HELP! DIY Residential Build - Need Advice

melonmanny

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Joined
Jun 2, 2021
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4
Greetings,

I am buying my first solar system ever and I need some help in making sure what I order is going to be enough for the house. I also wanted some recommendations on solar panels. I'm looking for a panel that will last 15+ years in very cold weather and starts with 19% efficiency.

The items I am looking to use for my house are as follows. My highest load day ever is usually 12 kwh in the winter where I use electric to heat my home. The average days are around 7-9kwh.

My questions are

1) How much KWH would I need to go grid-less with my current needs based on few calculators I've used are 8kw of panels needed per day.
2) Do the items I am purchasing make sense or am I missing something below?
3) How many inverters can I use for a 8kwh system? The reason I'm thinking this inverter would be enough for whole house is I know the inverter can be smaller than total solar panel build. Please share your thoughts. Do I need two or one inverter?
4) Any recommendations on residential solar panels at the moment and where to buy them?

Thanks for the help. Again, just looking at if I'm over doing it for my very small house in Vermont. I oversized some due to sunlight issues and not optimal sun facing house.

Plan:

$8000 for two 12 KWH solar battery: https://bigbattery.com/products/48v-kong-lifepo4-233ah-12kwh/
$3000 for two all-in-one inverters https://watts247.com/product/lv6548...erter-4kw-250v-mppt-bms-ul1741-built-in-wifi/
Lastly, I'm looking for recommendation for a .50 cent per watt solar panel for this system. There's no limits on size or weight that the system can be.
 

bgflyguy

Solar Enthusiast
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Jul 8, 2020
Messages
112


Those are the two flavors of the month, but even at those two vendors there are a lot of options. Since it's cold the bifacial panels might perform pretty well.
 

melonmanny

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Joined
Jun 2, 2021
Messages
4


Those are the two flavors of the month, but even at those two vendors there are a lot of options. Since it's cold the bifacial panels might perform pretty well.
Dude those panels 410w are PERFECT. You are amazing thank you SOOOO much for the recommendation. I doubt I could find better. Any thoughts on the 2 inverters and batteries as part of the panel. Am I missing anything?
 

bgflyguy

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Jul 8, 2020
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Glad I could help. I'm just parroting what the cool kids are saying these days. There are a lot of panel options right now.

Are you trying to go split phase?

Those are only 250v input, so you could only do a string of ~ 5 panels. I'm looking at those as well, but that's pretty limiting.
 

melonmanny

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Jun 2, 2021
Messages
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Glad I could help. I'm just parroting what the cool kids are saying these days. There are a lot of panel options right now.

Are you trying to go split phase?

Those are only 250v input, so you could only do a string of ~ 5 panels. I'm looking at those as well, but that's pretty limiting.
They have 2 solar connections so I'm guessing you could max have 10 panels ( two strings of 5 each ) I mean if I got two that would be 8kwh with the 410w panels, not too bad for a starter.
 

melonmanny

New Member
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Jun 2, 2021
Messages
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Glad I could help. I'm just parroting what the cool kids are saying these days. There are a lot of panel options right now.

Are you trying to go split phase?

Those are only 250v input, so you could only do a string of ~ 5 panels. I'm looking at those as well, but that's pretty limiting.
I think you're wrong. The 5 parallel panels are to connect 5+ of the inverter system together. This is not referring to the solar panels. Right?!
 

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bgflyguy

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You can attach more than 5 panels, but there is a 250V "Maximum PV Array Voc" which with a 50v panel limits you to a 5 panels in series.

I didn't notice it had two inputs, so that is 2x250v not just 250v. So you can run up to 2x4kw of panels. So with the Bifacial panels you could to something like 2p5s for 10 panels on each input.
 

svetz

Works in theory! Practice? That's something else
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Sep 20, 2019
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Welcome to the Forums!​

Don't know much about the hardware end of things, but can double-check the math!

My highest load day ever is usually 12 kwh in the winter where I use electric to heat my home. The average days are around 7-9kwh.
1) How much KWH would I need to go grid-less with my current needs

So, you consume 12 kWh, how much do you need to generate?

Let's assume an 85% battery round trip efficiency, a 90% inverter efficiency, a 98% MPPT efficiency, and assume the last two consume 30 watts, so over 24 hours that's 720 Wh. (You'd want to change the numbers to match your preferred gear).

So, your total power needs become (12000+30x24) / .85 / .90 / .98 = 17,000 watt-hours
(Update: During the day you can skip the battery round trip losses, only the energy stored in the battery is subject to that)

1) ... based on few calculators I've used are 8kw of panels needed per day.

How many kW of panels depends on where you live to get the insolation. You can get pretty accurate with SAM or PVWatts. We know your somewhere in Vermont, so let's guess Montpelier as it's in the calculator's list and sounds pretty cool. We also know you need 17 kWh per day in winter, so we should optimize the panel tilt for when you need the most power.

From a simple calculator we get:

1622719419563.png

So, 17,000 / 2.54 = 6700 watt solar array, minimum. You might want a bit more to get some more oomph for slightly overcast days.
If you got an 8 kW array, for that location in winter it would generate 20 kWh/day in winter and in August would generate 34 kWh/d.

If your location has a good net-metering agreement, going grid-tied will let you make use of that excess summer energy. You might even be able to shrink/optimize the array for year-round, that way you could bank summer credits to pay for winter usage, which would allow you to have a much lower cost system upfront and eliminate the most expensive part (batteries).

I oversized some due to sunlight issues and not optimal sun facing house.
Partial shade on panels is really bad, so bad it can negate the warranty of some panels (like my LG Neons). If you've a lot of crazy shifting shade, I'd say look at Enphase microinverters or SolarEdge. Be sure you understand what shade on one panel does to a string of panels if you're trying to plan around it.

3) How many inverters can I use for a 8kwh system? The reason I'm thinking this inverter would be enough for whole house is I know the inverter can be smaller than total solar panel build. Please share your thoughts. Do I need two or one inverter?
Most inverters cannot be stacked with other inverters. Be sure the one you've picked out does (often this called a "parallel" feature).

Grid-tied inverters are typically sized around the array size. For Hybrid and offgrid inverters you need to look at your Energy Audit.
For example, a 6 kW inverter can supply 50 amps at 120V, if you had something that consumed 60 amps you'd need 60 x 120 = 7200. Often times when the heat comes on, the hot water tank is on, and then someone turns the microwave on, it will trip the inverter because they sized for the average load rather than the true-usage load. The audit will show you the likely true maximum.

4) Any recommendations on residential solar panels at the moment and where to buy them?
Shipping is usually a big cost, if you buy from a local distributor and cutting out the shipping might make new quality panels affordable.

Hope that's of some help! Good luck!
 
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