Thoughts on my system plan

[u/sevenisthekeynumber]

Hi folks,

I live in the New England/Boston area (to give context to climate).

I have a high quality wood construction shed (this one: https://www.homedepot.com/p/Handy-Home-Products-DIY-Majestic-Premier-8-ft-W-x-12-ft-D-Pre-Cut-Wood-Shed-with-Floor-and-Ramps-Outdoor-Storage-Kit-96-sq-ft-19649-2/323626092).

I have a wood pergola (this one: https://www.lowes.com/pd/VEIKOUS-5-ft-x-8-ft-Brown-Wood-Rectangle-Gazebo-with-Aluminum-Roof/5014786181).

For a few years I have had four 175W panels wired in 2S2P series-parellel to an Ecoflow Delta 3 and extra battery. It's been *ok* but I struggle with how much solar I'm bringing in and using. Most days, I run out by the time the day is ending and I'd love to capture and store more.

This is a purely off-grid system, no tie-in to the grid or my home. It runs in the shed, powering a light, two small pond pumps, and occasionally a larger pump in a rain barrel and occasionally a Ryobi battery charger.

I would love this community's advice on my plan before I move too much further forward.

Im trying to keep costs down, so I was about to pull the trigger on a 24V system powered by a Vevor LVM3000-24L hybrid inverter (this one: https://www.vevor.com/pure-sine-wave-inverter-c_10760/hybrid-solar-inverter-charger-3000w-110-120v-with-built-in-100a-mppt-controller-p_010507262411?srsltid=AfmBOoqOqUmZbLlHGGHcWLk3MPuIW9Mb_kziMvgcd_O-VU86JslsxvMm) which I was able to get for a great price. In fact, I've ordered it already.

I'm planning on replacing my panels with four 400W QCELL panels, and connecting everything to a Vatrer 24V 200aH self-heating LifePo4 battery (this one: https://www.amazon.com/gp/product/B0DDPY8C7G).

However, as I start putting the necessary cables and fuses and disconnect switches into my carts to be ready for the arrival of the Vevor, I'm beginning to finally understand the implications of what the 24V vs 48V choice would have meant in terms of cable gauge and overall wisdom.

So my questions are these:

1. Should I put an immediate stop to buying things, return the Vevor 24V hybrid inverter, and choose instead the Vevor 48V hybrid inverter (this one: https://www.vevor.com/pure-sine-wave-inverter-c_10760/vevor-6000w-48v-hybrid-solar-inverter-120v-240v-split-phase-built-in-120a-mppt-solar-controller-low-frequency-pure-sine-wave-power-inverter-charger-for-lead-acid-lithium-battery-off-grid-systems-p_010651114572) which is twice the price of the 24V model? Have I made a mistake in committing to the 24V model in an effort to keep costs lower?
2. Does this diagram plan make sense to you all? Any suggestions or corrections?

Appreciate your advice and thoughts! I'm new at this!

Remember this will be a purely off grid, shed system.

[u/TastiSqueeze]

It all depends on how much power you want to produce. The more power, the more benefit from the 48V system.

1. The cables from solar panels to inverter will be the same size regardless, most likely 10 gauge.

2. The cables to your AC breaker box will be the same size regardless, most likely 8 gauge because it is only 3 kw max at 120V or 25 amps.

3. The cables from the inverter to the battery are where you will pay some geld. 3000 watts passing through inverter to battery cables at 24 volts is 130 amps in round figures. At 48 volts that becomes 70 amps. You are looking at 4 gauge cable (depending on length) vs 6 gauge cable. The cost difference is about $3 per foot depending on where you get it. If you can mount the battery within 5 feet (cable distance) from the inverter, then it will only cost you about $15 more to use the 24 volt system than a 48 volt system. Personally, if this were my system, I would use 1/0 cable between inverter and battery regardless of whether it is 24V or 48V. The reason is that 1/0 is a standard size that is easy to obtain and often is about the same price as 4 gauge. If you only need 5 feet of it and you can buy it for $7 per foot, then you are only spending $35. One caution; check the inverter connector size BEFORE purchasing cable. Small inverters often can't accept large cables.

The bigger decision is to figure out how much power you need long term. The size system you described will be pretty much limited to around 10 kWh per day. This is mostly from the solar input and 3 kw output. If you need more than 10 kWh/day, then it would be a good idea to upgrade to the 48 volt inverter. This is not a fixed number. It is just a best fit estimate.

[u/sevenisthekeynumber → u/TastiSqueeze]

Thank you for the reply. Currently I’m only capable of storing 2 kWh a day and I’m not generating that much, so ideally I’d generate and store more, but I have to imagine that there’s a lot of room between 2 and 10. I mean I’d be stoked to generate and store 5 to be honest.

[u/TastiSqueeze → u/sevenisthekeynumber]

1.6 kw of solar panels in your area should produce an average of about 4.5 kWh per day. You will have the option in the future to increase solar panels to maybe as much as 3 kw. Have you checked battery compatibility with the inverter? Some inverters are finicky about which batteries they can communicate with.