Solar Powering Radios

Your project served to inspire my own interest in starting solar ventures.

I have two different small solar collectors from Radio Shack from 10 or 20 years ago, and have never employed them for anything.

I have a book that says solar collectors can be used as microphones (really!) but with low output. Maybe I'll try that.

The sun feels warm on cool days, and those solar collectors probably feel the same warmth in their own voltic way.

I believe Harbor Freight still sells those 12 volt DC 1.5 amp solar panel units intended for trickle charging vehicle batteries by simply setting them on the dash and plugging into the cigarette/Acc socket.

Those panels are excellent and very easy to daisy chain for more current or voltage. Use steering diodes to isolate and combine.

RFB

I used to get those 1.5 watt panels from HF. The first project I built with them was 2 of them (in parallel) to run a 10 meter propagation beacon (made from a converted Midland 13-882C CB) that was turned down from 4.5 watts to about 1 to 1.5 watts. It also had 2 12V 8aH batteries (in parallel) that would run it at night. The ice storm of 2007 (here in the Mid West, or mid-waste as Carl calls it...) took care of that little project for me...it ran for years without so much as even a glitch...until the blue spruce fell and smashed it and the enclosure to bits (and then it got wet from the melting snow)...but it's fun to see what you can run from solar (and re-chargeable batteries), and it always starts small...good stuff!

Solar is one of favorite things. Now if we could just do something about the problematic battery part. 🙂

Folks recommended the Harbor Freight cells / kits. Those kits are overpriced today. About $4 per watt for film based solar technology that is ho-hum on efficiency. Much better prices and solar brands today.

The good part of the Harbor Freight panels are that they are still slightly productive when sun isn't direct. Throw the controller in the trash and get another one.

Rule of thumb with these panels is say 10 watts max off the 15 watt panel. Get tons of clouds like here or are anywhere much above say North Texas, you aren't going to see much out of these.

With any broadcast gear / repeater you are going to need to do the math to determine the solar watts you need as well as battery storage.

Here's the formula I use:

Watts consumed by gear x 24 hours = ____ 1 day total draw
(example 5 watts x 24 hours = 120 watts)

I then take that total and multiply it by 5. So a 5 watt an hour setup running 24/7 consumes 120 watts per 24 hours. That 120 watts I multiply by 5 = 600 watts.

600 watts is the total daily solar input we are going to need to reasonably maintain our batteries and not get put offline due to cloudy day(s).

Assuming we are working here with all 12 volt, that 600 watts = 50A. To generate 50A in 4 hours of daily sunlight we are going to need 12-13A per hour. This will require 144-156 watt rated solar panel.

Since our total input here per day is 50A our battery needs to be larger than 50A. Ideally, we'd sting 200AH of battery to this so a three day low sun / rain episode would draw our batteries down by 30AH. By doing this we are drawing batteries down by 15%, which should keep the batteries alive and result in longer life of the batteries.

Aside from this, you need a controller. There are lots of interesting controllers these days originating from China that are low cost and high amps. I'd look for something that deals gracefully with fully charged batteries and deals with overcharge/overvolt issue that could result.

If you live in the southern United States, you can reduce these specs some. The solar panel can come down to 75-100 watt range. The batteries can be reduced to around 120 AH.

Thank you Censoredship for
that.

I can see that I am looking
through a keyhole into a
world that I didn't know
was there.

But you've been in that
world for a long time.

Best Wishes,
Bruce, W 60 HZ

Solar is GREAT Bruce. It's just like the broadcast world. Simple formulas, conversions and some rules.

I neglected the part about why batteries are the weak point. Batteries do not deal with temperature spikes at all. Freezing a battery is bad news, as are 100 degree days.

All those range extremes play havoc on the batteries and cause cell failures.

Because of this, the common deep cycle batteries used by many solar folks aren't optimal for outdoor use in unheated/uncooled containment. They will work, like your car works one of these days - remember a battery in there to get things going. However, subject to premature failure and reduced battery life span. Total capacity on these extreme temperature days gets reduced also. Another reason to pack amply larger batteries in your setup.

Solar can be done on the "cheap" to power a low power setup. That is one of my upcoming projects 🙂 How cheap isn't clear until I get gear in place and all the parts operating and do power watt totals.

Bruce, if you are still considering the solar repeater, let me know. Glad to point you to the solar parts to do this cheap.

If it's just repeater you are powering, could probably pull this off with even a 20-30 watt panel. That's super do'able if your repeater is say daytime operating only.

As for Grundig S-350, neat little radios. I am fond of the Eton/Grundig S-250's. Mega low power. I ran one of mine playing AM radio for 3 months I believe it was - 24/7 on, on a low but audible level suitable for same room type listening.

Censoredship,

Let me comment a little bit about the calculations of energy requirements. In order to estimate the battery size and the solar recharging function it is best to work this in terms of energy, not watts. You may have been doing this but your description of your calculations weren't clear.

Energy is Watt-Hours (WH) and is Watts x Hours. So if a transmitter draws 2 watts for 6 hours the energy required is 2x6=12 WH. Now, lets plan, in this example, for an overnight operation of this transmitter. For this to work then the energy which will have to be stored in the battery for 12 hour operation is 12hours x 2 watts = 24 WH. During daylight, the panels will have to provide enough current to operate the transmitter and also to charge the battery for overnight use. Suppose the transmitter draws 167 mA (2 Watts at 12 volts) so the panel will have to supply this current plus enough current to charge the battery by 24 WH over the daylight time. The panel will need to provide 333 mA for this which is 0.333 mA times 12 volts = 4 watts from the panel on average during daylight. From this we know we need a 24 WH minimum battery and a panel capable of supplying 4 Watts (which is 333 mA at 12 V) on average during daylight. Since batteries are specified in terms of Amp Hours (AH) we can convert WH to AH by dividing WH by the voltage so here we need a 24WH/12V = 2AH battery. These are make-believe numbers used just for this example.

This can be ratioed up to your 5 watt example and the results are, for 12 hour light and 12 hour dark, 833 mA or 10 Watts from the panel during the day, and a 5 AH 12V battery. These would be the minimum specs. and need to be adjusted to account for clouds, etc.

I think this is what you were explaining but I am more accustomed to working in WH and AH with batteries and hope this doesn't muddy the waters for you.

Neil

Good rearrangement Neil 🙂

Essentially the same thing.

I run typically straight forward calculations based on the watts. Examples using your numbers:
2 watts x ____ hours this is running = total watts or watt hours (WH)
(i.e 2 watts x 12 hours = 24 WH)
24 WH is 2AH @ 12V power
(i.e. 24WH / 12V = 2AH)

Obviously, I, like most tend to focus on 12V as it's the most common feasible battery voltage and fairly prevalent runtime voltage for many products.

In this 2 watt draw with 2AH total 24 hour draw you would need battery storage of 10AH
(i.e. 2AH x 5 = 10AH)

Less conversion. Batteries are rated in aHr..

Don't forget the 20% loss in lead-acid/sla batteries. If you put 10 aHr. in, only expect 8 aHr. for actual load calculations..

Always figure your battery at 4 times your load. You shouldn't drain a battery (Flooded Cell or SLA) any lower than 25% of it's total aHr. capacity..

For remote outdoor installations, consider the temperature of the battery. Heat will kill a battery quickly and cold reduces the aHr. capacity by as much as 10-15%..

For a 12 v.d.c. system, use the divisor of 17 instead of 12 when figuring panels. This will give you more accurate results with a tiny positive fudge factor included..

Always figure backwards from your load requirements and add 20% to your load to help cover cloudy conditions..

Never overlook wire losses, especially between the panels and the charge controller. You're wanting to charge your battery, not make heat..

Just a few rules of thumb..

Hey Bruce.. Did ya get my PM?

Great rules of thumb @12vman!

Solar controllers are a big part of such a solar solution. I'd say they are only second in importance perhaps to the battery.

Look for MPTT controllers (MPTT is a charging feature).

Also look for auto-cutoff voltage feature. This is important so you don't over-discharge your batteries.

There are a slew of controllers coming out of China that can be had for rather cheap via Ebay most notably. < $30 for a 10A controller.

If you look hard, might even be able to find an outdoor sealer controller like this around $50.

I just purchased a used 2.4 kw. system that included this type of controller. I plan to series, 4 panels in a circuit (5 pairs,20-120 watt panels) and charge 8-L16 Trojan batteries..

http://www.windsun.com/ChargeControls/MPPT.htm

One of my installs was a Rangemaster ~300 ft. away from the house. I fed audio/power to it through Cat-5. I converted my 12 volts up to 24 volts to overcome wire losses. The Rangemaster only drew ~120mA. My audio level was earphone level from a small battery powered mixer. It worked fine. No problems feeding the Rangemaster with 24 v.d.c.

Had another set up using a SStran. Put a FM radio rcvr inside the weatherproof box to get the tx audio for the AM. Broadcasted on FM from the house with a DataKit FM xmtr. (stl) The power supply for the SStran was totally seperate from the house supply. (No wires between the house and xmtr) 96 watts of panel, charge controller and a small marine battery @ 12 v.d.c. (overkill but..) The FM rcvr in the box with the SStran needed 6 v.d.c. I used an LM7806 to power that. Worked fine.. Last long time.. 😉

My love chunks just bought me a Ramsey 25B for my birthday! I plan on broadcasting XM all around the house. I have a seperate solar system built for my porch and outdoor lighting. I have a kick butt stereo system built-in to the porch. Now I can easily listen to my Deep Tracks any time I wanna.. Gotta luv 'er..

Quite the system there 12vman!

The Outback controllers are nice. Out of the price range of many of us, especially for Part15 use 🙂

I'm looking at doing a transmitter site with tentatively 100-200 watt panel included in the antenna stack and a battery cabinet near ground level. Getting fancy on that proof of concept.

Are you currently broadcasting with the setup you described?

Not tx'in Am right now. I still have everything. Even some of my copper is still in the ground. Had some dozer work done and tore the area(s) up that I was using. I'll get it up and running one of these days..

I am doing some FM around the house. My sweets got me an FM 25B for me birthday! It should arrive next week. I've been wanting one for a year now. I'll put my J-Pole back up and see if I can cover my 10 acres..