Off grid Design- water pump and extra power

[pda1]

I need help in designing an off-grid system, here are the energy requirements;

- 12 vdc water pump (about 50 watts) https://www.nemopumps.com/
- Computers- (about 500 watts 120 VAC) (wouldn't be running all of the time- only a few hours a day)
- A few led lights (about 50 watts 120 VAC) (only when needed, which is a variable)

What I think I need, in basics are- PV panels, charge controller, inverter

System must be run off of lead-acid battery(s)

What system components would you recommend to satisfy the energy needed above?
Are there any other components I should add?

Thank you,

Peter

 

[Scottsdream]

I have about the same needs but I run a mini refrigerator instead of a computer
Here's what I have been using for 3 years
2- 300 watt panels (mounted with manual tilting capability) mono or poly doesn't really matter
1- farm lead acid battery (group 31; 175 minutes reserve capacity)
1- 1000 watt pure sine-wave inverter
1- cheap pwm 30A controller ( ebay or amazon) - my only recommendation here is get one that has a heat sink style back plate and mount it on stand-offs to allow good air flow for cooling)

 

[lupo]

Hey, I am currently building a very similar system. I also did a video about my design process (more to come)

In general, it really depends what budget you have. I would suggest a MPTT controller to be flexible in the future in case you want to change something (e.g. the panel or number of panels). As you have a max of around 10A (12V) which would mean you can pull the power for 10 hours from a 100Ah LiFePO4 or a 200Ah lead acid. The question is also how much sun you have? Cloudy weather means almost no energy and you need a bigger battery if you need power on cloudy days as well.

 

[pda1]

Ah, now that's most helpful.

Now, is there any reason why I can't increase the power to 800 or 900 watts....just to have enough standby power so to speak?

Any opinion on Low Voltage Disconnects?

Thank you for the help.

Peter

 

[Scottsdream]

Where are you located? You really don't need low voltage disconnects if you're using lead acid. When you say increase power to 800-900W what are you referring to? Standby or reserve is usually measured in Ah. Two 300 watt panels will easily charge a single 12v LA battery even on a cloudy day based on the loads you previously mentioned. And 500 watts of computer power is very high ( 10 laptops or so). Is it really 500 watts?

 

[Scottsdream]

Oops,
Read low voltage as low temp. Many inverters have a low voltage disconnect built in (in a simple system it will work just fine as long as it's set up for LA)

 

[lupo]

regarding sizing I can also recommend the video

 

[pda1]

Where are you located? You really don't need low voltage disconnects if you're using lead acid. When you say increase power to 800-900W what are you referring to? Standby or reserve is usually measured in Ah. Two 300 watt panels will easily charge a single 12v LA battery even on a cloudy day based on the loads you previously mentioned. And 500 watts of computer power is very high ( 10 laptops or so). Is it really 500 watts?

By "increase power to 800-900w" the assumption I'm making is that IF....IF....the battery is fully charged and the water pump isn't in use there will be plenty of power from the pv panels themselves to supply the computers.

What do you think?

Peter

 

[lupo]

By "increase power to 800-900w" the assumption I'm making is that IF....IF....the battery is fully charged and the water pump isn't in use there will be plenty of power from the pv panels themselves to supply the computers.

you mean increasing the power of the panels, like having 3 panels 300W each? Of course, that is not a problem but you have to make sure that all components can handle the current/voltage. If you have more panels you will need a bigger charge controller that can handle it. Btw, even if you have a 500W power supply for your computer, usually, the do not pull 500W all the time.

 

[pda1]

Yes, I understand the power draw of the computer isn't that much....my requirements don't particularly relate to computers but rather some nonspecific load that can be handled directly by the panels of the battery.

So here's what I'm think....and provide correction as needed...

800w solar array
12vdc battery (lead acid)
100a charge controller (better to have bigger than wish I had)
1000w inverter (bigger to provide more than wish I had)

Well, what do you think?

Thanks,

Peter

 

[pda1]

regarding sizing I can also recommend the video

If I hear him say "Battle Born" battery one more time I'll go nuts! Who has the money for that sort of battery?!

 

[lupo]

Yes, I understand the power draw of the computer isn't that much....my requirements don't particularly relate to computers but rather some nonspecific load that can be handled directly by the panels of the battery.

So here's what I'm think....and provide correction as needed...

800w solar array
12vdc battery (lead acid)
100a charge controller (better to have bigger than wish I had)
1000w inverter (bigger to provide more than wish I had)

I would consider a 24V system with this requirements. With lead acid you need more than one battery anyways. With 24V you are also more flexible and can use a smaller charge controller, no need for 100A (e.g. the victron 35A can handle up to 1000W PVs in a 24V system).

 

[Steve_S]

The general unwritten rule is to not draw more than 250A from a battery bank (excepting surge handling). Stackable inverters and such are another matter handled differently.
12V@250A=3000W (25A AC),
24V@250A=6000W (50A AC),
48V@250A=12,000W (100A AC)
-- for quick reference. The (50A AC) can be 120V/50A out to panel or 240V/25A split phase to panel.
In simple terms. -- AC 120V/15A=1800W, 240V/15A=3600W uncorrected
? 250A. Because it's recommended to be the MAX draw limit for a standard "single" system. Single, meaning non-stacked inverters and similar.
! Inverter Wattage has to support the watts required plus surge capacity. Should never be run at the limit for an extended period of time (that's undersized).

System Use Info.
My system will most often have the batteries full by noon in summer at which point in time the system goes into FLOAT Mode which trickles to the battery bank allowing everything to top off and level up. But say it's 1PM I turn on coffee maker (50A draw on 24V) the SCC ramps up and solar panels will provide all 50A without touching the battery bank at all. Now if the solar can only provide 35A, the balance is pulled from the batteries, as soon as the draw ends, the SCC (Solar Controller) goes into Bulk Charge and brings the batteries back up to full.

LEAD ACID INFO:
Car, Marine, Fam batteries are NOT INTENDED for Solar, they have thin plates wich will burn out, it works "for a while". Real Honest to Goodness Deep Cycle lead battery plates are double the thickness and HUGE ! They are also considerably more expensive. In reality, it is cheaper to DIY an LFP (LiFePo4) battery pack that it is to use Lead... Remember you can ONLY Draw a Maximum of 50% capacity from Lead otherwise your damaging them (and that's with proper deep cycle solar batteries).

Case in point, my Lead Bank cost me $3500 (428AH Gross / 214AH useable) using proper Rolls Surette S-550 Heavy Lead.
My DIY 280AH Packs cost roughly $1800 each. so for $3600 I've got 560AH useable...

DO Look at the first two links in my Signature, you'll get many questions answered nice & simple.
Hope it helps, Good Luck.

 

[pda1]

I would consider a 24V system with this requirements. With lead acid you need more than one battery anyways. With 24V you are also more flexible and can use a smaller charge controller, no need for 100A (e.g. the victron 35A can handle up to 1000W PVs in a 24V system).

I've already purchased a 12v water pump so I guess I'm stuck with using 12v. Also, it can also be connected directly to my car battery.

Any ideas?

 

[pda1]

The general unwritten rule is to not draw more than 250A from a battery bank (excepting surge handling). Stackable inverters and such are another matter handled differently.
12V@250A=3000W (25A AC),
24V@250A=6000W (50A AC),
48V@250A=12,000W (100A AC)
-- for quick reference. The (50A AC) can be 120V/50A out to panel or 240V/25A split phase to panel.
In simple terms. -- AC 120V/15A=1800W, 240V/15A=3600W uncorrected
? 250A. Because it's recommended to be the MAX draw limit for a standard "single" system. Single, meaning non-stacked inverters and similar.
! Inverter Wattage has to support the watts required plus surge capacity. Should never be run at the limit for an extended period of time (that's undersized).

System Use Info.
My system will most often have the batteries full by noon in summer at which point in time the system goes into FLOAT Mode which trickles to the battery bank allowing everything to top off and level up. But say it's 1PM I turn on coffee maker (50A draw on 24V) the SCC ramps up and solar panels will provide all 50A without touching the battery bank at all. Now if the solar can only provide 35A, the balance is pulled from the batteries, as soon as the draw ends, the SCC (Solar Controller) goes into Bulk Charge and brings the batteries back up to full.

LEAD ACID INFO:
Car, Marine, Fam batteries are NOT INTENDED for Solar, they have thin plates wich will burn out, it works "for a while". Real Honest to Goodness Deep Cycle lead battery plates are double the thickness and HUGE ! They are also considerably more expensive. In reality, it is cheaper to DIY an LFP (LiFePo4) battery pack that it is to use Lead... Remember you can ONLY Draw a Maximum of 50% capacity from Lead otherwise your damaging them (and that's with proper deep cycle solar batteries).

Case in point, my Lead Bank cost me $3500 (428AH Gross / 214AH useable) using proper Rolls Surette S-550 Heavy Lead.
My DIY 280AH Packs cost roughly $1800 each. so for $3600 I've got 560AH useable...

DO Look at the first two links in my Signature, you'll get many questions answered nice & simple.
Hope it helps, Good Luck.

Steve,

Very informative. I'm becoming a little more sympathetic to LiFePo batteries....it's just the sticker shock.

You have a lot more time and money than I'll ever have. The 2 links below your signature don't explain anything....maybe I'm not using the correct ones?

Thanks fellas'

Peter

 

[Steve_S]

My DIY off-grid Cabin setup in Ontario Canada (24vdc-120vac)

NOTICE: UPDATING November 2022 WIP Good Day everyone, Overview: There is no grid here, no phone lines, cell is so-so (to be polite) so satellite internet is here (not bad actually). I do not have 240VAC, this is a 120V system only. My Solar Panels are mounted separately from my Powerhouse...

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Luyuan Tech Basic Lifepo4 Guide

This document was posted to the forum by Amy from Shenzhen Luyuan and written by Steve S. It was meant to be posted as a resource. Below is her description of the resource: Dear all friends in the forum, This file in the attachment was...

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[lupo]

I've already purchased a 12v water pump so I guess I'm stuck with using 12v. Also, it can also be connected directly to my car battery.

It really depends on your load. If the inverter is your main load, I recommend a higher voltage and LiFePO4, it is just more reliable and on long term LiFePO4 is cheaper. You can also buy a cheap step converter (~15€ on Aliexpress) from 24V to 12V to use 12V appliances. 24V is more expensive as you need more battery cells but you can use a smaller controller and thinner cables.

 

[pda1]

It really depends on your load. If the inverter is your main load, I recommend a higher voltage and LiFePO4, it is just more reliable and on long term LiFePO4 is cheaper. You can also buy a cheap step converter (~15€ on Aliexpress) from 24V to 12V to use 12V appliances. 24V is more expensive as you need more battery cells but you can use a smaller controller and thinner cables.

Lupo,

Now I'm pursuing the 24v panel system. But I'm inclined towards a high wattage array, for me, of about 800w as mentioned before. What's the cheapest and most practical way to go about panel selection? It would nice to get everything off of ebay and it looks like a more reasonable single panel wattage is 200 (24v) and then connect them in parallel. Like this one-

200w 24v panel on Ebay


Any thoughts about that?

Thanks for explaining about the step converters.

Concerning batteries- Are you recommending a 24vdc LiFePO4 battery?

Thanks,

Peter

 

[Wellbuilt]

How about 2 215 ah battery’s from sams club for about 100 bucks each ?
I would look for a electrical supply house that can sell you solar panels
I bought 295 watt panels at 135 bucks 4 years ago and the same panels last year for 165 $ no shipping .
You would need mppt controller for that panel

 

[Hedges]

Lupo,

Now I'm pursuing the 24v panel system. But I'm inclined towards a high wattage array, for me, of about 800w as mentioned before. What's the cheapest and most practical way to go about panel selection? It would nice to get everything off of ebay and it looks like a more reasonable single panel wattage is 200 (24v) and then connect them in parallel. Like this one-

200w 24v panel on Ebay


Any thoughts about that?

Thanks for explaining about the step converters.

Concerning batteries- Are you recommending a 24vdc LiFePO4 battery?

Thanks,

Peter

That's over $1/watt for PV.

Check out SanTan Solar.
Shipping a pallet by truck gets expensive if you only want a couple.
I got many (several pallets) and drove my pickup to freight terminal to save on last mile delivery.
For small quantity, you can find local sellers with similar price.
PV panels can be ha for $0.15 to $0.50/W

DIY LiFePO4 can be smaller cash outlay than lead-acid. But it is a project in and of itself.
It will give longer cycle life (maybe up to 3500 cycles)
AGM can give 200 to 700 cycles depending on quality and DoD.
FLA is cheaper and can give 2x cycles of AGM if quality. Requires maintenance.

Which battery meets your needs depends on how often you plan to cycle.
Mine is only backup during grid failure. I chose AGM, expecting < 200 cycles in a decade. I sized it for 70% DoD.

If you avoid nighttime drain so battery is only a buffer during the day, then demand on battery is minimal. Even a used car starting battery would work fine if never cycled, only providing a surge to start motors.

Batteries are expensive and wear out. PV is cheap and lasts forever. So I try to over-panel and minimize batteries.