This chart shows solar isolation in kilowatt-hours per square meter per day in many US locations. For simplicity, we call this figure "Sun Hours / Day".

To find average sun hours per day in your area (column 5), check local weather data, look at the maps at the bottom of this page, or find a city in the table below that has similar weather to your location.

If you want year-round autonomy, use the lowest figure. If you want only 100% autonomy in summer, use the highest figure.
 

State	City	High	Low	Avg		State	City	High	Low	Avg
AK	Fairbanks	5.87	2.12	3.99		MO	Columbia	5.50	3.97	4.73
AK	Matanuska	5.24	1.74	3.55		MO	St. Louis	4.87	3.24	4.38
AL	Montgomery	4.69	3.37	4.23		MS	Meridian	4.86	3.64	4.43
AR	Bethel	6.29	2.37	3.81		MT	Glasgow	5.97	4.09	5.15
AR	Little Rock	5.29	3.88	4.69		MT	Great Falls	5.70	3.66	4.93
AZ	Tucson	7.42	6.01	6.57		MT	Summit	5.17	2.36	3.99
AZ	Page	7.30	5.65	6.36		NM	Albuquerque	7.16	6.21	6.77
AZ	Phoenix	7.13	5.78	6.58		NB	Lincoln	5.40	4.38	4.79
CA	Santa Maria	6.52	5.42	5.94		NB	N. Omaha	5.28	4.26	4.90
CA	Riverside	6.35	5.35	5.87		NC	Cape Hatteras	5.81	4.69	5.31
CA	Davis	6.09	3.31	5.10		NC	Greensboro	5.05	4.00	4.71
CA	Fresno	6.19	3.42	5.38		ND	Bismarck	5.48	3.97	5.01
CA	Los Angeles	6.14	5.03	5.62		NJ	Sea Brook	4.76	3.20	4.21
CA	Soda Springs	6.47	4.40	5.60		NV	Las Vegas	7.13	5.84	6.41
CA	La Jolla	5.24	4.29	4.77		NV	Ely	6.48	5.49	5.98
CA	Inyokern	8.70	6.87	7.66		NY	Binghampton	3.93	1.62	3.16
CO	Grandby	7.47	5.15	5.69		NY	Ithica	4.57	2.29	3.79
CO	Grand Lake	5.86	3.56	5.08		NY	Schenetady	3.92	2.53	3.55
CO	Grand Junction	6.34	5.23	5.85		NY	Rochester	4.22	1.58	3.31
CO	Boulder	5.72	4.44	4.87		NY	New York City	4.97	3.03	4.08
DC	Washington	4.69	3.37	4.23		OH	Columbus	5.26	2.66	4.15
FL	Apalachicola	5.98	4.92	5.49		OH	Cleveland	4.79	2.69	3.94
FL	Belie Is.	5.31	4.58	4.99		OK	Stillwater	5.52	4.22	4.99
FL	Miami	6.26	5.05	5.62		OK	Oklahoma City	6.26	4.98	5.59
FL	Gainsville	5.81	4.71	5.27		OR	Astoria	4.76	1.99	3.72
FL	Tampa	6.16	5.26	5.67		OR	Corvallis	5.71	1.90	4.03
GA	Atlanta	5.16	4.09	4.74		OR	Medford	5.84	2.02	4.51
GA	Griffin	5.41	4.26	4.99		PA	Pittsburgh	4.19	1.45	3.28
HI	Honolulu	6.71	5.59	6.02		PA	State College	4.44	2.79	3.91
IA	Ames	4.80	3.73	4.40		RI	Newport	4.69	3.58	4.23
ID	Boise	5.83	3.33	4.92		SC	Charleston	5.72	4.23	5.06
ID	Twin Falls	5.42	3.42	4.70		SD	Rapid City	5.91	4.56	5.23
IL	Chicago	4.08	1.47	3.14		TN	Nashville	5.20	3.14	4.45
IN	Indianapolis	5.02	2.55	4.21		TN	Oak Ridge	5.06	3.22	4.37
KN	Manhattan	5.08	3.62	4.57		TX	San Antonio	5.88	4.65	5.30
KN	Dodge City	4.14	5.28	5.79		TX	Brownsville	5.49	4.42	4.92
KY	Lexington	5.97	3.60	4.94		TX	El Paso	7.42	5.87	6.72
LA	Lake Charles	5.73	4.29	4.93		TX	Midland	6.33	5.23	5.83
LA	New Orleans	5.71	3.63	4.92		TX	Fort Worth	6.00	4.80	5.43
LA	Shreveport	4.99	3.87	4.63		UT	Salt Lake City	6.09	3.78	5.26
MA	E. Wareham	4.48	3.06	3.99		UT	Flaming Gorge	6.63	5.48	5.83
MA	Boston	4.27	2.99	3.84		VA	Richmond	4.50	3.37	4.13
MA	Blue Hill	4.38	3.33	4.05		WA	Seattle	4.83	1.60	3.57
MA	Natick	4.62	3.09	4.10		WA	Richland	6.13	2.01	4.44
MA	Lynn	4.60	2.33	3.79		WA	Pullman	6.07	2.90	4.73
MD	Silver Hill	4.71	3.84	4.47		WA	Spokane	5.53	1.16	4.48
ME	Caribou	5.62	2.57	4.19		WA	Prosser	6.21	3.06	5.03
ME	Portland	5.23	3.56	4.51		WI	Madison	4.85	3.28	4.29
MI	Sault Ste. Marie	4.83	2.33	4.20		WV	Charleston	4.12	2.47	3.65
MI	E. Lansing	4.71	2.70	4.00		WY	Lander	6.81	5.50	6.06
MN	St. Cloud	5.43	3.53	4.53

The charts below show the sun-hours per day for the U.S.

Worst case winter-time averages