On Friday, March 13, 2015 at 11:10:52 AM UTC-4, sms wrote:


Some of the newer grid-tied inverters also supply a limited amount of
power, in the daytime, when the grid goes down. See
http://www.sma-america.com/products/solarinverters/sunny-boy-3000tl-us-3800tl-us-4000tl-us-5000tl-us-6000tl-us-7000tl-us-7700tl-us.html.
No batteries so you only get as much power as your panels can produce at
the time.

That's interesting. I didn't know they existed. Looks like it's new.
We had this discussion here a few years ago, and I was pretty much
convinced it was impractical, if not impossible. I wonder how it will work?
I can see it working great in say NV, CA, AZ, ie where there is a lot of
full sun. But what happens in the rest of the county when clouds come and
go? You would think having intermittent power wouldn't be a good thing.
I guess they could have some intelligence in it, where if it sees it's
cutting out too much, it just stops trying for awhile until conditions
improve. But I guess whatever it does, if you can get it for basically
free, it's good to have.




You can also create a combination system with a devices like
http://www.wholesalesolar.com/grid-tie-to-off-grid.html.

Practically speaking, if your grid is pretty reliable, using a generator
is a much cheaper back-up system.

If your focus is backup power, I agree.




The payback on grid-tied solar systems is typically 6-8 years, but it
depends on how much of your usage you want to offset and it depends
tremendously on your KWH rate. For example, in my city, the top tier is
33¢/KWH from PG&E, a for-profit utility. If I go a couple of miles east,
the city of Santa Clara has a municipally owned and operated utility and
the top tier is 11¢/KWH so solar makes absolutely no sense.

You need all of these to make solar financially attractive:
1. Heavy usage
2. High KWH rate
3. Lots of sun and proper roof exposure

I want to scream when I see the Solar City people inside the local Home
Depot. In my area A/C use is rare, most houses don't even have air
conditioners and the few that do run it only for a couple of weeks per
year, and most houses don't have swimming pools. Almost everyone uses
natural gas for furnaces, water heating, and clothes drying. So
electrical use tends to be pretty low. When you eliminate air
conditioners and pool pumps from the equation electricity usage is low,
especially with greatly reduced usage with LED and CFL lighting; unless
you need to charge a Tesla or other electric car.

Yes, it depends on the numbers. I just did a quick estimation for here
in NJ. Electric is 12c. Assuming you have an average bill of $150/mth,
that's $1800 a year. NJ has a system where the electric companies are
required to get an increasing percentage of power from renewable, so they
hava auctions where the power comanies buy credits from homeowners that
accure them based on how much solar they generate. Five years ago,
homeowners were making like $3000 a year off of that. Now it's more like
$750. So, assuming you wiped out your electric bill and got the going
rate for your credits, that's worth $1800+$750 = 2550 a year. I would
think a typical system here is probably $25K now, not sure though.
You do get a fed tax credit, that could knock $7500 off. So, the net
cost is ~$18,000 giving a payback of 7 years. That actually looks
pretty good. But you may not wipe out the electric bill totally, so
that would extend the payback.