A simple, inexpensive, yet powerful solar storage system

[ERD50]

... In contrast with the UPS for home use, which switches on the inverter when AC power loss is sensed, Liebert UPSs supply the load with the inverter output at all time. The AC coming in is rectified to charge the battery and also to power the inverter. This means no transient whatsoever with AC interruption. ...

Question about this - I was looking into DIY or buying a small scale UPS of this type for my little computer/controller boards (< 1A @ 5V), and I needed that true "un-interrupted" power, no glitch between switching between line and battery (to avoid resetting the micro-controller).

The problem I saw was - how does the charge controller work with a Lithium that is under load? IIRC, they are looking for the currents to drop off at the end of the cycle, but the load current would mess with this.

I figured one approach was to just be conservative on the upper end of the voltage, and limit the charge voltage to maybe 0.2V below the normal high voltage cutoff? You'd lose some capacity (OK for my needs), but I guess that should be safe under any load conditions?

-ERD50

 

[NW-Bound]

Yes, setting a lower charge voltage will work. The last 0.1-0.2V of a lithium cell corresponds to a small percentage of its Ah capacity.

Remember my earlier analogy of a gallon milk jug. Once you fill it to the neck, raising the water level to the cap only adds another couple of tablespoons.

 

[NW-Bound]

After verification of proper operation of the Liebert 2-kVA UPS, I took out the smaller Liebert 1-kVA UPS and verified that it also worked perfectly.

Now, what I need to do is to figure out a way to disable the AC-to-DC part of the UPS, so that its inverter will not draw from the grid but from the external battery in normal operation. The external 48V LFP battery will be charged by external solar controller.

One thing I like to caution tinkerers who may want to do the same with a computer UPS. You cannot do what I do with the Liebert UPS without a lot of modifications. Basically, the inverter inside a home or small-office UPS is not meant to be running 24/7. The home UPS normal operation is in bypass mode, where the AC input is routed to the output, and the inverter is not running. Upon a power loss, the inverter is switched on, and runs for only a few minutes until the internal UPS battery is drained.

In contrast, the Liebert UPS is meant to be running full-time in inverter mode. And there's provision to plug it into an external large battery to extend the run time indefinitely.

If you wire in a larger external battery to keep the home/small office UPS to run longer than it is designed to, it builds up heat and either gets destroyed or a thermal cutout will shut it down. Buy a surplus Liebert UPS if you want to play with this stuff. The Liebert UPS also puts out a nice sine-wave output, compared to the cruddy "modified sine wave" like the inexpensive home/small-office UPS.

 

[Sunset]

Now that we have some home UPS , I'm surprised by how often I hear them click, as it seems we get more incredibly short power blips that even the microwave does not notice. It's only about 1 a week, but I feel we get a power failure once a year on avg.

I did test my new solar panels for a few minutes out on a cloudy day, for the VOC they each read 24 and 23.7 about 10 minutes apart as I did them one at a time. I'm guessing the difference is the cloud intensity.

I was unsure how to do the other test at the time, but felt better knowing the panels were generating some power.

 

[Sunset]

........
More than electric power or propane consumption, the ammonia absorption fridge cooling power is so weak, when the ambient temperature is high such as 90F, it can barely keep the interior temperature below 45F. We spent too much time worrying about food spoilage and had to keep eyes on the wireless thermometer all the time.

I figure that if we had an auxiliary portable 12V compressor fridge/freezer, we would open the main fridge less, and that should help it. It's easy to run this portable fridge off solar.

I'm wondering, with 2 100W solar panels, a lithium 12 V battery could I run this cooler for 60 days continuously ?

I like that it can run on 12V.

https://www.amazon.com/Alpicool-Portable-Refrigerator-Freezer-Vehicle/dp/B07L34Z6PZ?th=1

I'd probably use this battery:
https://www.amazon.com/dp/B08FMTRYPT/

 

[travelover]

I'm wondering, with 2 100W solar panels, a lithium 12 V battery could I run this cooler for 60 days continuously ?

I like that it can run on 12V.

https://www.amazon.com/Alpicool-Portable-Refrigerator-Freezer-Vehicle/dp/B07L34Z6PZ?th=1

I'd probably use this battery:
https://www.amazon.com/dp/B08FMTRYPT/

I think the answer is yes, as long as you have steady sun.

 

[NW-Bound]

The specs on the portable fridge say 60W. You have 200W worth of panel outputs. So, it looks like it's doable, but there are factors to consider.

First, you will never get a panel rated output. It is measured at a temperature of 25C (77F), and the standard solar radiation of 1 kW/sq.m. Your panel out in the sun will not be that cool and PV panel's efficiency goes down when the panel is hot, you may have high cloudiness, and the panels are not tracking the sun to face it squarely all day. And most importantly, you don't have 24 hours of sunlight.

On the load side, it's good that the fridge will not draw 60W 24/7 either. How much time does it run in a 24 hour period, meaning its duty cycle? I would surf the Web to see typical users' experience. It will depend a lot on the ambient temperature as we can expect.

To figure out how much you can expect from the solar panels at your location, use the calculator PVWatts by NREL.org. They use real solar radiation data collected throughout the US. This reflects actual atmospheric conditions throughout the year at different points. Really good stuff.

 

[travelover]

...... I would surf the Web to see typical users' experience. It will depend a lot on the ambient temperature as we can expect...........

Actually the reviews and Q&As for this refrigerator on Amazon provide a lot of customer experience including duty cycle and actual amp hours / day use for this fridge. From reading these reviews it looks like about 20 amp hours per day is a reasonable estimate, though higher temperatures would increase that. My experience with my own camper in the PNW is that I can get about 20 to 25 amp hours of power from a 100 watt panel per day with full sun exposure in the summer. So, with good sun, 200 watts of solar panel should run the fridge with a little overhead. Buy a larger controller so you can add in another 100 watts if you need to, as the panels are the cheap part, now.

 

[NW-Bound]

Actually the reviews and Q&As for this refrigerator on Amazon provide a lot of customer experience including duty cycle and actual amp hours / day use for this fridge. From reading these reviews it looks like about 20 amp hours per day is a reasonable estimate, though higher temperatures would increase that...

That's really good. Only 240 Wh/day for 58 qt. fridge.

And according to PVWatts, in Chicago a 100W PV panel will provide 500Wh/day, or 41 Ah/day in June.

So, it sounds like even a 100W solar panel can run this fridge. Amazing!

Sunset may be thinking about adding AC now.

 

[Sunset]

Why are bus bars so expensive for what they appear to be ?

To my eyes, they are a non-conductive base (example plastic) and some bolts with a bar of metal.

Seems like they should be $4 each, but the minimum seems be $12 ea, and easily twice that!

Am I looking in the wrong places or do people make their own, or do folks just accept $24->$30 for 2 bus bars (6 bolts and some metal) and move on

example photo of a bus bar:

 

[Sunset]

That's really good. Only 240 Wh/day for 58 qt. fridge.

And according to PVWatts, in Chicago a 100W PV panel will provide 500Wh/day, or 41 Ah/day in June.

So, it sounds like even a 100W solar panel can run this fridge. Amazing!

Sunset may be thinking about adding AC now.

While there is value in the 12V coolers, I realize 58 quarts is only 2 cubic feet.

Nice thing is compared to a regular cooler, one is not losing 1/4 of the space due to ice. Still small.

 

[travelover]

Why are bus bars so expensive for what they appear to be ?

To my eyes, they are a non-conductive base (example plastic) and some bolts with a bar of metal.

Seems like they should be $4 each, but the minimum seems be $12 ea, and easily twice that!

Am I looking in the wrong places or do people make their own, or do folks just accept $24->$30 for 2 bus bars (6 bolts and some metal) and move on

example photo of a bus bar:

I've noticed the same thing - friggin' rip off. If you have not discovered WAGO connectors, they can be an easy to use alternative.

 

[NW-Bound]

While there is value in the 12V coolers, I realize 58 quarts is only 2 cubic feet.

Nice thing is compared to a regular cooler, one is not losing 1/4 of the space due to ice. Still small.

Yes, it is small. But consider the advantages compared to a chest cooler.

This is a real fridge/freezer. It will keep ice cream. And you don't have to run off everyday to buy ice.

All the convenience for a little bit of money. And it makes use of the solar juice from the solar+battery set up.

No, one does not have to be living like a caveman when he has access to modern technology which is affordable.

Oh wait! Cavemen did not even have ice, unless it's the winter. But I bet that the time of year they had ice, they would not be thinking about a cold drink because they were too busy shivering.

PS. At this price, buy 2. One set to a really cold temperature for use as a freezer for ice cream, ice trays, and frozen food. The other set at a higher temperature as a fridge for veggies and fruits.

 

[NW-Bound]

Why are bus bars so expensive for what they appear to be ?

To my eyes, they are a non-conductive base (example plastic) and some bolts with a bar of metal.

Seems like they should be $4 each, but the minimum seems be $12 ea, and easily twice that!

Am I looking in the wrong places or do people make their own, or do folks just accept $24->$30 for 2 bus bars (6 bolts and some metal) and move on

You can make your own by using ground bars from Home Depot that are meant to be mounted inside a circuit breaker box.

Saw one in half; you now have two shorter + and - bus bars. Drill through the bars at the ends, and use the holes as mounting points on a small piece of hard oak.

The advantage of this ground bar over WAGO connectors is that it handles bigger gauge wires with a lot more current.

PS. I would be careful to not have the + and - bus bars touch. Firework! Perhaps the simplest way to prevent this is to mount both of them on a single piece of wood. Or mount them on the same wood tablet where you mount the various circuit breakers and switches.

 

[NW-Bound]

Speaking of doing a backup power source for the home during an outage, I ran across a video by this Texan who had his plumbing frozen and flooding his house last winter, when the Texas grid collapsed in a freak freeze.

He bought a 2kW Bluetti with a 2kWh internal battery, then added fix-mounted solar panels. When not having an outage, the Bluetti lets him run a window AC, and that saves him a bit off the utility bill.

He liked it so much he decided to wire a transfer switch to be able to power the lighting in other rooms as desired.

For people who don't know about this stuff, it is a good tutorial for a starter. One can watch this to have an idea of what it takes.

You can have a better system at a lower cost, and also more easily expandable, and it does not have to be more complicated. You simply give up the easy portability of the Bluetti.

 

[Sunset]

You can make your own by using ground bars from Home Depot that are meant to be mounted inside a circuit breaker box.

Saw one in half; you now have two shorter + and - bus bars. Drill through the bars at the ends, and use the holes as mounting points on a small piece of hard oak.

The advantage of this ground bar over WAGO connectors is that it handles bigger gauge wires with a lot more current.

PS. I would be careful to not have the + and - bus bars touch. Firework! Perhaps the simplest way to prevent this is to mount both of them on a single piece of wood. Or mount them on the same wood tablet where you mount the various circuit breakers and switches.

Amazing, I was in Menards on Sunday afternoon and saw these bars and thought, why can't I buy the long $11 one and cut it to use it as 2 bus bars, it would give me about 10 connections on each and I can just stick the wire in bare (or maybe dip the the end in solder first).

I took a picture as I was going to post the question here about doing that, but you already answered the question.

The $11 one might be too big, so I might go for the $8 or $6 one instead, will have to look again.

 

[folivier]

Rather than soldering the ends of wire you can use these crimps: https://www.amazon.com/Glarks-Conne...T6M7/ref=dp_prsubs_1?pd_rd_i=B08LG3T6M7&psc=1

 

[NW-Bound]

It's getting hot now. This time of year is when my solar+battery starts to fall short.

The high is now between 105-110F, while the low of the day right before sunrise is 80F. This means the ACs are running 24/7, though they run at a lower speed at night.

My battery is running out of juice at around 5AM, and all 4 inverters transfer to the grid. They switch off the grid and go back on solar+battery power at about 8AM.

The time when the grid transfer occurs moves up sooner and sooner, until at the peak of the summer, it happens shortly after 8PM. This is enough for me to escape the high utility rate of the peak-usage period. Still, I want more solar juice. The more the merrier.

 

[aja8888]

It's getting hot now. This time of year is when my solar+battery starts to fall short.

The high is now between 105-110F, while the low of the day right before sunrise is 80F. This means the ACs are running 24/7, though they run at a lower speed at night.

My battery is running out of juice at around 5AM, and all 4 inverters transfer to the grid. They switch off the grid and go back on solar+battery power at about 8AM.

The time when the grid transfer occurs moves up sooner and sooner, until at the peak of the summer, it happens shortly after 8PM. This is enough for me to escape the high utility rate of the peak-usage period. Still, I want more solar juice. The more the merrier.

Forecast for here (north side of Houston), is 107 F Thursday thru Saturday. That's with ~60% humidity. Will be tough.

 

[Sunset]

I'm thinking now, that I'll buy the bluetti 1500Wh device, and use my solar panels to charge it, so I can run the 12v cooler.

It will be a lot more portable for me, which is important as I can't leave things of value there or they will be stolen.

I did have a concern the 2 100w panels I have are not enough, and I came across an Amazon deal to buy a 100W polycrystalline panel for $65. I looked into the reduction of output I'll have by putting them in series and based on the output it should be small (guess).
The poly panel is rated:
Open-Circuit Voltage: 22V
Max Power Voltage:17.48V
Max Power Current:5.72A
Short Circuit Current:6.21A

The two Mono crystalline panels each are:
Open-Circuit Voltage: 24.3V
Max Power Voltage:20.4V (called optimum operating voltage)
Max Power Current:4.91A (called optimum operating current)
Short Circuit Current:5.21A

I worked out the numbers, and if I had 3 mono type panels they would ideally generate 300.5W , instead by adding the cheap panel as the 3rd one, it will generate 286W so it seems worth it.

Not sure how I can tell in the real world when it's set up, but I think regardless the mixed 3 panels should be better than just 2 panels as they are not too different.

 

[NW-Bound]

I worked out the numbers, and if I had 3 mono type panels they would ideally generate 300.5W , instead by adding the cheap panel as the 3rd one, it will generate 286W so it seems worth it.

Not sure how I can tell in the real world when it's set up, but I think regardless the mixed 3 panels should be better than just 2 panels as they are not too different.

Yes, you got your numbers right.

Doesn't the Bluetti display the power it receives from its PV input?

Just be aware that you never get the solar panel rating because your operating condition is never that ideal. If you get 80%, that's good.

 

[Sunset]

Yes, you got your numbers right.

Doesn't the Bluetti display the power it receives from its PV input?

Just be aware that you never get the solar panel rating because your operating condition is never that ideal. If you get 80%, that's good.

Thanks for confirming the numbers.
I knew as I was doing them, I'm showing optimal numbers and the real life will be lower.

I hope the Bluetti shows the input, I'm sure it shows the amount of charge, so I'll be able to tell if the device is able to maintain the power over many days or slowly declines.

 

[NW-Bound]

I looked briefly at the Bluetti info. The display does show the present power input in Watts. I don't know if it shows the cumulative charge.

 

[slaternuthink]

Can you mix different types of PV panels on the same charge controller?
What about different sizes? - e.g. - 100w with 50w.

 

[Sunset]

Can you mix different types of PV panels on the same charge controller?
What about different sizes? - e.g. - 100w with 50w.

I'm new to this, but I found this article explaining different setups of panels and how adding a low watt panel to existing panels can actually lower the total output.

https://solarpanelsvenue.com/mixing-solar-panels/