diy solar

diy solar

Correct me if I'm wrong please..

Concerning the last part.
It doesn’t sound like you understand that it takes 4 times the battery to equal the same Amp hours in 48 volt system than a 12 volt. That is why “Watts “ is a much better Value to use and less chance of math errors moving from one voltage to another.
?? Uhm no, I don't understand what you are trying to say here.
Yes you calculate your usage in Watts. But then you convert it. Batteries are rated in Amps not in Watts.

What do you mean by "it takes 4 times the battery to equal the same Amp hours in 48V system than a 12V"?

1 battery of 12V of say 260Ah is a huge battery. Or you can get 2 of 130 Ah in parallel.

And yes for 48V I would need 4 batteries, But only smaller ones to get to 65 Ah. In theory 4 small 17Ah battteries would do the trick. Not? (17Ah doesn't exist, I know)

Am I really seeing this wrong ?
 
I really seeing this wrong
Yes
258 amps at 12 volts
129 amps at 24 volts
65 amps at 48 volts
These are all the same ’size’ and capacity batteries. You have to have the same watts to provide an equivalent amount of power but that equivalent power is different amps for the various voltages. W=V*A is an equation that solves 96.378% of all wiring and battery capacity conversion questions.
what is a small system and when is it becoming a big system?
Of course that’s relative (I have a friend that’s an EE who only works on small megawatt inverter installations, not the big ones…)

Small is probably 3000W inverter at 24V or less. At about 2000W inverter need, 12V starts being questionable due to the huge amps. Probably 2400W+ needs at 120V needs really should be a higher voltage battery system. I think that may play into why the plethora of inverter choices at 12V pretty much drops away at 2200W. There’s higher wattage 12V stuff but not much

I think you can say less than 2500W inverter or panels is a “small” system.
FWIW I may try for a minisplit on 12V next summer (because I’m heavy on 12V lights and stuff) but there’s practical limitations on the success of that.
 
You state your inverter efficiency is 85% but that figure could be way OFF as the efficiency is rated at full load and at small loads it could be only 25% you need to find out what the no-load draw is off of the battery and add that in.
 
One question I have for the OP. Your original draw figures of 40 w X 20 hrs, etc. Did you also include the inverter idle power consumption? My Victron inverter uses 15w per hour. 15w X 24h = 360w
Some use 40w per hour 40w X 24h = 960w
On a small system these extra details matter. On a large system, not so much.
Just food for thought.

Ed
 
Well what is fancy.? We have a lot of stuff laying around here what I think I can use. If we leave this place we have to throw it away anyway. And I think I may call myself a handy enough DIY guy. If I can put something together that can tilt to make a better angle why wouldn't do it?

Manual tilt for season may be worth doing.

Motorized tilt to track sun during the day isn't worth it. Just have two orientations, with PV strings in parallel. This presents more area to the sun early and late as compared to single array facing South. Less area at Noon. SE and SW, about 90 degree angle, would present 0.7x as much area, so you can over-panel 1.4x without clipping production.

And then maybe overpanel beyond that, so it clips on best days but produces more on bad days.

Besides SCC Voc and Isc limits, consider maximum or target battery current. FLA has a preferred current to stir electrolyte. AGM has a maximum, maybe a minimum preferred. LiFePO4 is happy over a wide range, usually up to 0.5C at nominal temperature but reduced to around 0.1C a bit above freezing.

I haven't seen adjustable charge current vs. temperature in the controllers, but I think 0.15C is sufficient to recharge most days (might need to be higher for short winter days. Some SCC can regulate battery current by means of readings from a shunt, but supply more when used by inverter. Then you can set BMS to disconnect charging if temperature below that where your programmed charge current is allowed.
 
Thanks :cool:
But indeed a lot of things to consider.

Well yeah what is a small system and when is it becoming a big system?

@12VoltInstalls I get the point on the savings for cable costs. On the other hand, the cabling is all in your technical room.
From there you run it through an inverter to 110V or 220V, whatever your case.
Then you proceed with cable to run 110V / 220V through your house, trailer or what so for all your devices. Maybe you keep some lights direct on 12V/24V but not so much I would think.
So how many meters of cable for the actual solar/charger/battery/inverter part are we really talking about??
Maybe I'm not seeing things right for the moment because I didn't build a system yet.

On the other hand,

the 48V version sounds a lot better to me.
On 12V I would need an enormous amount of battery power/back-up.
258Amps on 12V is 1 day of power.
258Amps on 48V is 4 days. So actually: 1 day of power and 3 full days of back-up.
Besides that, working lower amps sounds more safe to me.
You are confusing Amperage, which is current or the rate of flow with Amp-hours or VA or Wattage which are expressions of capacity. 100A at 12 is equvilent to 50A at 24V to 25A at 48Volts Subject to losses inherent in the systems. Higher current systems are prone to larger losses
 
the 48V version sounds a lot better to me.
On 12V I would need an enormous amount of battery power/back-up.
258Amps on 12V is 1 day of power.
258Amps on 48V is 4 days. So actually: 1 day of power and 3 full days of back-up.
Besides that, working lower amps sounds more safe to me.
You are confusing Amperage, which is current or the rate of flow with Amp-hours or VA or Wattage which are expressions of capacity.
Yeah, I got mixed up here with Amps and Amp-hours for a moment.
The 3100W we talked about is usage 'at the moment' and pulls a certain amperage on a chosen voltage. Not storage in Ah.


Concerning the last part.
It doesn’t sound like you understand that it takes 4 times the battery to equal the same Amp hours in 48 volt system than a 12 volt.
100A at 12 is equvilent to 50A at 24V to 25A at 48Volts Subject to losses inherent in the systems. Higher current systems are prone to larger losses
But a 100A 12V battery can 'deliver' 1200Watts of power, as can a 50A 24V battery. --> W=V*A

And then we have the formula: Watt * hours = Wh --> followed by --> Wh / Voltage = Ah

That is how I came to the conclusion that ( 12V * 260Ah = 3,120Wh ) is the same as ( 48V * 65Ah 3,120Wh )
So putting 4 * 12V/17Ah batteries in serie would give me 48V and 65Ah

:rolleyes: ? ?‍?

I think I know where I got confused: 4 * 12V in series will get 48V. But in series you don't add up the Amps...
--->> Is that it??
--->> So the 17Ah on 48V will give a energy output of V*A= 816W And to get to that 3,120W value I would need to get quadruple that

My God, I've been wrecking my brain about this over Christmas....
 
You state your inverter efficiency is 85% but that figure could be way OFF as the efficiency is rated at full load and at small loads it could be only 25% you need to find out what the no-load draw is off of the battery and add that in.
Okay, thanks. I 'll guess this also depends on your inverter? I'll get there with the trial and error process.
As said I got some stuff coming in to do tests and measurements. So I will definitely pay some attention to this.
 
One question I have for the OP. Your original draw figures of 40 w X 20 hrs, etc. Did you also include the inverter idle power consumption? My Victron inverter uses 15w per hour. 15w X 24h = 360w
Some use 40w per hour 40w X 24h = 960w
On a small system these extra details matter. On a large system, not so much.
Just food for thought.

Ed
Nope. Also a good point. 360W to 960W of usage is actually quite a lot and something to consider in calculations.
 
Manual tilt for season may be worth doing.

Motorized tilt to track sun during the day isn't worth it. Just have two orientations, with PV strings in parallel. This presents more area to the sun early and late as compared to single array facing South. Less area at Noon. SE and SW, about 90 degree angle, would present 0.7x as much area,
Won't go into motorized system, no.
2 orientations will be problematic if they are mounted on a roof. But I can think about how I park the trailer, with in the limits of the property.
That is why I thought about angle adjustment. So at least the angle is as best I can get it.

so you can over-panel 1.4x without clipping production.
And then maybe overpanel beyond that, so it clips on best days but produces more on bad days.

What do you mean by "clipping production" ? If you don't mind me asking.

Besides SCC Voc and Isc limits, consider maximum or target battery current. FLA has a preferred current to stir electrolyte. AGM has a maximum, maybe a minimum preferred. LiFePO4 is happy over a wide range, usually up to 0.5C at nominal temperature but reduced to around 0.1C a bit above freezing.

I haven't seen adjustable charge current vs. temperature in the controllers, but I think 0.15C is sufficient to recharge most days (might need to be higher for short winter days. Some SCC can regulate battery current by means of readings from a shunt, but supply more when used by inverter. Then you can set BMS to disconnect charging if temperature below that where your programmed charge current is allowed.
I'm going to look up what you mean by this second part...
 
Won't go into motorized system, no.
2 orientations will be problematic if they are mounted on a roof. But I can think about how I park the trailer, with in the limits of the property.
That is why I thought about angle adjustment. So at least the angle is as best I can get it.
.
Trailer could have array hinged at one side, tilted up for a better angle.
Second array at front edge of roof could tilt up as well. That would give two orientations 90 degrees apart.

One array could lie down partially covering the other for storage/transportation, for somewhat larger total.
How big the arrays and where located would influence what sun angles could cause them to shade each other, can't locate as ideally as on the ground without making smaller.

Array flat on roof (or slightly tilted), and arrays on side and rear that can tilt out? Those would avoid shading.

For my pickup truck roof I'm considering two arrays (or panels) hinged on left and right. They would fold flat, one covering the other. Tilted up 60 degrees forms equilateral triangle. It would never present more than the area of one panel to the sun, but should produce better from morning to evening, during the summer. It would require tilting to the front as well to be good other seasons.

What do you mean by "clipping production" ? If you don't mind me asking.

If available PV is within scc (or GT inverter) limit, power produced follows a curve.
If in the middle of the day it exceeds max for scc, output is "clipped" at what scc can process.


I'm going to look up what you mean by this second part...

If you have a 100 Ah battery that can accept up to 0.5C, 50A charge rate at moderate temperature,
and enough PV to produce 50A (or even more),
50A charge is OK only if battery temperature doesn't get too cold (or too hot).

Mostly we've seen specs for minimum and maximum temperature at which it can be charged, e.g. not below freezing, 0 degrees C.
But some sources indicated at 5 or 10 degrees C, only a reduced charge rate was OK, higher charge would degrade battery.
Maybe 0.15C, 15A, would be OK all the way down to 10 degrees C.

If you had an all-in-one with PV MPPT input, battery connection, and inverter output, it could be programmed for 15A charge current.
But with 50A available from PV, it could use the other 35A to feed inverter when you have AC loads. Adjust harvested power so battery charge remains at 15A.

Victron equipment includes scc that can be commanded by data bus. With a battery shunt, charge current can be measured. One more monitor device (Cerbo?) can read the shunt and control scc, so extra power is collected for loads like inverter, but battery charge current is regulated.

My system is AC coupled (GT PV inverters plus battery inverter/charger). I've programmed it for 0.2C (80A into 400 Ah AGM battery) but PV inverters can deliver much more. While on-grid they backfeed for net metering. When grid is down, their output is adjusted to supply AC loads plus enough for battery charging.
 
.
Trailer could have array hinged at one side, tilted up for a better angle.
Second array at front edge of roof could tilt up as well. That would give two orientations 90 degrees apart.
Yes Actually think I can do that. Just thought of tilting them on the long side for now.

If available PV is within scc (or GT inverter) limit, power produced follows a curve.
If in the middle of the day it exceeds max for scc, output is "clipped" at what scc can process.
Still quite new in the world of solar. So just to be clear, what exactly do you mean by PV ?
I've been trying to read it as PanelVoltage, PeakVoltage, Power...

If you have a 100 Ah battery that can accept up to 0.5C, 50A charge rate at moderate temperature,
and enough PV to produce 50A (or even more),
Maybe 0.15C, 15A, would be OK all the way down to 10 degrees C.
What is 0.5C / 0.15C

Thanks.
 
What is 0.5C / 0.15C

Thanks.

0.5C means charge current = 0.5 x amp-hour capacity of battery, e.g. 50A charge for a 100 Ah battery. Would charge in 2 hours if that could be sustained (but voltage acceptance tapers off near full.)

0.15C would be 15A charge for a 100 Ah battery.

0.5C discharge seems to be typical for lithium batteries used for solar power. And 1.0C discharge rates.
For EV electric vehicles, maybe discharge of 3C.

Lead-acid automotive starting batteries have ratings like CA and CCA (cranking amps, cold cranking amps). That's the current they deliver at about 8.5V, often 600A to 800A. Their capacity might be 50 Ah (if that) so a discharge rate of 12C for a minute or so.
 
:rolleyes: ? ?‍?

I think I know where I got confused: 4 * 12V in series will get 48V. But in series you don't add up the Amps...
--->> Is that it??
--->> So the 17Ah on 48V will give a energy output of V*A= 816W And to get to that 3,120W value I would need to get quadruple that

My God, I've been wrecking my brain about this over Christmas....
All of a sudden it’s just going to make sense for you!

Voltage is like pressure
Amperage is the flow of current
Wattage is actual Work being done at that moment

12 volts @ 10 amps = 120 watts
120 volts @ 1 amp = 120 watts

its the same amount of work being done. But that’s all an instantaneous value.

When you add time to the value then you can talk about storage or total energy used.

If you run your 1000 watt microwave for 1 hour then you just used 1 kilowatt hour of energy. If you run your 100 watts of lights for 10 hours then you’ve used 1 kilowatt hour of energy.

lets say we have 4 12 volt 100 amp hour batteries

each battery has 1200 watt hours of energy in them. It doesn’t matter how you wire them up whether it’s parallel, series or series and parallel they still have the same amount of watt hours in them.

When in series the voltage increases but amp hours stays the same.
When in parallel the amp hours increases but the voltage stays the same.

Parallel
12v*100ah = 1200wh*4 batteries in parallel = 4800wh

2 batteries in series paralleled with another 2 batteries in series.
(24v*100ah) + (24v*100ah) = 4800wh

series
48v*100ah = 4800wh

Lead acid batteries do prefer to discharge more slowly. The faster you discharge them the less energy the have. That’s why you’ll notice different rates of discharge like c5, c10, c20 and c100.
You‘ll notice if you discharge this battery in 5 hours you’ll get 1,110wh of energy and if you discharge it over a 100 hour period you’ll get 1500 watt hours of energy.

72BA7148-A017-46DE-9042-0766FAEB8618.jpeg

That’s the advantage of a 48 volt system. Lower amps = more battery capacity due to slower discharge, smaller cables and less heat.
 
I’m not him, plus he’s smarter than me.
How polite to give credit where it is due... ;)
But I can answer that PV is vernacular for solar panel(s). Actually short for “Photo-Voltaic” or “photo voltaic panel”
Well it crossed my mind but I still couldn't rhyme it al together.

Sorry guys; I'm getting a crash course Solar here, on internet in another language...
--------->>>>>. And it all started so simple.... just W=V*A :p

0.5C means charge current = 0.5 x amp-hour capacity of battery, e.g. 50A charge for a 100 Ah battery. Would charge in 2 hours if that could be sustained (but voltage acceptance tapers off near full.)

0.15C would be 15A charge for a 100 Ah battery.
Okay clear. Now it makes sense
Now I can also make something of your earlier reply
Lead-acid automotive starting batteries have ratings like CA and CCA (cranking amps, cold cranking amps). That's the current they deliver at about 8.5V, often 600A to 800A. Their capacity might be 50 Ah (if that) so a discharge rate of 12C for a minute or so.
Yeah knew about Cranking Amps, not CCA though.
 
All of a sudden it’s just going to make sense for you!
Once I've cracked the code language you guys are talking in....

Voltage is like pressure
Amperage is the flow of current
Wattage is actual Work being done at that moment

12 volts @ 10 amps = 120 watts
120 volts @ 1 amp = 120 watts
.....
lets say we have 4 12 volt 100 amp hour batteries
each battery has 1200 watt hours of energy in them. It doesn’t matter how you wire them up whether it’s parallel, series or series and parallel they still have the same amount of watt hours in them.
When in series the voltage increases but amp hours stays the same.
When in parallel the amp hours increases but the voltage stays the same.
Parallel
12v*100ah = 1200wh*4 batteries in parallel = 4800wh
2 batteries in series paralleled with another 2 batteries in series.
(24v*100ah) + (24v*100ah) = 4800wh
series 48v*100ah = 4800wh
Never was any good in math where X * Y = really means nothing to me.
So took a minute but I got it. Got confused somewhere with multiplying 2 values at the same time.
Thanks for the confirmation that I'm seeing it right now.

Lead acid batteries do prefer to discharge more slowly. The faster you discharge them the less energy the have. That’s why you’ll notice different rates of discharge like c5, c10, c20 and c100.
You‘ll notice if you discharge this battery in 5 hours you’ll get 1,110wh of energy and if you discharge it over a 100 hour period you’ll get 1500 watt hours of energy.

View attachment 77209

That’s the advantage of a 48 volt system. Lower amps = more battery capacity due to slower discharge, smaller cables and less heat.
Yeah I under stood some parts of a higher voltage, (that is why the grid works on a higher voltage).
But I am getting at the point of seeing the whole picture now.



I hope my scc comes in soon. So I can connect things and go play with volt and amp meters.
Then with all other info you gave me on panel output, scc-losses, battery-losses, inverter-losses, cable length, and what not ( I really need to read it all back) I am going to try to make a estimation of our needs.

To be continued.
 
Yeah knew about Cranking Amps, not CCA though.

Auto store will test my battery briefly and say how many CCA it produces.
But that's not at the right temperature for CCA (rather CA), and I also find it inaccurate.

"What Is “Cold Cranking Amps (CCA)”?
Cold Cranking Amps (CCA) is a rating used in the battery industry to define a battery’s ability to crank an engine in cold temperatures.

It measures how much current (measured in Amps) a new, fully charged 12V battery could deliver for 30 seconds while maintaining 7.2V at 0°F (-18°C)."


Thought I remembered 8.5V, this says 7.2V
It will deliver more at room temperature (and car is easier to start when oil isn't as thick.)

The test voltage is reduced approximately 1/3 from no-load, so I estimate that into a short circuit current could be 3x.
If a battery is rated 800 CA, I'll assume it can deliver 2400A into a short, so fuses need AIC rating at least that high.
Lithium batteries have lower resistance, deliver more current with less voltage drop. Chemistry probably figures in too, but I only understand Ohm's Law.

I had a small Optima battery that suddenly wouldn't crank the engine. Turning on the headlights, they were quite dim.
Auto store tester showed 60 CA (new battery would be around 600 CA), but it obviously couldn't deliver even 6A.
My guess is a section of the lead interconnect inside the Optima battery fractures or corrodes through. I've had several exhibit that failure.
I don't think car alternator/regulator is set for optimum charging voltage of these AGM batteries, so under charging may cause conditions leading to the failure.
 
I hope my scc comes in soon. So I can connect things and go play with volt and amp meters.
The delivery from China came in :)

So I am going to make a test set up Saturday ! Lets hope for a little bit of sunshine.
 
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