Selling surplus off-grid via grid-tie inverter?

[SolarRoger]

Hello and a Happy Christmas to all!

I've written a small introduction to what we're planning here but in essence my question is this;

I'm planning a modest off-grid system of around 4Kw. It's likely that for perhaps 4 months of the year, we could have a significant surplus and I'm wondering if it would make sense to have a grid tie inverter as well so that we could sell any surplus back to the grid?

Essentially the way I'd like to structure the system is that we have a suitably sized off-grid solution with a grid connection to cover the winter power deficit but the option of selling some of the summer surplus back to help offset the winter grid costs.

I'm sure that at present, from a purely economic perspective, you'd tell me to forget the off-grid and just do grid-tie, and that may well be correct, however the competing factors are that a) I want us to have some independence from the utility company given our remote location and b) any likely feed in incentives may be short lived.

Does this make any sense?

Roger

[Sunking]

You need a hybrid inverter, they are made to do what you want.

[SolarRoger]

How do I sell off the surplus?

You need a hybrid inverter, they are made to do what you want.

Thanks Sunking. So the hybrid inverter seems to handle the input side and house power right? In other words it will charge the batteries from solar or grid with preference for solar and deliver suitable AC to the house. What about selling off surplus in the summer back to the grid? I'm hoping (perhaps wishful thinking) that in summer we'll perhaps have an excess available and my understanding is that normally the charge controller will just stop charging and so the power available from the panels won't be used? Can I do anything useful with it - like sell it back? Or is the reality that I won't actually have that much excess to worry about!?

Roger

[Sunking]

I do not have a lot of experience with Hybrid inverters but wait for RCinFlorida to respond. I do not want to stear you wrong. I sent him a PM. Be patient for reply it is a holiday.

With that said the hybrids have quite of few optional conditions, but I think most of them are grid tied all the time, and in emergencies revert to battery. However I am not familiar with all the options.

[Mike90250]

.....Does this make any sense? Roger

NO

If you have grid, why go off grid, unless it is so unreliable?

To sell back, you need approval, inspections, and clean power for 5 minutes for the inverter to sync and begin to sell. If you have glitchy power, inverter may never go to sell mode.

[TnAndy]

Thanks Sunking. So the hybrid inverter seems to handle the input side and house power right? In other words it will charge the batteries from solar or grid with preference for solar and deliver suitable AC to the house. What about selling off surplus in the summer back to the grid? I'm hoping (perhaps wishful thinking) that in summer we'll perhaps have an excess available and my understanding is that normally the charge controller will just stop charging and so the power available from the panels won't be used? Can I do anything useful with it - like sell it back? Or is the reality that I won't actually have that much excess to worry about!?

Roger

Roger: My system is set up somewhat like you want, but you need to understand "Hybrid" systems are really BACKUP systems....not mean to be used as a stand alone system for ALL of a home's needs ( unless your electrical requirements are VERY VERY small...or your system is REALLY REALLY big.... )

Yes, in grid tie mode, the inverter will take care of the battery first, then sell the excess back to the grid ( assuming you have permission of the local power company to sell back, and have their meter that allows that so you get credit for that sell.....otherwise, you may just be giving it away ). Also, in this mode, your house stays connected to the grid, and you use grid/solar power as needed......if you have a very small need, the solar "may" supply all your needs during sun hours, and the power company meter never turns....my system,for example, often supplies ALL the power we use during the day, plus turns the power co meter backwards as much as 10-12kw/hrs.

But at night/bad weather, you will be buying power as if you had no solar connection at all.....unless.....

Unless you manually flip off the grid connection breaker.

In doing so, you force the inverter into a "grid down" mode, in which it does not sense grid power anymore....then you will operate only off the system you have set up...directly off the batteries.

Again, the PROBLEM with that is unless you have a very large battery bank, and inverter(s) to take care of your entire house, you're gonna be without power in a short time when the system shuts down due to low battery.

MOST of these types of systems are designed to operate only a few key circuits in a home ( I put in a sub panel, and transfer switch, so I can operate my refrigeration, some lights and few important circuits like that in grid down situations )....they are NOT designed to operate theENTIRE home in an "either/or" situation of grid or non grid.

In the matter of excess kw/hrs, I'm going to guess ( not really knowing your solar hours in your location ) that a 4kw system will produce something on the order of 200-300kw/hrs per month, on a year round average.....but that "could" be quite a bit lower in winter. My local electric supplier says a fixed panel system here will produce 1,000kw/hrs per kw of solar per year. A battery backup system is less efficient than a 'pure' grid tie, so likely that figure is closer to 800-900 (here).

So, use that as some sort of basis when looking at your current electric bill, and trying to decide what to do.

[Keepsake]

monthly chart

Has anyone seen a simple chart showing seasonal/monthly output based on one's latitude. i.e. I'm at 28 deg N. How much more pv output can I expect in June vs. December ?

[vinniethePVtech]

Just an FYI. Unless you are a utility company you are not truly selling power. All utility companies do is offer a credit incentive. You will never see cash for the energy you make and utility companies charge a fee for use of their transformer. its a bad deal.

[TnAndy]

The trouble with broad statements like that Vinnie is you simply don't know the policies of ALL the utility companies in the country.

For example, ours gives us a monthly credit during the year, and at year's end, if we have a credit, they cut us a check. That's true for anyone on the TVA "green partners" program in Tennessee, Alabama, Mississippi.

[vinniethePVtech]

The trouble with broad statements like that Vinnie is you simply don't know the policies of ALL the utility companies in the country.

For example, ours gives us a monthly credit during the year, and at year's end, if we have a credit, they cut us a check. That's true for anyone on the TVA "green partners" program in Tennessee, Alabama, Mississippi.

I can agree to that statement. However even for credits the energy put back into grid isn't at the face value energy is sold to consumers for.
PG&E which has monopolized the industry in California plays a teeter totter effect on value to the consumer with a fluctuation on rates and charges dependent on consumption by the consumer.
The only advantage is the consumer isn't charged tax for being a producer of energy that is an apparent change in income.
Your lucky in your instance to have a check provided at the end of the year and not get taxed on that disposable income. However on the federal level if you make over $10 of income you are suppose to report it.
The way dirty politics are looking with our government and the lobbying that is supported by utility companies it's only a matter of time before we see taxation on the energy producers that put back into the grid and receive cash value for it.
In California there is a class action lawsuit between independent producers of energy vs. PG&E claiming the unfair advantage of dominating the market causes market manipulation on energy prices. These independent producers of power want fair face value for the energy produced, these producers also want cash not credit. These producers are also challenging PG&E's debatable transformer fee which is paid in cash by the producer and is not credit related. The producers I find in favor of since it saves billions in developing infra structure and stimulates the grid.

[TnAndy]

Your lucky in your instance to have a check provided at the end of the year and not get taxed on that disposable income. However on the federal level if you make over $10 of income you are suppose to report it.

Uh.....you DO realize any income I get from the local power company would be WAY MORE than offset by the cost of producing said income, right ??

Heck, I don't mind reporting it at all......as long as I'm allowed to deduct the COST OF PRODUCING THAT INCOME.....the same as any other business enterprise. So if I "make" a thousand bucks/yr, and get to Section 179 ( full depreciation in one year ) off the other 70% of the 30k or so in my system after the federal tax credit of 30%, I'd be REALLY HAPPY !

But since that income is merely incidental, and I'm not in it to make a profit, as such, the most I can claim as a deduction is the amount of expenses that equals the income, until that income exceeds those expenses.....which should be about never. Same as "hobby" income....you can't claim a huge loss for bowling fees, shoe rental, lane fees, beer & pizza, and so on if you win a $500 tournament.....the $500 income is merely offset by the $500 in expenses, assuming you have that much.....and it's a zero sum.

[vinniethePVtech]

Uh.....you DO realize any income I get from the local power company would be WAY MORE than offset by the cost of producing said income, right ??

Heck, I don't mind reporting it at all......as long as I'm allowed to deduct the COST OF PRODUCING THAT INCOME.....the same as any other business enterprise. So if I "make" a thousand bucks/yr, and get to Section 179 ( full depreciation in one year ) off the other 70% of the 30k or so in my system after the federal tax credit of 30%, I'd be REALLY HAPPY !

But since that income is merely incidental, and I'm not in it to make a profit, as such, the most I can claim as a deduction is the amount of expenses that equals the income, until that income exceeds those expenses.....which should be about never. Same as "hobby" income....you can't claim a huge loss for bowling fees, shoe rental, lane fees, beer & pizza, and so on if you win a $500 tournament.....the $500 income is merely offset by the $500 in expenses, assuming you have that much.....and it's a zero sum.

How does that make sense? Profit or no profit the government still wants there cut.
Example one of my sole proprietorships has operated on losses for the last 3 years. I've still had to pay the government just because there was income supported to me as an individual.
The fed never considers a zero sum game, it's all percentage based no matter how negative the defecits get.
If you can write off expenses to your home business or not, you can take 5 years of depreciation on your solar system. That's if you own the equity.

[russ]

Has anyone seen a simple chart showing seasonal/monthly output based on one's latitude. i.e. I'm at 28 deg N. How much more pv output can I expect in June vs. December ?

Try PV Watts - the link is on the forum page and I am placing it here - it is easy to use - try it and ask questions if you have a problem.

http://mapserve3.nrel.gov/PVWatts_Viewer/index.html

Russ

[russ]

How does that make sense? Profit or no profit the government still wants there cut.
Example one of my sole proprietorships has operated on losses for the last 3 years. I've still had to pay the government just because there was income supported to me as an individual.
The fed never considers a zero sum game, it's all percentage based no matter how negative the defecits get.
If you can write off expenses to your home business or not, you can take 5 years of depreciation on your solar system. That's if you own the equity.

Your knowledge of taxes seems similar to your knowledge of PV!

You were taking income from the sole proprietorships - thereby taxable income.

[TnAndy]

Your knowledge of taxes seems similar to your knowledge of PV!

Amen..................