Smallest system possible

Hi.
I am hoping to learn as much as possible about solar charging systems so that I can in some way reduce my dependence on grid energy .

Eventually, I would like to have my workshop powered by off grid power but before that I would like to learn-by-making a smaller project.

The project I have in mind involves placing motion activated led lights at critical points in my home, so that after a certain time ( night time), when I move around my home I would not need to turn on grid energy ( this would also be useful whenever there are power outages in my area).

The project would involve 6 led lights of 5 watts each and I have estimated that an average daily load of 7.5 watt hrs per day.

apparently I should estimate my pv panel size based on the estimated watts hrs per day divided by the number of hours sunlight most likely in this part of the world (Ireland) during summer (4 hrs) and winter ( 1 hr) giving me a maximum required panel size of 7.5 watts

This I realize is just not practical so I,ve decided to get a 25 watt panel and allow for a lot less sun!!!!!.... this is Ireland after all!!

details of the panel are:
Pmax. 25W
Vpm: 17.9V
lpm: 1.4A
Voc: 22.41V
lsc : 1.54A

I have also bought a solar charge controller to go with the panel.

Solar Charge controller details:
PWM
12/24V
20A
built-in timer
full ptotected
settable voltage
usb
self-consume <10mA
float charge 13.7V ( default.adjustable)
discharge stop 10.7V ( default.adjustable)
discharge reconnect 12.6V ( default.adjustable)

my intention was to connect a power inverter ( pure sine wave ..... so that it can be used on digital gear after this project) and run the 220 v led bulbs using 220 v twin and earth wiring rather than using 12volt wiring and fitting .

after finding an inverter that was small enough (Victron energy Phenoix 12 /250) discovered that the minimum battery size needed to use with this inverter was 30 Ah which was considerable more than the 9Ah battery my initial calculations suggested I needed.

If anyone has any advice on how I might alter my design to achieve my goal , I would be really grateful.

Best wishes and stay safe

EdK

I have the same system but with one huge difference.
I have 12V LED 5W bulbs and don't need an inverter.
So buy 12V LED and your problems are gone...

Hi Evado,

thanks for your quick reply.

sounds like a good plan... will do that and see how I go.

I was a little concerned about the safety of a 12 volt system but will test it out and be wiser at the end.... hopefully.

cheers again.

Your Solar Charge controller has a built-in timer so you can program it to switch on and off whatever you like.

Mine Victron is programmed to switch on at sunset and switch off at sunrise.
And it is working perfectly.

That’s great.
I haven’t hooked anything up yet ,but have noticed the timer feature in the specifications. I’m thinking there might be some App interface that will be accessible through one of the two USB ports on the controller.

what kind of load is on your system and do you mind me asking also what size battery you have?

edK

I made a small system like that last winter for about $100 and wrote it up as a show-and-tell. See the link in my sig.
I was running some yard lights. I managed to kill my small lead-acid battery in a -20C Canadian winter so now I'm just running the 12v lights in the basement for fun off the 25w solar.
Take a read through and feel free to copy anything you see that applies to your situation.
I will try to answer any questions you have but there are lots of people on here that know way more than me.

You were originally considering an inverter. I think it is on this sheet:


"Max. efficiency 87%
Zero-load power 4.2W
Default zero-load power in ECO mode (default retry interval: 2,5 s, adjustable) 0.8W"

Delivering 7.5Wh would consume 7.5/0.87 = 8.6Wh/day
If left running 24 hours per day waiting to be used, 24 x 4.2 = 100 Wh/day
Using ECO mode, 24 x 0.8 = 19 Wh/day.

Because you aren't simply enabling the inverter when a light switch is manually enabled and load presented, but rather using a motion sensor which needs to be powered, ECO mode probably wouldn't work. You would have to see how fast the sensor powers up, and during the time power is off it there would be a delay in detection.

Obviously DC powered motion sensor is likely to be the best solution for the stated application. Solar battery powered motion sensitive lights are an off the shelf product. But the exercise of figuring out how much power and storage it takes to make this work is useful for your future project.

25w solar is tooooo small to play with. Try to find some deal from craigslist.

I got my first panel of 175w at $50 (3.5w/$), then 185w at $40 (4.6w/$), and my most recent harvest is $275w at $25 (10w+/$). They are from local solar contractor who install new panel and remove old panels. Just have some patient to search and wait.

Not have chance to test the "new" cheap panel yet, but the previous panel still have 90% from the rated watt.

45North said:

I made a small system like that last winter for about $100 and wrote it up as a show-and-tell. See the link in my sig.
I was running some yard lights. I managed to kill my small lead-acid battery in a -20C Canadian winter so now I'm just running the 12v lights in the basement for fun off the 25w solar.
Take a read through and feel free to copy anything you see that applies to your situation.
I will try to answer any questions you have but there are lots of people on here that know way more than me.

Click to expand...

Hi 42North,

Im at 53 North,so id imagine we might have somewhat similar sunfactor strengths ?.

I’ve had a quick look at your setup and it looks like what I had imagined mine would be like ,when I started .

It’s early a.m. here and I’m off to work but will give you posts a good read later.

thanks for replying..... really appreciate it.

Hedges said:

You were originally considering an inverter. I think it is on this sheet:

https://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-VE.Direct-250VA-1200VA-EN.pdf

"Max. efficiency 87%
Zero-load power 4.2W
Default zero-load power in ECO mode (default retry interval: 2,5 s, adjustable) 0.8W"

Delivering 7.5Wh would consume 7.5/0.87 = 8.6Wh/day
If left running 24 hours per day waiting to be used, 24 x 4.2 = 100 Wh/day
Using ECO mode, 24 x 0.8 = 19 Wh/day.

Because you aren't simply enabling the inverter when a light switch is manually enabled and load presented, but rather using a motion sensor which needs to be powered, ECO mode probably wouldn't work. You would have to see how fast the sensor powers up, and during the time power is off it there would be a delay in detection.

Obviously DC powered motion sensor is likely to be the best solution for the stated application. Solar battery powered motion sensitive lights are an off the shelf product. But the exercise of figuring out how much power and storage it takes to make this work is useful for your future project.

Click to expand...

Hi Hedges,

Thanks for your reply, it gives me a lot to think about.

I‘ve been interested in motion sensors since I began playing with microcontroller boards ( arduino and raspberry pi) and perhaps some of the issues with the inverter triggering could be sorted via one of these but at the moment I’d be happy to get a simple system up and running and then tweet it to improve and expand.

As I mentioned to 45North , I’ll give your reply another read after work today and see if I can fully grasp your ideas.

thanks again.

Pearce said:

25w solar is tooooo small to play with. Try to find some deal from craigslist.

I got my first panel of 175w at $50 (3.5w/$), then 185w at $40 (4.6w/$), and my most recent harvest is $275w at $25 (10w+/$). They are from local solar contractor who install new panel and remove old panels. Just have some patient to search and wait.

Not have chance to test the "new" cheap panel yet, but the previous panel still have 90% from the rated watt.

Click to expand...

Hi Pearce,

thanks for getting back to me.

unfortunately Craigslist is not an option in this part of the world (Ireland) and solar power is a relatively new industry here so second hand units are not freely available, but I will make some enquiries with installers about the possibility of getting second hand panels.

might be an option in the future?

yep
It's not very hard to find used panels in Ireland tbh
I know I tried at one time (Nearly all of them seem to be in US which defeats the point of the cheaper price because of shipping and import tax sadly)

Hedges said:

You were originally considering an inverter. I think it is on this sheet:

https://www.victronenergy.com/upload/documents/Datasheet-Phoenix-Inverter-VE.Direct-250VA-1200VA-EN.pdf

"Max. efficiency 87%
Zero-load power 4.2W
Default zero-load power in ECO mode (default retry interval: 2,5 s, adjustable) 0.8W"

Delivering 7.5Wh would consume 7.5/0.87 = 8.6Wh/day
If left running 24 hours per day waiting to be used, 24 x 4.2 = 100 Wh/day
Using ECO mode, 24 x 0.8 = 19 Wh/day.

Because you aren't simply enabling the inverter when a light switch is manually enabled and load presented, but rather using a motion sensor which needs to be powered, ECO mode probably wouldn't work. You would have to see how fast the sensor powers up, and during the time power is off it there would be a delay in detection.

Obviously DC powered motion sensor is likely to be the best solution for the stated application. Solar battery powered motion sensitive lights are an off the shelf product. But the exercise of figuring out how much power and storage it takes to make this work is useful for your future project.

Click to expand...

based on what you’ve said regarding the inverter and the non functionality probability of the Eco mode on this
particular inverter, I think I’ll go down the 12volt feed road and see if I can build a motion sensor with sensor and relay+resister circuit that will trigger a 12volt led .

I will let you know how I get on

Thanks again for your advice