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Author Topic: Solar Power for remote operation  (Read 1270 times)

Posts: 5

« on: April 02, 2018, 02:44:28 AM »

Hi all.

I have read a LOT of articles about Solar Panels for remote operations and oh boy...what a controversial subject (!!).

I don't think I ever read another subject with so many people having different ideas and different approaches even with complete different ideas.

So, my question here is pretty simple and don't want to go into the details of how the system works as I already have a good idea.

I have a simple HF rig with 100W operation in SSB.  Also already have a 35 Ah lead acid battery. 

What type of solar panel and watts I need from the panel to keep the battery on 13.8Volts (min), assuming a sunny day, for a regular operation of the radio remotely ?  I know a need a regulator as well.

Can anyone give me ideas of brands, where to buy, prices, quality, etc ?  What is your experience with solar panels for HF SSB radios ?

Thanks a lot

Posts: 321

« Reply #1 on: April 02, 2018, 06:14:16 AM »

that 100w rig could pull above 20A at full stick,
& so your 35Ah battery won't last that long.
you can get 150w / 250w /300w panels:
and you could buy those panels at any camping shop,
but you need to watch the Quality of them, especially if you plan on carrying them anywhere.

if you know of anyone traveling to Melbourne:
is a reputable supplier of Ultralight Solar Panels

Posts: 1565

« Reply #2 on: April 02, 2018, 06:35:24 AM »

At 100W the 35ah battery has a short operating life since most 100W radios
require about 20A at full power out.  It can support the radio in short bursts if
there is adequate recharge capability.   With no solar charge that battery is
likely down to 12V within hours just receiving.  Very few 100W radios draw
less than 1.5A o receive (some old full analog transceivers might, but
remoting them is unlikely.).

Your remoting hardware is that also running on battery?  That needs power and
may not be frugal on power either.

So adding solar means adding enough to support the required operating time
and that is likely more than many believe.

The amount need to be great enough to recharge the battery between
transmit sessions.  It needs to be greater if there are clouds or shadows
that decrease output.  I will assume you have excellent weather meaning
it is rare there is rain or other weather events that mean a day or more
without sun.

Since you want voltage support that means you need enough amps out of the
panel to hold the battery up.  That puts the lower limit at maybe 6A.
You always want to be charging the battery and most 100W radios key down
no power out consume 3.5 to 4A and even at 5W out may easily hit 5-7A.
Your upper limit is about the batteries C/3 rate or 11A as more than that will
boil the battery dry, charge controller cannot fully help that.  So 11A of solar
would require about 140W of solar.  Even with that you cannot guarantee 13.8V
will be sustained, maybe 12.6 is possible and within what most radios require.

I believe you truly need a larger battery, 60ah is still too small but better.  
the problem is as the battery gets bigger you need more solar to insure it
is being fully recharged.    The other part is that 12V batteries have a
voltage of 12.6V when the surface charge is used up.  Only automotive
systems and bench power supplies are 13.8V.  So in reality you need
to stay at 13.8V +- 15% or above 11.6volts and that is at the back of
the radio power connector as cables contributes to lower voltages
unless very thick.

If you try to do it with undersized battery and solar it may work but the
duty cycle (transmit to receive time) will be very limited.

While my station is not remote it is off grid and runs 100w sometime for VHF
contesting 200W.  To do that 400W of solar and an industrial 150AH NiCd
battery do the job (nearly 160 pounds).  That is combined with a MPPT
charge controller that is also has to be radio silent, I could not buy one
so I made my own.   The NiCd have a discharge voltage 1.25V so 10
of them net 12.5V.  With a charge current  of about 4A 13.6 is maintained
for intermittent operation and 13.0 for extended.  FYI 400W can easily
supply 23A (27A with MPPT controller) but cannot run radios directly
due to the panels high internal resistance and wide swings in terminal
voltage. That is why a big battery is required.  Also big fuses!  That's
what is needed to support a station that does weekend long VHF
contesting in the winter of New England (about 5 hours of direct
sun (insolation) useful for charging.).  



Posts: 12629

« Reply #3 on: April 02, 2018, 07:06:32 AM »

At 100W the 35ah battery has a short operating life since most 100W radios
require about 20A at full power out.

Exactly how many rigs have you actually test vs quoting spec sheet that show worst case scenario at 15.9 volts (15% or 13.Cool Many seem to not understand this at all. Typically you will draw about 10 to 15% LESS than max rated draw in specs. Also the lower the supply voltage the less the draw because most of rig is powered off a regulated internal suply of 10 volts or less and excess input voltage is lost to heat in regulators,

 So in reality you need
to stay at 13.8V +- 15% or above 11.6volts and that is at the back of
the radio power connector as cables contributes to lower voltages
unless very thick.

As above you want to stay at 13.8 or LESS (less is better for longer charge life because current drain is reduced. Also bear in mind that voltage spec is at rig input terminal not at supply so if you plan to be able to draw voltage on battery to under 12 volts and want good rig operation use a larger diameter power cable than normal to reduce voltage drop with battery voltages at or below 12 volts. As stated above most of rig operates off a regulated power supply of 10 volts or less so a lower average supply voltage will reduce internal power losses in regulators. Furthermore, do not worry about maintaining a full 100 watts out (some are very anal about this) even a drop to 85 watts or less as supply voltage drops less than 1db loss in signal strength which is a none issue. (though some will try to claim it is) So letting voltage drop and output drop some REDUCES battery draw and extends useful charge life. The last thing you want to do is to use a battery voltage booster for rig because it increase power draw because of losses in booster and additional losses in rig from internal regulators.

One more thing, for serious remote solar power use, a 35 amp is too small for a few reasons. First of all you will only get 35 ah at rated 20 hr discharge rate and a draw to 10.8 volts too neither of which you will do so your 35 ah battery is closer to a 20 to 25 ah battery at most. You really want at least a 100 amp rated battery here for reliable operation when sun is not available.

Ham since 1969....  Old School 20wpm REAL Extra Class..

Posts: 2575

« Reply #4 on: April 02, 2018, 09:02:15 AM »

I have done these types of calculations professionally for commercial/industrial applications where someone would be exceedingly unhappy if radio communications was lost due to a poorly designed system. You can do the power budget by hand. Here are the factors you need to consider;

Transmitter duty cycle (minutes per hour vs current draw)
Receiver duty cycle (minutes per hour vs current draw)
Charger efficiency (inverting chargers are more efficient than linear devices)
Battery efficiency (to take a charge)
Temperature derating of battery (at higher temperatures batteries derate, charging also heats up a battery)
Age derating of battery (as batteries age (1-2 years) their capacity is reduced)
Solar insolation due to seasonal effects of sun angle
Sun-hours per day (for winter, and for summer. In fact run calculations for each season also considering temperature derating on the battery)
Solar panel losses due to dirt (usually some percentage like 5-15%)

You want your battery capacity to be great enough for the radio system to operate for at least 36 hours of no-charge (that assumes one day where you do not get any charge at all, plus another night cycle). For critical applications you may increase the battery capacity requirements to 72 hours of no-sun.

There are on-line calculators to help you out. You can determine the accuracy of these calculators by reviewing if they take these factors in to consideration.

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
Free space loss (dB) = 32.4 + 20 × log10d + 20 × log10 f

Posts: 1565

« Reply #5 on: April 02, 2018, 10:08:15 AM »


As far as spec or other criteria its not an of extreme importance unless one is being pedantic.  For the purpose
of sizing a solar system, it is not that fine grained, too many variables.  You need a lot of battery to have solid
terminal voltages and fat wires to the radio or resort to voltage conversion.

The other factor is 13.8 is something that only power supplies and cars have. Lead acid tech is nominal 12.6V.
so for all practical cases your close to the minimum to start with and as you said when you draw more current
matters get worse.  The only fix then is some form of voltage conversion to correct for that or a radio that tolerates
low operating voltages.

Hence, maybe the controversy he mentions.

We agree, a 35ah battery is way too small.  I've done it with solar support and got
by but that was daytime only.  The battery for all intents was a buffer between the
panel and near useless for any length of time without solar support. It was short
term thing for a test.  That and someone else paid for the battery so maximizing
its lifetime was not a worry.

That is why my off grid system uses a larger 150Ah NiCd (the other is I got them free
in near new condition). They have a higher terminal voltage under large loads.  Not
everyone can be that lucky.  Otherwise it would be a 60AH AGM, in a 24 volt system
so I could utilize the battery discharge deep enough to use maybe 60% of the
useful watt hours without killing the batteries too quickly with deep discharge cycles.

If I were doing it from the ground up I'd go with a 48 or higher voltage system, technology
has improved to make that much better approach.  That and high power 24 and 48V
solar panels go cheaper (per watt).

That leads to the alternate way to do this is lots of low AH batteries in series...  APC does
this in their large UPS systems.  With efficient down conversion it works well.  

There are many ways to approach a solution.  The 12V battery is tough case as
I^R losses at high currents are problematic, discharge rates can be limited, and
terminal voltages tend to  less than optimum.



Posts: 12629

« Reply #6 on: April 02, 2018, 12:18:41 PM »

If I were doing it from the ground up I'd go with a 48 or higher voltage system, technology
has improved to make that much better approach.  That and high power 24 and 48V
solar panels go cheaper (per watt).

This has some merit but I think I would lean toward 24 volts. 24 volt inverters and chargers are cheaper than 48 volt yet provides a better power to current ratio and less voltage drop as a percentage of supply voltage than 12 volt systems. Also you would only need to series two 12 volts batteries rather than 4. Some large construction equipment and some large trucks are 24 volt too which means there would be off shelve 24 volt lighting options too.

Ham since 1969....  Old School 20wpm REAL Extra Class..

Posts: 589

« Reply #7 on: April 02, 2018, 02:45:27 PM »

We agree, a 35ah battery is way too small.  


That is why my off grid system uses a larger 150Ah NiCd (the other is I got them free
in near new condition).



Of course, if you got them free, use them.  But for anyone reading;  NiCd is about the worst possible choice
for Solar Storage you could make.  NiCd suffers from a memory effect.  Repeated cycling of less than full
discharge and recharge will permanently reduce the capacity of the NiCd.  And this is exactly what a Solar usage
profile is.

Then, let's talk about battery choice and capacity;  Standard lead acid and AGM, as correctly shown by Allison, is
already close to voltage limits.  And since any discharge below approx 10.5 volts will damage a lead acid battery,
you are really only going to get approx 17 Amp hours out of a 35AH lead acid battery (Half the capacity, twice the weight).  

This is the reason that many people are saving up and spending more on Lithium Iron Phosphate cells;
LFP cells have a very flat discharge curve, keeping voltage up for most of their cycle, and then dropping rapidly.
Unlike regular Lithium Iron, that has a lifespan of approx 250 cycles (charge/discharge), the Lithium Iron Phosphate (LFP)
cells are good for at least 2,000 cycles.   LFP cells are also the safest of all Lithium chemistries, and are not prone to
thermal runaway like standard Lithium Ion, or the dreaded dangerous bombs called LiPo (Lithium Polymer) used by the RC industry.

Some of the posters tried to show calculations and variables, but I found these exercises relatively useless for Ham needs;
Your variables will be far different between calling CQ, or receiving and hunting for a signal, or having a rag chew, or doing
field day contesting.   Your duty cycle variables again change between SSB and Digital modes like RTTY, PSK31, or FT-8.

I played with a lot of combinations, and what I like to have is approx 2 or 3  100watt solar panels feeding an MPPT controller
in series (higher voltage, less voltage drop, smaller copper coming from the panels).  The output of the MPPT controller is
then feeding us 12 volts, ranging from 10 to 17 amperes, recharging the battery.  Assume, based on changing time of day,
some occasional overcast, and other variables and lies, that you will get between 50 and 75% out of each solar panel.

For field day style experimentation, I just lean my solar panels against cardboard boxes.  The cables are all quick-connect.
It takes 5 to 10 minutes to set it all up with the controller and the battery.

To ask what size battery is going to be OK, you really need to know what the user wants to accomplish?
For example, someone  wanting to operate during the day could use that 35AH battery, because at less than 50% duty cycle,
they are always getting at least 10 to 15 amperes from the solar panels to rapidly replenish the battery.

On the other hand, someone wanting to stay up all night running digital modes and pushing 100 watts into a compromise antenna
for FT-8, they might need a very much larger battery bank.  But then, someone who runs digital only, and never pushed more
than 25 watts, might need a lot less battery.  Especially if they search and search and answer CQs, rather than endlessly calling

Since the usage model and time of day can be so variable;  I personally found there was no substitute for experimentation.
PWM solar charge controllers SUCK EGGS.  Switching to a MPPT controller was worth every penny and extracted more than twice
the output from the solar cells.   The first time I used an MPPT controller, it was a Jaw Dropping experience.  You will never touch
a standard PWM controller again :-).

Back to my specific setup? During the day, I never quit having fun (on digital) with a 40 AH battery.   Night would be an
entirely different game.   Maybe 200AH that charged up during the day would last until morning?  But maybe a single 100AH
battery would yield fun at least until midnight?  Again, try it out.  Your usage and setup will not match anyone else's.

Depending upon SSB, AM, Digital, time of day, type of rig, how much power needed?   Just try it out
and play.  You might find it works very fine.   But avoid those garbage PWM charge controllers.
MPPT is the gold standard.  You get what you pay for.

A caution about Solar Panels;  They can all look the same, but they perform WILDLY different.  The industry silicon fabricators
test their cells coming out of the batch; and they sort them into grades A, B, C, and D.   A lot of resellers on Amazon and eBay
are selling grade B and C cells.  You do get what you pay for.   We bought some grade A panels (100 watt, Monocrystaline),
and some grade B or C panels to test.  There was more than a 50% difference in output power, really.
[Hint:  If the seller does not claim Grade A cells in writing, they are NOT going to put out published spec :-) ]
Make sure you buy from a local country supplier, who will accept returns if the cell does not meet specs.


« Last Edit: April 02, 2018, 02:52:07 PM by N6YFM » Logged

Posts: 5483


« Reply #8 on: April 02, 2018, 04:48:57 PM »

What type of solar panel and watts I need from the panel to keep the battery on 13.8Volts (min),

Looks like about a 300W panel, plus.  For that terminal voltage, you need a panel that will supply 100% of the load.  You will never use any of the capacity of the battery, because 13.8V is the float voltage.  A lead acid battery does not supply any of its capacity until a terminal voltage of 12.78V at 100% charge.

Mark K5LXP
Albuquerque, NM

Posts: 1565

« Reply #9 on: April 02, 2018, 07:39:12 PM »

>>>Of course, if you got them free, use them.  But for anyone reading;  NiCd is about the worst possible choice
for Solar Storage you could make.  NiCd suffers from a memory effect.  Repeated cycling of less than full
discharge and recharge will permanently reduce the capacity of the NiCd.  And this is exactly what a Solar usage
profile is.<<<

Depends on usage.  With NiCd I can run them hard and they like it.  When I
did that to lead they would fail faster then I liked.  Lead does not like a deep
discharge at all.  I also had to pull more amps to run a upconverter to
overcome the terminal voltage issues.

The only factor that really counts is lousy charge efficiency when the charge
is above 80% range.  These are the large wet (Alcad L series) where
60% of the battery is electrolyte.  These are not sealed NiCd AA/C/D cells.   
I have no qualms about knocking them flat, though its hard to do.  They
tolerate overcharging well with only higher water consumption as a
negative (hydrogen production) issue.   Testing after 5 years I have not
seen memory issues.   Normal use in the evening does take out a bit. 
Full charge voltage is 1.51V cell (15.1) which helps (though that means
topping with water once a year). The voltage is fairly flat at loads to 40A,
that's radios, VHF amp, LED lights and computer.   They are seriously
rugged and have a lifetime that has exceeded any lead I've had before
them, by several years.  They ran the back up radio system for the local FD
and test like new.

When I contest I use solid state 12V amps and run them hard for 6 and 2M
to the 150W level or higher never had an issue with them.  Other than the
10 of them weigh in at about 160 pounds! 

If wishes were puppies, yes, LiFeP04 would be the thing.   I use
lithium tech for small batteries to 11AH, its lighter.  Save for finding
a charge controller that I can hear over.  MPPT can be very noisy!
I like MPPT performance but on the low bands the racket those I've
tried is bad (still looking).  The other thing is where to put them.
Outside is safer, save for this winter we hit -20 and the summer
can hit 100 both are bad temps to charge Lithium tech at.  Indoors
is out of the question for something like that but they need a
controlled temp range.

I have tested a system around four 12V 8Ah gel-cells, four
20W panels each with a cheap Sunsaver controller per battery.
and a 48V 150W switchmode downconverter to 13,8V.   It
tests good for over 300WH on a load and regulates well to 12.5A
(power supply current limit).  Switching noise required a
diecast box and a lot of ferrite and Corcom filters to tame. 
The system could scale well save for the downconverter
48V and high power (300W plus) are scarce and not
cheap compared to the 150W unit.  The 48V systems
are getting more typical of Marine use.  Lighting Voltage
is not an issue as you either go up to 120V or down to 13.8V
and use common material.  Scaling up looks to be workable.

When it comes to batteries...
From cheap to very costly.... Lead, industrial NiCd, LiFePo4
Performance its exactly the other way around.  The issue is
safety, charging, space, and availability.

There is also the saltwater cells by Aquion but they tend to work
better for really big systems. The smallest is 2.2kW! They are
not cheap.


Posts: 872

« Reply #10 on: April 02, 2018, 07:40:57 PM »

Hi Neal,

For NiCd batteries, it depends on what type you have.  I would guess that you are speaking about sealed NiCd cells as used in consumer devices.  Considering the size Allison quoted for hers, it is most likely a flooded wet cell type.  These are very durable and can take deep or even negative discharges without damage.

Reading on Wikipedia, some call the memory effect an urban myth.




Mark -- N7EKU/VE3

Posts: 653

« Reply #11 on: April 02, 2018, 10:21:35 PM »

And now for an alternate answer that may also work...

Honda EU1000i (or Euro equivalent) inverter generator.  29 lbs, 900 watts continuous, 1000W peak, very quiet.  RF spurs, such as they are, easily tamed with some ferrites and not a problem at all on higher bands.  For my loads, easily runs 5 hours on 1/2 gallon of gas (about 400W continuous).  Very quiet.  Easy to maintain.  Rock solid reliable.  If you have access to SOME fuel, its the way to go.  Once you add up solar panels (4x100W, about $500), MPPT charge controller (about $160) and battery (cheapest and not the best is a 100 A/H SLA - $160), you've already exceeded the cost of this unit.  And the running fuel cost is tiny.  So if you have just a little access to fuel, you are good to go.

BTW- I have solar, too, just for kicks:

4 x 100W LightCatcher monocrystalline Grade "A" solar panels:  (EXCELLENT PRODUCT)

1 x 30A SolarEpic MPPT negative ground charge controller with remote monitoring head (works fine, noise not too bad in my application):

1 x Universal 100 amp-hour sealed AGM lead-acid battery (not too good, but it was free):

Samlex 300W true sine wave DC to AC inverter (efficient, works great but still gulps plenty of amps): PST-300-12, or the poor-power-factor tolerant version:  SA300112

From about 10:30 AM to about 3:30 PM here in sunny SoCal, this system can provide 20-25 amps at 14 volts to power an HF rig, accessories and a computer with no problem at all.  It's basically an Astron 35 run by the sun.  BUT... when the sun goes down or clouds drop by, the battery has only about 50 A-H (at MOST) of usable capacity before it begins to lose charge/recharge capacity.  And, as Allison (KB1GMX) rightly pointed out, the voltage droops with use and starts out low, so better have a rig that does not drop out until you hit about 10.5-11 volts, or operate at reduced power out.   Neal (N6YFM) points out that LiFePo is a way better choice from a usable capacity standpoint, at least in SoCal's moderate temperatures.  But at a very steep cost - about $450 for 50 USABLE A-H.

Allison:  Sounds like you have a fine solar installation and lots of practical experience.  Nice battery bank - but the type that is VERY expensive new.  The equipment I design professionally ran off of very similar NiCad cells, until we switched to Li-ion.  They are very tough and very reliable.  If you can get them used/good, that's the way to go.

Brian - K6BRN

Posts: 5

« Reply #12 on: April 03, 2018, 03:03:18 AM »

Thanks a lot for all your replies. a 35 Ah battery is too small ?   But I am not a radio station and will not leave the mike open all the time. Probably will be talking 1//3 of the time and listening the rest.

I know that this guy is quite controversial and have read many negative comments about him. I have nothing against him, actually really like his movies.  He uses a 35Ah battery with a 120Watt solar panel and is doing very well.


Posts: 12629

« Reply #13 on: April 03, 2018, 04:34:03 AM »

A single 35 ah is too small. You have to remember that your 35 ah is really only about 20 ah usable because as stated earlier, that 35 ah rating is for a 20 hr discharge to 18.0 volts not for higher rate discharge to 11.5 volts or so. Since you have a 35 ah battery you could buy another and put them in parallel. This will actually give you a bit more than double the usable capacity of a single one because when combined the load is split between them and the reduced rate of discharge improves efficiency and  reduces voltage drop under load per battery. You are likely to get 45 to 50 amps usable from two batteries. Remember a battery is not like a glass of water in that that glass of water yields same amount no matter how fast you empty it, your 35ah battery does not.

Ham since 1969....  Old School 20wpm REAL Extra Class..

Posts: 168

« Reply #14 on: April 03, 2018, 05:40:52 AM »

If weight and size and efficiency aren't problem, but temperature extremes and the ability to withstand misuse are, it could be worth considering the NiFe cell. Apparently some solar installations use them.....
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