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Solar System Sizing - Capacity Factor

2015 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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Not many people can afford to size a system to cover them 100%. It will be a lot cheaper to make a system that will cover your needs 95% of the time. Part of sizing figuring out more panels or more battery is the cost effective compromise. Battery chemistry is an important factor. Lithium iron phosphate will likely die from old age rather than cycle life so you could use the the whole battery 100 to 0 % instead 100 down to 80 % for a lead acid.

Second is you will likely/want need a generator at some point - a duel fuel gas/propane unit would be ideal. As long as you can keep it in the can propane is good. Buried tanks with isolation valves would be ideal. The generator needs to be able to properly supply the battery bank.

Go watch a lot of Will Prowse vids on youtube.
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Just a reminder that new things tend to work better than old things. Deteriorated panels produce less, batteries hold less, refrigerators need more power so factor that in to your calculations for the sizing criteria.
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