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Solar System Sizing - Capacity Factor

2016 Views 45 Replies 14 Participants Last post by  saln
Just wondering if anyone has any real time information on what their solar array produces. Total panels vs average production. If you know your "sun hours" please let me know that also.

Short story long:
I started a renovation and wiring a house for my kid. It's gutted and I am starting from the studs. All new electrical including new incoming/meter/disconnect and a new 200A load center/breaker panel.

The goal at the house being renovated is to put most outlets and lighting to a transfer panel and run off an inverter, solar, and batteries most of the time. Larger 120 Vac loads like microwave, toaster oven, and bathrooms would normally be on grid power (and GFCI), unless there's a grid outage. If grid is down, appliances could be could be moved to "inverter" outlets, and use them selectively (so not to overload the inverter) from battery back up.

If grid is down, HVAC (mini splits), dryer, electric range and electric hot water are also down. Those loads are too big to even consider right now.

Sun hours for solar panels in NW PA is poor. Energy storage via batteries will be a big part of the system. System will not be grid tied.

I am questioning the calculation done with an online calculator. They recommend 4.5KW (4500 watts) of solar panels based on a winter "sun hours" of 2.64 hours/day. In the last 27 days, the sun has come out 6 days. Two of the six days was only for a couple hours in the late afternoon. Essentially four days of sun in the last 27. I know solar panels generate some power even with cloud cover. (10-25%?). A friend has 12,000 watts of solar. On one of the sunny days, they generated 20.2 Kwh.

I think the 2.64 hours/day for my area is very optimistic. My AO is between Cleveland, Buffalo and Pittsburgh which are the #3,4, and 5 gloomiest places in the country.

What they recommend, I assume, is based on a "capacity factor" for my zip code. But I think they are a little low at 4500 watts of panels.

I may also need to rethink my battery back up (go to multiple commercial server rack batteries) and upgrade to 48vDC/120vAC inverter. Assuming no more than 3000 watt peak, and about 6000 watts/day.

Worst case-grid down, cold weather and on batteries:
Hours On per Day​
Watt Hours per Day​
Coffee Machine110000.2200
Fridge - 20 cu. ft. (AC)135341412
Toaster Oven112000.2240
TV - LCD11503450
Freezer - Chest - 15 cu. ft.127041080
Smart Phone- Recharge161060
Video Game Console11501150
Box Fan120061200
LED Bulb - 100 Watt Equivalent92351035
System Calculation Results​
Total watt hours per day6863
Killowatt Hours per Month:206 kWh
Peak Load: (4650 watts .....BUT selective/controlled use of electrical so not to exceed 3000 watts peak on a 3500 watt inverter when on battery power)4,650 watts
Sun Hours:2.64 hours/day
System Size:4.51 kW

I am not affiliated with this company but the information is from:

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Are you trying to cover most of the conveniences that electricity offers? When power is down, you cut back on anything that is not necessary to get thru the day.

A larger bank is good to focus on. This way it covers night time and the off days when sun is not producing.

You can add panels until at a comfortable level of power to recharge. Securing alternative heating sources would seem to be paramount that far north.

Coffee maker and microwave should be considered luxuries when grid is down. Focus on keeping food from going bad and learn to see in the dark. Re-learn how to read real books to pass your time if everything else is under control.

After that last arctic blast before Christmas, I had enough of relying on propane to keep warm. It gets expensive fast. I finally installed a pot belly stove and worked a way to have quasi central heating so the upstairs and downstairs is relatively at the same temperature.

All of my lighting is LED and most of the standard bulbs only draw 4 watts. I carefully watch what is drawing current later in the afternoon until I loose all sunlight for panels. During the day, not so much. The batteries need some load so they get a full charge, instead of in float.

During milder weather and longer days, I might not draw enough from battery bank to take the control charger out of float. Sometimes this has been a inconvenience at night if I dont want to let the voltage drop too much.

There are enough things from your list that will be a constant drain on your battery bank. So at night, your batteries have to be in full charge or you drop below a save margin for longevity.

Hopefully you are not in a large populated area or inner city. Having some acreage or at least access to wood to burn if necessary sometimes. At least some deadfall during emergencies.

My solar array is fairly small, but runs everything I need for now. I have south and west facing panels on the roof. Around 3 pm during the winter months, my panel output drops off substantially for a half hour as the sun transitions between the two rood angles.

It took me a while to even figure this out. During the summer months, not even noticeable. Even with the leaves blocking a lot of the panels. But the winter angle of sun really cuts down on output. It does not take too many branches or limps to block a few cells to drop voltage down a bunch.
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I am out at my cabin, and future residence, while the weather is below freezing and full heavy cloud cover. Checking out how well my pot belly stove works for the first time since it was just installed. Yesterday my batteries were fully charged and I had no problems running things as usual.

Saturday was sunny and battery bank was full charged. But without sun yesterday and all today I had to watch things and be careful so not to drain them down. I avoided using much power today since panels were not very productive.

Tonight my battery bank is up but not fully charged. Looks like for most of this week is going to be mostly the same. I have 1800 watts of panels but more than one day with heavy overcast and freezing drizzle, not much happening in the way of output from panels.

I have not run in to this problem before. Usually I can cut back and problem. But the cloud cover, drizzle and almost what looks like fog is not letting any rays thru.

If too heavily overcast tomorrow like today, I will expect my batteries to not charge enough so they wont be getting much use. Will rely of generator in that is the case. Most the time especially when not so cold I dont loose so much like this week.

Must be Al Gores fault
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