Help with system design

[eavaria]

Hello. I'm new to this and have been reading for a while, bu can't find the answer I'm looking for. Maybe someone here can point me to the right direction.

I have a crypto mining rig that consumes about 600W. It's constantly on, and the main power source is on 12V (only 5% tolerance). I have a regular PSU for the host and a separate 12V PSU for the cards on the rig. I'm considering the next step and put some solar panels to feed the rig, maximizing the solar energy, so I want to avoid conversions. I would like to run without a battery (or one only for regulation purposes) and be always on grid, but consume all the solar power available first.

I have a fair knowledge of the electronics involved, but can't figure out the configuration I I need.

I need a constant supply of 12v, solar first, 12 PSU after. If it gets interrupted the whole rig needs to be restarted.
I have a few questions I haven't found the answer yet.

Can the MPPT give me exactly 12V or it will give me what the battery have in that moment?
Can a 48V MPPT give me 12V?

So far the configuration I'm tjinking is a 48V system, connected to a dc to dc converter for ~12.5V output to the load, that will be connected in parallel with the 12V PSU to get priority on the consumption. Can you comment on that? Should I use a diode? Is dc-dc efficient enough?

Any idea is greatly apreciated. Thanks a lot.

 

[sunshine_eggo]

Can the MPPT give me exactly 12V or it will give me what the battery have in that moment?

This

Can a 48V MPPT give me 12V?

Most 48V MPPT will work on 12 and 24V systems.

So far the configuration I'm tjinking is a 48V system, connected to a dc to dc converter for ~12.5V output to the load, that will be connected in parallel with the 12V PSU to get priority on the consumption. Can you comment on that? Should I use a diode? Is dc-dc efficient enough?

Any idea is greatly apreciated. Thanks a lot.

How is the 12V PSU powered?

 

[eavaria]

Thanks for the answer. The PSU is 220V on grid, and so is the ATX PSU that drives the rest of the computer. The idea is to make good use of the sun when available and rely on the grid for normal operation. Eventually I plan to have a separate 220V system , but now I'm focused on going greener, so minimizing waste is the priority (i.e. skipping the batteries, alternator, and the ac-dc conversion) . The big question is:

Can the 12V PSU be connected to the load (maybe with a diode to block back current) and adjusted to 11.5V and at the same time a 12. 0V buck converter connected to the same load, so if there's enough juice from the solar system it will use it, if not, will draw power from the 11.5V from the grid. Sounds reasonable? I would also want to somehow limit the MPPT to keep the batteries topped, so I can use cheaper lead-acid and avoid the waste of using power from the battery, but I believe that one is easier, disconnecting it at 51V or so, and waiting for the voltage to raise again to connect the buck converter.

 

[sunshine_eggo]

Thanks for the answer. The PSU is 220V on grid, and so is the ATX PSU that drives the rest of the computer. The idea is to make good use of the sun when available and rely on the grid for normal operation. Eventually I plan to have a separate 220V system , but now I'm focused on going greener, so minimizing waste is the priority (i.e. skipping the batteries, alternator, and the ac-dc conversion) . The big question is:

Can the 12V PSU be connected to the load (maybe with a diode to block back current) and adjusted to 11.5V and at the same time a 12. 0V buck converter connected to the same load, so if there's enough juice from the solar system it will use it, if not, will draw power from the 11.5V from the grid. Sounds reasonable?

That sounds plausible provided you can source a ~70A diode rated for ~800W.

I would also want to somehow limit the MPPT to keep the batteries topped, so I can use cheaper lead-acid and avoid the waste of using power from the battery, but I believe that one is easier, disconnecting it at 51V or so, and waiting for the voltage to raise again to connect the buck converter.

If you select a MPPT with load ports of sufficient rating, you can have the load ports cut out below a certain battery voltage thus cutting out the source to the buck.

The most important question is how many Watts are you planning to install, and how much solar is available for your planned array location?

 

[eavaria]

I'm in central Chile, so I'm literally on ne of the best skies of the world ? haven't figured out the numbers, but the idea is to get panels sized to the load (that is completely predictable) ... It depends on the actual gpus used. Right now I'm on 5 x 60W and 1x125W for 425W on the 12V load. The other ~175W are from the rig itself on a normal ATX PSU.

The idea is to keep things "modular" in about 600W each to avoid transmission and other scale issues... If things goes right, and mining is still profitable after the incoming changes, I plan to move the modules to a better dedicated location, so keeping it modular is a must for now.

 

[sunshine_eggo]

I'm in central Chile, so I'm literally on ne of the best skies of the world ?

I take exception to that

600W array in Santiago, Chile on the left, my spot on the right. Arizona has great sun year round.

haven't figured out the numbers,

But this is really important. You need to know what to put in.

but the idea is to get panels sized significantly larger than the load (that is completely predictable) ... It depends on the actual gpus used. Right now I'm on 5 x 60W and 1x125W for 425W on the 12V load. The other ~175W are from the rig itself on a normal ATX PSU.

Revised for accuracy. You will likely need 1.5-2X the PV wattage than your loads.

The idea is to keep things "modular" in about 600W each to avoid transmission and other scale issues... If things goes right, and mining is still profitable after the incoming changes, I plan to move the modules to a better dedicated location, so keeping it modular is a must for now.

I really think you need to do a complete scenario to determine feasibility before you start buying hardware and experimenting.

 

[eavaria]

Thanks a lot for the info.

I have nothing indeed, and was surprisingly difficult to find information for my use case. Once I have a design I like, will start doing some numbers.

Right now the idea is to have 24 or 48V (not 12 because y need to step down to 11.4-12.6V before reaching the load and would be difficult from 12) and have a 12V on grid backup that can be switched to without interruption. Now that you mention it, probably I should consider an inverter for the times where sun produces more than the load needed. I need to do the math there too to know if it's better to go into 220V and feed the ATX PSU or charge the batteries and use it after sunset... But using batteries mean that I will need to dispose batteries in tje future, so I'm more inclined to use everything on the spot... I guess it will depend on the calculated efficiency...

Anotjer question... I've seen solar panels sold as 15x15 cm silicon squares to build the panels at will. Does it worth trying that way? It sounds tempting, but to me it's obvious that i'll get a percentage of defective parts others will get damaged on the construction, the protecting layers will interfere tbe radiation or who knows... Ending with 50% or less the power... That is the case right? ?

 

[sunshine_eggo]

There are hybrid inverters that work off only AC and solar, battery optional. Essentially, you would have PV and AC in to the inverter, AC out to whatever you want. Loads would be fed by solar first and then by grid - even partial solar would count.

The downsides are:
50W idle load - you pay this price even with no loads.
Probably about 80% efficient going from PV to AC to DC.

There is likely a 230VAC/50Hz version of this:

HYBRID LV2424 – 24V 2.4kW, 120V Output, 2kW Solar Input 80A Mppt (Grid Feedback Optional) – Watts247 Wholesale

watts247.com

Can accept 2000W of PV input.

This unit is made by Voltronix, which makes other brands as well.