Off-grid system miscellaneous questions

[suprasteve44]

Hi All, new to the forum and trying to educate myself on off-grid solar. The family is purchasing some land without electrical service for a "camp" of sorts, and figure a combination of solar, propane, and generator power will be used. In short, I'm trying to size a solar power system to handle smaller electrical loads while we are visiting (NOT heating, cooling, or cooking), or anything that runs while we are not there (so the generator doesn't have to be running). Roughly looking for it to run a water pump, some lights, bug zapper, that sort of stuff. But before we get to that and ultimately a design, I have some (hopefully) basic questions:

1. Since power goes into banks of 12V batteries (generally speaking), is there an efficiency advantage to running 12 VDC lighting? I'm assuming that the voltage drop in a low volt DC system is a lot more of an issue than 115 VAC, which may mean any efficiency loss in the conversion from DC to AC is outweighed by the size of wiring that would be needed to run 12 VDC say, 100' or so. I'm not completely new to wiring in boats, so I do have a little bit of experience with 12 VDC. Asked differently, how efficient are good inverters at converting from DC to AC?

2. I'm 99% sure the answer to this next question is "yes", but just to confirm: the inverters will only pull enough power to match the load requirement at any given time, up to is rated capacity, right? In other words, just because you have, say, a 2000 watt inverter doesn't mean it's always drawing 2000 watts unless the demand is that high?

3. I'm planning on electricity for any "big" loads (air conditioner, power tools) being provided by a generator. I have seen some inverters with built-in transfer switches. Next question is: does the inverter rating still matter for the load being pulled if the generator is running and the inverter has a transfer switch? Explained differently, let's say I have a 2000 W inverter and a 5000 W generator hooked to the inverter's transfer switch. Would I be able to run a 3000 W load, or would that still overload/damage the inverter even with the generator running? Or is this a "it depends" answer depending on the manufacturer?

4. I've also seen battery protectors that shut off at a certain low voltage level. I'm planning to use lead-acid batteries due to cost, and think this would be a good way to help protect them considering the system will be unmonitored for long stretches. Question is: do these also turn back on once the voltage level rises from charging, or do they need to be manually reset like a circuit breaker? Or does it depend on the model/manufacturer?

5. Finally (for now), suggestions on manufacturers to use and/or avoid? This is all new to me so I don't have prior experience with any of the companies manufacturing this stuff. There's nothing life critical that will run off this solar, but it should be able to be left alone for a few weeks at a time without constant adjustments/fixes/resets. Looking for robust more so than feature-rich if that's a better way to put it. In case location matters for what's available in my market, this will be in Florida, USA.

Next step will be to determine my constant and transient load requirements, and try to work out a design that matches. Trying to get some of the basic questions answered on how the systems work first. Thanks in advance for your help!

[Mike90250]

I've not studied much in the small inverters for RV's with transfer switches. With the large inverters, the switch (relay) is rated for a specific amperage. Mine is 60A @ 120VAC. A common failure mode is welded contacts from switching max loads with generator cutting on and off. bad !

For a small, super efficient inverter, I like the Morningstar 300w (600w surge) https://www.morningstarcorp.com/products/suresine/
It's designed to be wired in, it has no outlets.
Inverters have both a self-consumption load, and added to that is the power delivered + efficiency losses. different inverters have different self-consumption, larger inverters have more self-consumption than smaller inverters. Better inverters have lower self-consumption.

Running a water pump, can mean many things. A little 12V pump like in an RV or boat ? Or a big well pump ?

Many charge controllers have a pair of LOAD terminals for low power devices, and the LOAD terminals are controlled by Low Battery Cut Off. Usually, a 10A controller has a 10A load limit, only small loads should be connected, not a large load like an inverter. Inverters have their own LBCO - but that's to protect the inverter and it also protects the battery

[organic farmer]

Hi All, new to the forum and trying to educate myself on off-grid solar. The family is purchasing some land without electrical service for a "camp" of sorts, and figure a combination of solar, propane, and generator power will be used. In short, I'm trying to size a solar power system to handle smaller electrical loads while we are visiting (NOT heating, cooling, or cooking), or anything that runs while we are not there (so the generator doesn't have to be running). Roughly looking for it to run a water pump, some lights, bug zapper, that sort of stuff. But before we get to that and ultimately a design, I have some (hopefully) basic questions:

1. Since power goes into banks of 12V batteries (generally speaking), is there an efficiency advantage to running 12 VDC lighting?

One of my neighbors setup solar and wind for his his house in the 1980s. His entire house uses 12vdc.

His home stereo is an automobile radio mounted flush in one wall.

RV camper stores have full selections of 12vdc refrigerators, microwave ovens, TVs, etc.

... 2. I'm 99% sure the answer to this next question is "yes", but just to confirm: the inverters will only pull enough power to match the load requirement at any given time, up to is rated capacity, right? In other words, just because you have, say, a 2000 watt inverter doesn't mean it's always drawing 2000 watts unless the demand is that high?

Plus 10%.

An invertor will draw whatever amount of power is needed for the appliance it is powering, PLUS 10%.

A 1,000 watt load you should likely expect to see it consuming 1,100watts.

... does the inverter rating still matter for the load being pulled if the generator is running and the inverter has a transfer switch?

Yes.

The power going through an invertor is limited to the capacity of the inverter.

... 4. I've also seen battery protectors that shut off at a certain low voltage level. I'm planning to use lead-acid batteries due to cost, and think this would be a good way to help protect them considering the system will be unmonitored for long stretches. Question is: do these also turn back on once the voltage level rises from charging, or do they need to be manually reset like a circuit breaker?

Mine is automatic.

It is called 'Low Battery Cutt Off' [LBCO]. Once the Charge-Controller senses LBCO it shuts down and it refuses to power up.

If my battery bank is below the LBCO preset, then I need to find some other source to recharge the batteries to get them up above the LBCO level.

[suprasteve44]

Thank you Mike! This is all very much like trying to drink from a fire hose.
An example product may help with some of this. I came across AIMS Power that has inverters with built-in transfer switches, low voltage shutoffs, etc (https://www.aimscorp.net/24-volt-pur...r-charger.html). I have no idea if it's a quality product or not, or if it's cheaper to do individual components than packing all these things into one "box". To be honest, until I try to size up the loads required, not even sure what wattage rating I'm looking at yet. Barring discussions on all that for the time being, I'll use their 2000 watt inverter as an example: on the page for the 2000, it lists "30 amps automatic transfer switch". I'd assume this is measured on the 115VAC side (since generator produces 115VAC), so does that mean the inverter itself can provide 2000 watts off batteries (understood on the 3x temporary load capability for a short time), and with the generator running, the max the transfer switch can handle is a 3450 watt (30 amps x 115 volts) load? Also, I would need to account for its idle load consumption (in this case 26.5 watts) at 24 hrs/day with the calculations for whatever the other "stuff" (lights, etc.) I'd want to run on solar, right?
Could you help me understand the switching max loads thing? If it helps, here's what I'm thinking: if we're running an air conditioner, I assume it HAS to be powered by the generator and I am assuming the transfer switch will stay "on" for lack of a better term. Is this more of an issue if we were hovering right around 2000 watts and the inverter keeps going back and forth between batteries and the generator? Continuing with this example, if I'm right on my 30 amp switch rating understanding above, if the air conditioner (plus anything else that was on) pulled more than 3450 watts, it'll fry the inverter's transfer switch no matter the capability of the generator?
As for the pump, there's one already installed and it is a decent sized one (jet well pump, pulling maybe 30'), but it won't be a continuous load. Just on demand with water use. From what I've read, the inverter must be able to meet the power demand (wattage) of the pump, but I only need to consider the actual amount of use per day for my battery storage/recharging requirements (for sake of example, call it 1 hour/day)? My short term to-do list includes figuring out exactly what pump it is and the corresponding power draw the next time I'm there.

[suprasteve44]

Thanks Organic! A small chest freezer is in the "maybe" column for solar depending on how much more investment it would take to reliably power it. And understood on the 10% over actual demand. For the LBCO, say there was a stretch of cloudy days and the battery bank dropped below the threshold and cut off. Once the sun returned, would the system continue to charge up the batteries and everything turn back on, or does it require you to do something manually?

[Mike90250]

......
As for the pump, there's one already installed and it is a decent sized one (jet well pump, pulling maybe 30'), but it won't be a continuous load. Just on demand with water use. From what I've read, the inverter must be able to meet the power demand (wattage) of the pump, but I only need to consider the actual amount of use per day for my battery storage/recharging requirements (for sake of example, call it 1 hour/day)? My short term to-do list includes figuring out exactly what pump it is and the corresponding power draw the next time I'm there.

Few successful 12V installs can run a pump, because the batteries and cables cannot deliver the power needed for the starting surge
Here's a chart of start surge requirements. Your jet pump would fall in the 2 wire category.

1/3 hp = supply 26A @ 240VAC, is a load of 6,240 watts ( for 1 second ) The battery and cables have to carry 520A or the inverter will starve and shut down.
So you either get a much smaller pump, or step up to a 24V DC system, same wattage, but only 260A @ 24V. Even that is going to be tough, but doable.




Well Pump Motor Specs.jpg

[suprasteve44]

Gotcha, I might need to look into an IBC tank and just a transfer pump on solar then, reserving the well pump for generator only and filling up the IBC with it. I'll try to find more info (horsepower, amperage draw) on the pump on the next visit. I've got an idea of the other stuff I'm hoping to run off solar, so from there I think I can at least make progress on charging/storage calcs. Thanks again!

[robertoguerrero]

Has anyone had a off grid complete system shutdown? My father in law's cabin is completely off grid - batteries are just under 10 years old. He went to open up the cabin for the summer and no juice at all. He thinks the batteries need to be replaced. Do batteries just suddenly shut down? I think its perhaps the inverter or maybe a circuit breaker. 24V system; 6 DEKA AGM batteries (12 V, 245 AH), 6 panels. The overall system is low use so I would think the batteries would have a bit more life in them. Thanks for any thoughts.

[Mike90250]

Unless maintained properly, batteries go dead on their own self-discharge. 10 years for AGM is well past their design life of 4 years

The cheap way to find out is to get a pair of 12v deep cycle marine batteries, and see if the system will start up. There may be controls to be reset and things to be measured If that works, and the solar charge controller works, and the inverter works - the 2 batteries would be woefully insufficient to run the system, but the easiest way to test it out. Maybe a solar installer in the area can test it.
If the system gear works, I'd suggest using four, 6V 200ah golf cart batteries wired for 24V. That will run lights and an occasional appliance, but only costs $450 for the batteries.

[robertoguerrero]

Thanks Mike for the suggestion! Will take a look at doing that. - Bert

[SunEagle]

Has anyone had a off grid complete system shutdown? My father in law's cabin is completely off grid - batteries are just under 10 years old. He went to open up the cabin for the summer and no juice at all. He thinks the batteries need to be replaced. Do batteries just suddenly shut down? I think its perhaps the inverter or maybe a circuit breaker. 24V system; 6 DEKA AGM batteries (12 V, 245 AH), 6 panels. The overall system is low use so I would think the batteries would have a bit more life in them. Thanks for any thoughts.

I see 2 problems with that system. First off those batteries are over 5 years old and second for 6 x 12V to get a 24V system you would have to wire them in parallel in 3 sets of 2. Multiple parallel wired batteries do not charge or discharge equally which only hurts their life span.

I would look into using those 6V high AH batteries and wire them in series like Mike suggested.

[checkthisout]

Hi All, new to the forum and trying to educate myself on off-grid solar. The family is purchasing some land without electrical service for a "camp" of sorts, and figure a combination of solar, propane, and generator power will be used. In short, I'm trying to size a solar power system to handle smaller electrical loads while we are visiting (NOT heating, cooling, or cooking), or anything that runs while we are not there (so the generator doesn't have to be running). Roughly looking for it to run a water pump, some lights, bug zapper, that sort of stuff. But before we get to that and ultimately a design, I have some (hopefully) basic questions:

1. Since power goes into banks of 12V batteries (generally speaking), is there an efficiency advantage to running 12 VDC lighting? I'm assuming that the voltage drop in a low volt DC system is a lot more of an issue than 115 VAC, which may mean any efficiency loss in the conversion from DC to AC is outweighed by the size of wiring that would be needed to run 12 VDC say, 100' or so. I'm not completely new to wiring in boats, so I do have a little bit of experience with 12 VDC. Asked differently, how efficient are good inverters at converting from DC to AC?

2. I'm 99% sure the answer to this next question is "yes", but just to confirm: the inverters will only pull enough power to match the load requirement at any given time, up to is rated capacity, right? In other words, just because you have, say, a 2000 watt inverter doesn't mean it's always drawing 2000 watts unless the demand is that high?

3. I'm planning on electricity for any "big" loads (air conditioner, power tools) being provided by a generator. I have seen some inverters with built-in transfer switches. Next question is: does the inverter rating still matter for the load being pulled if the generator is running and the inverter has a transfer switch? Explained differently, let's say I have a 2000 W inverter and a 5000 W generator hooked to the inverter's transfer switch. Would I be able to run a 3000 W load, or would that still overload/damage the inverter even with the generator running? Or is this a "it depends" answer depending on the manufacturer?

4. I've also seen battery protectors that shut off at a certain low voltage level. I'm planning to use lead-acid batteries due to cost, and think this would be a good way to help protect them considering the system will be unmonitored for long stretches. Question is: do these also turn back on once the voltage level rises from charging, or do they need to be manually reset like a circuit breaker? Or does it depend on the model/manufacturer?

5. Finally (for now), suggestions on manufacturers to use and/or avoid? This is all new to me so I don't have prior experience with any of the companies manufacturing this stuff. There's nothing life critical that will run off this solar, but it should be able to be left alone for a few weeks at a time without constant adjustments/fixes/resets. Looking for robust more so than feature-rich if that's a better way to put it. In case location matters for what's available in my market, this will be in Florida, USA.

Next step will be to determine my constant and transient load requirements, and try to work out a design that matches. Trying to get some of the basic questions answered on how the systems work first. Thanks in advance for your help!

The inverter/charger will have a rating listed for it's transfer amperage.

Inverters have an idle power draw when on but not in use. Maybe 50 watts or so but their power draw in use is whatever the appliance draws plus some waste of 10-15% or so.

For your setup I would get a 20 amp transfer switch and wire that between the panel fed by the generator and the circuit it's powering and your inverter. Then just Power that one circuit off the transfer switch which will then toggle between the inverter and generator. You can also do this manually with a 3 way switch if you wanna save some bucks.

I would stay away from inverter/charger/transfer switch combos.
If your charger breaks then you are also out a transfer switch and inverter until you can get it replaced or repaired.

Your charge controller has a low battery cutoff function among other things on a switched outlet. If it can't handle the amps you can control a relay that can with the same output.

As far as stuff to avoid, I dunno. I got $2400.00 in returns to Amazon of doa and dead within 30 day charge controllers and inverters in the past few months. My EPEVER 100 amp (replacement has been going good for almost two months now. My replaced under warranty aims 3kw inverter is still sitting in it's box waiting to be installed.

Good luck!

[bouree]

Have you also looked at going to a 24V system? I am looking to purchase an inverter, and considering 24V as they allow for more growth with a relatively small charge controller. I hear that you also save a bunch on wires and the only extra you need is a step down 24V to 12V converter to run your DC appliances. I *may* have a need for alternator charging in the future and that's what making me lean towards 12V. Once I make the inverter purchase, I really cannot re-configure the system to 12V/24V without investing in a new inverter.

One of the inverters I looked at is the Victron Phoenix which does have an adjustable LBCO - I am sure there are others that offer that feature, but there are many that are not configurable and set to too low a number for Lead batteries.
Good luck on your journey!!