Proposed Solar System Design

To all,
Could I please get some advice/comments on this proposed solar system design. Based on what I want to run would 2 batteries and a 3,000 watt inverter be sufficient? This is for a hunting cabin in southern Tennessee that sees intermittent use (every two weeks).
Thank You All

10 panels - 5 pairs wired in series. This does not make sense when you consider your combiner box.

Do you mean 2S5P? Five groups of 2 panels wires in series with each of those groups in parallel?

4awg is a little excessive. 6awg would be under 3% drop.

I would likely choose 5S2P for 100Vmp and 10A Imp (rounded). 10awg would result in a 1.2% drop.

If shading or partial shading is a concern, all bets are off. Shade destroys solar.

ROUGHLY speaking, your 1000W array will likely only generate 2-3kWh/day in winter and 5-6kWh/day in summer, so it falls short of even your non-"as neede" list.

With only 9600Wh of storage - 4800Wh usable, your battery is very undersized for your needs. Your available solar is about right for your battery capacity.

You will need a generator and some way to charge the battery.

Concerning your as needed loads:

It's very important to make sane estimations of power usage. Specifying a full 24 hours of uninterrupted consumption is almost worse than doing nothing at all.

• If your 10 cuft fridge is a compressor type (residential), then your consumption will be about 800Wh/day.
• Your water heater will use dramatically less than this if you manage its use. They tend to take 1-2 hours of continuous running to come up to temperature. Are you sure about the power? Most hot water heaters have at least a 1500W element.
• Water pump. if this is a 12V RV-type water pump, it's unlikely that you'd ever use this for more than an hour in a day.

I would put your max use around 7500Wh/day assuming leaving the fridge on 24/7, 2 hours of water heater at 1500w and 1 hour of pump use per day.

First up is your load list. Some of the numbers seem a bit off , for instance I run a 30 gal water heater with 2000w elements for about 2 hours to reach temp with about 4000wh used. You list a 6 gal heater running at 430w all day (as needed) for 10,320wh. Your refrigerator seems high as my larger refrigerator is about 1500wh a day. And your water pump seems off also. Plus you say that lights are 12v with no indication of how you get that.

Knowing your daily loads is essential to calculating the amount of solar, battery and inverter. Take the number in your image of 19,464wh. To supply that means your panels over a sunny day would likely need to be 19464wh/5h=3892.8w

Your batteries are storage to carry you when no PV is available so must be sized accordingly. If they were to carry you an entire day without PV and your loads were 19464wh you would divide 19464wh/24vDC=811ah

Your inverter must be sized to not only run items but to start them. 3000w is adequate in my experience for most 120vAC plug in items.

Calculating the loads is somewhat difficult from a usage perspective. This install is for a hunting cabin that I use every week or so during the winter and 2-3 days every week or so during the summer. Nothing will run 24/7 and water heater/water pump will be used for showers so probably only a couple of hours to heat up water for a shower and then it is turned off. I had a hard time coming up with wattage use for a 10 cubic foot fridge (have not purchased yet) with no stats on the shopping sites I looked at so I went with 100 watts as an estimate which may be too high.

@sunshine_eggo I do have another string in the box if I wanted to add two more panels but for now that is all I have. I am going to assume I can leave one string empty and add two more later. The "2S5P" is a typo so ignore that. Considering what I have is wiring the solar panel array as I outlined OK or is there a more optimal way.

Arrowshot said:

Calculating the loads is somewhat difficult from a usage perspective.

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it's always a challenge, but a sensible best guess works.

Arrowshot said:

This install is for a hunting cabin that I use every week or so during the winter and 2-3 days every week or so during the summer. Nothing will run 24/7 and water heater/water pump will be used for showers so probably only a couple of hours to heat up water for a shower and then it is turned off. I had a hard time coming up with wattage use for a 10 cubic foot fridge (have not purchased yet) with no stats on the shopping sites I looked at so I went with 100 watts as an estimate which may be too high.

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There's a Magic Chef 10.1 cu-ft unit. I highly recommend it. i put these in our RVs when their propane fridges failed. They sip power. 60W when running and never more than 800Wh/day in summer. Much less when it's cooler.

Arrowshot said:

@sunshine_eggo I do have another string in the box if I wanted to add two more panels but for now that is all I have. I am going to assume I can leave one string empty and add two more later.

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Putting 5 strings into a 6 string combiner box is no concern.

Arrowshot said:

The "2S5P" is a typo so ignore that. Considering what I have is wiring the solar panel array as I outlined OK or is there a more optimal way.

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I can't glean how your panels are wired based on your description. I presented you with 2S5P and 5S2P numbers.

Arrowshot said:

To all,
Could I please get some advice/comments on this proposed solar system design. Based on what I want to run would 2 batteries and a 3,000 watt inverter be sufficient? This is for a hunting cabin in southern Tennessee that sees intermittent use (every two weeks).
Thank You All

Click to expand...

Only comment I have is that I would recommend choosing either 12V or 48V. There is far more equipment available for them than 24V.

To get real world measurements of plug-in 120 AC items buy a kill-a-watt meter.
At least that would educate your guesses.

All right, gonna keep plugging away at this till I understand what works and I very much appreciate your patience helping me figure this out. I revised the figures in the Daily Wattage Calculation chart to reflect as closely as can what the useage will be and the number has been revised down quite a bit. Responding as well as I can also to your questions with answers below. Please be patient, I’m 70 years old and although not quite as dumb as a stump I come close.

@Mattb4
You list a 6 gal heater running at 430w all day (as needed) for 10,320wh.
- This is a mini-tank water heater and pump which I only intend to run for showers for a few hours when I am there and then shut down. Revised my figures for the heater and pump in chart.

Your refrigerator seems high as my larger refrigerator is about 1500wh a day.
- sunshine_eggo noted the same and suggested a fridge that would run about 60 watts so I redid my numbers in the chart based on his suggestion

And your water pump seems off also.
- Specs listed for that pump are ECO-WORTHY Diaphragm Pump 110V 1.5 max amps

Plus you say that lights are 12v with no indication of how you get that.
- Corrected on chart.


@sunshine_eggo

If shading or partial shading is a concern, all bets are off.
- Full sun once it comes up till very late in afternoon. No trees or anything else blocking (except clouds of course). Should have mentioned I am in South Tennessee near Nashville.

Are you sure about the power? Most hot water heaters have at least a 1500W element.
- Specs on the web site state 1300W. Taking it for granted it is accurate.

4awg is a little excessive. 6awg would be under 3% drop.
- Already have the 4awg so it will probably be used. Have about a 60’ run from panels to controller.

You will need a generator and some way to charge the battery.
- Have 8,000 and 3,000 watt generators if needed. The 3,000 watt one resides there permanently.

With only 9600Wh of storage - 4800Wh usable, your battery is very undersized for your needs.
- Revised the figures to reflect more realistically what could be used each day. Still adding in a few things even though they might not be used (i.e. toaster and microwave (have gas stove) and table fan (depends on how hot it is).

10 panels - 5 pairs wired in series. This does not make sense when you consider your combiner box. Do you mean 2S5P? Five groups of 2 panels wires in series with each of those groups in parallel? I would likely choose 5S2P for 100Vmp and 10A Imp (rounded). 10awg would result in a 1.2% drop.
- Yep, you done lost me there. I was under the impression that I could wire each pair of panels (5 total) in series and connect each pair to one of the strings in the combiner box and run the 4awg wire from there to the controller??? Is there a better way to set up the panels? If I have a 24v system nominal PV power for my charge controller is 2,000W per below and other stats if that helps.



Thanks again!!!

Arrowshot said:

@sunshine_eggo

If shading or partial shading is a concern, all bets are off.
- Full sun once it comes up till very late in afternoon. No trees or anything else blocking (except clouds of course). Should have mentioned I am in South Tennessee near Nashville.

Are you sure about the power? Most hot water heaters have at least a 1500W element.
- Specs on the web site state 1300W. Taking it for granted it is accurate.

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I wouldn't sweat 1300W vs. 1500W, but you indicated 430W.

Arrowshot said:

4awg is a little excessive. 6awg would be under 3% drop.
- Already have the 4awg so it will probably be used. Have about a 60’ run from panels to controller.

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No harm in using thicker especially since you have it.

Arrowshot said:

You will need a generator and some way to charge the battery.
- Have 8,000 and 3,000 watt generators if needed. The 3,000 watt one resides there permanently.

Click to expand...

What charger?

Arrowshot said:

With only 9600Wh of storage - 4800Wh usable, your battery is very undersized for your needs.
- Revised the figures to reflect more realistically what could be used each day. Still adding in a few things even though they might not be used (i.e. toaster and microwave (have gas stove) and table fan (depends on how hot it is).

Click to expand...

Arrowshot said:

0 panels - 5 pairs wired in series. This does not make sense when you consider your combiner box. Do you mean 2S5P? Five groups of 2 panels wires in series with each of those groups in parallel? I would likely choose 5S2P for 100Vmp and 10A Imp (rounded). 10awg would result in a 1.2% drop.
- Yep, you done lost me there. I was under the impression that I could wire each pair of panels (5 total) in series and connect each pair to one of the strings in the combiner box and run the 4awg wire from there to the controller??? Is there a better way to set up the panels? If I have a 24v system nominal PV power for my charge controller is 2,000W per below and other stats if that helps.

Click to expand...

You can do what you propose. The way you describe it implies that you put two panels in parallel, then place each of those parallel pairs in series:



What you describe appears on the left. I believe you really mean 2S5P on the right.