solar power (grid connectected) question

[platinumdude]

http://www.wholesalesolar.com/anti-islanding.html

Electric utility companies refer to residential grid-tie solar power arrays as distributed generation (DG) generators. They use this term because your solar panels are producing and distributing electrical power back into our utility grid.

Islanding refers to the condition of a DG generator that continues to feed the circuit with power, even after power from the electric utility grid has been cut off. Islanding can pose a dangerous threat to utility workers, who may not realize that a circuit is still “live” while attempting to work on the line.

Distributed generators must detect islanding and immediately stop feeding the utility lines with power. This is known as anti-islanding. A grid-tied solar power system is required by law to have a gridtie inverter with an anti-islanding function, which senses when a power outage occurs and shuts itself off.

One common misconception is that a grid tied system will continue to generate power during a blackout. Unless there is a battery back-up system, the gridtie solar system will not produce power when the grid is down.

Does this mean that if the power goes out, you only have the charge in the battery to carry you until the utility power is restored? Or will the panels continue to charge the batteries?

[platinumdude]

From further web searching, I found the answer.


http://info.ussolarinstitute.com/blo...a-Power-Outage

Even though the price of a battery based system represents a larger investment, there is a great deal of value and security in having an uninterruptable power supply for all or part of the loads in one’s home. It is a common misconception that just because a house has solar panels on the roof, there will be a source of power whenever there is a power outage. The only way this can happen is if the inverter is battery based. That means that the inverter runs on batteries rather than solar panels. Both types can and will use power from the photovoltaic array and put it into the grid. Both will disconnect from the utility in the event of a power outage, but the battery based inverter will continue to energize loads on the downstream side of the inverter while at the same time using the solar array to maintain a charge in the battery bank. Another advantage is multiple DC inputs. A straight grid-tie inverter will only run on solar panels. A battery based invert will make use of any DC sores that can charge the battery like wind generators, hydro, or traditionally fueled generators.

[TnAndy]

http://www.wholesalesolar.com/anti-islanding.html






Does this mean that if the power goes out, you only have the charge in the battery to carry you until the utility power is restored? Or will the panels continue to charge the batteries?

As you noted, you found the answer.....the panels will continue to charge the batteries.

Grid tie ONLY inverters drop out of service when no grid power is sensed. Grid tie W/battery backup inverters have two sets of contacts....in "normal" mode, the grid tie contacts are closed allowing power to flow to the grid AFTER the batteries are fully charged. The second set of contacts for off grid use remains open.

If the grid goes down, the contacts reverse....the grid tie set opens ( no more power to the grid ), and the off grid set closes, continuing to charge the batteries, and allow excess after that ( which would have gone to the grid ) to flow where ever you have it wired to flow.

What you do with this type system is the same as a whole house generator setup.....you have a transfer switch and a subpanel in your house that operates circuits you consider critical.....refrigeration, lights, etc......and when the grid goes down, the transfer switch ( either automatic or manual ) flips the power to JUST that subpanel and those designated circuits. When grid power returns, you have to flip back the other way.

As your second post notes, battery backup systems are more expensive....you have way more components and complexity to the system ( charge controller(s), batteries, transfer switch, more wiring, more disconnecting means, etc ), AND you have to decide which way you're going from the get-go....you can't easily convert a grid tie ONLY system into a battery backup.....about the only component in common with them are the panels themselves.

It comes down to a decision in purpose of the system.....if you want 'payback', go with a grid tie only system...cheaper initially, and more efficient in terms of power produced that goes back to the gird ( battery based systems lose more power due to the various components (like batteries) in the system, and are only 70-85% as efficient as grid only systems).

If you want security of some power as backup ( don't get the notion you're gonna run your electric stove, water heater, oven and so on off a battery based solar system unless your checkbook is REAL deep ), with the 'gravy' of cutting your power bill some also, then you go grid tie with battery backup.........and when people ask "how long will it take to payback", just smile and say "probably never".

[platinumdude]

Thanks for the info. In your setup, do you have utilities hooked-up, or are you all on your own power 24/7?

I currently live in a city, so not sure if a battery back-up unit makes sense. If I'm the only one with power for a long period of time, I will have to keep things on the down low. I guess this beats having a noisy gas power generator where all the neighbors could hear.

One possible scenario may be not a lights out but a long years out protracted inflation of utility prices increasing and decline of the economy. In this case a battery-free setup may make more sense.

[TnAndy]

I'm grid tied with battery backup. I wanted the option of a chance at power in a non grid world, and as a buffer against what I think will be much higher prices and possible spotty supply down the road.

We have a 6kw system now ( built in 3 stages ) (5,950 actual rated panel watts ), and it produces about 600kw/hrs/month of power.....more than enough for refrigeration, lights, some other items in a non grid world, and due to the rate structure of our power supplier (TVA), we run about a 40 buck/month credit on our electric bill. They cut a check to us at the end of the year if we have a total year surplus.

[platinumdude]

So say I just want something small like around 1.5kw/hr in total panels. Using the grid tie with batteries option. Could I have it hooked up to my entire 120 v circuits in the house and only use something small like a light in one room, then maybe later turn it off and use a washing machine with cold water. So that I'm not drawing a lot of amps at once. The things I would not use when the utilities power goes out is stuff like the full size oven, the dryer, the AC unit. Maybe just the furnace fan and hope the gas stays on.

[ttazzman]

fwiw.........motors for the furnace fan and the washer will probably use approx 500watts continuous each ......and take 750-1000 watts to start them

[Fiat Metaler]

plat - i'll try to answer your original question.

with solar, you have an irregular supply and irregular demand. if you create a surplus supply, what do you do with it? you could charge a battery, but that requires a substantial investment. if you are close to the grid, you could sell it back to the electric company. congress passed laws requiring this but the electric company doesn't like it because they slowly lose their monopoly and have no control over distributed generation. so they promote the idea that some guy with a solar array is going to electrocute one of their workers who otherwise is going to touch a live wire.

[spacecase0]

I have been wondering how to make a grid tie inverter act on it's own,
I was thinking that maybe a large syncronus AC motor with a large flywheel attached and a regular true sine wave inverter powering it connected to the larger grid tie ones would make it think the grid is still there,
I was looking for grid tie inverters that would do the island effect but it looks like no one makes them and that no one has hacked one to do it,
I guess the answer is just to get the regular grid tie inverters, but they often need a very narrow range of input voltage as to where many of the grid tie versions will run on whatever you give them in a large range.

so far I have settled for just using switching power supplies with large input ranges and down converting to 12V to run things directly, and this lets me run solar (when there is sun) with no batteries at all.

[anotherdave]

The bottom line: Solar is not competitive economically, period.

With subsidies it can be cheaper, but somebody, somewhere, is paying the rest of the bill.

And it's probably you.

.

[gnome]

The bottom line: Solar is not competitive economically, period.

With subsidies it can be cheaper, but somebody, somewhere, is paying the rest of the bill.

And it's probably you.

.

On a private rooftop, yes. On a utility scale, solar has already passed nuclear power and peaking gas plants in a great many places. And with costs for solar dropping 15-20% per year, it will soon be cheaper than all fossil fuels - without subsidies.

And keep in mind, oil, gas and nuclear are all subsidized as well, primarily through billions in tax breaks. Oil has the mother-of-all subsidies - the Pentagon budget.

Opponents of renewables decry the subsidies, but ignore the beam in their own eye.

[TnAndy]

The bottom line: Solar is not competitive economically, period.

With subsidies it can be cheaper, but somebody, somewhere, is paying the rest of the bill.

And it's probably you.

.

In a "survival prep" forum, it would be remiss of me not to point out economics is NOT the only reason to install some solar.

People often look at my system and ask "when will it pay for itself"......and I respond "I don't care".

[platinumdude]

Does anyone here recommend not placing panels on a roof. I'm debating where to install when I do eventually get them. Either installed on the roof or in the backyard with cement posts to hold them in place.
There are some trees in the way, and it would block maybe 15 or 20 minutes of the early 9:00 time period. I still have to observe the pattern later in fall and winter.

[anotherdave]

In a "survival prep" forum, it would be remiss of me not to point out economics is NOT the only reason to install some solar.

People often look at my system and ask "when will it pay for itself"......and I respond "I don't care".

I agree! There can be good reasons to have solar backup, solar supplementation, or solar primary. There might be good reasons for being a solar producer as well, just not ones that make any economic sense.

.

[anotherdave]

On a private rooftop, yes. On a utility scale, solar has already passed nuclear power and peaking gas plants in a great many places. . .

'Tis not.

Another solar boondoggle just ran off with its massive federal funding today. How many of these welfare babies have to go tits-up to prove they're not competitive? Or maybe I should ask if there are any left!

And don't confuse the issue with peaking plants, or any plan for sane nuclear, even though I'm leaving myself open for witty zingers on that one!

.