Newby - Solar System for Farm Questions.

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Newby - Solar System for Farm Questions.

Postby FarmerBrown » Sat Jan 23, 2016 4:34 pm

Hi, hoping that someone can assist with my complete lack of knowledge of solar systems and i apologise if this question has been asked 1000 times before.

I recently purchased a small farm that has a shed with a small solar system installed. It comprises of:

1) 4 x solar panels (North facing on roof at approx 45 degrees) - not sure of wattage?
2) Invertek Supercombi 1500W inverter(Pure Sinewave)
3) Control (protection panel i think?) panel
4) Bank of 12 x batteries all wired together with thick cabling(around the size of car batteries but with no writing on them to indicate size)
IMAG0086.jpg
solar power system
IMAG0086.jpg (46.29 KiB) Viewed 5126 times



I turn all power off via master switch when i am not there but leave the inverter turned on all the time. Inverter usually says that batteries have 12.6 -13.2V but drops to around 12.0 - 12.9V if under normal load(TV, lights, charger).

Q1) Do i need to leave the inverter on or will the batteries keep charging regardless?

I usually just run a couple of flouro lights, TV/DVD player, fan and charge the odd power tool battery but have had no issue with lack of power previously (i can run lights, TV etc all night and batteries will hold 12+ Volts)...until last weekend when i took a small bar fridge up for the first time.The Inverter cut out at dusk(40 degrees day) and said' Battery Under Volt'(battery volt 10.5V) - no power for the rest of the day! The next morning when i got up it read 11.5V and climbed to normal Voltage throughout the morning.

Q2) I assume this is a protection so the batteries dont get ruined if drained too much?

As i say, excuse my lack of knowledge but i have done some maths with some assumptions:

Assuming that i have 4 x 80W panels on the roof and they charge for 8 hours a day. That gives me a total of
2560W. Given that it was 40 degrees, take 20% off for heat inefficiencies = total watts generated that day 2048W.

Domestic 115L fridge(with 6Ltr freezer) = 40W/hr x 24 hours = 960W(min because of repeated start up)
Large fan (on high)= 70W/hr x 9 hours = 630W
Phone/Ipad charger = 12W/hr x 2 hours = 24W
2 x Flouro lights = 25W/hr x 1 hour = 50W
Cordless drill charger - 50W/hr x 1 hour = 50W

Total Watts used throughout day = 1714W

Q3) Is that maths correct? ie, panel input and appliance output is all that i need to calculate to prevent running out of power again?

Q4) Do i need to worry about the voltage or will this be determined by the wattage input/output?

Q5)Do i need to consider Amps in this at all or will the wattage method suffice?

Obviously the fridge and the fan drew too much power(watts) and i will be more aware of that in future.

Now...

Q6) Can i assume that the 1500W inverter means that it can convert DC(batteries) to AC(240V) at the rate of 1500W per hour for every hour of charge from the panels?

Q7) To give me more power storage, do i need more panels or more batteries?

I appreciate your time in reading this and probably just needed to put my thoughts in writing to get my head around the solar power system i have. So please let me know if i have any of the above incorrect and i would appreciate it if you could answer my questions throughout this post.
Last edited by FarmerBrown on Sat Jan 23, 2016 6:18 pm, edited 1 time in total.
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Re: Newby - Solar System for Farm Questions.

Postby davef » Sat Jan 23, 2016 5:43 pm

Perhaps if you had numbered the questions it might help others to respond. Try editing the posting.

Battery efficiency didn't seem to be mentioned. Maybe 75-80% depending on charge conditions.

If it is an inverter/charger then it would need to be left on all the time. Unless you have some other way of charging the batteries.

Correct on the low voltage cutout.

I doubt your freezer runs 24/7. My Samsung fridge sucks about 50 Watts when it is running but only 400Watts for the day, that is a 33% duty cycle. Your freezer should be better than that.

You appear to have the voltage/amps/watts calculations OK. Worry about voltage ... well worry about how much voltage drop there is and therefore power wastage. Worry about amps ... when it comes to selecting fuses and wire sizes.

Q) Can i assume that the 1500W inverter means that it can convert DC(batteries) to AC(240V) at the rate of 1500W per hour for every hour of charge from the panels?

Don't think it is useful to look at it this way. You don't know how much wattage your panels supply over typical days. And you don't know how much storage you really have.

By watching your battery voltage during the day you will gain some appreciation for whether or not you are limited by the generation side or the storage side. I don't know your charger, so if it drops back to float, say by lunch time and your batteries were down near min in the morning then you need more or better batteries.

If your batteries are not fully charged at the end of a sunny day and they were down near min in the morning then you need more PV panels.

More information is needed: like what are the battery specs and some idea of their condition. And it will be really useful to be logging PV current to get some idea of the max current and how much of typical days it is NOT bulk charging the battery, ie is it spending time floating. You will see this as low PV current in full sunlight.
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Re: Newby - Solar System for Farm Questions.

Postby Gordon-Loomberah » Sat Jan 23, 2016 5:49 pm

G'day Farmer Brown, welcome to the Energy Matters Forums :)

How many terminals do those batteries have, and what voltage are they?
I assume the Invertek is also a charge controller? If so, can you turn the inverter part off and leave the charge controller running?

If your battery voltage droped to 10.5V after a day of slightly larger loads, I'd suspect a sick cell, or probably multiple sick cells in the parallel batteries.

Unless all your cells are in equal health, relying on low voltage disconnect (LVD) to protect the batteries is really only going to ensure they die sooner rather than later.

Your calculations for how much energy you will produce from your solar panels may be a touch on the optimistic side :(
I don't know your location, but typically allow 4-5peak sun hours per day averaged over the year.
320W of PV would be expected to produce under half of what you thought. It will be better than that on sunny summer days, and cooler sunny days with or without a little bit of cloud any time of the year, but you will have minimal energy available in wet overcast days any time of the year.

If your charge controller is a PWM type, it forces the panels to operate at battery voltage, which may be significantly under their rated maximum power voltage. Maximum Power Point Tracking charge controllers extract the maximum from PV panels, do you know what sort you have there?

On terminology, energy generated (or consumed) is measured in (kilo) watt hours, not watts, which is a rate of power production/use.
Power X time = energy
PV power production under normal conditions is 70-80% of the rating, and can be lower in particularly hot weather, especially in calm conditions.

Charging of Lead-acid batteries is only likely to be 85-90% efficient for batteries in good condition. I suspect yours are on the way out, so efficiency will be down on that, meaning even less energy available from your panels.

A 1500W inverter would normally deliver 1500W continuously, however, some inverters are misleading in that they advertise the maximum, not continuous rating. You'd need to check your specs to be sure.

Regarding terminology again, "1500W per hour" is meaningless, 1500W is already a rate, no need to add per hour to it.

Whether or not your batteries can deliver 1500W is important too, and for a 1500W load, the inverter will probably be consuming 1700+W, due to its efficiency factor.
Not only that, but Lead-acid batteries suffer from the Peukert Effect, whereby the available capacity decreases significantly under higher loads. Battery manufacturers show this as a rated AH capacity at various discharge rates- 5 hour 10 hour, 20 hour etc, always lower capacity it faster discharge rates.

You need more panels, but you really need to determine the health of your batteries too, they may need replacing. If they are flooded cells, you need to charge them fully, then measure the specific gravity of each cell. You also need to check how they are wired up to make sure it is correct.
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Re: Newby - Solar System for Farm Questions.

Postby FarmerBrown » Sat Jan 23, 2016 6:31 pm

Thank you so much guys. Post edited to identify individual questions.

What you both say makes sense and more importantly tells me i have a lot to learn about solar!

The system i have has all the readings you describe...float, current, amp hours, amp hours total etc. I am up again next weekend so will get some better photos and readings of individual components and post them to assist.

Batteries reach full charge pretty quick ie 12.6V almost straight away and can stay on that all day with lights and TV etc. dont know if that helps. I have seen the word float a bit on the charger unit and it has three modes - charge, ?, ? - i will check next weekend.

Property is in the Hunter Valley, NSW and i think the best way to determine the health and capability of my system is to get someone to come out and explain it all and test individual components at some stage.

Thanks again and i will post again this time next week. Hopefully you can assist further?
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Re: Newby - Solar System for Farm Questions.

Postby Privatteer » Sat Jan 23, 2016 6:48 pm

FarmerBrown wrote:T 12.6V almost straight away


12.6V is not full charge. While it depends in the battery I would expect around 13.4 to 13.8V for a float charge.
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Re: Newby - Solar System for Farm Questions.

Postby Gordon-Loomberah » Sat Jan 23, 2016 7:03 pm

Very rapid voltage rise in the battery with only a relatively low charging rate can indicate the battery is just about stuffed too.
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Re: Newby - Solar System for Farm Questions.

Postby sean » Wed Jan 27, 2016 1:24 pm

Hi,
I don't think the invertec super combi 1500watt has a built in charge controller, just a mains or gen set charger.
I have a 3000watt invertec super combi and it needs a separate charge controller between the panels and the battery bank, then the two main + and- leads go up to the super combi, the charger under the combi unit is a mains of gen set charger only.
I hope tis helps a bit.
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Re: Newby - Solar System for Farm Questions.

Postby Gordon-Loomberah » Wed Jan 27, 2016 1:36 pm

OK, we need to wait for more info then, as there is no mention of a separate solar charge controller in the list of items in the shed.
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Re: Newby - Solar System for Farm Questions.

Postby Bthree » Wed Jan 27, 2016 2:13 pm

As you have so many batteries for 12 volt it would be worth while checking out this thread for connection methods.

http://www.smartgauge.co.uk/batt_con.html
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Re: Newby - Solar System for Farm Questions.

Postby FarmerBrown » Sat Jan 30, 2016 5:15 pm

Hi all. After not providing anywhere near sufficient info for you to guage the health of my solar power system last week, i have returned with some more details. Hopefully you can assist with a health status from the following data?

Solar diagram.pdf
(99.57 KiB) Downloaded 403 times

This is a layout of the solar power system including battery type and wiring diagram(hopefully it works)

Here are some other details that might be of assistance:

When i arrived at the property last night(930pm), i had the following readings from the inverter:
Note that all power is off during the day except the actual inverter which is left on 24/7.

Batt Volt = 12.6
Batt current - 7.2A (2 x flouros and 1 x 20W LED); -5.6A(1 x flouro and 1 x 20W LED); -1.6A(1 x flouro)
Battery ripple Volt = 0.0

Q1) What does ripple volt mean?

Sunstar SS-60C Charge/load controller readings:

Amp = 0.0
Watts = 0.0
Batt V 12.6
Mode = Charger
State = Bulk
Bulk 14.0V Float 13.4V

Q2) What do the last three mean?

When i plugged in the F&P 115ltr fridge (Current 0.7/230V) - these were the readings:

Start up:

Fan on inverter started straight away
Batt Current = -71.1A
Batt Ripple Volt = 0.4V
Batt Volt = 11.6
AC Out current = 3.2A
Batt temp sender = 25 deg

After 5 mins:

Fan on inverter still
Batt Current = -60.9A

Q3) Why did the fan go instantly and the battery temps rise so rapidly?

After 7 mins with fridge compresssor off:

Fan off inverter
Batt volt back up to 12.4V
AC Out current = 0.2A
Batt temp sender 28 deg
Batt Current = -1.5A
Batt Ripple volt = 0.0V

Fridge compresssor on:

Fan off inverter
Batt Volt to 12.2V but stable
Batt out Current 0.6A
Batt temp sender 23 degrees
Battery current = -14.6A (drops to -10.7 within 5 mins)
Ripple volt = 0.1V

Left fridge on all night...

Morning readings(730am and no sunlight on panels)

Batt Volt 12.2V
Temp sender 19 deg
Batt Current 0.0A
Ripple Volt 0.0V

Charge controller readings at 730am:

Amp 3.0 Watt 37 BattV 12.4V

Inverter at 930am = 13.1V(no power being used - fridge off)
Charge controller at 930am = 16.0A 213W 13.2V

I tried to attach a layout of the system including wiring of batteries so hopefully that will work.

I guess what i am trying to understand is if my system is healthy and i expect too much from it or if it needs some attention and i am hoping that this information will be enough for solar savy techs.

The only thing i still dont know is the type of panels(4 off) on my roof. The full panel array would be 2.2mW x 1.0m high roughly)

Thanks again and i look forward to any replies.
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