Adding a 48v inverter to an existing 12v system - Questions

[Green81]

I have asked some questions about this in another thread, but I thought I'd start a new one as my questions have changed considerably since I started the other thread

I just bought an off grid cabin this year. It has an existing solar system which isn't really meeting what I'd like for power. Currently there is a mish mash of panels that go into a PWM charge controller and then into 4 x 6v FLA batteries. They are wired to give 12V which then goes into a Samlex 12v to 120v 3000w inverter. There is also a number of 12v lighting circuits and a 12v water pump being run off the 12v feed and a 12v breaker.

I thought about completely ripping the old system out and just using the panels into a new inverter and adding more panels. I found out that would be difficult as it's PWM and most inverters are now MPPT charger.

I think I've decided on keeping the old system in place. I'd use it for the existing 12v wiring and I'd also use it as a backup in case there is ever a failure of my new system.

My initial thinking was to get an EG4 6000 inverter with a 3 pack of the EG4 48v server rack batteries and power them with a new batch of solar panels. I'd then have the output of this inverter go into a switch of some sort along with the output of the old inverter. That way if I ever had an issue with my new inverter I could just flip the switch over to my old inverter until I could rectify the problem.

Where I now am hitting an issue is that the EG4 inverter is split phase and my old inverter is just 120v single phase. That isn't ideal as I'd likely also need to change my panel and then if I did switch to the old inverter I'd only have power to half of the circuits in the new panel. I could likely work around that, but would prefer not to.

So now I'm wondering is there a way to get 120v single phase output out of one of the new EG4 6000 inverters? Alternatively, are there any good 120v single phase inverters still being offered that are still being supported and warrantied that would fit the bill? Is there another solution I'm not aware of that would work for me?

 

[Glock24]

To change from one inverter output to the other you would need an AC transfer switch.

To get one leg of 120V out of a split phase inverter you could use a autotransformer.

You can always change the old PWM charge controller for a MPPT change controller and connect the old panels to the MPPT charge controller.

 

[robbob2112]

I think it might have been mentioned in the other thread - power audit is your starting point.

Figure out what you want to run and how many things at the same time you want to run and for how long.

Nothing wrong with going to bigger/higher voltage stuff but if 3000w is enough to meet your needs and the inverter is functioning well why replace it? 3000W will run a high tech RV, a cabin in the woods, a small house without the need to have split-phase.

Seemed like the best step with what you have now is get panels and a MPPT that can do 12/24/48v stuff... Victron makes several .... the only reason I suggest changing the panels is you described them as a mix and match set. If any are newer you can keep them and plug them into a MPPT....

If your batteries are trashed and just don't last through the night you still need to know what size batteries you actually need in terms of Watt Hours....

Hypothetically
For instance if you have 500Whrs of lead acid and they are at 20% maxed out they are only giving you something like 100Whrs of power..... swapping the MPPT a couple panels and using a 12v200ah LFP will give you 2560 Watt Hours - or 25 times the runtime you are currently getting for a rather minimal cost.

If you are planning on adding a fridge, AC, TV, etc to the existing cabin that is where the power audit is needed even with a new system to size it.

#1 rule of solar - don't buy anything until you have a plan
#1 for a plan is energy audit

Otherwise you can just throw money at it and still land with a system that doesn't actually do what you need. And you will end with a lot of spare gear that doesn't fit.

 

[Mattb4]

There are split phase AIO's that can be set for single phase 120vAC operation. The EG4 lacks that capability. However if all you have is 120vAC loads in your panel it is not hard to take advantage of each 3000W hot leg of the EG4. Bit more difficult to use your old setup alongside of this but could be done.

As Robbob2112 suggested, work out what you want/need to have powered and then you can work out how you will do it.

 

[Green81]

Is there a good starting point for an energy audit?

The previous owner only used a fridge and a some lights off of the system and said he never ran out of power. I've added a TV and a microwave and would like to add some more plug ins in the guest house (no power in there now). Since the cabin is new to me I'm really not sure how much power I'm going to be using. After adding the TV and microwave and using a drip coffee maker. I found I hit the low voltage cutoff of the batteries a couple of times and had to run a generator to charge the batteries. I've since avoided using the microwave unless absolutely necessary. I also went back to using a percolator for coffee. I'd prefer to be able to use some of these appliances, but can't currently

Currently on a bright sunny day I think my output from the solar panels tops out at about 500w. (There's a meter in the cabin and that's about the max I remember it getting to).

The batteries I have are 4 x US L16HC 6 volt FLA batteries. I found they are supposed to be 420AH each when new. If my calculations are correct they should give me about 2500Wh per battery so about 10K total for the bank and assuming 50% discharge for the bank I should get about 5000Wh for that bank of batteries. Is there a way to tell how much they are actually outputting?

 

[Green81]

So I found this website - Solar off grid calculator

I ran my numbers through and I came up with 8500 watt hours per day. I think I'd want at least 10000 to be safe. I'd mostly be using this in May through October with possible use in the Winter in the future. I could run the generator some in the Winter as I suspect I'd have to really size up to cover winter use. It'll be in Northern Saskatchewan which is 55 degrees latitude.

I found this site which has some information for my location - solar calculator for location. They have daily output per 100KW of panels. I'm assuming I can take their figure and divide by 100 to tell me how many KW of panels I should have? From there would having enough battery storage for 2 days be typical?

I have an empty section of roof that points at about 120 degrees (ESE) and is angled at about 45 degrees. I was thinking I could easily fit 6 of the 7 foot x 4 foot panels on there without much effort. That would give me about 2400-3000 watts of panels depending on the supplier. I thought I'd add as many panels as I could fit on that roof pitch and if that is more than I need that's a good thing. Adding more than that would be troublesome as there isn't really another good section of roof and the yard doesn't have a great place. The current panels I have are on top of a shed and on a small tower and there isn't room for additional panels on there.

 

[Glock24]

Is there a good starting point for an energy audit?

The previous owner only used a fridge and a some lights off of the system and said he never ran out of power. I've added a TV and a microwave and would like to add some more plug ins in the guest house (no power in there now). Since the cabin is new to me I'm really not sure how much power I'm going to be using. After adding the TV and microwave and using a drip coffee maker. I found I hit the low voltage cutoff of the batteries a couple of times and had to run a generator to charge the batteries. I've since avoided using the microwave unless absolutely necessary. I also went back to using a percolator for coffee. I'd prefer to be able to use some of these appliances, but can't currently

Currently on a bright sunny day I think my output from the solar panels tops out at about 500w. (There's a meter in the cabin and that's about the max I remember it getting to).

The batteries I have are 4 x US L16HC 6 volt FLA batteries. I found they are supposed to be 420AH each when new. If my calculations are correct they should give me about 2500Wh per battery so about 10K total for the bank and assuming 50% discharge for the bank I should get about 5000Wh for that bank of batteries. Is there a way to tell how much they are actually outputting?

You cannot use 100% capacity of a lead-acid battery. You can use around 40% of the capacity. For a 420AH that is 168Ah. 6Vx168Ah=1Kwh for each battery.

Technically you could use 100% of the capacity but they would not last very long, they would degrade quite fast.

 

[Glock24]

So I found this website - Solar off grid calculator

I ran my numbers through and I came up with 8500 watt hours per day. I think I'd want at least 10000 to be safe. I'd mostly be using this in May through October with possible use in the Winter in the future. I could run the generator some in the Winter as I suspect I'd have to really size up to cover winter use. It'll be in Northern Saskatchewan which is 55 degrees latitude.

I found this site which has some information for my location - solar calculator for location. They have daily output per 100KW of panels. I'm assuming I can take their figure and divide by 100 to tell me how many KW of panels I should have? From there would having enough battery storage for 2 days be typical?

I have an empty section of roof that points at about 120 degrees (ESE) and is angled at about 45 degrees. I was thinking I could easily fit 6 of the 7 foot x 4 foot panels on there without much effort. That would give me about 2400-3000 watts of panels depending on the supplier. I thought I'd add as many panels as I could fit on that roof pitch and if that is more than I need that's a good thing. Adding more than that would be troublesome as there isn't really another good section of roof and the yard doesn't have a great place. The current panels I have are on top of a shed and on a small tower and there isn't room for additional panels on there.

For this consumption you're better off with a 48V system. You'll need to harvest at least 8.5KWh during the times there's sun, and as you point out going after 10KWh would be safer. If you choose lithium you can use 90% of the battery's capacity but lithium cannot be charged at freezing temperatures, so take that into account.

Here you can input your location and info about your planned solar energy system and get an approximate of how much sun you can harvest per month.

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

 

[robbob2112]

Order a kill-o-watt meter and plug each thing into it and running for an hour. It will tell you the wattage used... you can take that and calculate your actual usage if you combine the items that might run at once.

The audit calculators tend to think everyone runs all items at once for a long time.

If you come up with 8000w I would bet your actual simultaneous usage is more like 2000w and a typical usage of under 1000w.

A fridge - old ones 1200w, new one 300w...and both cycle on/off something like 20%on, 80% off each hour. Depends on the efficiency and how often you stand there looking for something to munch on.

Most appliances have a duty cycle and they all the way on, but for short times.

The calculator typically skips that

 

[Rednecktek]

That's a LOT of power for a cabin! Something's not right there or it's assuming you're microwaving popcorn while blow drying your hair as the espresso machine brews while Netflix streams from the Starlink in the background.

So, steps to take:

1: Figure out the specs (Voc, Vmp, Isc) on all your panels.

2: Buy or build some high capacity LFP batteries and junk the lead.

3: Get a proper MPPT controller and get your panels working as efficiently as possible.

I highly suspect between the PWM controller nerfing your panels and worn out lead your system is severely handicapped. You've got a great inverter so why junk it and go to a different voltage then have to deal with 12v step down converters to power all the 12v stuff. Get a solid battery bank in there and get your panels actually working and I'd lay money most of your problems will go away.

 

[Green81]

You cannot use 100% capacity of a lead-acid battery. You can use around 40% of the capacity. For a 420AH that is 168Ah. 6Vx168Ah=1Kwh for each battery.

Technically you could use 100% of the capacity but they would not last very long, they would degrade quite fast.

They got the low voltage cut off at around 11v. Not sure what capacity that is. I had read about 50% useable capacity so not far off. In any event, all batteries together are not quite equal to 1 server rack lithium battery

 

[Green81]

That's a LOT of power for a cabin! Something's not right there or it's assuming you're microwaving popcorn while blow drying your hair as the espresso machine brews while Netflix streams from the Starlink in the background.

So, steps to take:

1: Figure out the specs (Voc, Vmp, Isc) on all your panels.

2: Buy or build some high capacity LFP batteries and junk the lead.

3: Get a proper MPPT controller and get your panels working as efficiently as possible.

I highly suspect between the PWM controller nerfing your panels and worn out lead your system is severely handicapped. You've got a great inverter so why junk it and go to a different voltage then have to deal with 12v step down converters to power all the 12v stuff. Get a solid battery bank in there and get your panels actually working and I'd lay money most of your problems will go away.

There isn’t much for panels there currently. I suspect I only have about 50 Sq feet of panels.

They are a real mish mash of various sizes so wouldn’t it be hard to put them on an MPPT controller.

I’ve attached a picture of what I have.

 

[Green81]

That's a LOT of power for a cabin! Something's not right there or it's assuming you're microwaving popcorn while blow drying your hair as the espresso machine brews while Netflix streams from the Starlink in the background.

So, steps to take:

1: Figure out the specs (Voc, Vmp, Isc) on all your panels.

2: Buy or build some high capacity LFP batteries and junk the lead.

3: Get a proper MPPT controller and get your panels working as efficiently as possible.

I highly suspect between the PWM controller nerfing your panels and worn out lead your system is severely handicapped. You've got a great inverter so why junk it and go to a different voltage then have to deal with 12v step down converters to power all the 12v stuff. Get a solid battery bank in there and get your panels actually working and I'd lay money most of your problems will go away.

I was planning to keep this system to power all the 12v stuff and use the inverter as a backup.

I thought about adding more panels to the existing array but then I’d have yet another different power of panel to try to connect together. As it is I think I have 3 different sizes and if I added more panels I’d have 4 different sizes. This is why I thought it would be best to just add a second modern 48v system and use the current for 12v and as a backup

 

[Green81]

Order a kill-o-watt meter and plug each thing into it and running for an hour. It will tell you the wattage used... you can take that and calculate your actual usage if you combine the items that might run at once.

The audit calculators tend to think everyone runs all items at once for a long time.

If you come up with 8000w I would bet your actual simultaneous usage is more like 2000w and a typical usage of under 1000w.

A fridge - old ones 1200w, new one 300w...and both cycle on/off something like 20%on, 80% off each hour. Depends on the efficiency and how often you stand there looking for something to munch on.

Most appliances have a duty cycle and they all the way on, but for short times.

The calculator typically skips that

So if Im likely only going to use up to 2000w at a time the inverter could still be used as it’s not a bottleneck currently. I will use tools at times but then I won’t be running the microwave at the same time.

What about hooking 2 MPPT controllers up to the same battery bank? Could I use one controller for the older panels and another for some new panels?

 

[Green81]

I did a bit more research on going with 12 volt LFP batteries. It seems the biggest charge controllers are 100 amp. Wont that limit me to a maximum of app 15v x 100 amp or 1500 watts of solar charging? Will I be wasting some of the output of the panels?

Edit - looks like I could use more than 1MPPT controller. So if I bought 6 450w panels I could hook up 3 panels to one controller and 3 to another? I suspect if I had 4 LFP batteries in parallel they’d easily be able to handle that much current

 

[Rednecktek]

The important step is getting your panels squared away. You've got a mish-mash of panels up there and when you start mixing & matching panels you have a lowest common denominator issue where 1 panel can really nerf the rest of them.

Example with napkin math with 3 panels:

You have 1 panel rated for 100w with a Voc of 22v, a Vmp of 20v and an Isc of 5a. 20v × 5a = 100w.

You have 1 panel rated for 200w with a Voc of 22v, Vmp of 20v, and Isc of 10a. 20v × 10a = 200w.

You have a 3rd panel rated for 200w with a Voc of 45v, a Vmp of 40v, and an Isc of 5a. 40v × 5a = 200w.

In theory you have 500w of panels if you string them all together, right? Nope! If you put them all in Series, the voltage adds up and the amps all go to the Lowest common number, or 5a. Now you've got a string of 80v at 5a which is only 400w!

Ok, so you decide instead to parallel them up, right? In parallel the Amps add together, but everything goes to the lowest Voltage, so 20v. Now you have a string of 20v @ 20a which is again 400w.

But wait, you have a PWM controller which means amps in = amps out at battery voltage! So that 40v panel at 5a? Yeah, now that's a 15v panel at 5a for only 75w. That's how all 3 panels will go, so your 500w of power is now 15v @ 20a or 300w. Ouch!!!

There are ways to mix & match panels but you need a complete list of what you have so you can do the math. Sometimes it ends up being best to have multiple controllers so one can handle the higher voltage panels and another can handle the lower voltage panels without the small ones nerfing the larger ones.

Does that make sense?

Also, because I don't know you so I ask, do you understand the difference between a PWM and an MPPT controller and how they affect panels and batteries? Why you would use one over the other and why Voc on a panel means anything?

 

[Green81]

I have the general gist between PWM and MPPT and am learning. I know he has a couple of combiner boxes with all those panels. I'm assuming they all would need to be connected in parallel to keep voltage down. If I'm not mistaken wouldn't all those panels need to be low voltage panels to work with a PWM system. I'm assuming that's why all the panels are relatively small.

Another poster had mentioned that some of the newer equipment, such as EG4 isn't quite as reliable as some of the higher end stuff like Victron and Samlex so than I thought I could keep the old system as a backup and use it for all the existing 12 volt stuff

Even if I do get more out of those panels I'm still going to be limited as there isn't much for panels there currently. I would guess at most it would be equivalent to 3 full size panels, if that.

 

[Green81]

There are split phase AIO's that can be set for single phase 120vAC operation. The EG4 lacks that capability. However if all you have is 120vAC loads in your panel it is not hard to take advantage of each 3000W hot leg of the EG4. Bit more difficult to use your old setup alongside of this but could be done.

As Robbob2112 suggested, work out what you want/need to have powered and then you can work out how you will do it.

Which of the split phase AIO allow you to set them to 120v AC? Are they similar price bracket to EG4? Now I'm curious.

 

[Mattb4]

I just was looking at one today (got a lower price offer from a company I have bought from in the past). It is a 6500W 48vDC split phase or single phase capable. It is from PowMr. SRNE, Sungold and others carry a 10kW split phase model that can also be setup as either/or. There are reviews of the SRNE and Sungold units on the Forum here. This PowMr 6.5kW unit is a brand new offering.

 

[Green81]

So I've did some more thinking and cost analysis

If I replace my 12v batteries and get 6 400w panels that will require 2 MPPT controllers (The MPPT controllers I could find maxed out at 1500w of solar input for 12v charging so I'd require 2 controllers). I was thinking of getting about 15kw of LFP batteries. That will give me 2-3 days of use without any sun and if I go past that I can hook up a generator to charge batteries

All prices in Canadian dollars

Keep 12v system and upgrade batteries and add panels with MPPT controllers

4 x 12v 300AH LFP batteries - 4000$
2 x MPPT Controller - 1500
6 x 400 watt solar panels and wiring - 2000$

Total of 7500$


Add 48v system and use current system as a backup

3 x 48v 100AH rack batteries - 6000$ (Price varies depending on supplier but EG4 seem to be 2000$ each)
48V inverter - 2000$ (more or less depending on model and supplier
If I go with split phase inverter I'd need a new panel and installation, but if I avoid a split phase inverter I can likely keep my existing panel. So for now I won't put a cost for that as I think I'll likely avoid split phase to make it simpler
Solar panels and wiring 2000
This would also require a transfer switch if I'd like to be able to use the old inverter as a backup. I've did a little research and it looks like they are about 200$ so not really a cost factor

Total cost 10000$


For my thinking it seems to me that spending the extra 2500$ to get a 48v system which would also then allow me to add more panels in future (if I thought it necessary) may be worth the cost now

Am I missing something in my thinking here?