MPPT controller sizing recommendation

[sbsyncro]

I have a small trailer that I use for off-grid camping (a Turtleback Getaway). It came with a Zamp PWM charge controller and Trojan Group 31 AGM battery back in 2018. The battery just finally stopped holding a charge and I can't bring it back to life. I want to switch to a pair of LiFePO 100ah batteries (to effectively triple or quadruple my reserve power). For charging, I use either a 220w folding panel that has an open circuit voltage of 57.6v (if there is no wind and I have space) or if it is windy or have less available space, I use a rigid "suitcase" type 120w panel with Voc of 23.4v. (I also have a NOCO AC-DC charger for "shore power" charging as well as a direct feed via the 7-pin connection for ~2 amp DC-DC charging while driving.)

Based on my research and reading up on specs, etc. it seems like the Victron SmartSolar MPPT 75/10 would meet my requirements, but I want to make sure I'm not missing something. It has a max voltage input of 75v, but I'm confused by the spec that says
"Nominal PV power, 12 V 1a,b): 145 W. (1a) If more PV power is connected, the controller will limit input power.)"

Does this just mean that if the panel is operating at 12v output then the max panel output that can be accepted is 145 watts (12.08 amps)? (in other words, I don't need to worry about it because my 220 watt panel operates at 48v/4.58 amps, so well within the 10 amp spec for this controller?

I want to make sure I'm not under-sizing this controller. I also am not sure about whether I need to introduce a DC-DC controller to this scenario or whether the Jeep's charging regulator as an input to this controller will work. (Again it is not a "serious" DC-DC connection - just the stock trailer wiring harness which limits the charging current to about 2 amps)

Thanks in advance for the advice!

 

[rickst29]

Hi, sbsyncro - welcome to the forum.

Your new battery pair can accept power (from the solar controller) at voltages up to 14.60 volts (3.65 volts in each of 4 cells) , although it is VERY SMART to configure the included JBD BMS units (Battery Management Systems) to stop accepting input charge power when the internal voltages have reached a somewhat lower limit. Limits between 13.5 and 14.0 volts are pretty widely used here, although the camper batteries would also benefit from even lower maximum voltage during long term storage (e.g., winter)

My own battery packs will accept charging power when their cells are below 13.8 volts total (3.45 per cell) during trips, but I modify the BMS parameters to disallow charging above 13.2 volts (3.30 per cell) in long term storage. JBD provides a cellphone app for doing that, if you care to use it that way.
- - -
The Victron has maximum OUTPUT CURRENT of only 10 amps, and their specification shows that limit being applied with 14.5 maximum volts. The battery packs will accept power from the Victron until their internal cells reach the BMS limit.

The INPUT VOLTAGE from panels can be much higher, and both of your alternate panel setups qualify with respect to maximum voltage going into the controller. But the total power being offered by the "folding panel" will exceed the output capability of the Victron feeding "12v" batteries at only 14.5 volts, when it is near noon on a cloudless day.

The panel offers 220 watts under those near-perfect conditons, and the Victron can only sned out 145 watts to charge batteries (and optionally power other camper "stuff"). On a perfect day, near noon, some of the power your foldable panel could provide will be left unused, because the controller WON'T accept it.
- - -
Your most important question, though, isn't whether those unused watts (up to 60 watts at most, only when the panel is tilted exactly into the sun near noon with no clouds or shade -- maybe 80 watt-hours unused on a "great" day) matter a lot,. The key question is how much power you need to get from your panels in LESS-THAN-PERFECT conditions, through the number of days you are on a trip with no plug-ins.

I recommend thaqt you start by estimating the watt-hours you will consume each day, and then determine the length of time your batteries will last if you start "full" and have only limited solar power available to refill them each day - both values to calculated in watt-hours. At best, in June, you can expect maybe 700-watt hours from the foldable (bigger) panel on a cloudless day. Your 100Ah batteries each have a capacity of about 1050 watt-hours each (you can't run the "1280 watt hour" batteries all the down to zero remaining power withouth destroying them. At other dates, and under less optimal cloud and shade conditions, you'll be getting less. I would not expect to AVERAGE more 500 watt-hours per day from your folding panel, used throughthe entire summer season in the places I go.

Your proposed controller, IMO, is adequate for your larger panel - it will reject some panel power only for 30-60 minutes on a perfect day. But whether 220W maxmimum, yelding maybe 500 watt-hours per day average through your camping season, can "refill" yur batteries enough to support your camping requirements is a question I can't answer for you. My own "camping requirements" are incredibly piggy, and my the panels on my camper are rated for a total of "700 watts". They barely meet my "needs" in extended use.

If you add more panel power power later, then this controller will be inadequate - and you might go ahead and start with a bigger controller than you need right now, if you wish to ultimately use TWO of the those "220W" foldable panels in parallel (with only one controller).

 

[sbsyncro]

Hi, sbsyncro - welcome to the forum.

Your new battery pair can accept power (from the solar controller) at voltages up to 14.60 volts (3.65 volts in each of 4 cells) , although it is VERY SMART to configure the included JBD BMS units (Battery Management Systems) to stop accepting input charge power when the internal voltages have reached a somewhat lower limit. Limits between 13.5 and 14.0 volts are pretty widely used here, although the camper batteries would also benefit from even lower maximum voltage during long term storage (e.g., winter)

Thanks for offering additional information - if I understand your comment correctly, you're not really addressing my original question of whether this particular charge controller is suitable, but rather suggesting that whichever controller I use, to make sure to set up the BMS to cut off charging input once the battery reaches 13.5 to 14.0 volts. I see from the Victron data sheet that this particular unit charges at 14.4v during absorption phase and 13.8v during float phase, but I think that's a different stat than the battery's internal voltage which is the indicator of its SoC, right? Did I understand correctly? (thanks for your patience as I learn my way through this).

 

[Tomthumb62]

I have a small trailer that I use for off-grid camping (a Turtleback Getaway). It came with a Zamp PWM charge controller and Trojan Group 31 AGM battery back in 2018. The battery just finally stopped holding a charge and I can't bring it back to life. I want to switch to a pair of LiFePO 100ah batteries (to effectively triple or quadruple my reserve power). For charging, I use either a 220w folding panel that has an open circuit voltage of 57.6v (if there is no wind and I have space) or if it is windy or have less available space, I use a rigid "suitcase" type 120w panel with Voc of 23.4v. (I also have a NOCO AC-DC charger for "shore power" charging as well as a direct feed via the 7-pin connection for ~2 amp DC-DC charging while driving.)

Based on my research and reading up on specs, etc. it seems like the Victron SmartSolar MPPT 75/10 would meet my requirements, but I want to make sure I'm not missing something. It has a max voltage input of 75v, but I'm confused by the spec that says
"Nominal PV power, 12 V 1a,b): 145 W. (1a) If more PV power is connected, the controller will limit input power.)"

Does this just mean that if the panel is operating at 12v output then the max panel output that can be accepted is 145 watts (12.08 amps)? (in other words, I don't need to worry about it because my 220 watt panel operates at 48v/4.58 amps, so well within the 10 amp spec for this controller?

I want to make sure I'm not under-sizing this controller. I also am not sure about whether I need to introduce a DC-DC controller to this scenario or whether the Jeep's charging regulator as an input to this controller will work. (Again it is not a "serious" DC-DC connection - just the stock trailer wiring harness which limits the charging current to about 2 amps)

Thanks in advance for the advice!

Hey, welcome to this forum!

Those Aolithium batteries are excellent. A very smart investment.

Not sure which NOCO charger you have, some of the older ones are not well suited to charge lithium. Personally I prefer to be able to better control my charging parameters, with something like the Victron IP22 12/30. This is the 12v, 30A (adjustable down to 7.5A) with bluetooth, single output, approx $200 but can be found as 'open box' from the same seller for about $150. The IP22 allows for fine-tuning your charging or you can simply select one of the pre-programmed charge profiles specific to LiFePO4. Plus the IP22 has a "power supply" mode which can be very useful if you ever need to bring the battery's four internal cells into better balance with each other.

"12v panel" or "24v panel" is confusing. A "12v panel" will usually output 18-20v in daylight hours, which your MPPT will tune down to the charge voltage of your battery, usually 14.0 to 14.6v (lower is better IMO) and the "extra" voltage gets converted into additional amps.

As for charging your batteries from the 7-pin, there are posts about this, but I don't recommend it. If you want alternator charging of your lifepo4 batteries, you will want a DC-DC charger, like this one, I think the 12-12 18A model is a decent value, but go for the 30A model if your budget allows and your alternator can handle it.

 

[Doggydogworld]

It has a max voltage input of 75v, but I'm confused by the spec that says
"Nominal PV power, 12 V 1a,b): 145 W. (1a) If more PV power is connected, the controller will limit input power.)"

The 75/10 will only supply 10A to the battery.
If you connect it to a 12V battery that charges at 14.5V then it can supply up to 14.5V * 10A = 145W.
If you connect it to a 24V battery that charges at 29V then it can supply up to 29V * 10A = 290W.
It will limit power coming from the panels to match the amount of power it passes on to the battery.
The MPPT limits power by adjusting your panel's operating point away from the Vmp/Imp optimum.
Adding panels or using a bigger panel won't help, you're still limited by the 10A battery charging limit.
If you want more power going to the battery you need to upgrade to a more capable MPPT, e.g. 75/15.

You may want to limit LiFePO4 charging to a slightly lower voltage, say 14.0V. At 14.0V the 75/10 supplies a max of 140W.

 

[sbsyncro]

Hey, welcome to this forum!

Those Aolithium batteries are excellent. A very smart investment.

Not sure which NOCO charger you have, some of the older ones are not well suited to charge lithium. Personally I prefer to be able to better control my charging parameters, with something like the Victron IP22 12/30. This is the 12v, 30A (adjustable down to 7.5A) with bluetooth, single output, approx $200 but can be found as 'open box' from the same seller for about $150. The IP22 allows for fine-tuning your charging or you can simply select one of the pre-programmed charge profiles specific to LiFePO4. Plus the IP22 has a "power supply" mode which can be very useful if you ever need to bring the battery's four internal cells into better balance with each other.

"12v panel" or "24v panel" is confusing. A "12v panel" will usually output 18-20v in daylight hours, which your MPPT will tune down to the charge voltage of your battery, usually 14.0 to 14.6v (lower is better IMO) and the "extra" voltage gets converted into additional amps.

As for charging your batteries from the 7-pin, there are posts about this, but I don't recommend it. If you want alternator charging of your lifepo4 batteries, you will want a DC-DC charger, like this one, I think the 12-12 18A model is a decent value, but go for the 30A model if your budget allows and your alternator can handle it.

Thanks for the info!

I'm using the NOCO Genius 10x1 - I've used other versions of the Genius for my boat and other applications and have been very very happy with them, but I've never used them for anything other than AGM batteries. They say they have a LiFEPO profile and they are a very reputable company, so I tend to trust them. (perhaps naively).

The panels I have are rated as follows:

Panel one (flexible)
Power output: 220w
Working voltage: 48v
Working current: 4.58a
Open Votage: 57.6v
Short Circuit current: 4.81a

Panel 2 (Suitcase)
Power Output: 100w
Peak Voltage (Voc): 23.4v
Max Power Voltage (Vmp): 19.8v
Short Circuit Current (Isc): 5.35a
Max Power Current (Imp): 5.05a

I'm assuming that since the Victron MPPT 75/10 Max. PV open circuit voltage is 75v, then it will be a good match to these two power sources?
(edit: it looks like the max charge output of this unit is 145w, so I'd need to step up to the 75/15 to support a 220w panel)

With respect to the DC-DC charging, since the max current is about 2 amps, why can't I just tie it to the DC input side of the Victron controller? (since it will never be used at the same time that the solar panels are deployed). The controller would just think it was a 12v panel putting out about 24-30 watts depending on the alternator output. If not, I'd honestly rather disable that charging input because going with a fancy DC-DC charger would require that I completely re-wire a separate heavy gauge pair from the engine compartment to a separate Anderson connector that I would then have to snake across the trailer tongue along with the regular 7-pin harness. That juice ain't worth the squeeze to me. ;-)

 

[sbsyncro]

The 75/10 will only supply 10A to the battery.
If you connect it to a 12V battery that charges at 14.5V then it can supply up to 14.5V * 10A = 145W.
If you connect it to a 24V battery that charges at 29V then it can supply up to 29V * 10A = 290W.
It will limit power coming from the panels to match the amount of power it passes on to the battery.
The MPPT limits power by adjusting your panel's operating point away from the Vmp/Imp optimum.
Adding panels or using a bigger panel won't help, you're still limited by the 10A battery charging limit.
If you want more power going to the battery you need to upgrade to a more capable MPPT, e.g. 75/15.

You may want to limit LiFePO4 charging to a slightly lower voltage, say 14.0V. At 14.0V the 75/10 supplies a max of 140W.

Ah! This is super helpful - I didn't realize that this limitation was on the power passed FROM the controller. So if I want max transfer from my 220w panel in ideal conditions I need to step up to the 75/15 unit. But then I will never be able to add more panel wattage (either by adding a second panel or replacing with way a 400w panel). It looks like the 100w/20a unit is limited to 290 watts. Not much better. Is that pretty much the max charging power for a 12v system?

 

[rickst29]

Thanks for offering additional information - if I understand your comment correctly, you're not really addressing my original question of whether this particular charge controller is suitable, but rather suggesting that whichever controller I use, to make sure to set up the BMS to cut off charging input once the battery reaches 13.5 to 14.0 volts. I see from the Victron data sheet that this particular unit charges at 14.4v during absorption phase and 13.8v during float phase, but I think that's a different stat than the battery's internal voltage which is the indicator of its SoC, right? Did I understand correctly? (thanks for your patience as I learn my way through this).

sbsynco, I have just finished my very long post, which FINALLY answered your original question. This controller is OK for your larger panel, the maximum panel power "200 watts" will only exceed the capability of the controller under near-perfect conditions, and only for about 1/2 hour near noon. But the single folding panel (220W) is at the limit of the controller, it will NOT be adequate if you choose to add another folding panel panel in the future.

The Victron charging algorithm is a great choice for your batteries. and it will (itself) reduce output power when the batteries reach about 13.8 volts.

 

[rickst29]

Thanks for the info!

I'm using the NOCO Genius 10x1 - I've used other versions of the Genius for my boat and other applications and have been very very happy with them, but I've never used them for anything other than AGM batteries. They say they have a LiFEPO profile and they are a very reputable company, so I tend to trust them. (perhaps naively).

The panels I have are rated as follows:

Panel one (flexible)
Power output: 220w
Working voltage: 48v
Working current: 4.58a
Open Votage: 57.6v
Short Circuit current: 4.81a

Panel 2 (Suitcase)
Power Output: 100w
Peak Voltage (Voc): 23.4v
Max Power Voltage (Vmp): 19.8v
Short Circuit Current (Isc): 5.35a
Max Power Current (Imp): 5.05a

I'm assuming that since the Victron MPPT 75/10 Max. PV open circuit voltage is 75v, then it will be a good match to these two power sources?
(edit: it looks like the max charge output of this unit is 145w, so I'd need to step up to the 75/15 to support a 220w panel)

With respect to the DC-DC charging, since the max current is about 2 amps, why can't I just tie it to the DC input side of the Victron controller? (since it will never be used at the same time that the solar panels are deployed). The controller would just think it was a 12v panel putting out about 24-30 watts depending on the alternator output. If not, I'd honestly rather disable that charging input because going with a fancy DC-DC charger would require that I completely re-wire a separate heavy gauge pair from the engine compartment to a separate Anderson connector that I would then have to snake across the trailer tongue along with the regular 7-pin harness. That juice ain't worth the squeeze to me. ;-)

The smaller 75/10 will reject "excess power" from the panel at times when when it is putting out more than about 150 watts. But that situation will occur only during a short portion of the day, rioght at noon, on a cloudless day.

Let me make a new post concerning DC-to-DC charging from the Jeep.

 

[sbsyncro]

All this info has been super helpful so far - thanks everyone for your input. now you have me thinking about "future-proofing" the system and I'm on the hunt for something that would allow for 2x220 panels in order to maximize my power production. I see that its a big step up to the Victron MPP 100/30 and then I also see a Renology unit that also supports DC-DC charging from an IGN port which could be good for the car charging input...

 

[rickst29]

"Stock" trailer wiring in a Jeep (and within the 7-pin cable connecting your Trailer) can typically support more than 10A continuous current on the "Trailer Battery Charge" wire and the grounding return wire.

But the current which will actually flow is limited by two factors: the relatively low under-hood Voltage of the Jeep, and "voltage drop" which occurs along the wires. (That "voltage drop" corresponds to the power lost along the thin wires, due to resistance.) Voltage drop increases with the amount of current.

The normal flow of current (and power) from a '12v" tow vehicle into a Trailer is pushed by only a small voltage differential (13.5 volts under the hood, and maybe 12.7 volts in the Trailer- depending on battery State-of-Charge). "Voltage drop" further reduces that differential, and the amount of power which can be delivered into trailer batteries usually becomes very small - with hardly any voltage differntial left at the battery terminals, when the long and thin wires carry significant current.

DC-to-DC charging units pull power from the Tow Vicle at low voltage (less than 13.5) with high current, and then boost the voltage UP to a value which is useful for charging or maintaing the Trailer batteries. Some cheaper units have non-programmable "maximum current" which are too high, in my expert opinion, for many alternators running at idle speed and many cable wirin configurations. With your jeep, you should probably impose a maximum of 10A current on a programmable unit.

DC-to-DC charging units try to judge the battery statse of charge, and adjust their maximum output voltage and current accordingly like a solar controller does). When it perceives the battery to be well-charged, it will reduce output voltage and current to stop pushing too much power into the trailer battery packs. This decisionn is based on the VOLTAGE at the output of the batteries: The DC-to-DC unit momentarily stops creating increased voltage to send power into the batteries, insteasd measuring "what is alreasdy there".

At up to 10A maximum, your jeep could delivery up to 140 watts for battery charging. This added load on the alternator is trivial while cruising down the road, but might be an issue if you leave the DC->DC connection active while merely idliong for extended times.

 

[rickst29]

All this info has been super helpful so far - thanks everyone for your input. now you have me thinking about "future-proofing" the system and I'm on the hunt for something that would allow for 2x220 panels in order to maximize my power production. I see that its a big step up to the Victron MPP 100/30 and then I also see a Renology unit that also supports DC-DC charging from an IGN port which could be good for the car charging input..

There are many reports of problems with less complex Renogy components on this board, and the usual summary is "friends don't let friends buy renogy". Their DC->DC controllers have had numerous "issues" reported, and their MPPT controllers have had even more problem reports. That unit combines both functions, I feel that combination is therefore even more problematic.

The Victron units are first class and more configurable, but they are far more expensive.

 

[Tomthumb62]

With respect to the DC-DC charging, since the max current is about 2 amps, why can't I just tie it to the DC input side of the Victron controller? (since it will never be used at the same time that the solar panels are deployed). The controller would just think it was a 12v panel putting out about 24-30 watts depending on the alternator output. If not, I'd honestly rather disable that charging input because going with a fancy DC-DC charger would require that I completely re-wire a separate heavy gauge pair from the engine compartment to a separate Anderson connector that I would then have to snake across the trailer tongue along with the regular 7-pin harness. That juice ain't worth the squeeze to me. ;-)

I can't speak with great authority as to why what you want to do isn't a good idea, but I know enough to say I know it's not. There is a genuine reason why DC-DC chargers are a thing and that reason isn't just about squeezing more money from you.

In short, a real DC-DC charger (especially a quality one like the Victron) will protect your alternator by not drawing too many amps from it at once. There are plenty of real cases where someone hooked their alternator directly to their lifepo4 battery and since lifepo4 can handle high amps, the battery took all it could take (your aolithium can take up to 200A each, so 400A total!!) and then the alternators go smokey-smokey or even catch on firey-flames. Some try a poor-man's fix by using the 7pin and the tiny wiring (usually 10-12AWG), which can somewhat limit how many amps can make it through the wire, but will suffer severely from voltage drop. In short, don't do this and simply pony up for a real DC-DC charger.

 

[sbsyncro]

Sounds like I will just be disconnecting the power feed wire from the trailer harness (I don't need to charge while driving, usually). Victron charge controller it is FTW, then! Now I just need to decide whether its worth $100 to buy capacity I might or might not need in the future... Size might also be an issue.

 

[Doggydogworld]

I'm assuming that since the Victron MPPT 75/10 Max. PV open circuit voltage is 75v, then it will be a good match to these two power sources?
(edit: it looks like the max charge output of this unit is 145w, so I'd need to step up to the 75/15 to support a 220w panel)

I'd first measure your panel's output. It may be a lot less than 220W in typical use. Many people and even large solar farms "over-panel". It's not worth the extra cost of controllers, inverters, etc. to capture those last few Watt-hours for a few hours on the best days.

With respect to the DC-DC charging, since the max current is about 2 amps, why can't I just tie it to the DC input side of the Victron controller? (since it will never be used at the same time that the solar panels are deployed). The controller would just think it was a 12v panel putting out about 24-30 watts depending on the alternator output.

Alternators can put out a lot more than 2A. Max current on a given circuit is determined by resistance. Trailer lights and such are designed with high resistance to keep current low. An MPPT controller varies the resistance continuously to find the "maximum power point" aka MPP for your solar panel under the specific conditions at an instant in time. The MPPT algorithms are designed for solar panels, not alternators. The result is unpredictable. If the MPPT sets resistance too low it could damage your alternator. Or more likely melt the skinny wires leading to your 7 pin plug.

 

[sbsyncro]

Thank you. I realized after reading the spec sheet on the Victron MPPT 75/15 that the charging input must be +.5 volts above battery voltage. That alone makes it a no-worky solution. So I've also added a Victron Orion TR (9 amp) to my shopping cart, as that will limit the current coming from the alternator to something the wiring can handle.

 

[Tomthumb62]

realized after reading the spec sheet on the Victron MPPT 75/15 that the charging input must be +.5 volts above battery voltage. That alone makes it a no-worky solution.

Not sure what you meant by this. But if you read the specs again, you'll see it's +5v above battery voltage, not 0.5v. In any case, this makes little real-world difference for charging from solar. By the time the panel voltage (if you're using "12v" panels aka 18-20v in full sun, but 14-17v at dawn or just before sunrise, especially in winter) raises to +5v, you're now in the type of daylight that you will just start to produce some watts. Meaning, there is no real-benefit for the MPPT to wake up before then, unless you care about a couple of watts. My 400W array on a Victron 100/30 produces about 18W when the MPPT first wakes up and the sky is anything but bright yet and the sun hasn't even risen.

 

[Aussieguy]

get a decent controller and as many panels you can
make the controller big enough to handle any future upgrades to panels


Then .... if that covers your power usage no need to look at dc-dc upgrade to truck
my style of camping doesn't have a lot of driving... trailer gets parked for a week or so then I go home.

 

[sbsyncro]

Not sure what you meant by this. But if you read the specs again, you'll see it's +5v above battery voltage, not 0.5v. In any case, this makes little real-world difference for charging from solar. By the time the panel voltage (if you're using "12v" panels aka 18-20v in full sun, but 14-17v at dawn or just before sunrise, especially in winter) raises to +5v, you're now in the type of daylight that you will just start to produce some watts. Meaning, there is no real-benefit for the MPPT to wake up before then, unless you care about a couple of watts. My 400W array on a Victron 100/30 produces about 18W when the MPPT first wakes up and the sky is anything but bright yet and the sun hasn't even risen.

Sorry that was a typo - I meant 5.0v. And what I meant was that since the Victron MPPT controller requires battery voltage +5.0 volts, let's say it will typically require ~18 volts (~13.x + 5.0) of input before it will start charging the battery. The tow vehicle's alternator will never put out more than about 14.5 volts (and then quickly settle to something like 13.8v). Since this will never exceed the ~18v required by the MPPT controller, the input from the alternator of the tow vehicle would essentially be ignored. I hope that makes more sense this time - I was using too much shorthand before.

 

[sbsyncro]

get a decent controller and as many panels you can
make the controller big enough to handle any future upgrades to panels


Then .... if that covers your power usage no need to look at dc-dc upgrade to truck
my style of camping doesn't have a lot of driving... trailer gets parked for a week or so then I go home.

Roger that! My camping varies a lot - sometimes I move camp every day for 10 days other times I just park and never move for 3 or 4 days. The trailer only uses power to run some small LED lights, a water pump, the ignition circuit for the propane water heater, and a safety switch for the propane stove (so that if one slides the galley shut with the stove on, the propane cuts out). That last bit is actually the biggest draw requiring >2 amps to keep the solenoid open, so I slide the galley closed when not in use. My fridge is in the tow vehicle powered by a 1500 wh power bank, and I use another 1500 wh power bank to run my Starlink when I'm working off-grid (as I am fortunate to be able to do once in a while). If I wanted to power the Starlink from the trailer, I would add another 100ah battery and double the charging power capacity. But that would cost about $400 (battery)+$100 (larger MPPT controller)+$400 (additional 220w panel to match the one I have). $900 to basically duplicate what I already have in a portable unit. I realized that didn't really make much sense for my use case ;-)