Building a solar generator

[BeerCan]

I am going to build a solar generator for use at my house and with my trailers. Has to be easily movable so I am using an old hand truck I have. I plan on adding some plywood to the handle part and that is where the solar controller and the power outlets will go. It will also have regulated 12vdc fuse block (on order) so I can attach various 12vdc items if needed, such as my portable fridges. Right now my 24v to 12v converter only handles 40 amps but I will up that in the future. I will be using these outlets, they have usb connections in them. The usb-c is able to charge laptops so that is good. They have 40 milliwatt vampire draw so I will probably have a disconnect for long term storage. I am using a very oversized 4000w inverter. It is an expensive one because it is low frequency and somewhat programmable. It is very heavy @ ~55lbs I did this on purpose because I will eventually have a distribution box mounted in the house that it will be able to connect to. The inverter also has a battery charger and an internal transfer switch. This will handle most of the charging needs for now. Batteries for now will be 2 12V 105Ah Lithium Iron Phosphate (LiFePO4) Batteries connected in series for 24vdc. Batteries are expensive these were a mint but should last a very long time. Eventually I will have a seperate battery box on wheels for long term storage. I am trying to source some used Tesla or Nissan leaf cells to build a big box. Still need to source so solar panels, probably going to buy used ones from the solar farm that is near me (hopefully). I also have 2 100 watt panels that are easily portable. This is a costly project and in no way am I doing this thinking I am going to recoup the money by going solar. I am doing this because I wanted a portable, silent energy source for when I am travelling with my trailers. This will also be good for power outage scenarios as it will run many household appliances for quite a few hours or more depending on the sun. I estimate it will hold my fridge for 30 hours with no sun and if I don't open the fridge a lot.

 

[fsdork]

Looks like a fun project! I've been spending entirely too much time lately watching Will Prowse's videos on YouTube. Does your inverter have a function that allows you to monitor amp hours in and out of your battery bank? I recently picked up a Victron BMV-712 to monitor the pair of flooded lead acid golf cart batteries on my travel trailer, and really like the peace of mind it will give me while camping off grid. Trying to guess state of charge based on battery voltage under (light) load was getting old.

 

[BeerCan]

Originally Posted by fsdork

Looks like a fun project! I've been spending entirely too much time lately watching Will Prowse's videos on YouTube. Does your inverter have a function that allows you to monitor amp hours in and out of your battery bank? I recently picked up a Victron BMV-712 to monitor the pair of flooded lead acid golf cart batteries on my travel trailer, and really like the peace of mind it will give me while camping off grid. Trying to guess state of charge based on battery voltage under (light) load was getting old.

I have Will Prowse's book and have seen a few of his videos. I like what he put's out for the most part. The Victron you got is very similar to the battery monitor I got. Before I decided on the Magnum inverter I was going to use all Victron, good stuff. I'll be honest, I went with Magnum because of the high quality and the USA build. For the inverter it has a seperate battery monitor that plugs into one of the ports on the side. You also have to install a shunt between the battery and the inverter, then you will get the following info -- • State of Charge (SOC) 0 - 100% • DC volts • DC amps • Amp hours in/out • Resettable amp hours out • Total amp hours out • Minimum volts DC • Maximum volts DC • Temperature compensated You also have to have their remote control to see the info. I have both items so I am good to go.

 

[JHZR2]

Looks like fun! Might want to have some dedicated DC/DC sources in there, as it may be wasteful to make ac to make DC through that big inverter, if that inverter isnt very efficient at very low loading. Make sure you think about protection for the batteries. I assume thats an off-grid inverter? If so, how will it connect to your house? If not, how will it find a 60Hz sync to make it turn on and be useful? I was kind of thinking that I wonder if it would be better to have a small off-grid inverter, and then a few panels with enphase microinverters. Then your AC bus would be expandable and more resilient, and your cursory 60Hz sync would come from the off-grid source. You could then essentially play the game of charging the batteries via a dedicated 120V smart charger... maybe... and then use that same charger in a standalone mode connected to mains AC power in your home when the system is packed away. 105Ah*24V = 2520Wh... Which isnt very useful to run a lot of stuff or for very long. Thus I think youll want to be able to expand the system at least if youre going to try to distribute in your home to run any meaningful loads. Depending upon what you have, Id think youll want 3-4 panels (270-330W rating each), and then charge the battery to keep some lights on at night - manage loads so it operates the fridge and whatnot during the day off of solar.

 

[EdwardC]

Sounds like a fun project! What are you planning to use for your charge controller? I've wanted to do something like this (on a smaller scale), but like you said, batteries get expensive. I have a small off-grid setup that uses lead acid batteries, it runs some load through the night, but I'd be able to plug the fridge into the inverter to run for a little while (longer if it's day time) as an emergency backup. I really do need to get more batteries, but even good deep cycle lead acid batteries get expensive! I agree with JHZR2, I probably wouldn't bother with the outlets with built-in USB ports. I'd hate to power up the inverter just to charge a phone or laptop. A quick Google yields some panel mount USB PD adapters on Amazon for ~$15 or so, even allows for up to 24V input, so you can skip the 24V to 12V conversion as well.

 

[daves87rs]

I wanna see this! Always thought it would be cool to try it....

 

[Linctex]

Originally Posted by BeerCan

I also have 2 100 watt panels that are easily portable. I am doing this because I wanted a portable, silent energy source for when I am travelling with my trailers. This will also be good for power outage scenarios as it will run many household appliances for quite a few hours or more depending on the sun. I estimate it will hold my fridge for 30 hours with no sun and if I don't open the fridge a lot.

In addition to the panels that go with the portable cart,. you may as well permanently hard mount a few panels on the trailer itself. The extra capacity won't hurt a thing. Use some quick electrical connectors. What is the "Idle current draw" from the big MagnaSine inverter when it is on, but not powering anything?

 

[thastinger]

To be "portable" you're not going to run much of any load for very long as those LiFePo4 batteries can't go below a 70% SOD. You've got about 750Wh there...in other words, you made the world's most expensive 1000 watt inverter generator that you can only run for 30 minutes at max load, then 2 days worth of charging to build it back up.

 

[BeerCan]

Originally Posted by JHZR2

Looks like fun! Might want to have some dedicated DC/DC sources in there, as it may be wasteful to make ac to make DC through that big inverter, if that inverter isnt very efficient at very low loading. Make sure you think about protection for the batteries. I assume thats an off-grid inverter? If so, how will it connect to your house? If not, how will it find a 60Hz sync to make it turn on and be useful? I was kind of thinking that I wonder if it would be better to have a small off-grid inverter, and then a few panels with enphase microinverters. Then your AC bus would be expandable and more resilient, and your cursory 60Hz sync would come from the off-grid source. You could then essentially play the game of charging the batteries via a dedicated 120V smart charger... maybe... and then use that same charger in a standalone mode connected to mains AC power in your home when the system is packed away. 105Ah*24V = 2520Wh... Which isnt very useful to run a lot of stuff or for very long. Thus I think youll want to be able to expand the system at least if youre going to try to distribute in your home to run any meaningful loads. Depending upon what you have, Id think youll want 3-4 panels (270-330W rating each), and then charge the battery to keep some lights on at night - manage loads so it operates the fridge and whatnot during the day off of solar.

DC-DC is going to be from my 24 to 12 v regulated PS, not as efficient as if it was straight 12v but better than 120ac - 24dc. The batteries have a bms and also I am putting a 250 or 300 amp fuse inline one of the battery cables It will be an off grid inverter and it was originally going to tie into the house with some type of transfer switch but last night we decided we are moving so I am not spending money on that The microinverter setup would be nice and probably the way to go in a totally new house system. Because I want this to be transportable and now that we are moving the string inverter is probably best. The battery setup is just for this part of the system, I had intended to build a powerwall for the house and maybe another battery pack on casters for mobile, but all of that is in flux now.

Originally Posted by EdwardC

Sounds like a fun project! What are you planning to use for your charge controller? I've wanted to do something like this (on a smaller scale), but like you said, batteries get expensive. I have a small off-grid setup that uses lead acid batteries, it runs some load through the night, but I'd be able to plug the fridge into the inverter to run for a little while (longer if it's day time) as an emergency backup. I really do need to get more batteries, but even good deep cycle lead acid batteries get expensive! I agree with JHZR2, I probably wouldn't bother with the outlets with built-in USB ports. I'd hate to power up the inverter just to charge a phone or laptop. A quick Google yields some panel mount USB PD adapters on Amazon for ~$15 or so, even allows for up to 24V input, so you can skip the 24V to 12V conversion as well.

Probably going to use the EPEVER 40a charge controller for now and perhaps add a second one later. The usb plugs in the outlets are there purely for convenience, there will never be a situation where I pull this out to usb charge

Originally Posted by Linctex

In addition to the panels that go with the portable cart,. you may as well permanently hard mount a few panels on the trailer itself. The extra capacity won't hurt a thing. Use some quick electrical connectors. What is the "Idle current draw" from the big MagnaSine inverter when it is on, but not powering anything?

Got some used panels inbound now, the black trailer will get a lot of them, because that will be my "workshop", eventually it will have its own battery bank as well. The airstream will get as many as will reasonably fit, but I will have them installed by someone better than me. the magnasine is under 8 watts in search mode

Originally Posted by thastinger

To be "portable" you're not going to run much of any load for very long as those LiFePo4 batteries can't go below a 70% SOD. You've got about 750Wh there...in other words, you made the world's most expensive 1000 watt inverter generator that you can only run for 30 minutes at max load, then 2 days worth of charging to build it back up.

I will take these down to 20% SOC without second thought

 

[BeerCan]

Got the inverter out of storage today. OMG this thing is bigger than I remembered, it's gigunda

 

[wag123]

There is a lot of useful advice above BeerCan. I have personal experience in this area, and I have some advice (echoing much of what the others have said)... 1. Wire the batteries in parallel for 12v. There are MANY 12v powered accessories available that can be used directly off of the battery bank and will be MUCH more efficient with the power that you have available. 24v to 12v converters are a waste of available power. Also. you don't want to use the inverter unless you absolutely have to. 2. Buy an MPPT solar charge controller. They are MUCH more efficient and can be used in conjunction with 24v-48v solar panel voltage inputs and 12v battery banks. 3. If you purchase an MPPT controller, buy your solar panels in pairs and wire them in series for 24 volts. If you purchase 3 solar panels, wire them in series for 36v. This can provide you with useful solar charging capability in lower light situations when combined with an MPPT controller and a 12v battery bank. 4. Buy a smaller inverter. A 4000 watt inverter is major overkill for what you are building. The idle current draw is MUCH higher on the bigger inverters. I would not go more than 2000 watts, but a quality 1000 watt inverter with high surge current capability would be a MUCH better size for your configuration. 5. Use large enough 100% copper wire throughout your system. In DC circuits bigger is ALWAYS better. Watch out for copper plated aluminum wire, it is cheaper but has a much higher resistance. 100% copper wire is expensive. Don't chince-out on this! Also, keep the wire lengths as short as possible.

 

[BeerCan]

Originally Posted by wag123

There is a lot of useful advice above BeerCan. I have personal experience in this area, and I have some advice (echoing much of what the others have said)... 1. Wire the batteries in parallel for 12v. There are MANY 12v powered accessories available that can be used directly off of the battery bank and will be MUCH more efficient with the power that you have available. 24v to 12v converters are a waste of available power. Also. you don't want to use the inverter unless you absolutely have to. 2. Buy an MPPT solar charge controller. They are MUCH more efficient and can be used in conjunction with 24v-48v solar panel voltage inputs and 12v battery banks. 3. If you purchase an MPPT controller, buy your solar panels in pairs and wire them in series for 24 volts. If you purchase 3 solar panels, wire them in series for 36v. This can provide you with useful solar charging capability in lower light situations when combined with an MPPT controller and a 12v battery bank. 4. Buy a smaller inverter. A 4000 watt inverter is major overkill for what you are building. The idle current draw is MUCH higher on the bigger inverters. I would not go more than 2000 watts, but a quality 1000 watt inverter with high surge current capability would be a MUCH better size for your configuration. 5. Use large enough 100% copper wire throughout your system. In DC circuits bigger is ALWAYS better. Watch out for copper plated aluminum wire, it is cheaper but has a much higher resistance. 100% copper wire is expensive. Don't chince-out on this! Also, keep the wire lengths as short as possible.

1. Issue is that the inverter I have is 24v, I planned on using what I have but the size of this is making me have second thoughts 2. Yes, agreed and what I plan to do, the epever are mppt controlers 3. I purchased a pallet of used solar panels 4. I may buy a smaller inverter, this one is giant. I do however like the hybrid style so I may keep this one. Good inverters are over 1K usually. So I agree but may use what I have because $ 5. Agreed and Agreed. I am building 4/0 for the DC side battery to inverter.

 

[EdwardC]

If you're re-thinking the inverter, maybe you can reconsider an all-Victron system? My small off-grid system uses a Victron controller and I really like the user friendly interface. I don't know their product line very well, but I think you can get an integrated system that could make packing easier, plus give you more control and a single dashboard for monitoring. I think the EasySolar line is an all-in-one MPPT controller, inverter and battery charger, but you could probably pick and choose from their product line to put a system that fits your needs earlier. I thought of a question. I know you just mentioned that you're moving, so your plans are probably changing, but when you talked about connecting the inverter to the house as a backup, would you just connect it to a single phase, and have your essential appliances running on that one phase? I've never looked, but I assume they make 240V split-phase inverters that would likely work better than a big single 120V inverter for a household backup application.

 

[JHZR2]

Originally Posted by BeerCan

Originally Posted by thastinger

To be "portable" you're not going to run much of any load for very long as those LiFePo4 batteries can't go below a 70% SOD. You've got about 750Wh there...in other words, you made the world's most expensive 1000 watt inverter generator that you can only run for 30 minutes at max load, then 2 days worth of charging to build it back up.

I will take these down to 20% SOC without second thought

70% Depth of discharge is good for life and not far off from 20% SOC, so I think youre both saying the same thing. Id actually try to keep them at 90% SOC and go 20-90% if routinely cycling. Store at 25-30%. Top up on mains power once in a while to keep the cells balanced.

 

[BeerCan]

Originally Posted by JHZR2

Originally Posted by BeerCan

Originally Posted by thastinger

To be "portable" you're not going to run much of any load for very long as those LiFePo4 batteries can't go below a 70% SOD. You've got about 750Wh there...in other words, you made the world's most expensive 1000 watt inverter generator that you can only run for 30 minutes at max load, then 2 days worth of charging to build it back up.

I will take these down to 20% SOC without second thought

70% Depth of discharge is good for life and not far off from 20% SOC, so I think youre both saying the same thing. Id actually try to keep them at 90% SOC and go 20-90% if routinely cycling. Store at 25-30%. Top up on mains power once in a while to keep the cells balanced.

Pretty much my plan but I was going to long term store them at 80% charge, Hopefully will get a lot of use for it and not be worried about long term storage. I am really thinking about that inverter though . . .

 

[BeerCan]

Big day today, my batteries arrived The cost of these things is crazy. I got these through costco with the special deal they were running. I think I am going to mount them close to the inverter like this, and do the electrical connections toward the bottom of the hand truck (fuse, shunt for meter)

 

[BeerCan]

Not sure if anyone is looking at this but I am going to post pics until it's finished Today I layed out the DC side. I changed everything around from what I originally planned, I think it will work out like this and the longish connections to the battery will allow me to connect to external battery packs in the future. DC is sized up for future connections 4/0

 

[BeerCan]

AC side getting some work

 

[Cujet]

Originally Posted by thastinger

To be "portable" you're not going to run much of any load for very long as those LiFePo4 batteries can't go below a 70% SOD.

That just does not seem to be accurate. "Most lead acid batteries experience significantly reduced cycle life if they are discharged more than 50%, which can result in less than 300 total cycles. Conversely LIFEPO4 (lithium iron phosphate) batteries can be continually discharged to 100% DOD and there is no long term effect. You can expect to get 3000 cycles or more at this depth of discharge. " Of note: Draining a new 100AH LiFePO4 battery down 100% is not completely draining the cells. They generally have significant excess capacity until about 2500 cycles.

Originally Posted by BeerCan

Not sure if anyone is looking at this but I am going to post pics until it's finished :

Of course we are looking at it. Very cool project, BTW.

 

[BeerCan]

Originally Posted by Cujet

Originally Posted by thastinger

To be "portable" you're not going to run much of any load for very long as those LiFePo4 batteries can't go below a 70% SOD.

That just does not seem to be accurate. "Most lead acid batteries experience significantly reduced cycle life if they are discharged more than 50%, which can result in less than 300 total cycles. Conversely LIFEPO4 (lithium iron phosphate) batteries can be continually discharged to 100% DOD and there is no long term effect. You can expect to get 3000 cycles or more at this depth of discharge. " Of note: Draining a new 100AH LiFePO4 battery down 100% is not completely draining the cells. They generally have significant excess capacity until about 2500 cycles.

Originally Posted by BeerCan

Not sure if anyone is looking at this but I am going to post pics until it's finished :

Of course we are looking at it. Very cool project, BTW.

Thanks Got it working on shore power today. Tomorrow I connect the output box