wont be useing the 1hp ac pump unless emergency or i need to drain the batteries

looking more into a dankoff 12v slo pump that can pump slo and run off the diversion load i get from the array during float
id like to have water pumping to my upper cistern while the ac inverter is off and im not around

does anyone have experience running a water pump with a diversion load ,my array is more than needed to run the pump so im wondering if i need to get a second controller to adjust the power or will the pump only use what it needs

another question is i already ran wire 10/2 meant for the ac pump 135 feet to water source i know that with a dc system there will be more voltage drop with a longer wire run but because i have more dc power than needed to run this 1/4 hp pump could i get away with using smaller wire ??? id rather not run more wire

do you think i need to get a linear current booster as well??
• Solar Expert Posts: 235 ✭✭
Re: question about utilizing excess power

vtmaps,

I am a little confused about what you said and think it may be misunderstood. I am definitely a proponent of the "larger array, smaller battery" philosophy, and agree that if the OP'er was shopping for batteries, then sure, he should get a smaller bank than what he has now. He asked if he should intentionally cycle his batteries because they arent getting much use. I cant see how cycling for the sake of cycling could be good for anything - you only get so many cycles. IF they are floating then they arent in danger of sulphating and a good automatic equalize should keep the electrolyte good and mixed up to avoid stratification.
• Solar Expert Posts: 3,741 ✭✭✭✭
Re: question about utilizing excess power
I cant see how cycling for the sake of cycling could be good for anything - you only get so many cycles. IF they are floating then they arent in danger of sulphating and a good automatic equalize should keep the electrolyte good and mixed up to avoid stratification.

As I mentioned earlier in this thread, repeated shallow cycling can cause lead dioxide clumping on the positive plates. As to whether it is a good idea to discharge the battery (deeper than a shallow discharge) occasionally, that is controversial. But I do agree that generally, the shallower the discharge, the more cycles in the battery's lifetime.

Something else that is controversial is automatic equalization. I'm all for equalization when needed, but I don't trust automatic. I equalize manually, and wouldn't do so without supervising the process.

btw, some european controllers have a feature that is useful for folks with oversized, shallowly cycled batteries... the controllers can skip days of charging if the battery starts out at too high an SOC. This lets the battery get cycled deeper which reduces the number of cycles in the battery's lifetime. But since each cycle may last two or three days, a given number of cycles will provide more years of service. This is proven to be more cost effective than daily, shallow cycles.

The Midnite controller can also skip days of charging, but, if I recall correctly, it just skips the number of days that you specify... it doesn't (yet) make the daily decision about whether to charge based on SOC.

--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i
• Banned Posts: 17,615 ✭✭✭
Re: question about utilizing excess power

Waste of money to buy 'X' Amp hours and use only 10% when the lifespan is almost identical at 25%. After that the lifespan drops off more drastically. As with so many things, batteries aren't linear.
• Solar Expert Posts: 3,009 ✭✭✭✭
does anyone have experience running a water pump with a diversion load ?

No, but - - - - I have used a freezer in such a way. It would run continuously when controller was in float, then revert to normal operation when controller not in float. The idea was to super cool the freezer contents when excess power was available, which it was hoped would reduce it's power consumption at night. After a short test, I discovered there needed to be a 10 minute delay timer to prevent rather rapid restarting of the compressor at less than full sunlight. Controller would go to float, freezer would start and thus load down the system. Controller would exit float, compressor would shut down. Without the load, voltage would go up again, controller switch to float, compressor would fail to restart because back pressure had not yet drained down. Delay timer cured that.
Point of the story is - - - - watch for too much cycling if light levels are low. You're proposed arrangement may or may not experience cycling under similar conditions. AND in your case, IF such cycling does occur, it may, or may not be a problem for your equipment. Just something to be aware of.
BTW, during dry periods in Summer when my garden is drying up, I manually turn on a pump to water the garden and let it run all day till the sun is about to do down. Been doing that for a few years. Single cylinder piston pump, 1/4 hp (motor shaft hp), 5 amp 115 VAC, powered by inverter. And yes, the pump could be considered antique. Same make and basic design as my domestic water pump, only singe piston, instead of dual piston, and like my domestic water supply pump, at least 60 years old. See photo above my user name. Gotta love old and very heavy cast iron pumps.