A simple, inexpensive, yet powerful solar storage system

[NW-Bound]

... I'm more interested on how to have off grid power for the long term. Our electricity use is low enough the grid tie in solar panels aren't cost effective for us. If we could really pull off your 20kwhs for $2K we'd be almost energy self sufficient...

The system I show in post #1 of the thread is with 2kW of solar panels, which can produce about 12 kWh/day in July, and 6 kWh/day in December. It will let one survive through an outage, but will not replace the grid connection. You would need more for comfortable living.

I also describe the 6 lead-acid batteries, which can store 3 kWh, and that can get you through the night with the fridge and some lighting. A single 2.4 kW inverter/charger is used.

My own 22-kWh lithium battery, 3 inverters putting out 7.2 kW, plus several charge controllers cost a lot more than $2K. If you buy retail, the lithium battery is already $20K.


PS. The number of 12 kWh/day in the summer and 6 kWh/day in the winter is for the location of San Jose. I pull that from government data. Over 1 year, the total energy produced is 3400 kWh, as mentioned previously. And that is assuming good orientation of the panels, with no shading from trees and housing structures.

 

[daylatedollarshort]

The system I show in post #1 of the thread is with 2kW of solar panels, which can produce about 12 kWh/day in July, and 6 kWh/day in December. It will let one survive through an outage, but will not replace the grid connection. You would need more for comfortable living.

I also describe the 6 lead-acid batteries, which can store 3 kWh, and that can get you through the night with the fridge and some lighting. A single 2.4 kW inverter/charger is used.

My own 22-kWh lithium battery, 3 inverters putting out 7.2 kW, plus several charge controllers cost a lot more than $2K. If you buy retail, the lithium battery is already $20K.


PS. The number of 12 kWh/day in the summer and 6 kWh/day in the winter is for the location of San Jose. I pull that from government data. Over 1 year, the total energy produced is 3400 kWh, as mentioned previously. And that is assuming good orientation of the panels, with no shading from trees and housing structures.

Ah, got it. Sorry, I just skimmed it the first time through and misread your numbers. I checked last months PG&E bill and we averaged 10 kWhs a day, plus we still have quite a few projects we could do to get that lower. So if I can get the the average usage to 8 kWhs a day, at least in spring and fall when we don't need much heat or cooling, and put up your small system, that would still cover a big chunk of our electricity needs, right?

 

[NW-Bound]

I don't think you want to be cut off the grid anyway. With electricity costing as much as it is in California, you will save a lot more money than I do here, with electricity costing as little as $0.07/kWh in off-peak period, but $0.24/kWh in on-peak hours.

And as I show, you can get a 327W solar panel for $108. Once you have the basic system, additional panels provide a lot of return. The only thing that holds me back is space to have my own mini solar farm. Adding batteries is also easy.

A simple way to figure out how much power you will get from a panel is that you have about 6 hours of equivalent max solar radiation in the summer, and 3 hours in the winter. This means a 327W panel will give you 1 to 2 kWh/day. In one year, a single panel will give you 500 kWh.

And then, you may use 1/2 of it while generating it, and save 1/2 of it in the batteries to use at night.

My ground-mounted 5.5 kW solar panels have not been producing enough to fill up my 22-kWh battery. The sun angle is now low, and they are partially shaded by my 2nd story in the winter.

In the summer, I can get 20-25 kWh/day from them, but only about 12-14 kWh/day now. Even in the summer, I still got some late afternoon shading by neighbor's trees.

I am contemplating putting 2 to 3 kW worth of additional panels on the roof. No additional costs of batteries or electronics needed.

 

[NW-Bound]

With lithium batteries, excess storage is a good thing. Lithium batteries if charged to full all the time will have their life shortened.

Lead-acid batteries are the reverse. You want to charge them to full each day, to keep them from getting sulfated. Hence, you want to have just enough, and not excess capacity, lest you do not produce enough to have them full at the end of the day.

 

[daylatedollarshort]

I don't think you want to be cut off the grid anyway. With electricity costing as much as it is in California, you will save a lot more money than I do here, with electricity costing as little as $0.07/kWh in off-peak period, but $0.24/kWh in on-peak hours.

And as I show, you can get a 327W solar panel for $108. Once you have the basic system, additional panels provide a lot of return. The only thing that holds me back is space to have my own mini solar farm. Adding batteries is also easy.

A simple way to figure out how much power you will get from a panel is that you have about 6 hours of equivalent max solar radiation in the summer, and 3 hours in the winter. This means a 327W panel will give you 1 to 2 kWh/day. In one year, a single panel will give you 500 kWh.

And then, you may use 1/2 of it while generating it, and save 1/2 of it in the batteries to use at night.

Sounds like a fun project for us to try to copy in the future. Thanks for posting all the info.

 

[NW-Bound]

Another reason beginners will want to play with lead-acid batteries first, instead of lithium batteries:

Lithium batteries of all kinds do not want to be overcharged. When full, they are really full. Even a trickle charge will cause them to eventually blow up, and may burst in flames. Yet, trickle charging is what done with NiCad, NiMH, and lead-acid batteries all the time.

Lead-acid batteries love to be slightly overcharged. This is intentionally done periodically to equalize all the cells. Equalizing lithium cells is trickier, and requires precise electronics.

I did a lot of research and reading before I started to play with my expensive LFP batteries.

 

[daylatedollarshort]

Another reason beginners will want to play with lead-acid batteries first, instead of lithium batteries:

Lithium batteries of all kinds do not want to be overcharged. When full, they are really full. Even a trickle charge will cause them to eventually blow up, and may burst in flames. Yet, trickle charging is what done with NiCad, NiMH, and lead-acid batteries all the time.

Lead-acid batteries love to be slightly overcharged. This is intentionally done periodically to equalize all the cells. Equalizing lithium cells is trickier, and requires precise electronics.

I did a lot of research and reading before I started to play with my expensive LFP batteries.

What about small solar gadgets with lithium batteries like lights and chargers? Is it an issue if they get left in the sun too long?

 

[NW-Bound]

All gadgets with lithium batteries have embedded electronics to monitor the battery state and to control the charging process, in order to avoid over-discharging them and overcharging them. It takes just a small IC chip or two to implement this function.

The problem is with the public buying the bare cells without any attached electronics, then abusing them.

 

[Sunset]

.... And I bought a low tech solar shower bag for hot water, in case the gas gets shut off next time.

I never found in 3 months of summer use, that the black bag warmed enough for a nice shower. Especially since there was 2 of us, so even if it did, it would be good for 1 person.

We did find however, a propane stove heats up a kettle of water, and a 20lb tank of propane lasts weeks.

We would put in a pail of water into the black bag, and then pour in the kettle of hot water (close to boiling) and that provided a hot shower, and easily repeated for the next person.

 

[NW-Bound]

By the way, we have all heard stories about lithium batteries in laptops and cellphones exploding sometimes. I believe that happened because the battery monitoring circuit failed, as any electronic chip or circuit could fail. The battery got overcharged and burst into flames.

See the following video at 7:30.

 

[HFWR]

Costco is currently selling this battery for $650...

 

[NW-Bound]

I have not heard of the above brand but the price is decent for the typical size of 100Ah, although this one is a bit smaller at 90Ah.

On the Web, I ran across this company that sells directly out of China: BLS. One deal they offer is 48 large cells of 200Ah each for $6505, shipping included. That's 48 x 3.2V x 200 Ah = 30.72 kWh, for $212/kWh.

With shipping included, the above price is amazingly low. BLS is listed as a trading company, so they are selling batteries made by somebody else. They also sell CALB cells, a reputable Chinese company, so it appears that this BLS company is legitimate. However, the less expensive batteries are of unknown make.

PS. My solar array of 5.5 kW is already too small to produce enough to fill up my 22-kWh battery. I've got to find out where to mount more solar panels before I can buy more batteries. Dang, used solar panels are so cheap now. My wife asked if we should fill in the pool to have room for more panels.

 

[Sunset]

By the way, we have all heard stories about lithium batteries in laptops and cellphones exploding sometimes. I believe that happened because the battery monitoring circuit failed, as any electronic chip or circuit could fail. The battery got overcharged and burst into flames.

...https://www.youtube.com/watch?v=ehcGWLOH-Js

Very scary..

I just got a new battery for my phone, it was $7.75 so I charged it by the door when I was in the kitchen.
I just felt nervous about charging the battery, especially the first time, and didn't want the house to burn down.
It all went well.

 

[NW-Bound]

Yes, very scary.

Here's what looks like a laptop bursting into flames in an airplane overhead compartment. It was not even being charged!

Here's a woman whose headphones also burst into flames during air travel between Beijing and Melbourne.

Between March 1991 and December 2016, the Federal Aviation Administration documented 138 incidents at airports and in airplanes of devices smoking and catching on fire. The tally "should not be considered as a complete listing," the agency says. Culprits included e-cigarette devices, laptops, loose batteries and small devices crushed in seat-adjusting mechanisms.

Yes, you absolutely do not crush these lithium batteries, as that causes an internal short.

What I still don't know is the mechanism for batteries to explode in flames when they are not being charged, nor physically abused. There have been a few occurrences of Tesla cars bursting into flames while parked, but it was not known if they were being charged.

A source says that batteries that are charged under freezing conditions may explode later due to a latent failure. I am still watching out for more details on this failure mode.

And that's the reason for me to use LFP batteries, rather than the more common type. LFP batteries do not have the same energy density, hence are heavier for the same capacity. However, they are fairly tame, and typically last 2000 cycles, instead of the 500 cycles of the common types.

I used to entertain the idea of salvaging smaller cells from discarded laptop batteries to build a big bank, like you can see many Youtubers and bloggers doing. No more. Too much work, and not worth the risk to me.

 

[Sunset]

I know this is an old thread, but now I'm going to start out with a small solar system for my remote no electricity cabin.

Initially I want to be able to charge up cell phones, so we can reduce trips to go charge the phones, and hopefully power up a 900W coffee maker for fast morning coffee.

I tried looking online for used commercial panels, but none are local and the shipping made it costly for 1 panel.

Today I bought this instead: Renogy 2PCS 100 Watt Solar Panels 12 Volt Monocrystalline for $158 + tax on Amazon.

Now I'm wondering:
How can I test my old 12v lead acid car batteries to see if they have some useful life. I charged them up but don't really know how to test them.

When thinking of the Solar panel to controller connection should it be 10 or 8 AWG for up to 20 feet of length. ?

I'm open to recommendations for a MPPT controller and an inverter (1,000W continuous). I know NW-BOUND recommended an all in 1 unit, but normally I like separate devices so when 1 fails the rest is fine, and I won't be charging my batteries from the grid/generator.

Anything wrong with the connecting wires or something I missed, as once I get to the cabin, I can't order stuff, and will have to travel for 35 minutes to hope a hardware store has what I need.


To join the 2 solar panels in parallel (as sticking to 12V for now as my end up with just 1 battery) I was going to buy this:
BougeRV Solar Connectors Y Branch Parallel Adapter Cable Wire Plug Tool Kit for Solar Panel
https://www.amazon.com/BougeRV-Connectors-Branch-Parallel-Adapter/dp/B0753X68PS/

Then to run the power to the controller using:
BougeRV 10 Feet 10AWG Solar Extension Cable with Female and Male Connector with Extra Free Pair of Connectors Solar Panel Adaptor Kit Tool (10FT Red + 10FT Black)

 

[NW-Bound]

I am going to answer your questions in separate parts.

First, about your PV panels.

Today I bought this instead: Renogy 2PCS 100 Watt Solar Panels 12 Volt Monocrystalline for $158 + tax on Amazon.

To join the 2 solar panels in parallel (as sticking to 12V for now as my end up with just 1 battery) I was going to buy this:
BougeRV Solar Connectors Y Branch Parallel Adapter Cable Wire Plug Tool Kit for Solar Panel
https://www.amazon.com/BougeRV-Connectors-Branch-Parallel-Adapter/dp/B0753X68PS/

Then to run the power to the controller using:
BougeRV 10 Feet 10AWG Solar Extension Cable with Female and Male Connector with Extra Free Pair of Connectors Solar Panel Adaptor Kit Tool (10FT Red + 10FT Black)

The price you show is indicative of a pair of panels of 50W each. As these are labeled as 12V panels, the construction of each panel will be with 36 cells wired in series, which are physically arranged in a rectangular array of 12x3.

Yes, you can use Y cable adapters to join them in parallel, then run the combined output to the charge controller. These are not very powerful panels, so 10AWG wires for a run of 10ft are quite sufficient.

One thing to note about these 12V panels: they are meant for charging 12V with low-cost PWM controllers. Hence, they use the 36-cell design to provide a max power point of 18V, which will work well to charge 12V lead-acid which will go up to 14V when near full. This leaves a 4V headroom for the controller and wiring loss.

If you get an MPPT charge controller, then the 4V difference is too low for the controller to work well. You may get more power by wiring the panels in series to double up the voltage. The same wiring is used, but you now don't need the Y-combiners.

If you use the panels in series, then you need to be sure that they see the same lighting. With the series connection, the combined current is limited to that of the weaker one, so the panel in poor light will limit the output of the better lit one.

 

[NW-Bound]

I'm open to recommendations for a MPPT controller and an inverter (1,000W continuous). I know NW-BOUND recommended an all in 1 unit, but normally I like separate devices so when 1 fails the rest is fine, and I won't be charging my batteries from the grid/generator...

I personally prefer a 3-in-1 unit. In my home solar system, I have 4 of the Taiwanese MPP Solar units, each providing 2,400W. The first one was installed in 2018, so will be starting its 5th summer. All 4 have been running 24/7 since installation. No problem so far.

The unit for your application would be the MPP Solar PIP1012LV-MS. It integrates a 1000W 120V pure sinewave inverter, a 40A 500W solar charger, and a 20A utility charger (run from the grid or generator). Price I see on eBay is $290+$125 shipping.

If you don't need the utility charger, then yes, you can do better with a separate inverter, plus a separate charge controller. I have not bought Renogy, but heard it's a good brand. Renogy 1000W inverter runs $161, and Renogy 20A MPPT charger runs $88. So, you do save some money.

Be sure to use big beefy cables for the battery-to-inverter wiring. A 1000W power is 83A at 12V, and that does not include inverter loss. You can reach current of 100A easily. If you keep the wiring under 1 ft, a 4AWG cable can work.

 

[NW-Bound]

Now I'm wondering:
How can I test my old 12v lead acid car batteries to see if they have some useful life. I charged them up but don't really know how to test them...

This is the hardest part.

The only way to truly measure a battery's capacity is to charge it up, then discharge it while measuring the power delivered until the stopping point.

Obviously, doing this on a primary cell (alkaline, zinc-carbon, etc...) means you lose the battery after the test. On a rechargeable battery, you can discharge to take a measurement, then recharge the battery and it's all honky dory, right?

No, the above is true only with a lithium battery or NiCad or NiMH, and within certain limits. On a lead-acid battery, deep discharging is not recommended as it shortens the battery's life. So, what can you do?

They say you should not discharge even a deep-cycle battery (marine, golf-cart, or AGM) below 50% capacity. But what if you don't even know the capacity in the 1st place?

The only thing you can do is to measure the voltage. The problem is the battery voltage drops under load. So, you can only measure when the battery is not loaded and at rest for a while.

Here's what a Web site says (quoted from https://www.solar-electric.com/learning-center/deep-cycle-battery-faq.html/)

I will talk about how to measure power later.

State of charge, or conversely, the depth of discharge (DOD) can be determined by measuring the voltage and/or the specific gravity of the acid with a hydrometer. This will NOT tell you how good (capacity in AH) the battery condition is - only a sustained load test can do that. Voltage on a fully charged battery will read 2.12 to 2.15 volts per cell, or 12.7 volts for a 12 volt battery. At 50% the reading will be 2.03 VPC (Volts Per Cell), and at 0% will be 1.75 VPC or less. Specific gravity will be about 1.265 for a fully charged cell, and 1.13 or less for a totally discharged cell. This can vary with battery types and brands somewhat - when you buy new batteries you should charge them up and let them sit for a while, then take a reference measurement. Many batteries are sealed, and hydrometer reading cannot be taken, so you must rely on voltage. Hydrometer readings may not tell the whole story, as it takes a while for the acid to get mixed up in wet cells. If measured right after charging, you might see 1.27 at the top of the cell, even though it is much less at the bottom. This does not apply to gelled or AGM batteries.

 

[skyking1]

Great thread revival
I have a pair of HQST 100 W panels with that 18v best voltage, and a renogy PWM controller. I run them parallel right now with the same kit above, and have not mounted them on the RV yet. We get where we are going and I set them up where they get the most sun. Our favorite campsite for the 4th of July is in shade for much of the day and if I set the panels out in front I can get ~6 hours of decent sun. On the roof in a permanent mount, they would get a shadow on one or the other panel almost all day, killing the system.
They keep our two GC2 6 volts topped off indefinitely for the basic house uses of fans, lights, water pump. We are not heating in July. Keeping the batteries up in heavy heating season would be a challenge, as the LP furnace in RV's hit the batteries pretty hard and it is also usually short and cloudy days.
I switched to GC2 golf cart batteries several years back. They have a great deal more capacity than the standard group 27 deep cycles typical in RV's.
I made my own battery box using marine plywood sealed with epoxy, properly vented and sealed.

 

[travelover]

..........Now I'm wondering:
How can I test my old 12v lead acid car batteries to see if they have some useful life. I charged them up but don't really know how to test them........

I wouldn't even mess with them. Car batteries are not really designed to be run down significantly, whereas marine / deep cycle batteries are. On a bang for the buck basis, probably the cheapest battery is a marine battery from Walmart, though on a longer term basis a lithium battery would be cheaper on a watts delivered over life / $.

 

[NW-Bound]

I wouldn't even mess with them. Car batteries are not really designed to be run down significantly, whereas marine / deep cycle batteries are. On a bang for the buck basis, probably the cheapest battery is a marine battery from Walmart, though on a longer term basis a lithium battery would be cheaper on a watts delivered over life / $.

Ugh, I missed the "car battery" part. Yes, a marine/deep cycle or golf-cart battery is what you want.

 

[NW-Bound]

Back on measuring power.

A battery capacity is typically spec'ed in Ah (ampere-hour or amp-hour). It's a measure of charge (coulomb), and not really a measure of energy though the two are related.

If you draw a current of 10 amps over 2 hours, that's 20 Ah of charge delivered. A current of 1A over 20 hours delivers the same charge of 20 Ah.

A Group-24 12V marine battery may have the spec of 80Ah. This means if you draw 1A, the battery should last 80 hours. Or if you draw 80A, it should last 1 hour, right?

No! Only if the battery is ideal, and sadly lead-acid batteries are far from that.

Enter Peukert, the German scientist who noticed that the duration of a lead-acid battery was not inversely proportional to the current drawn. It's similar to the endurance of a human runner. If you let a man walk at 3 mi/hour, he can do that for 5 hours non-stop and covers 15 miles before he drops. But if you make him run at 15 mph, can he run for 1 hour to go the same 15 miles? No, he drops in minutes.

Lead-acid battery capacity is measured at the 20-hour rate. It means your 80Ah marine battery is good for a 4A current draw over 20 hours.

If you draw 8A, the duration is shortened, not to 10 hours, but 7.6 hours.

Double the current again to 16A, and the duration is not 5 hours, but 2.9 hours.

If you try to get 1 kW from this battery using the 1kW inverter, let's say the current is 100A, the duration will be 13 minutes.

Again, notice that you should draw only 1/2 of the 80Ah capacity to avoid shortening the life of the battery. So, your 1 kW load depletes the battery in 6 minutes.

* I computed the above times for our hypothetical lead-acid battery using a Peukert factor of 1.4, which is in the middle of the range of 1.2-1.6 for flooded lead-acid batteries. The higher the Peukert factor, the worse the battery is.

 

[Sunset]

I am going to answer your questions in separate parts.

First, about your PV panels.

The price you show is indicative of a pair of panels of 50W each. As these are labeled as 12V panels, the construction of each panel will be with 36 cells wired in series, which are physically arranged in a rectangular array of 12x3.

Yes, you can use Y cable adapters to join them in parallel, then run the combined output to the charge controller. These are not very powerful panels, so 10AWG wires for a run of 10ft are quite sufficient.

One thing to note about these 12V panels: they are meant for charging 12V with low-cost PWM controllers. Hence, they use the 36-cell design to provide a max power point of 18V, which will work well to charge 12V lead-acid which will go up to 14V when near full. This leaves a 4V headroom for the controller and wiring loss.

If you get an MPPT charge controller, then the 4V difference is too low for the controller to work well. You may get more power by wiring the panels in series to double up the voltage. The same wiring is used, but you now don't need the Y-combiners.

If you use the panels in series, then you need to be sure that they see the same lighting. With the series connection, the combined current is limited to that of the weaker one, so the panel in poor light will limit the output of the better lit one.

I believe these are 100W panels each. I know the price is good, but I was pretty sure they are each 100W in size.

https://www.amazon.com/gp/product/B07JXYTFF7/

If I got the wrong ones I'll return them.
Can I test them to know for sure with a volt meter ?

 

[Sunset]

I wouldn't even mess with them. Car batteries are not really designed to be run down significantly, whereas marine / deep cycle batteries are. On a bang for the buck basis, probably the cheapest battery is a marine battery from Walmart, though on a longer term basis a lithium battery would be cheaper on a watts delivered over life / $.

I will keep the marine battery in mind, as my BIL is selling me his old boat and I don't know if I'll need to get a battery for it.
Also don't know if it has any battery charger or I'll be moving a panel to the boat every week or two to charge up the battery.

 

[Sunset]

Back on measuring power.

A battery capacity is typically spec'ed in Ah (ampere-hour or amp-hour). It's a measure of charge (coulomb), and not really a measure of energy though the two are related.

If you draw a current of 10 amps over 2 hours, that's 20 Ah of charge delivered. A current of 1A over 20 hours delivers the same charge of 20 Ah.

A Group-24 12V marine battery may have the spec of 80Ah. This means if you draw 1A, the battery should last 80 hours. Or if you draw 80A, it should last 1 hour, right?

No! Only if the battery is ideal, and sadly lead-acid batteries are far from that.

.......

Lead-acid battery capacity is measured at the 20-hour rate. It means your 80Ah marine battery is good for a 4A current draw over 20 hours.

If you draw 8A, the duration is shortened, not to 10 hours, but 7.6 hours.

Double the current again to 16A, and the duration is not 5 hours, but 2.9 hours.

If you try to get 1 kW from this battery using the 1kW inverter, let's say the current is 100A, the duration will be 13 minutes.

Again, notice that you should draw only 1/2 of the 80Ah capacity to avoid shortening the life of the battery. So, your 1 kW load depletes the battery in 6 minutes.

....

I can see 1 battery has some limitations, but the good news is my coffee maker uses 900W probably for 10 minutes , which I calculate to be 7.5Amps for 10 minutes. Meaning I'll be able to make coffee every morning.