Thanks for the ping - a couple of questions?
With your inverters, do you have to have batteries also? If so, how many and what kind?
Why two inverters instead of one, is one just a backup / stand by? Or, two inverters are needed for the number of panels you have?
How many panels does it take for you to generate ~1800 kwh/month in the summer?
Thanks - I always want to understand things. One cannot make a good decision without quality data!
1. I do have batteries: I now have 18 5.14kWh each (total 92kWh storage). For the first year I had 6 of them as part of Phase I to study the results for a year before adding to it in Phase II (last month) to have the full system I originally was shooting for. They are Gyll brand name (the only part of the system made in Cheyna) LifePo4. They each put out at 48V/100Ah (in some ways it's 51V/100Ah) for a total of 4.8kW at a time.
2. I have 2 inverters so that they work in parallel. If I was buying the original system this year I'd have a handful of smaller inverters working in parallel. As it is I bought a good one last year in Phase I with the understanding that if I liked the results I'd buy a 2nd one to double the inverter capacity (and charge controller capacity). Together they give me a total of 18kW continuous AC power from DC (whether the DC power comes from the panels or the batteries or a combination of the two). So if my clothes dryer is on high (6kW) while the old A/C was running (4kW) plus 1kW of various consumption in the house, with just one 9kW inverter it'd have to pull the remaining 2kW from the grid even if my batteries were fully charged and it was a bright sunny day. Then there was my switching over my two natural gas appliances to electric (which increased my power load some, though when doing so I got rid of the old A/C unit and I now use a variable speed heat pump for both A/C and most of my heat). And yes, since the inverters are also charge controllers I needed to double my inverter capacity anyway during Phase II when I doubled my solar panel capacity. Then on top of that I now have an EV -- one of the reasons I got this inverter brand is because it has an optional feature to power a separate electrical panel only on the condition that my home batteries are charged at least so much (I have it set right now to 80% SOC). Thus, if my EV isn't fully charged, but charged enough to get me at least 100 miles, I plug the EV into an intermittently powered 240V outlet (I'll get a charge only if it's free solar power I had no other use for anyway). Of course, if I come home with the EV on a low charge or if I planned a weekend getaway the next day, I plug the EV into a constantly powered 240V outlet that's tied to the normal electrical panel.
3. How many panels does it take to generate ~1800kWh?month in the summer? I used http://tsi.tyconsystems.com/html/nrel_lookup.htm to get the average daily peak solar hours each month in your area, assumed a 10% loss in efficiency, and was almost spot on in my calculations with my initial solar install (for Phase II this year my calculations are based on my first year's performance alone). Let's say for July it shows 5.3 peak solar hours in your area.
1800 X 100 ÷ 90 ÷ 30 ÷ 5.3 = 12.6 kW needed per peak solar hours on sunny days. (That was 1800 desired kWh/month X 100 ÷ 90 to account for a 10% efficiency loss, divided by 30 to convert from monthly to daily, divided by peak solar hours per day that month.) To achieve 12.6kW daily, if your panels are 330W that's 12600 ÷ 330, which is 38 panels.
I'd also suggest going to https://www.wunderground.com/history (I hope no connection to old school domestic terrorists like Obama's man Bill Ayers and that Weather Underground). Pick some dates that you know were extremely hot and extremely cold (if heating with electricity like I'm now doing). I was pleased to find out that in my area, almost every time it's either really hot or really cold it's a sunny day. Thus I have free solar power when my home needs it most (for the extra power needed to cool the house our heat the house to handle the temperature extreme). If that's not the case for you then you might not want to go solar -- winning the battle over cooling and heating is the primary battle in winning over the power bill.
If your attic gets really hot like mine does, you might also want to consider a hybrid water heater whether or not you go solar. (Winning the battle over the water heater is probably the 2nd most important battle of saving on home energy costs.) A hybrid water heater has a built-in heat pump and heats the water tank by drawing heat from the air around it. In my case, I duct the air intake from the attic: pulling in really hot air with plenty of heat so the water heater doesn't have to work as hard to find heat from the air. For the cold air output of the water heater I sometimes vent that into my living quarters so my home A/C (variable speed heat pump) doesn't have to work quite as hard during the 8 or 9 months I'm cooling the house. During the winter months I flip a wye lever on my output duct and push the cool air output into the attic (but away from the air input). That one trick is helping me save power on both keeping my home cool and on heating my water -- all while the water heater draws only 300 watts anyway (but admittedly it does run for 2 hours during the summer and 4 hours during the winter, but it's till better than a 4kW normal electric water heater running for 30 minutes).