Am I Crazy?

[russ]

for your area's sun hours and potential production try http://pvwatts.nrel.gov/

[sandiegolloyd]

Starting to understand

Ok I think I am beginning to understand the instantaneous versus total. So what is the formula to calculate the number of panels required for a desired annual power output? I was using the following:

Total desired annual 13,500 kwh

divided by

365 days

divided by 24 hours

equals 1.5411

multiplied by 5 (hrs of good sun in my area)

equals 7.7055 kw system

I then divided this number by the power output rating of the panels 250 versus 305 and get a different number of panels depending on which panel output I use . It seems like this formula is not accurate since the inverter output is a gating factor and I don't see where I would take into account that with a higher output panel you get 25% more "total" output. thanks!

[Wy_White_Wolf]

....
7.8kw/ 250w panel = 31 panels
7.8kw/305w panel = ~26 panels

How can this be when the micro- inverter is max 250w so it seems like I would always have to buy the 31 panel system to get my annual output. Any comments would be appreciated!
Thanks!

Because you are only thinking about instintaous outout instead of total daily production.

A 250W panel with a 250W MI will only put out out 25W under ideal conditions. While a 305W panel on a 250W MI will put out the maximum that the inverter can handle for hours on end. At the end of the day the larger panel would have provided about 25% more then the smaller one.

WWW

[Naptown]

Then save a few bucks and use a solar edge system. all the advantages of M250's monitoring wise, will meet the 2014+ NEC and costs less.

[slopoke]

I plan on designing and installing a solar PV system on my roof. I contacted two solar equipment wholesalers and got strange responses regarding how many panels that I need. They stated that the greater power producing panels that I buy the less of them I need. This does not make sense to me when the micro-inverter that I like has a max output of 250w.

Here are my specific:

San Diego Ca.
South facing roof
Would like to generate 13,500 kWh ANNUALLY.

Their calculation
13,500/12/30/24hours = 1.562
1.562 x 5 = a system size of 7.8kw

7.8kw/ 250w panel = 31 panels
7.8kw/305w panel = ~26 panels

How can this be when the micro- inverter is max 250w so it seems like I would always have to buy the 31 panel system to get my annual output. Any comments would be appreciated!
Thanks!

The output of the micro inverter is 250w AC. The recommended input is 210-300 watts DC. The output of the panels is DC. I have the M250s on my 300w LG panels.

[Naptown]

Check the Enphase site regarding compatibility between the panels and inverters.
If they are compatable you might be better off with the larger panels.

[sandiegolloyd]

I plan on designing and installing a solar PV system on my roof. I contacted two solar equipment wholesalers and got strange responses regarding how many panels that I need. They stated that the greater power producing panels that I buy the less of them I need. This does not make sense to me when the micro-inverter that I like has a max output of 250w.

Here are my specific:

San Diego Ca.
South facing roof
Would like to generate 13,500 kWh ANNUALLY.

Their calculation
13,500/12/30/24hours = 1.562
1.562 x 5 = a system size of 7.8kw

7.8kw/ 250w panel = 31 panels
7.8kw/305w panel = ~26 panels

How can this be when the micro- inverter is max 250w so it seems like I would always have to buy the 31 panel system to get my annual output. Any comments would be appreciated!
Thanks!