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pi-tastic
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12v battery + 25 watt Solar = always powered 4B?

Wed Sep 11, 2019 6:11 pm

https://www.harborfreight.com/25-watt-s ... 63940.html
and
https://www.walmart.com/ip/EverStart-Le ... S/49988441

with a buck converter 25watts at 5v is 5amp.
so it can run the 4B and charge too during the day.

then in the night can run from battery.

Seems like a setup that can have some ROI rather quickly. + many LCD screens should already accept 12v.
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pcmanbob
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Re: 12v battery + 25 watt Solar = always powered 4B?

Wed Sep 11, 2019 6:23 pm

The biggest problem is that you are unlikely to get a full 25W from your solar panel unless you live in a very sunny climate.

From my own experience in the UK with solar panels on my house I rarely average more than 60% of there total output in the summer and considerably less in the winter.
Last edited by pcmanbob on Wed Sep 11, 2019 6:23 pm, edited 1 time in total.
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davidcoton
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Re: 12v battery + 25 watt Solar = always powered 4B?

Wed Sep 11, 2019 6:23 pm

There are several threads around here which discuss this.

Basically a 25W panel will only produce 25W in good sunlight -- less than 12h a day even in the tropics.
Allow for bad weather, conversion losses, winter, etc, etc, and you end up needing a much bigger panel and an enormous battery.

The link doesn't specify the battery capacity, but marine batteries are designed for intermittent high current, not regular low(ish) current.
Also, note the operating temperature range -- does that suit your location?

YMMV.

EDIT: typo, insert "not"
Last edited by davidcoton on Wed Sep 11, 2019 10:10 pm, edited 1 time in total.
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pfletch101
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Re: 12v battery + 25 watt Solar = always powered 4B?

Wed Sep 11, 2019 9:54 pm

pcmanbob wrote:
Wed Sep 11, 2019 6:23 pm
The biggest problem is that you are unlikely to get a full 25W from your solar panel unless you live in a very sunny climate.

From my own experience in the UK with solar panels on my house I rarely average more than 60% of there total output in the summer and considerably less in the winter.
Are you talking about power (measured in Watts) or Energy (measured in Watt/hours)? A properly designed and configured Solar installation should produce close to its rated power around solar noon with a clear sky in the summer. If yours doesn't, that is a problem that needs addressing. Energy ratings are somewhat trickier, but a competent installer with standard tools should be able to predict the annual output of an installation, taking account of all the relevant variables, within 5-10%. Again, if the calculations were done right and you are only achieving 60% of predicted production, there is a problem.

Nevertheless, it is important for anyone planning to use solar panels + batteries to run equipment 24/7 to remember that the power rating of the panels is their maximum output capacity, and to do the energy calculations to work out how many panels they need.

dickon
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Re: 12v battery + 25 watt Solar = always powered 4B?

Wed Sep 11, 2019 10:13 pm

FWIW, I have a 120Ah 12V deep-cycle leisure battery and a 80W panel in southern England, oriented south, with a solar charge controller and a cheapish <24V->5V converter, and I get almost a full year on a Pi 1B. It fails for about a month of nights, and misty days, in the middle of winter. It would probably be fine on a Zero.

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Imperf3kt
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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 12:39 am

Consider those 20W solar garden LEDs you can buy at most hardware shops, garden stores and thrift stores. They power a single LED for about 8 hours (less with age) from a full day of charging in a sunny subtropical climate.

How many LEDs does the Pi have?
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Gavinmc42
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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 1:15 am

Even here in sunny Oz, the basic rule of thumb is 4 times the Watts = the number of Watt/hours on average per day.

25Watts = 100Watt/hours/day.
5volts to the Pi = 20Amps/hr/day
24 hours = 0.83amps or the Pi must use less than about 4watts.
If you allow 4 days overcast battery storage, then getting down to 1watt is better.

25watts panel ~ 1W Pi for 365/24/7
A Zero may work.
Pi4's get up to 15watts, about 300+watts of solar panels.
More if the monitor is on 24/7

Now if we can figure out how to power Pi's on stored solar thermal :D
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jcyr
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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 1:26 am

Imperf3kt wrote:
Thu Sep 12, 2019 12:39 am
Consider those 20W solar garden LEDs you can buy at most hardware shops, garden stores and thrift stores. They power a single LED for about 8 hours (less with age) from a full day of charging in a sunny subtropical climate.

How many LEDs does the Pi have?
Garden LEDs at 20 watts... PI LEDs at 50 milliwatts or less. Apples and oranges.
It's um...uh...well it's kinda like...and it's got a bit of...

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Imperf3kt
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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 1:37 am

jcyr wrote:
Thu Sep 12, 2019 1:26 am
Apples and oranges.
That should have been 2W.
But the point was to demonstrate how long (or how short) a thing will run from one day of charging from such a solar panel.
If a 2W solar panel can only give enough energy for a single LED (mW of current) to run for 8 hours, how does OP expect a ~5-15W Pi expect to run 24/7 including rainy days.
25W is only 12.5 times 2w, but 15w is a lot more than 12.5x a few mW an LED will use.


Perhaps not the best comparison.
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rin67630
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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 2:01 am

dickon wrote:
Wed Sep 11, 2019 10:13 pm
FWIW, I have a 120Ah 12V deep-cycle leisure battery and a 80W panel in southern England, oriented south, with a solar charge controller and a cheapish <24V->5V converter, and I get almost a full year on a Pi 1B. It fails for about a month of nights, and misty days, in the middle of winter. It would probably be fine on a Zero.
I have made the same experience in Germany.

You need a huge battery able of powering your equipment for about a month without any relevant solar contribution in the rainy/foggy/snowy winter days.
0,25 A * 24h * 30 days = 240 A/h @ a 12V battery is a good start.

Of course, a day with few hours sun may change the deal, but a full month without direct sunshine is plausible.
Additionally you need to protect your battery from freezing.

Off grid solar power 24/24/365 is not easy.

Must it be a 4B?
The first thing with off-grid stuff is to be greedy on power.
I moved to Arduinos to get the data acquisition and data compacting, then LoRa radio to transmit the values to a location where grid power is available and a 'Pi can take over. And remember: an "always-on" 'Pi 4 will require about 50 KWh/year. In three years, you will have paid more for electricity than for the hardware.
Last edited by rin67630 on Thu Sep 12, 2019 7:52 am, edited 1 time in total.

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Gavinmc42
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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 2:31 am

This is just one Pi.
Some guys now have figures for 100W paneled Pi's, 365/24/7.

The basic principle still applies when you scale it up to powering the planet from solar.
That's why I don't like "renewbles" greenies saying we can save the planet by just having solar panels.

The mathes are napkin calculations.
A 1GW base load power station can be replaced by 25GW (+/- 20GW) solar plus batteries?
Perhaps if there was a big cable around the equator, the day side can power the night side.
That might be cheaper than the batteries needed?

ROI?
Perhaps if you get the solar panel/battery free.
What is the price of your power locally?

But solar/battery is getting closer to good ROI, if you are away from the grid.
Assuming you have the money to Invest and can replace the battery every few years and panel every 10-25 years.
Mind you, a nice little 25W nuclear reactor might last 50-100years.

Try it and see.
Pi4?
Grab a few secondhand 200W panels, good prices are about $50?

Anyway in a newsletter today, MIT has made a Carbon Nanotube 16bit RISC-V CPU.
Carbon based CPU's can use less power and or run faster.
Within 5 years?
Pi6 or 7 could be carbon based and run off old solar garden lights?
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jcyr
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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 2:39 am

rin67630 wrote:
Thu Sep 12, 2019 2:01 am
I moved to arduinos to get the data acquisition and data compacting, then LoRa radio to transmit the values to a location where grid power is available.
Similarly, I've used Cypress PSOC (has extremely low power sleep mode) and Bluetooth LE powered by lithium ion battery and small solar panel to communicate periodic measurements to a mains powered Pi3b. Freezing is indeed an issue for exterior work (in this case, a backyard weather station).
It's um...uh...well it's kinda like...and it's got a bit of...

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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 7:41 am

jcyr wrote:
Thu Sep 12, 2019 2:39 am
Similarly, I've used Cypress PSOC (has extremely low power sleep mode) and Bluetooth LE powered by lithium ion battery and small solar panel to communicate periodic measurements to a mains powered Pi3b.
Yes I forgot that. Sleep is frequently an option. Not for me, halas.

dickon
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Re: 12v battery + 25 watt Solar = always powered 4B?

Thu Sep 12, 2019 9:44 pm

I'd probably use an ESP32 these days, rather than a Pi1. With the deep sleep mode on that, I suspect a 120Ah battery is very much overkill for a system to monitor a couple of temperature probes, report them back to base (BLE or wifi; I'm not fussed), and later to water the plants for me.

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rin67630
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Re: 12v battery + 25 watt Solar = always powered 4B?

Fri Sep 13, 2019 11:07 am

dickon wrote:
Thu Sep 12, 2019 9:44 pm
(BLE or wifi; I'm not fussed), and later to water the plants for me.
You must have got a pretty small backyard. BLE or WiFi are really narrow-range.

dickon
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Re: 12v battery + 25 watt Solar = always powered 4B?

Fri Sep 13, 2019 11:15 am

92m for wifi outside. I have an AP within ~15m of the greenhouse, albeit inside a set of bifolds.

As for BLE, that same AP can read a Ruuvitag BLE beacon in more or less the same spot quite happily.

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jcyr
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Re: 12v battery + 25 watt Solar = always powered 4B?

Fri Sep 13, 2019 2:01 pm

dickon wrote:
Fri Sep 13, 2019 11:15 am
92m for wifi outside. I have an AP within ~15m of the greenhouse, albeit inside a set of bifolds.

As for BLE, that same AP can read a Ruuvitag BLE beacon in more or less the same spot quite happily.
Ditto, BLE at 10 meters going through single exterior wall.
It's um...uh...well it's kinda like...and it's got a bit of...

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Re: 12v battery + 25 watt Solar = always powered 4B?

Fri Sep 13, 2019 2:16 pm

I have used a "moteino" which is Arduino with RFM69HW radio module. Range is plenty good enough for me:

"~540 meters range @38400kbps with lots of trees and one or two buildings inbetween."
https://lowpowerlab.com/forum/rf-range- ... range-test!/

The same unit is also available with a LoRa module. LoRa can apparently go 40 km under some circumstances:
https://lowpowerlab.com/guide/moteino/lora-support/

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