Help needed! - SunPower, LG, or Panasonic?!?

[scrambler]

There is a simulation site you can use for that called PVWatt at https://pvwatts.nrel.gov/
You can enter your exact location, the power of your array like 20 x 300W panel is a 6kW array
Then you enter the orientation of the array and its tilt, and that will estimate the yearly production for that array.

This will allow you to figure out what array power will produce the yearly energy you need.

There is also a book called solar for dummies often recommended here for a more complete education.

[J.P.M.]

Sorry - one more question. I've been quoted for different levels of power. I'm not sure what I need. As a refresher, I average about 730 kWh/month (or 8760 kWh/year). I know the power I *actually* produce depends on a million different factors. But, if I want 100% offset, how many watts should my panels total?

Don't be sorry, but don't be surprised if/whenyou get more answer than you think you were asking for either.

As I suggested, read the book. most of your questions may well be answered. Until then, to your question of array size, first get your historical usage by month or more granular time frame from Rochester Gas & Electric. Then, also as I suggested, get familiar with PVWatts. Again, read all the help screens a couple of times first. Get your orientations as close as you can, and do a few runs.

SEE EDIT NOTE BELOW Depending on an array's orientation, at your location you can expect an unshaded south facing array with maybe a 30 deg. tilt to produce something like approx. 1,300 or so kWh/yr. per installed STC kW - and note, LESS maybe, and very approx. 150 -200 kWh/yr. per installed STC kW for snow that will sit on the array. Trust me - it will happen. Maybe more, maybe less.

So until the PVWatts model with good input tells you something different, and provided it makes economic sense - that probably means and includes the availability of Net Energy Metering from your POCO ( = POwer COpany), for a 100 % offset, divide your annual kWh usage from Rochester Gas & Electric by, say, maybe 1,100 kWh (that 1,300 kWh/yr less, say 200 kWh/yr for a snow penalty, and that might be a very rough 1st approximation of an array size.

So, if your annual usage is, say, 9,000 kWh/yr., a first rough cut on an array that's south facing at a 30 degree tilt might be: (9,000 kWh/yr)/(1,100 kWh/yr per installed STC kW) ~ = 8.2 STC kW. Not: your roof tilt will probably be different than 30 deg. Different array orientations, both for tilt and azimuth will produce different annual outputs. The SWAG for west facing might be closer to ~ (9,000 kWh/yr.)/(875 kWh/yr. per installed STC kW) = 10.3 kW.

The optimum for your location is probably close to due south (maybe just a bit east of south by a few degrees) at a tilit of maybe 35 to 45 degrees off the horizontal. Most roofs (if you're stuck with a roof mount) are probably not at an ideal array orientation. PVWatts allows for relatively easy manipulation of the tilt and azimuth. If I were to guess, from the numbers your reporting from vendors, you're considering mounting on a roof that has a somewhat less than optimal orientation.

Q: Why are you considering PV. Or, how much do economic factors enter into your considerations ? Reason for asking: a 100 % electrical offset with PV may or may not be the most long term cost effective choice. If economics don't matter, size without regard to cost effectiveness. If they do matter, to the extent they do, add solar process economics to your required reading list.

Take what you want of the above. Scrap the rest.

Edit/add: Just noticed your info on roof mounting and azimuth. Change my snow influenced SWAG/estimate downward to ~ maybe 850 - 900 kWh/yr. per installed STC kW.

[J.P.M.]

Haha it's supposed to snow again tomorrow. Typical upstate NY weather!

Yea, no stuff !

A short story:

After living in/around Buffalo for > ~ 20 yrs., on a day in early May in the early 1990's, I was sitting in my kitchen after dinner looking at ~ 6" of snow on my back deck after I had barely made it home from work after leaving early because of a snow storm. That was the final straw for me. I started planning/investigating places where winter either didn't exist or at least didn't give me a 6 month war mentality once a year. I now live in zip 92026. Most folks around here don't have a clue what it's like living in such a climate. I still have many friends and fond memories of times back then and there. Many of those friends spend some time with me each winter. Not many dull moments around my house from New Year's 'til about Easter or so.

[blueman2]

As for LG panels, I have already had 3 of my 16 panels fail within 8 months of installation. Not sure what is going on, but LG did confirm they had failed and replaced them. But it took 6 months to get their approval and get the new panels installed. It appears LG quality is not what it used to be. Installed Nov 2019, first failure occurred Dec 2019, and 3 had failed by Feb 2020.

[Mike90250]

As for LG panels, I have already had 3 of my 16 panels fail within 8 months of installation. Not sure what is going on, but LG did confirm they had failed and replaced them. But it took 6 months to get their approval and get the new panels installed. It appears LG quality is not what it used to be. Installed Nov 2019, first failure occurred Dec 2019, and 3 had failed by Feb 2020.

Well, that's a bummer. Lets hope all the weak ones have failed and the rest will be ok