Going Solar is in South Poland - final push needed!

[timomer]

Hey everyone,

I have been reading and info gathering for the last few weeks to get my head around getting my first solar system, I am keen to build myself and not purchase a "package" (cells, inverter, batteries, bms etc) as I wish to understand the system the best I can and also grow it over time. Im really lacking the confidence to do this and the temptation of a "package" buy has been getting more tempting, until I found this forum

While there is some great details here, we all have slightly diffrent needs and I am keen to get some direction and not assume other setups are right for me. I feel slightly lazy \ cheating making this post and appreciate any feedback - I just need one last push before committing to buy!

Quick intro to my situation \ needs...

• Located in South Poland with wife and child, I am English from London
• Been renovating a log cabin approx 200 m2 for 3 years, well insulated, air tight-ish, 3-phase power. Just moved in
• Have ran DC cabling 4mm2 along with AC in all rooms - plan is to have lights and USB-C powered by DC
• 800 ltr thermal store thats connected to a fire with back boiler
• Land that is south facing and gets a lot of light over winter and summer: Approx 50m of cable run to utility room
• Deep well pump that runs for 1 hour a week to fill two holding tanks on the hill: 550W
• Looking at PV only as like the flexibility / simplicity and wish to avoid solar thermal panels
• Not interested in being grid tied

What I want my system to do now...
Main aim now is to heat water and charge a modest battery bank so we don't have to rely on having a fire come summer for hot water and enough battery capacity for me to start tinkering with DC lights and USB-C sockets. My current thoughts are...

• 48v system
• 48v DC immersion heater
• mppt controller to charge batteries and then any surplus power direct to immersion heater
• solar tracker - will try and build my own, looking at ideas now
• The ability to monitor the mppt controller and any other parts of the system worth monitoring via Home Assistant
• 400w panels seem like a good price to watt, so maybe start with a few of them

What I want the system to grow too...

• Larger battery bank - unsure of our true needs right now
• Supply a single phase of AC to the house
• Supply 3 phase to the workshop
• Ability to divert surplus power to mutiple destinations, immersion heater \ well pump \ smaller pumps to move water for the fields
• Ideally, off grid (adjusting our power consumption to support this)

Questions I have...

• Is 50m from panels to batteries, etc classed as a large distance?
• I like the sound of the all in one units (MPPT, Inverter, BMS, etc) as I am not very experienced in this area and they seem "safer" for me to setup. Or, would it be much more flexible based on my needs to have a full DIY solution?
• How would I divert surplus power? I hear a lot about "dump loads" for wind and units to detect if you are passing to the gird and diverting this back to a AC immersion or direct panel to DC immersion heater but not my example use case. Ideally I would wish to control such devices via relays and use my own logic to decide what gets the surplus power (DC immersion heater, deep well pump, other pumps for moving water for the fields)
• Sounds like the LiFePO4 batteries are popular here, assuming as long as I end up with 48v im good here and its best to invest in LiFePO4 now and grow the bank as needed
• Really need some assistance regarding the schematics of such a setup, can anyone recommend a book \ guide on how to cover the basics? Wiring, correct fuses, etc
• How best is it to match the DC immersion heater to the correct panels, if I look at getting a 48v 2000w immersion heater assuming I would want a min 2000w of solar panels? Or is this too much messing around and its best to have a AC immersion heater via a inverter? Or is that bad for the batteries (so I have read)?
• How would I connect the inverter to the house phase, is it as simple as plugging it in!? Would I need to cut my supply from the grid to pull the power from my batteries via the inverter?

Many thanks all, sorry for the long post, I hope there are a few keen eyes willing to dish out some advise

Pic of our new home and sawbuck project from last weekend, behind me is where the solar panels would go

 

[KBWaldron]

Check out this page for dump load information.

 

[timomer]

Hi KBWaldron, thanks for the reply and pointing me towards diversion load controllers - I have been reading up on them and started drawing up some schematics of what my system may look like with the information I have found to date.

This is WIP and can be found here: https://docs.google.com/drawings/d/1JbJBruTpPzdCwkRkKjjj_AlenhAZl5_u9hocHYJmk-I/edit
Image also attached.


Im slowly getting there, have a few questions about how the diversion load controller is connected...

• Based on my drawing, is this the correct way to add a diversion controller to the system?
• Would the diversion controller manage the batteries and not the MPPT?
• If I get an MPPT with an AUX \ relay - do I need a diversion controller?

Welcome any additional comments on my schematics, this is based on what I have learnt to date and still have more to learn before I click that buy button.

Many thanks

 

[kernel]

Some of the conductor and fuse sizing could be revised.
Inverter fuse and conductors.
Main bus fuse and conductors.

Also you may get a little cleaner if everybody rides the bus aside from the bms disconnect and overcurrent protection which feeds it.

Not sure if your inverter needs a precharge resistor in order to work with the bms disconnect properly.

If you are going to employ diversion be sure its a stoutly built circuit, especially if employing a solid state relay or contactor and for everything but these type circuits should have overhead in the current and voltage ratings for good power handling and enhanced safety.

Looks like a good situation for Dacians electrodaccus diversion modules.

If your controller has a relay driver and or relays great, you wouldnt need an accessory diversion control. This is good because battery voltage/soc and or pv voltage or current can be used to trigger diversion with dwell.

A diversion control would go from the bus to the diversion loads if you can disconnect the bus.

You may have to have two or more bms controlled disconnects, one for loads and one for chargers, possibly one for the diversion depending on how much current it all adds up to.

My deepth of knowledge of system architecture for re applications basically ends at lithium and their associated bms and accessories, so im hoping someone will help you align that bit.

 

[timomer]

Hi Kernel,

Many thanks, I have been reading up and slowly progressing my understanding, a few questions on your reply if I may...

conductors

This is the cable size?

Also you may get a little cleaner if everybody rides the bus aside from the bms disconnect and overcurrent protection which feeds it.

Q: "rides the bus" what does this mean? BMS should connect to the BUS as well?
Q: "bms disconnect and overcurrent protection which feeds it." can you expand on what part of the system this is? Im worried im missing something?

good situation for Dacians electrodaccus diversion modules.

Im very impressed by this, unfortunately it only supports up to 24v systems


Also I maybe over complicating my understanding of a diversion load controller after reading up on this some more.

• Am I correct in thinking that a "diversion load controller" or "load output" \ "Aux" feature of a MPPT watch the charge state of the battery and once the battery is full activates a relay to activate a DC "load" ie immersion heater?
• If so, if I connect a suitable relay to the bus bars that I can control and I am able to monitor the battery charge in real-time that I can control this relay myself without the need for a off the shelf "diversion load controller", etc?
• How would the MPPT know how to control the panels in such a setup? Would it not just be monitoring the batteries and then shut the array down once fully charged? How would it be aware there is a diversion load active that is consuming power its providing?
  • Or, does the BMS have to control these loads so it can pass power to the batteries or diversion loads and the MPPT is none the wiser, it just keeps feeding the BMS?

Or, have I over simplified this?

 

[timomer]

fyi have reworked my design with my knowledge to date ?

Solar Setup | Draft

5kw 5kw Fronius Symo 5.0-3-M Fronius Smart Meter 63A-3 200m AC 3-fazowy DC Modbus FRONIUS OHMPILOT Galmet multi inox 800 GrzaÅka 9kW 400V 100m 100m Cat6

docs.google.com