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eHam Forums => Emergency Communications => Topic started by: KF7YED on February 28, 2022, 06:48:24 PM

Title: Building a small solar system
Post by: KF7YED on February 28, 2022, 06:48:24 PM
I currently have four 100W 12 volt Siemens solar panels. They each put out about 17VDC. I've been using a couple of them for camping and Field Days, one for the camper battery and one for the radio battery (with a Buddipole Mini charge controller which is really great, by the way), but I'm thinking of putting together a small system for emergencies using all four panels. Pack it all away in the basement for a rainy day (EMP). I've read articles until my head is spinning so I thought I start a conversation and soak in the ham knowledge here.

As usual, cost is everything and I don't intend to run a welding shop or the whole house on this system. Anything that will support some wall wart chargers for various electronics, maybe a laptop (which I never use except on AC because the battery isn't great). Running a fridge for a while during the day would be an extreme high-end load for this or maybe the microwave in the camper.

Some questions:

Is it even possible to run this 400W solar array directly to an inverter and skip batteries altogether, understanding it will only work in full sun?

If I have to use batteries, can I use a couple of plain old SLA 12v batteries, maybe 100 Ah each, just because they're cheap(er)?

How many batteries would make the most use of the 400 watts available or is that a function of the inverter output?

I have this bundle in my Wish list:

https://smile.amazon.com/Renogy-Converter-Controller-Parameter-Adjustable/dp/B09QKM28H9/ref=sr_1_10?crid=C7V6KSW8P2GY&keywords=mppt%2Bcharge%2Bcontroller%2Bmppt&qid=1646100641&sprefix=morningstar%2Bmppt%2Bcharge%2Bcontroller%2Bmppt%2Caps%2C337&sr=8-10&th=1

Couple of questions on that:

Is 2000 watts just a ridiculous expectation for my 400 watts of solar? Or does that just mean I need more batteries to make the most of the 2000W? i.e., fewer batteries would discharge quicker with that kind of load?

If I wire the panels as a 24V array, 2 in series and 2 in series and then the two pairs in parallel, do I use that current rating as the input for the charge controller? It says "40 AMP" so is that the max it could draw from the panels? I know they won't put out that much but is that a specification that's meant to stay under or to make sure I can deliver?

Wiring as 24V means I can get by with smaller wire, between and from the panels to the charge controller? 10ga? 4?

Thanks in advance. 73

Title: Re: Building a small solar system
Post by: KA4DPO on February 28, 2022, 08:31:14 PM
In order to build a small solar system, you will need a small sun, and some even smaller planets. ;D ;D

Sorry, carry on.... :D :D :D
Title: Re: Building a small solar system
Post by: N4UFO on February 28, 2022, 08:47:13 PM
In order to build a small solar system, you will need a small sun, and some even smaller planets. ;D ;D

Sorry, carry on.... :D :D :D

I know I thought the same thing when I saw the thread title.  ;D

I might suggest you look to a local solar installer for guidance... they run TV ads in my area constantly and even offer incentives like a free generator to sign up. I know you may not want a full house unit, but honestly with the tax breaks and savings, it might be the cheaper way to go. Most I ever did was I had a roll up panel and a small SLAB for a QRP rig. Donated that to an alternative energy education project in Vermont. (Never been to Vermont, I shipped it.)
Title: Re: Building a small solar system
Post by: AF5CC on February 28, 2022, 11:10:26 PM
In order to build a small solar system, you will need a small sun, and some even smaller planets. ;D ;D

Sorry, carry on.... :D :D :D

And 9 of them-including Pluto!!

73 John AF5CC
Title: Re: Building a small solar system
Post by: W9FIB on March 01, 2022, 03:59:31 AM
Typically you would want battery storage for 2 big reasons. You would have power when it is dark, and you could run heavier loads intermittently and then the panels recharge the storage when on light loading.

Probably would want to use 2 good sized batteries and keep them topped off before you deploy the system. Size would depend on how heavy is your biggest load and then your best charge rate between heavy loads. You want the ability to recharge what was used by the heavy load.
Title: Re: Building a small solar system
Post by: KD6VXI on March 01, 2022, 04:27:46 AM
400 watts isn't a lot, and that 400 watts is high nooon, all panels at 100 pct illumination.  Expect 350 watts or so in your calculations.

In Bakersfield, CA we looked at 8 hours of continuous sun and sometimes as low as 6.  Yes, your panels will be illuminated more, but the sun will be lower in the sky so you won't see peak production.  Here in the Carribean they plan for 10 hours(ish)....  However that's a bit optimistic IMHO since we have more clouds that meander across the sky here

That gives you anywhere from 1800 to 2400  watts of charge a day.

Your calculations can be made from there.

Yes, 24 volts or even 48 volts would be better.   The inverter will have a higher conversion efficiency the higher in DC voltage you go.  We used 600 volts DC on homes and over a kilovolt on the commercial (utility grade solar fields).

When you size your batteries, you now have a size to go with.  You have 2400 watts.  If you want to be able to pull all that in a few minutes (microwave or fridge) then you need a good size battery bank to supply the peak current.  Then it will slow charge all day. If you are talking about running a few 15 watt light bulbs and a 95 watt laptop, smaller batteries in a bank will work.

Hope this helps.  Without more information it's hard to size anything.  Microwaves run from 600 to 1800 watts, etc.

--Shane
WP2ASS / ex KD6VXI
Title: Re: Building a small solar system
Post by: W9IQ on March 01, 2022, 04:29:07 AM
I currently have four 100W 12 volt Siemens solar panels. They each put out about 17VDC.

That voltage will vary according to the amount of solar energy hitting the panels (called solar irradiance) and the load on the panel. An MPPT charge controller finds the optimum load for the solar array in order to transfer the maximum energy to the battery/load.

Running a fridge for a while during the day would be an extreme high-end load for this or maybe the microwave in the camper.

You will require a battery to store enough energy to run a small fridge or a microwave oven. Always look at the inverter specifications to see what inductive load it can handle during a motor starting scenario to make sure it won't burn out a motor or trip the inverter. Then remember that a fridge will take energy all day long so you need to look at your total energy requirements and make certain you can convert and store sufficient solar energy to supply to the inverter when needed.

Is it even possible to run this 400W solar array directly to an inverter and skip batteries altogether, understanding it will only work in full sun

Yes but then the total load will need to be far less than 400 watts as this is what it will likely put out on most sunny of days near noon time. Then you have losses in the charger controller/regulator. You will also quickly become aware of cloud cover and other weather issues as your solar system will drop out due to more energy being used than it can supply.

If I have to use batteries, can I use a couple of plain old SLA 12v batteries, maybe 100 Ah each, just because they're cheap(er)?

Just about any lead acid 12 volt battery will work on these systems. It is only a question of cost, lifetime and their ability to store and deliver the desired energy. The charge controller you reference appears to specify SLA batteries so do your research.

How many batteries would make the most use of the 400 watts available or is that a function of the inverter output?

It is time to start thinking in terms of energy (typically kw-hr in the US) instead of power. You need to consider how much energy your panel will generate on the average day. It will be less on rainy or partly cloudy days and it could be more on a sunny day. If you panel has 3 perfectly sunny hours in a particular day, you may generate 1.2 kw-hr (400 watts * 3 hours) but you will store less due to the inefficiency of the charge controller and the battery.

To calculate the average annual energy generation, you start with a map (https://www.nrel.gov/gis/solar-resource-maps.html) to show you the average solar irradiance for your area. You can then use this to calculate your overall infrastructure requirements. Monthly versions should then be checked to make sure it will meet your needs in winter when there is less solar irradiance:

(https://i.postimg.cc/fyLhnsq0/solar-annual-dni-2018-01-1.jpg)
Sengupta, M., Y. Xie, A. Lopez, A. Habte, G. Maclaurin, and J. Shelby. 2018. "The National Solar Radiation Data Base (NSRDB)."
Renewable and Sustainable Energy Reviews  89 (June): 51-60.


Is 2000 watts just a ridiculous expectation for my 400 watts of solar? Or does that just mean I need more batteries to make the most of the 2000W? i.e., fewer batteries would discharge quicker with that kind of load?

That is the general idea but again start thinking in terms of energy both from a charging and discharging perspective. Your energy into the batteries must exceed the energy drawn from the batteries in order to overcome inefficiencies in the battery charging and the converting of battery power to AC.

The battery also needs to be able to deliver the peak power needed for the inverter and the load. A 2000 watt load translates to 95 to 100 amps at 24 volts out of the battery. Just like starting a car, that type of load will quickly drain a battery. You may only get 166 watt-hr of AC energy if the battery can only do this for 5 minutes.

If I wire the panels as a 24V array, 2 in series and 2 in series and then the two pairs in parallel, do I use that current rating as the input for the charge controller? Wiring as 24V means I can get by with smaller wire, between and from the panels to the charge controller? 10ga? 4?[

It generally works out best to put the panels in series up to the allowable voltage of the charge controller. The controller you reference appears to support 100 volt strings so you could put all four of your panels in series. Then check the amperage. If your entire string is in series, it will source less than 10 amps. Unless you have an unusually long run from the panels to the charge controller, 14 gauge wire would be more than sufficient. Use 12 gauge if your budget can support it. Check that the terminals on the charge controller can take the gauge your choose. Respect the potential voltage levels and wire it as if it were normal house wiring.

Don't forget to do your research on the RFI generated by the charge controller and the inverter if you have any hopes of using radios in the vicinity of the installation.

- Glenn W9IQ
Title: Re: Building a small solar system
Post by: KT4WO on March 01, 2022, 04:59:00 AM
Glenn posted alot of good info. Take advise from someone
who has "been there, doing that"   
What ever the size you decide you need----
DOUBLE IT!!!
I came up with a 400watt system just to run a few radios,(back-up)
and it did work but not as long as I thought it would.
All the numbers used to size a system are for "A good day"
Just when you need it....you will have 30 BAD days!!! and no/little
power when needed.
Really---- Double the size you think you need!
Title: Re: Building a small solar system
Post by: KG4RUL on March 01, 2022, 05:25:12 AM
Something to Consider
+++++++++++++++++++++++++

SOLAR POWER IS “DIRTY”

Solar power is not “clean” power.  The manufacture and disposal of photovoltaic panels produces enormous amounts of toxic waste.  Among these are:  Cadmium compounds like Cadmium Indium Gallium (Di)selenide, Silicon Tetrachloride, Hexafluoroethane and Lead.

The production process of manufacturing solar panels is energy-intensive and polluting.  The process starts with mining of quartz sand. An oxidized form of silicon, non-crystallized silica, is the most common component of quartz sand.  Silicon is a perfect material for photovoltaic solar cells because of its ability to conduct electricity even at high temperatures, making it the most commonly used material in photovoltaic systems.  But in order to get silicon in the form required, it has to be treated in a process that pollutes the environment and releases greenhouse gases.

Solar panels do not use water to generate electricity, but the manufacture of solar components and their maintenance does require water.  In fact, the amount of water required for large-scale solar farms can reach as high as 396 million gallons during the installation process and 6.8 million gallons a year for cleaning.  Water is also used during the manufacturing process; water works as a medium to chemical reactions. The outcome of these reactions is water contaminated with chemicals like hydrofluoric acid.  Careless disposal of such wastewater poses risks to our fresh water sources.

Solar proponents claim that panels can be successfully recycled.  The reality is that if a recycling plant carries out every step, by the book, their products can end up being more expensive than new raw materials.

Approximately 90% of most photovoltaic solar modules are made up of glass that often cannot be recycled as float glass due to impurities including: plastics, lead, cadmium and antimony.  That glass is often disposed of in landfills where pollutants such as lead or carcinogenic cadmium can be almost completely washed out of the fragments of solar modules over a period of several months, for example by rainwater.

There are firms that may advertise themselves as "solar panel recyclers" but instead sell panels to secondary markets in nations with less developed waste disposal systems.  Governments of poor and developing nations are often not equipped to deal with an influx of toxic solar waste, leaving poor and developing nations are at higher risk of suffering the consequences.

The truth is that solar panels create 300 times more toxic waste per unit of electricity generated than nuclear power plants.   If solar and nuclear produce the same amount of electricity over the next 25 years that nuclear produced in 2016, and the wastes are stacked on football fields, the nuclear waste would reach the height of the Leaning Tower of Pisa (52 meters), while the solar waste would reach the height of two Mt. Everests (16 km).

While radioactive waste is strictly monitored with precise steps for its disposal, the regulations of solar technology disposal are sorely lacking.

In the end, in addition to the trail of toxic waste that follows them, solar panels do not produce electricity at night, or as much when it is cloudy, and in northern climates, none when they are covered with snow and ice.  When they do produce power, there is no economical way to store excess power for later use.  And they make little economic sense, unless heavily subsidized.
Title: Re: Building a small solar system
Post by: K5LXP on March 01, 2022, 06:42:19 AM
Some really good responses here out of the chute, including RUL's.  Just wait until spent lithium batteries from all the electric cars kicks in...

To the OP's question, all of this discussed so far is the "means", but in order for you to assembly a functional system you have to know what the "end" is.  What would the "ideal" system do for you, specifically?  Points to ponder:

What equipment do I want to run? What would be the minimum and maximum loads to expect?
How long does it need to run - hours, days, weeks?
How long, with no sun (clouds/snow)?

What you end up with is a load profile of minimum watts times x minutes per day and a maximum watts times x minutes per day.  You can then roll that up to what kind of inverter you might need if any, and the battery storage it will take to run the amps, and amp hours per the min/max/time requirement.  You can hand wave the efficiencies or deep dive into specific equipment profiles if you like, and you think it might matter.

The solar side can be done a few different ways, you've already zeroed in on MPPT which is fine.  Running a 24 or 48V battery as a system choice is OK, but it ties you into always running voltage conversion equipment to step up or step down the bank voltage to run your equipment.  That's fine, it's done all the time but there is a cost and efficiency tradeoff for that.  It may be "less" efficient to charge a 12V battery bank but "more" efficient to run your gear directly off the bank without an inverter or converter.  Then you consider your latitude, season and average insolation for your location, to see what you can reasonably expect for daily/weekly/monthly power (W9IQ's map) for different months of the year (winter is nominally ~1/2 of summer).  You compare that to your load profiles and see how close you are to net positive or deficit power for your operation.

None of this is guesswork, each section of the system can be modeled and most issues revealed with basic review.  I use a spreadsheet which can include as many or as few variables as I choose to include depending on the system goal.  A change to one parameter then gets rippled through the rest of the system and it's easy to play "what if" to dial the net result into a final configuration.

Now, with all this in mind you can also go with slapping a bunch of parts together and seeing how it works.  Most anything will "work", and maybe what you end up with is "good enough".  Don't let "ideal" get in your way, generally something is better than nothing and you'll learn a lot about this as you go.  If some part doesn't work out great then tweak it and see the result.

The only part of your plan I part with is the "rainy day".  Like any part of "emcomm" you have to train and practice or when "all else fails" you likely won't have the result you intend.  Put the stuff up, play with panel orientation, learn about batteries, experiment with different equipment and generally get comfortable running the system in it's deployed configuration.  Once a year for field day or whatever isn't enough practice to be able to set the thing up correctly and know what to do when there's an issue.  If it's in frequent use and you end up needing it, then it's just a matter of using it or relocating it to where it's needed, and it's ready to go.

Mark K5LXP
Albuquerque, NM
Title: Re: Building a small solar system
Post by: W9IQ on March 01, 2022, 08:02:27 AM
Just to give you a starting point, let's calculate the energy that your panels might produce annually assuming you are using them near your home QTH. The average annual solar irradiation for that area will produce 4-5 kWhr/day per kW of panel. Your panels will produce 0.4 kW when illuminated with 1000 watts of solar power. Using conservative numbers:

     0.4 kW * 4 kWhr/day/kW of panel = 1.6 kWhr per day (annual average)

In the worst sun day in December and by titling the panels toward the lower sun, the solar production drops to 2 to 3 kWhr/day:

     0.4 kW * 2 kWhr/day/kW of panel = 0.7 kWhr per day (worst case sunny day)

Since the MPPT converter is not 100% efficient, multiply the above by 90% to the maximum energy available. So annually, your system could produce:

     1.6 kWhr/day * 365 days * 90% = 525 kWhr annually

That sets the absolute limit that your system will produce - the annual energy consumption of all of your loads cannot exceed this number. But as Mark and others have point out, you now need to consider the short term effects due to cloudy days, peak loads, etc.

Just to put these numbers in perspective, a small 4.8 cu ft, energy efficient refrigerator consumes over 200 kWhr annually. That is nearly 40% of the total energy generated by the solar panels without accounting for inverter inefficiency. So on an annual average basis, this should work. Keep in mind, however, that your daily energy production in December drops to less than half of the annual daily average. And if you had to keep the refrigerator running for a cloudy week with little or no solar energy generation, you then need to look at your battery and inverter system to determine if it could supply all of the needed energy.

- Glenn W9IQ
Title: Re: Building a small solar (POWER!) system
Post by: KF7YED on March 01, 2022, 09:50:22 AM
Some great info here to digest. QRM aside, it's been very illuminating, pun intended.

So, a little clarification on the intended purpose: I know it's very limited in capability but the use will be more as a "better-then-nothing" power source for occasional recharging of a few items, I forgot to mention cordless tools before. The reference to the 'fridge was dreaming and not intended to run 24 hrs. 4 - 6 hrs would be nice but the 'fridge would probably be toast anyway so forget that. Same for the microwave: probably toast.

I agree with the point that after the grid falls is the wrong time to learn how to do this, and yes, I'd be playing with it quite a but to see what works and how far. But at some point the electronics, including the panels, will be stored underground in between uses. I have all my surplus gear and test equipment down there now in ammo cans, except when I use them for camping/FD, etc.

So all in all, I'm hearing that I'm kinda on the right track. MPPT, 24V for thinner wire but not crazy thin, as many batteries as I can afford... And nobody really ripped my choice of charge controller and inverter so that might be good to go.

As for location, my best sun spot is beside the south side of my garage and I can put the batteries inside the garage just inside that wall, so that would only be about 10 - 12 ft of cable from the panels to the charge controller. If I mount the controller and the inverter all on one hunk of wood with the attendant fuses, etc., it can be easily disconnected for storage. Same with the panels: wood frame remains in place but the panels come off for storage.

Thanks all. More thoughts welcome. :)

Title: Re: Building a small solar system
Post by: KT4WO on March 02, 2022, 02:32:56 AM

"SOLAR POWER IS “DIRTY”"

Brought to you by BP and Shell.

Solar also caused AIDS and COVID.   Ohhh wait,,,  5G Cell towers caused COVID--my bad.

Title: Re: Building a small solar system
Post by: KT4WO on March 02, 2022, 02:59:15 AM
"And they make little economic sense, unless heavily subsidized."

Oil and Gas are VERY "heavily subsidized"

Tell ya what RUL--  You fire up your "jenny" in your bedroom and take a nap
and I will do the same with my panels. Lets see who wakes up first. 

Also ---that radio you use is full of stuff that was toxic to make and will be
after it's disposed of.  So I guess you should not have a radio.  HAHA
Title: Re: Building a small solar system
Post by: KG4RUL on March 02, 2022, 03:48:22 AM
"And they make little economic sense, unless heavily subsidized."

Oil and Gas are VERY "heavily subsidized"

Tell ya what RUL--  You fire up your "jenny" in your bedroom and take a nap
and I will do the same with my panels. Lets see who wakes up first. 

Also ---that radio you use is full of stuff that was toxic to make and will be
after it's disposed of.  So I guess you should not have a radio.  HAHA

Yes, oil and gas are heavily subsidized.  Never said they were not.  Solar power ONLY makes sense with plans like "net metering" in place.  The equivalent of a retailer being legally forced to buy a product from a wholesaler and reselling it at the same price.

My "jenny" (which is a female Donkey not an electrical power generating device) is outside my home with 250 gallons of propane to fuel it.

AND, I assume that you will be responsibly disposing of all your "toxic" radios also?
Title: Re: Building a small solar system
Post by: W9IQ on March 02, 2022, 05:02:57 AM
Solar power ONLY makes sense with plans like "net metering" in place.  The equivalent of a retailer being legally forced to buy a product from a wholesaler and reselling it at the same price.

While this may have a historic basis, I think this is over-reaching in the current context. With continued cost reductions, solar is now more affordable than ever. In many parts of the country, a home owner can produce solar energy for an amortized cost, without subsidies, that is quite below their retail price of electricity. Where there is still an economic challenge, is with regard to the storage of this harvested energy so as to provide an uninterrupted source of energy for the home. Clearly the advances in battery and other technologies will soon push this past a break-even investment.

As a side note, in Missouri the electric companies are only required to buy back solar energy at their wholesale rate and only to the dollar limit that the consumer has spent with the electric company, sans infrastructure (meter) costs, for that particular meter. The later clause effectively prevents an individual from erecting a remote solar array in order to make a profit. Our electric utilities, especially rural ones, generally aren't interested in solar since the peak demand in the majority of the land mass of Missouri occurs at night.

- Glenn W9IQ
Title: Re: Building a small solar system
Post by: KA4WJA on March 02, 2022, 01:24:08 PM
Rich,
You ask some good questions, and I hope to provide you with some good answers....and, I think I'll also give you even more info than you asked for, if that's okay?  (I promise to try to NOT add more to spin your head even more!)
 
Please allow an honest (if somewhat sarcastic) preface:

--- You can have easy, efficient, and cheap....as long as you only pick two of these!  :)   (meaning, you can't have all three in the same system, no matter what the marketing-hype might imply.....so be prepared to compromise somewhere...)

--- And, please, please don't get bogged-down in the math / engineering in this!  Yes, there is some, but for the most part, if you follow at least some of my recommendations, you can gloss over most of the math/engineering here (at least to start with)....this isn't rocket science, and you do NOT need to spend hours delving into the minutia, yet.  :)

--- Further, unless you have absolutely no shading of any part of any panel, wire them in parallel not in series....and, eat the cost of larger wiring....(see below for details)


1)  First, you must do an energy survey / write-up an "energy budget".....figure out how much energy you need, over a specific period of time, and how long will you need to provide this energy....(even if all you want is to run your frig, do an energy budget, so you will know what you need)

Without this, you're just spinnin' your wheels.  :)



2)  A few specific answers / clarifications here:
I currently have four 100W 12 volt Siemens solar panels. They each put out about 17VDC.
<snip>
I'm thinking of putting together a small system for emergencies using all four panels. Pack it all away in the basement for a rainy day (EMP). I've read articles until my head is spinning so I thought I start a conversation and soak in the ham knowledge here.

As usual, cost is everything and I don't intend to run a welding shop or the whole house on this system. Anything that will support some wall wart chargers for various electronics, maybe a laptop (which I never use except on AC because the battery isn't great). Running a fridge for a while during the day would be an extreme high-end load for this
All the above is understood, and is all very do-able! 
And, it's pretty inexpensive to do....(mainly 'cuz, as long as you don't need to run high-power/high-current devices, you can run some/many things directly off 12vdc batteries, use small/inexpensive DC-AC inverter, and use smaller/less-expensive storage batteries)

or maybe the microwave in the camper.
Hmm....still do-able...
But, due to its high-power/high-current use, it will require a large inverter and larger storage batteries .... (see details below)


Some questions:
Is it even possible to run this 400W solar array directly to an inverter and skip batteries altogether, understanding it will only work in full sun?
Nope, that isn't going to work...(although, in an emergency, you could give it a try....it's possible, but unlikely, that you could force the inverter to work for a short while....but, in the unlikely event that you could get it to work for a few minutes, chances are it would be damaged afterward....so, the answer is a qualified No.)

See below, for details on understanding that this IS a "system", no matter even if you just want it for use in times of emergency (although not on a "rainy-day", as solar doesn't work as spec'd under overcast skies!)....but, 'til you read the details below, please understand that, if you must run some 120vac appliances (such as your home refrigerator) versus running things off of a nominal 12vdc, then you must have some batteries to run an inverter....

And, fyi...you "size" the inverter based on a few major factors:
  a)  the highest load any device you will need to use (frig, microwave, etc.) could draw...
  b)  the real-world capacity of your batteries (and/or solar array) can provide to the inverter, over a specific period of time.


If I have to use batteries, can I use a couple of plain old SLA 12v batteries, maybe 100 Ah each, just because they're cheap(er)? You "could" use any nominal 12vdc battery....but, please understand that "plain old SLA 12v batteries" generally are not designed for extended deep-cycling, and while they'd work for a few cycles in a pinch, for more regular use they'd fail quickly (and will end up costing you many more $$$ than you think)....and, if this system is supposed to "work when you need it to work", then they'd be a bad choice.

Simple fact is this....for least expensive, and very-good capacity, still to this day nothing beats "golf-cart batteries"....yes, a pair (or two-pair) of 6 volt GC2-sized golf-cart batteries are still almost unbeatable in the application of daily-use / daily-charge (or almost daily use 'n recharge)...a typical pair of 6volt golf-cart batteries will provide you ~ 220 - 245 A/H's of capacity for ~ $190, all-in....and, if charged / kept charged and/or used-n-charged daily, they will last you years! (fyi, a local battery shop here will deliver to you a pair of Crown 6v GC-2 golf-cart batteries for $95 each, $190 for the pair, delivered!)  But....

But, of course, these cannot be left alone (not being charged) for months, etc....as they do need to be charged / kept charged,  and maintained (water added) regularly....so, some folks start looking for an "easier" solution, such as "sealed" battery....and, yes, I also have experience with them (sealed AGM batteries)....

A sealed AGM has a much lower "self-discharge" rate, but they do still need to be charged regularly (or better, charged all the time) and make sure they are never allowed to be in partial state-of-charge for more than a day, otherwise their capacity will decline quickly (yes, this is true....despite what the manufacturers may try to tell you when marketing them....have a look at the real spec sheets, manuf recommendations, and their warranties....and, you'll see...they do work, but are more critical to being kept at 100% state-of-charge than simple "flooded" batteries, like golf-cart batteries)
However, in your specific application, if you can get them to 100% charge (and keep them charged) often (daily?), these would be a good choice for you....certainly more expensive than golf-cart batteries, but low-maintenance might trump the cost?  (that's a decision you must make)

Sure, Lithium-Iron-Phosphate (or some other lithium-compound) batteries. size-for-size and weight-for-weight, have higher capacities and can be discharged to much lower state-of-charge, as well as maintain their nominal voltages for greater time period while being used, and can be left partially-charged without serious effect....but, they are pricey and require battery-management-systems (BMS) to maintain perfect cell balance and perfect individual cell-charge, etc...(and while some of these BMS's are included with the batteries, almost all BMS's seem to produce some RFI, many of them produce a great deal of RFI!)

To be clear, most of these newer Lithium-Iron-Phosphate batteries have VERY low self-discharge rate, and can be left alone for months without charging as well as left in partial state-of-charge, without ruining them!
But, as I wrote, they're pricey!  (and need BMS)  :(
So, while they would be a great choice for your application, the ain't cheap!

{are you starting to grasp my preface above?}


How many batteries would make the most use of the 400 watts available or is that a function of the inverter output?  Actually, you need to start your design with the knowledge that this is a "system", not just some various devices wired-together....with sources (solar array, batteries, commercial AC Mains, generator, wind power, etc.), storage (batteries), and MOST IMPORTANTLY the energy "consumers" (such as refrigeration, radios, lights, etc.)....

And, you generally size the "system" according to your energy needs (how much you consume, and over what period of time) AND how much room/space you have for unshaded solar panels (and room/space for batteries)....and, of course what is your budget!!



I have this bundle in my Wish list:

https://smile.amazon.com/Renogy-Converter-Controller-Parameter-Adjustable/dp/B09QKM28H9/ref=sr_1_10?crid=C7V6KSW8P2GY&keywords=mppt%2Bcharge%2Bcontroller%2Bmppt&qid=1646100641&sprefix=morningstar%2Bmppt%2Bcharge%2Bcontroller%2Bmppt%2Caps%2C337&sr=8-10&th=1

I'm not a fan of Renogy....poor QC, usually lots of RFI, and pretty cheaply-made-overall...in my opinion, not reliable enough to rely on for emergency situations...


Couple of questions on that:

Is 2000 watts just a ridiculous expectation for my 400 watts of solar?
In general, yes....
Or does that just mean I need more batteries to make the most of the 2000W? i.e., fewer batteries would discharge quicker with that kind of load?
In general, yes....but, you can run a 2000 watt inverter for very short periods of time (a couple minutes) with smaller battery banks of ~ 250 A/H (see some details, below), but not very advisable!


If I wire the panels as a 24V array, 2 in series and 2 in series and then the two pairs in parallel, do I use that current rating as the input for the charge controller?
Well, yes...assuming your series-connected max voltage is within spec of the controller voltage rating...BUT.
But, unless you absolutely have NO shading of the panels, series-connection is a bad idea!
Yes, I'm aware this is a minority view....but, please understand that the majority of folks' experiences here are in fact with rooftop / barn-roof / out-in-the-clear solar panel installations, where shading is all but nonexistent, so they have no experience with panel shading and/or the negative effect is either not noticed by the end-user (or even worse, the so-called "experts" designing or selling these systems, simply don't care about the end-user's satisfaction, and all they care about is saving $$$ on using smaller gauge wiring)....please see details below (some diagrams directly from the panel manufacurers), before you flame me...


It says "40 AMP" so is that the max it could draw from the panels?
Good question...ask Renogy...
But, in general, no....this is usually the max output spec (max current into the batteries)....
But, since I'm not Renogy, I cannot give you a 100% certain answer about their marketing specs....so, again, ask them....or better idea, buy better controllers!

I know they won't put out that much but is that a specification that's meant to stay under or to make sure I can deliver?
Not sure what you're asking here....but, in general, you size the controller to your panels / array size....I think that answers your question?


Wiring as 24V means I can get by with smaller wire, between and from the panels to the charge controller?
Yes....but, as I write.....unless you have absolutely no shading of any part of any panel, do not use series-connections, just wire them in parallel (and pay for good/proper-sized wiring)....
10ga? 4?
Wire size depends on length (round-trip length) and current that is being carried....so, that's an answer you need to look up on a chart, based on your wiring length and your max current expected (figure 35 amps max...even if you'll only ever see 30 amps out of four 100-watt panels)

Thanks in advance. 73


3)  Next, right after doing your energy budget, please understand that solar panels only produce usable power when they are not shaded!  So, place the panels out in the clear, where they are NOT shaded at all during the peak ~ 5 - 6 hours of the day (local noon +/- 2 to 3 hours), during the entire year....and, if possible, not shaded at all, at anytime of the day, the whole year long!  (fyi, Montana has shorter winter days and longer summer days, than we do down here....and, much lower sun angles....so, judge array size and location accordingly....btw, while you do have fewer hours of sunshine in winter up there, and lower sun angles, too....understand that the panels work great in cold weather!  Cold air temps and clear-skies, especially high-altitude locales, are GREAT for panel output!! So....so, while your sun angles are slight, your air temps are wonderful!)

Trees, etc. shading the panels, will kill your solar output!

And, please note, it doesn't take shading the whole panel to kill its output!!!  Shading just a small part of a panel, will do it!  :(

Have a look here....Here is an image (courtesy of Kyocera Solar) showing the shading needed to reduce panel output by 50%:
(https://i.ibb.co/y4MNgfD/Kyocera-Array-Shading-50-power.png)


And, here is an image (courtesy of Kyocera Solar) showing the shading needed to reduce panel output by 100%....yep, zero output, or darn close to zero!
(https://i.ibb.co/FXjqjWc/Kyocera-Array-Shading-100-power.png)


And, here is a short video (done by some friends of mine, who make MUCH better videos than I do...I'm much better at the engineering, they're better at videography!) which show the above shading in real time, as well as the serious issues / effect of running the panels in series (which is why I recommend parallel, unless you can guarantee they'll never be shaded!)....sure, while running the panels in series does save some $$ on wiring, and can save a bit in voltage drop, in series-wired panels if you have any shading at all, your output is all but zero....so, paralleling panels is almost always best (unless they are all mounted up and in the clear, without any shading)...

https://www.youtube.com/watch?v=1qD3mN8VotQ

Spend the 12 minutes, and watch this video!  :)

So, after you've made-up your energy budget / consumption budget, before you spend anymore time running the math....nor any money at all, nor any more time "researching" this....go outside and find out where you're going put these panels....how are going to keep the shade off of them....(and, keep the snow off of them in the winter, etc.)....how are going to run the wiring....where are you going to put the batteries, charge controllers, and where are going to put the inverter, etc...

You really need to do all of this first....'cuz, until you have all of that figured out, the rest of this is moot!  :(

Then, go and look at your energy survey / energy budget (you can use the power consumption / current draw specs on your devices like refrigerator, etc. and estimate how many hours-per-day that each of those devices will need to operate)....and, then you can start to figure out how much money/time/effort you wish to invest in this.
(I suspect you'll go-for-it, using a much smaller inverter, and even some native 12vdc lighting/chargers/devices....along with a couple golf-cart batteries, and you'll be good-to-go!)

In my life on-board, where everything (except the seldom-used air conditioning and domestic hot-water) is 12vdc (and I cook with propane), we just boil everything down to "amp-hours-per-day" at 12-13vdc.....(abbreviated A/H-per-day, but some just take the short cut and say "amps/day")   But, on-shore, many use "watt-hours-per-day", just be 100% sure you calculate your watts correctly, and understand the losses / efficiencies of any inverters...

 

4)  BTW, just about everyone (including me) now-a-days uses MPPT solar charge controllers....which keep the solar panel outputting at its peak power output while providing the batteries with their maximum possible charge current....this is all good....just remember that the "cheap" ones should be avoided, as they usually produce serious RFI as well as not being as efficient....(I use Blue Sky 2512ix controllers.....but some of the Morningstar MPPT controllers are also good)

 

5)  Rich, please know there is a lot to all of this....but, the main problem for most laypersons is that there is so much BS out there....and, unfortunately some comes from supposed "experts"....and, worse, "internet experts" who may be well-intentioned, but have never done any of this in the real-world...

So, before you spend the time / effort and $$$$ to move forward, have a look at what really works, in the real world....and, that does not include the "local guys selling solar for your house", 'cuz 99% of them are salesmen that have no clue about solar systems!  :(


6)  I hope you don't mind me adding some of my personal experience here....just to show you that there ARE some of us out here that have done this....and, we are willing to share our experiences / recommendations....especially to my fellow hams and sailors....(yes, I know the math / engineering behind all of this....been doing it for decades....but, I also walk-the-walk....meaning I have lived this, in the real world, for decades, not just "a guy who bought some panels"...hi hi...)

While I played a bit with solar as a teenager in the 1970's (and installed a panel here and there, usually on boats....but they were wickedly expensive!!!)....I designed/installed my first professional remote/off-grid solar array in 1984, and while I did a few more land-based systems over the years, most of my solar array designs/installs in the past 4 decades have been on-board offshore sailboats (i.e. those that sail across oceans and stay in remote locales for months, etc.).....and, these days (last 10 - 15 years) it has become fairly easy to generate (and store in batteries) sufficient power to run all basic electrical systems/devices....

On my present boat, my panels / array are now nearing 15 years old....they've survived a few crossings of the Atlantic ocean, a few extreme storms / full-Gales, one serious tropical Storm, and dozens of severe summer T-Storms....out in the hot/sunny/wet/salty environ of the ocean being only a couple feet away!

And, as I wrote....in my life on-board, where everything (except the seldom-used air conditioning and domestic hot-water) is 12vdc (and I cook with propane), we just boil everything down to "amp-hours-per-day" at 12-13vdc....and, as long as the sun shines at least every 3 days or so, my present 520 watts (and ~ 900 A/H of batteries) provides all my on-board power for refrigeration and freezer, all electronics (including navigation, radios, radar, etc.), lighting, fans, etc....(I cook with propane)....this is not camping-out, this is luxury-living on a 47' sailboat (think of this like a 2-bedroom/2-bathroom house, with large living room/kitchen, huge patio, etc....lots of fresh water, cold beverages and hot food....and, I can go anywhere in the world)

While I do plan on upgrading to ~ 750 watts of SunPower panels (and ~ 250 watts of old-school / Kyocera panels), with all new controllers....my current set-up is 520 watts (four 130 watt Kyocera panels), all up in the clear, unshaded....with two Blue Sky 2512ix controllers....all working well.

Have a look:
(https://jerodisys.com/C470/470pix/4711201f.jpg)

(https://jerodisys.com/C470/470pix/4700416f.jpg)

(https://jerodisys.com/C470/470pix/4700101f.jpg)

(https://jerodisys.com/C470/470pix/4700307f.jpg)

(https://jerodisys.com/C470/470pix/4714801f.jpg)

(https://jerodisys.com/C470/470pix/4700413f.jpg)


I do hope this helps some?

73,
John,  KA4WJA
Title: Re: Building a small solar system
Post by: N7EKU on March 02, 2022, 02:01:54 PM
Excellent post John,

Thanks for writing that!

73,  Mark
Title: Re: Building a small solar system
Post by: AC7CW on March 02, 2022, 02:26:10 PM
You indicated that you had read enough to make your head swim already but if you recover and want to zero in on batteries this is the best source I've found https://batteryuniversity.com/
Title: Re: Building a small solar system
Post by: KA4WJA on March 02, 2022, 02:38:20 PM
Mark,
You're welcome!  :)

Btw, just a bit of additional info / clarification..(especially on the Wynn's video)
Trees, etc. shading the panels, will kill your solar output!

And, please note, it doesn't take shading the whole panel to kill its output!!!  Shading just a small part of a panel, will do it!  :(

Have a look here....Here is an image (courtesy of Kyocera Solar) showing the shading needed to reduce panel output by 50%:
(https://i.ibb.co/y4MNgfD/Kyocera-Array-Shading-50-power.png)

And, here is an image (courtesy of Kyocera Solar) showing the shading needed to reduce panel output by 100%....yep, zero output, or darn close to zero!
(https://i.ibb.co/FXjqjWc/Kyocera-Array-Shading-100-power.png)

As much of my personal experience in designing/installing solar arrays in the past ~ 40 years, is with smaller arrays, in space-limited locales (sailboats), shading is the number one issue...so, hence my somewhat strident concern over making sure you get your array out away from shading...
If, you've got lots of open ground / open space, you might think my words are too intense....so, sorry about that!  :)


And, here is a short video (done by some friends of mine, who make MUCH better videos than I do...I'm much better at the engineering, they're better at videography!) which show the above shading in real time, as well as the serious issues / effect of running the panels in series (which is why I recommend parallel, unless you can guarantee they'll never be shaded!)....sure, while running the panels in series does save some $$ on wiring, and can save a bit in voltage drop, in series-wired panels if you have any shading at all, your output is all but zero....so, paralleling panels is almost always best (unless they are all mounted up and in the clear, without any shading)...

https://www.youtube.com/watch?v=1qD3mN8VotQ

Spend the 12 minutes, and watch this video!  :)

When you all look at this video (which is mostly about how much effect shading has on panel/array output, but also has some VERY important info that you can see subtlely), you'll see that they wanted to prove that there wasn't a "panel issue" they changed out their two 160 watt Go-Power panels, for two 140 watt Kyocera panels...the two 140 watt panels should have produced 40 watts (~ 3 amps) LESS power than their two 160 watt panels....but, the two 140 watt Kyocera panels produced MORE power...

Yes, their comment in the video narration is that they believed it was due to a high sun angle...but this still wouldn't make up for such a significant difference (see the minor 10% difference, ~ 1.5 amps difference when they tilted their panels exactly perpendicular to the sun...so, even their own tests don't back up their sun angle assumption)
Then they even changed back quickly (same sun angle), from the two 140 watt Kyocera panels, to their higher output (two 160 watt Go-Power panels)....and, still saw higher output (by only one amp), when they should have seen 3 amps lower output! 
That's a 4 amp difference (20% - 25% difference), in favor of name-brand panels (which, in general are the only ones I recommend).

And, this corresponds nicely to my own personal experience having four 130 watt Kyocera panels....where I've seen 39 - 40 amps out (two different amp meters), under full sun, in low-latitudes (high sun angles)
And, anecdotal reports (I know, not scientific!) of others with off-brand / made-in-China panels producing less, even with higher wattage arrays!


Just sayin'....ya' pays ya' money and ya' takes ya' chances!  :)
(or what was that old Fram oil filter commercial:  "you can pay me now, or pay me later!")


73,
John,  KA4WJA
Title: Re: Building a small solar system
Post by: W9IQ on March 02, 2022, 03:12:48 PM
That video is a typical FB type of 'technical' video. Zero understanding of what they are doing. They cannot even properly differentiate between series vs parallel connection. They base their entire analysis on amps even though they call it "power" on occasion. But most of the time they are quoting "amps" as a comparison of "goodness". Now if they only recognized the differences between panel charge controller technologies.

A technician class licensee should be able to spot the problems with this pathetic video.

- Glenn W9IQ
Title: Re: Building a small solar system
Post by: K5WLR on March 02, 2022, 03:15:23 PM
In order to build a small solar system, you will need a small sun, and some even smaller planets. ;D ;D

Sorry, carry on.... :D :D :D

And 9 of them-including Pluto!!

73 John AF5CC

Pluto just found out he's been demoted, and BOY, is he MAD!  >:(

Please continue, couldn't help it!

Will Rogers
K5WLR
Title: Re: Building a small solar system
Post by: KA4WJA on March 02, 2022, 03:15:45 PM
Oh goodness Glenn....I was 100% certain you'd make a critical comment on my friend's video! 
It did seem to surprise me though....
(yes, I'm aware those are contradictory statements!) 
Guess I was just trying to be optimistic.

Sure, they have no training or technical expertise....but, perhaps you could jump off your holier-than-thou horse for just a few minutes and ask yourself if you could just be kind and generous to some of your fellow men and women....
Not, forever of course....just for a few minutes here...
Just long enough for the original poster here to watch the video and use his own brain and his own knowledge to fully grasp (and criticize) the video himself?
Or, are you assuming he isn't capable of that? 


In any case, Glenn my friend, I do wish you well....I really do....

That video is a typical FB type of 'technical' video. Zero understanding of what they are doing. They cannot even properly differentiate between series vs parallel connection. They base their entire analysis on amps even though they call it "power" on occasion. But most of the time they are quoting "amps" as a comparison of "goodness".

A technician class licensee should be able to spot the problems with this pathetic video.

- Glenn W9IQ

For the rest of you here....if you have some further questions about how-to do all of this, I'm sure all of us here on eham (including Glenn) will be glad to help...


73,
John,  KA4WJA
Title: Re: Building a small solar system
Post by: W9IQ on March 02, 2022, 04:58:51 PM
Oh goodness Glenn....I was 100% certain you'd make a critical comment on my friend's video! 
It did seem to surprise me though....
(yes, I'm aware those are contradictory statements!) 
Guess I was just trying to be optimistic.

Sure, they have no training or technical expertise....but, perhaps you could jump off your holier-than-thou horse for just a few minutes and ask yourself if you could just be kind and generous to some of your fellow men and women....
Not, forever of course....just for a few minutes here...
Just long enough for the original poster here to watch the video and use his own brain and his own knowledge to fully grasp (and criticize) the video himself?
Or, are you assuming he isn't capable of that? 


In any case, Glenn my friend, I do wish you well....I really do....

That video is a typical FB type of 'technical' video. Zero understanding of what they are doing. They cannot even properly differentiate between series vs parallel connection. They base their entire analysis on amps even though they call it "power" on occasion. But most of the time they are quoting "amps" as a comparison of "goodness".

A technician class licensee should be able to spot the problems with this pathetic video.

- Glenn W9IQ

For the rest of you here....if you have some further questions about how-to do all of this, I'm sure all of us here on eham (including Glenn) will be glad to help...


73,
John,  KA4WJA

No matter how much lipstick you put on the pig, it is still a pig.

- Glenn W9IQ
Title: Re: Building a small solar system
Post by: KD0VE on March 06, 2022, 07:09:34 PM
I am just completing a 12KW ground mount grid tie solar system. (plan was to have it done by winter 2021 but I ran out of time before the snow.)

My installed cost is about $16k including oversizing the 220v. feedline and the associated distribution panels so i can add another 12k in the future. Array structure was homebrew, elec feed and panels was by a contractor.

Without the oversize premium my installed cost is $13k.  net cost is $9.62k after the 26% fed tax credit.  payback is less than 5 years assuming no increase in elec rates.

I got 2 turn key bids for comparison, one was $25k and the other was $40k.  The companies doing residential solar are making a LOT of money.

I will likely add a battery bank in the future but the battery technology is changing so rapidly it's probably worth it to wait a bit.  In the near term I'll have a modest bank of flooded lead acid (FLA) "golf cart" batteries they are the lowest initial cost and have a 7-10 year life.  Seems reasonable to expect a better option 7-10 years down the road.

The engineering part was very interesting as there are a lot of tradeoffs and design considerations.  An unobstructed southern exposure ground mount was the simplest and cheapest option but it does require some substantial construction as the panels have a huge sail area.

fun project.  a lot less complicated than antennas.
Title: Re: Building a small solar system
Post by: KK4GMU on July 26, 2022, 06:08:37 AM
In order to build a small solar system, you will need a small sun, and some even smaller planets. ;D ;D

Sorry, carry on.... :D :D :D

Loved it!
God built trillions of them. :o
Title: Re: Building a small solar system
Post by: KF7VXA on August 16, 2022, 07:14:10 PM
I have my basic system, 800 watts solar, Charge Controller, 800AH of LIFEP04 and a 2K inverter. I also have a back up system in a faraday cage that includes another charge controller, BMS and inverter in case of EMP. Panels and the batteries themselves should not be affected by an EMP. I have extra panels also. If I got to the point that the original system were not enough, I can hook up the extra panels to the extra charge controller and then hook that into the battery bank, increasing the charge rate. If not doing that, I'd be charging my other batteries with the back up system to power other things and take the load off the main system. In any case, I'm not powering the whole house. Having extra parts, protected but available is never a bad idea. I also have my small set up for portable operation. One is none and two is one.
Title: Re: Building a small solar system
Post by: KB8VUL on August 20, 2022, 11:17:54 AM
One other thing to consider with solar is grid tying, if available. 
Obviously if you have to be off grid, none of this applies.  But if you have grid power and are doing this for backup purposes then putting in a switch mode supply to assist in keeping the batteries topped off is not a bad thing.  If it's there and available then use it.  Now, DON'T design the system around the grid tie amp capacity, and instead design for solar / wind source capacity.  That way you will be able to run for an extended period with no utility power if that's required.  But having the grid tie will charge you back up quicker from a discharge point if the power is up and down for a while. 

Just a thought.
Title: Re: Building a small solar system
Post by: W9IQ on August 20, 2022, 11:53:27 AM
I have been researching batteries for my off grid solar system. So far, the best AGM battery for the price / warranty that I have found is the 12 volt Renogy AGM200 (200 amp / 20 hour) currently available for $395.99 shipped. The battery weighs 127 pounds.

Can anyone recommend a better AGM battery - either by lifetime, specification or price?

- Glenn W9IQ
Title: Re: Building a small solar system
Post by: K0UA on August 20, 2022, 12:00:14 PM
I have went LiFePO4 in my "tiny" solar system, I got a new charge controller set up for Lithium and took out the gell cells and little controller for them. We are just talking about 4 of the 7 amp hour gel cells in a nice commercial case made just for them which are now sitting on a battery tender jr. to maintain them. but if someone wants them, I would let them go cheap. I really like the Lithium and have two of them in the system a 20 amp hour and a 50 amp hour. I need a bigger solar panel.