I was told that if a person operates a solar or wind generator, and if
they produce more power than they need, this power is put back into
the grid, and the producer is actually paid for the energy they make.
Ok, this all makes sense, but I'm a bit confused how this works.
First off, I assume that a home solar panel or wind generator produces
either 120VAC or 240VAC. And if I'm correct, the solar panels
actually produce DC which is converted to AC.
Now, here comes the confusing part. If there is a surplus of power,
it backfeeds into the grid and makes the persons electric meter go in
reverse. But there is a pole transformer. On the input side of this
transformer there is a high voltage of 15K (or other amount of volts).
So lets say I'm back feeding 120V into my pole transformer. Does this
transformer actually work backwards and increase the voltage? Or does
the person need some special transformer? And lets say that this back
flow is putting 20amps of 120VAC into the grid. Don't the much higher
current from the power company just sort of fight against this low
current, or do they just blend together. I understand how power is
generated using wind power, solar cells, or even a gasoline generator,
but I cant comprehend how back flow into the grid works.
On 9/9/2010 9:12 PM firstname.lastname@example.org spake thus:
Short answer: yes, transformers work both ways. So if you put power into
the secondary side (the side that normally feeds power to your house,
for example), it flows out of the primary side into the rest of the
grid. Of course, it's a little more complicated than this, but it does
work that way. And you don't increase the voltage on the line; the
voltage remains constant--120-0-120 from your house to the service drop.
You increase the *current* flowing through the line (amps).
Another detail: the inverter (the part of the solar system that converts
the DC from the photovoltaic cells to AC) must be synchronized to the
exact power line frequency, so that the power put back into the grid is
exactly in phase with the power coming out. Otherwise, the power you put
into the grid would, most likely, be fighting against the power
By the way, it's not always true that the power company has to buy your
power. This is what we've been told for many years, but here in
California, for example, it turned out that PG&E didn't pay people who
generated power back into the grid. This is now being addressed by the
various regulatory agencies who are in charge of this area.
The fashion in killing has an insouciant, flirty style this spring,
with the flaunting of well-defined muscle, wrapped in flags.
Good point. In many places the power companies do pay you for what
you put back. But at the very least, how they pay you, the amount,
etc varies widely. NJ for example is supposed to have the most
generous payback in the US. You can get paid several thousand
dollars a year for a typical home system. A small part of that is
that the power company does pay you once a year for the excess you put
back to the grid. But 90%+ of the thousands is actually from
renewable energy credits. You get one credit for every so many Kwh of
solar energy your system generates REGARDLESS of whether you use the
energy or it goes back into the grid. In turn, NJ utilities by law
have to acquire a certain percentage of their electricity from
renewable sources. To meet that requirement, they buy these credits
from homeowners and that is where the thousands come from. Of course
the rest of the poor saps are paying for it in higher electricity
In other areas where they pay you for the electricity, it's at some
wholesale rate, not the retail rate you pay on your bill when you use
Bottom line, how you get paid, or if you get paid varies widely.
On Sep 10, 12:12 am, email@example.com wrote:
To do this you would have a spcial system that syncronizes your local
power exactly to the grid power. Allowing the gird and your local
power source to be connected together. Then when you are using power
your local source contributes slowing the meter. If you are not using
power then your loal source would backfeed the grid. Transformers
work in either direction. They are just two coils. The step up or
step down is determined by the number of windings on each coil. So a
pole transformer can be used in either direction. But unless you are
in a rural area the odds are your local power source would be used by
your neighbors before it ends up back on the hv part of the grid.
On Thu, 09 Sep 2010 23:12:37 -0500, firstname.lastname@example.org wrote:
The grid tie inverters are driven by the grid and then allow excess
power to flow back into the grid.
If the grid is down the inverter shuts down. That is how they stay in
sync. The voltage they generate is slightly higher than the grid so it
will flow backward through the meter. If you have the standard meter,
you will get 100% credit for the power you are feeding back. Most
utilities would rather pay you less but this would require a special
meter and for most installations the cost is not justified by the net
amount you would be selling them. There are probably not a dozen
residential installations in the country that actually generate more
than they use over time.
The trend is going toward micro inverters that simply plug into a
regular outlet. This will not really require much in the way of
permits or even telling the utility you are doing it.
This is totally scalable. You just buy more as you can afford them and
plug them in.
i've had mine installed for 3 months, and each month i've generated surplus
power. i get a credit for future use, and get paid at the end of the year
for excess credits.
i expect to generate surplus power every month, given that summer is the
highest usage in my area (phoenix, az).
in the 3 months, i've already had $500 off my power bill from last year.
payoff is expected to be in 4.5 years just from savings with current rates,
although my electric company has already filed for rate increases. if i get
any $ back from the power company, it will be less than 4.5 years.
there should be no almost no maintenance except washing them off. warrantee
for the converter is 10 years, and 25 years for the panels.
I don't understand how this could be paid off in 4.5 years. Assuming
$500 saved every 3 months, that's $2K a year. Around here, NJ, a
$7.5KW system costs about $50K. The federal tax credit can bring it
down to $35K and there can be other incentives, but still seems a long
way from 4.5 year payback. ???
well, you're not here :)
in a word: rebates. in my area at the time i placed the reservation with my
power company, the total rebates (federal, state, and power company) were
about 80%. due to the popularity, that's now down to about 40% in my area.
also, the manufacturing of panels is done in my city, so they're a bit
cheaper as my installer is the largest in az and buys local in large bulk.
further, note that the savings from above are in the summer, my high peak
a/c season (phx, az). i should generate higher savings during the winter,
unless i fire my kilns more. i actually sized the system to power my kilns
(8kw), but i don't fire them constantly.
why? shortness of days? the data logger i have on it shows actually a
decrease in production as temperatures rose during august and are just now
showing a decrease due to day length. however, it's very gradual since the
daytime temps are also starting to fall under 115. during june i was
producing ~50kwh/day and it's down to maybe 45kwh/day now.
i doubt i'll see much more of a decrease, but we'll see. my normal winter
power consumption is about 25% of summer consumption (gas heat) at most.
even if i get a 50% drop, the savings will be more in winter than summer.
furthermore, we don't get snow or more than 4-5 days frost/winter, and don't
get any rain so 99% of the time the sky is clear. we probably get 340+ days
of sun/year. it's also cooler than summer, increasing power production.
peak power production here for pv is feb-june.
remember, location counts.
How are you going to generate higher savings when you use LESS
electric? I guess you mean you'll be getting credit because you'll
be generating more electricity than you use. But usually the solar
system is sized to provide Kwh over the total year to be about equal
to your total usage. So, usually what excess you get credited for in
winter you wind up using yourself in summer, no? Also, what rate do
the pay you for any net excess you have, if any over the year?
it's sized to run my kilns, or oversized to my total year kwh if i chose not
to run them as much. the excess generated is sold back at the cost i would
pay for (actually, it's a kwh credit 1 for 1, which i draw down during the
night or at high usage day time, depending if i generated that power credit
during peak or non-peak time). so the payment for excess is what i would
have paid for it if i were a net purchaser.
furthermore, i try to use more power at night or weekends, when i'm
purchasing power at a lower rate (time differential billing), and generate
during the day, when my reselling profit is more than my nighttime cost.
You have a good deal on the electricity buyback. In many states, if
they pay you for net generation, it's at the wholesale rate that the
electric utility would buy power from it's regular sources. That
amounts to a fraction of the price they charge retail customers.
I looked into a solar system but from what I understand there will be a MUCH
cheaper solar cell available soon.
I have the perfect roof for a solar cell system. Faces south with full
sunlight in Central TX.
I figure it's like computers or plasma TVs (we paid over $700 for our 1st
VCR); wait awhile and the price will drop dramatically. The quotes I got on
available solar cell systems are not in my budget.
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