Completely Confused Newbie to Solar

What 12 VDC voltage do you want to feed your radios... Most that I have seen require at least 13.8 VDC to output rated transmit power.

An off grid Flooded Cell Lead Acid battery system will generally see a battery bus voltage between 10.5 and 15.5 volts (from "dead" to equalize charging/charging a battery bank at near freezing temperatures).

There are lots of 13.8 Volt HAM power supplies (AC to DC, and DC to DC buck+boost switchers, etc.).

Gets into the whole losses/practical wiring questions of using a DC to DC switcher vs an AC inverter or Inverter to DC power supply.

Another method that has been done is to setup solar for your main 24 volt (or higher) battery bank, and use an MPPT solar charge controller (or other DC to DC buck switcher) to down convert from (a variable) 24 volts to 12 volts and hold the 12 volt battery at 13.8 volts for float charging. And you still have the 12 volt bank for backup power if something failed on the 24 volt side.

As always, actual power usage matters when designing the system... A 100 Watt transmitter will draw ~200 Watts or ~14.5 amps @ 13.8 volts. And most of the time, you are probably listening 95% of the time and only transmitting 5% of the time.

This MorningStar MPPT 15 amp Solar Charge controller has been used in the "24/12" volt battery setup:

You have competing requirements here (what the batteries need vs what your transceivers need)--But you are correct that you need a solar charge controller of some sort to keep the battery bank(s) "happy". Generally, you can only run "regulator free" at 1% of rated charging current for flooded cell lead acid batteries ("float charging"). Anything more than ~2%, you run the risk of damaging the batteries and possibly even boiling them dry and starting a fire.

Generally, recommend a 5% minimum rate of charge for sunny weather/weekend/seasonal usage systems. And 10%-13% rate of charge for full time off grid usage (i.e, 200 AH battery, 5%=10 amps minimum, 10%=20 amps nominal).

The solar array suggested for your 12x 6 volt 225 AH battery bank:

• 12 * 7.8 volts charging * 225 AH capacity * 1/0.77 panel+controller deratings * 0.02 rate of charge = 547 Watt array "float" (not cycling)
• 12 * 7.8 volts charging * 225 AH capacity * 1/0.77 panel+controller deratings * 0.05 rate of charge = 1,368 Watt array minimum
• 12 * 7.8 volts charging * 225 AH capacity * 1/0.77 panel+controller deratings * 0.10 rate of charge = 2,735 Watt array nominal
• 12 * 7.8 volts charging * 225 AH capacity * 1/0.77 panel+controller deratings * 0.13 rate of charge = 3,556 Watt array "cost effective" maximum

A 5% rate of charge array for a fixed array in Pearl City Hawaii (69 degrees from vertical) is 4.84 Hours of sun minimum (December):

• 1,368 Watt array * 0.52 off grid system eff * 4.84 hours of sun (Dec) = 3,443 WH per average December day
• 3,443 WH per day / 13.8 VDC battery bus = 249.5 AH @ 13.8 VDC per December day

Anyway--Some guesses and suggestions from my side.

-Bill

Generating power is generally a game of numbers (sorry for the math--But it does work pretty well at sizing a system for a "known" set of loads).

Regarding wind turbines, in general, you are doing really well if you can harvest 10-15% or so of nameplate rating. There are a few major offshore (Europe 20-25%+??? as I recall) that can do. If we assume that your turbine will do 15%, then:

• 400 Watts * 0.15 of name plate * 24 hours = 1,440 WH per day (1 year average)

Just to "break even" with one 300 Watt tower system and 400 Watt wind turbine (assuming 15% of nameplate);

• 300 Watts * 1/0.15 nameplate = 2,000 Watts of nameplate wind turbine to "break even" with tower computer (no inverter+battery losses included).

And in the case of small wind turbines (not utility scale), a well made DIY wind turbine is probably better than most any you can buy (unless that has changed recently with higher grade systems).

Looking a wind speed average--Seems like 10-12 MPH in decent months average wind... But really need know the V^3 average... Energy harvest from a wind turbine goes with the cube of the wind speed. Most horizontal axis wind turbines seem to start outputting around 10-12 MPH (on a good size 30'+ tower in "clean" / non-turbulent airflow).

I would highly suggest that you get some numbers from somebody that has a Watt*Hour or Amp*Hour meter installed on their system and take, at least, monthly system readings and see what they actually produce.

Today, there are a "ton" of WH meters with very pretty displays:

https://www.amazon.com/s?k=DC+watt+hour+meter&ref=nb_sb_noss

You can get some pretty nice meters in the $20-$50 range--Put one on the source (wind turbine), and another on your loads--And see what is really happening.

For AC, just a simple Kill-a-Watt or similar meter will do fine on your 120 VAC loads:

https://www.amazon.com/s?k=kill-a-watt&ref=nb_sb_noss

Just measure 24-72 hours (1-3 days of typical usage) and see how many WH you actually need for each major piece of gear.

Regarding Pulse Desulfators... Some people swear by them. Others find that they do not really do anything. We have seen a few installations here where the desulfator created enough electrical interference on the battery bus that it confused a couple MPPT type charge controllers (they generated more energy over the day if the desulfator was off). In times past, the desulfator threads were the only ones that I have had to lock because people were so "excited".

The rating of a laptop computer power brick is not really too useful for calculating WH/kWH used per day. The compute may use 30 Watts, but take 85 Watts when running and charging the laptop battery at the same time.

Of course, I do not know what you are using the tower computers for--But if just data logging and such, you might want to try and borrow a laptop (windows/Mac/Linux/etc.) and run it at low power (low clock speed, use one of the, smaller, computers) and see if it can keep up with the load. If the screen is too small, getting an LED HDTV might be a cheap/low power way to get big screen performance with 8-10 Watt draw.

Anyway, the long way around is that energy conservation is going to be key to avoiding spending a huge amount of money on Wind+Solar+Genset backup power.

At a starting point, a 3.3 kWH (3,300 WH or ~ 239 AH @ 13.8 volt) system is what I would aim for as a first time DIY type system (roughly a 2-3 kWatt maximum AC inverter/DC loading). That would be with a battery bank (flooded cell lead acid) that would be 2x your daily (no-sun) load and 50% maximum discharge (for longer battery life).

And, at least at first, look at backup genset that can run for a week (or whatever is your need) when your HF transceiver/emergency traffic loads are.

To size a battery bank large enough to run your "emergency loads" during a hurricane at full needed power (2x tower computers, HF transceiver running 50% transmit, etc.), this is a lot to expect from solar (and many wind turbines are designed for furl/brake at much more than 30 MPH)--Expensive, lots of maintenance, and "wasted capacity" for 95% of the year (solar is great for base loads--8 hour to 24hx7--Not very cost efficient sizing for 5% emergency outages--Unless it is what you need).

-Bill

A 40 Amp MPPT controller will work fine... You have to watch the Vpanel max input voltage (Voc-cold--In Hawaii, "cold" is not usually a solar panel issue unless you are in the high mountain(s)).

For example, a 24 volt battery bank should have Vmp-array, at least, 1.3x the battery charging voltage:

• 30 Volts (charging) * 1.3 = 39 volts Vmp-array minimum

Two of your panels in series is (probably) 2x 17.5 volts = 35 volts. Generally, this means your MPPT controller is really behaving more like a PWM type controller. So, for "12 volt" panels, on a 24 volt battery bank, you really need 3x in parallel (Vmp-array~52.5 volts).

And, many (lower capacity, imports) MPPT controllers have a maximum input voltage of ~70-72 volts. Your panels are probably around 21 volts Voc--3x 21 volts Voc = 63 volts (and in sub freezing climates, Voc and Vmp can climb as much 1.25x Standard Temperature rating). Higher end "typical" MPPT controllers run around 140-150 Vpanel maximum input rating).

So, if your controller is not >~70 Volts Vpanel-input rated, then you can only put 3x of your 12 volt panels in series, leaving 1x unused panel. With PWM controllers, you would have 2x in series by 2x parallel strings and use all 4x of your panels.

HAM and off grid solar power--Another $64,000 question. Yes, MPPT controllers and AC inverters can have tweeters at HF frequencies (in FM bands, RF noise is not as big of problem).

The typical suggestions. No long loops of cables (unless you wrap them in a figure "8). Twisting cables to reduce differential noise.

And a "trick" we used to pass FCC Class A and B, is to use at least 10' of shielded cables from noise sources. The capacitance tends to shunt RF energy back to the chassis of the source (shield/conduit needs to be connected/grounded to source chassis). Over 10' of shielding, does not do much more to reduce RF emissions.

Using small 0.001 and 0.1 Ceramic or similar high frequency capacitors across DC outputs and inputs (to reduce differential noise). Lossy Ferrite Beads and Cores around cables to kill common mode noise--All can help.

Watch for "slot antenna". Roughly a 1/4" slot can transmit a 1 GHz signal. Short with copper foil tape or similar. If I recall correctly, most signals under ~180 MHz come from I/O and power cables. Over that, slot antenna tend to be the radiation source.

In the Old'en days, there were people (Mfg'rs) who believed that Off Grid solar products did not need to meet FCC Class A/B requirements. And there were only a couple of US mfg. who did go for Class A/B ratings for their products. So--Checking for FCC markings on the products was another method of finding "quieter" controllers and AC inverters.

Here is a 10 year old discussion about HAM and charge controllers--Back then, there was only only manufacturer in the US that had FCC A/B... The Xantrex now Schneider MPPT XW MPPT 60 (60 amp) controller.

https://forum.solar-electric.com/discussion/4685/radio-noise-from-pv-system/p1

Today, there are others (Schneider Morningstar units are FCC class B):

https://www.solar-electric.com/lib/wind-sun/XW-SCC.pdf

https://www.solar-electric.com/lib/wind-sun/TS-MPPT.pdf

I have talked with friends (HAM) that said they could hear a Prius coming a mile away on their HF sets. And the new hybrid cars seem to be dumping the AM radio because of self generated noise (and Europe is getting rid of AM band, and less than 20% of US drivers listen to AM... So it is claimed):

https://www.greencarreports.com/news/1098893_bmw-i3-electric-car-quirk-no-am-radio--but-why

-Bill

Yep, you got it.

-Bill

You may want to look for an SSD (silicon storage device) or similar.

Hard drives are very slow (relative to memory chips). If your operating system and or database in the electronic storage, it may speed up your tower tremendously (if your programs are file intensive).

As always, backup what you cannot afford to lose (hard drives tend to throw errors and lose a little bit of data. SSD and similar, tend to work great, then dead).

Bill

Sounds like you have a good handle on what you are doing with your computers.

One other caution... An off grid Deep Cycle Lead Acid storage battery bus can range from 10.5 to 15-16.5 volts (Dead to Charging-Equalization).

Many "12 volt" car adapters are designed (it seems) to run from ~11.5 to 14.5 volts. We have had a few reports here of "12 volt car" to laptop computers have failed when the battery voltage approached 15.0 volts or more.

Having spare "DC power bricks", using DC to DC converters (to 13.8 volt stable power), or using a small/efficient DC to AC inverter--And run the standard 120 VAC computer power bricks--And let the AC inverter (which usually is designed to run to 15.0 and others to 16.5 volts) "buffer" the your electronics from the deep cycle battery bus.

If you are already using a 24 to 12 volt down converter for your 12 volt stuff--Then there should be no issue.

-Bill

They may make more noise... It all depends on their design (and many are open frame switching supplies--You may find you need to make a metal enclosure for them if the noise is a problem.

And for DC, common mode chokes are what normally are spec'ed (both wires go through choke, wired in the same direction).

Single wire chokes don't usually work well for DC power circuits--Most magnetics (lossy ferrites) that are generally available staturate over a few Amps of DC current.

Wrapping both +/- wires the same way through the choke--The opposite current flow creates zero magnetic field (self canceling) and work well at reducing the RF noise.

-Bill