Grid tie inverter for batteryless install and no grid feed

[Trevarthan]

I've been following solar for a while. Looks like 250w monocrystaline panels are down to $380 at Home Depot. Might be time to go for it and install a system.

I'm an avid handyman, a pretty good woodworker, and I've got a tig welder, so I figure I can handle mounting systems myself. I'll just have to figure out the install angle and the location. I'm a software engineer for a living, so I might even rig up a heliostat setup later. Without installation costs, it looks like a 6kw system would be about $9k for the panels. I can buy that a panel or two at a time and grow into a nice system over the course of a year or two. Payback for the panels alone would be about five years. That's pretty good and makes sense to me.

I don't want batteries. They just add additional cost and complexity to the system, especially over time. Also, I live in Tennessee and my power company doesn't do grid tie. They don't want me feeding power back into the grid. I don't know if that's a technical decision or a political decision, but essentially it means I want to generate the bulk of my own power, draw the rest from the grid, and not feed any surplus back into the grid.

Can anyone recommend a good grid tie inverter that will scale from 0-6+kw and meet those criteria? I'm trying to get an idea of the cost involved.

Thanks!

[Sunking]

I don't want batteries. They just add additional cost and complexity to the system, especially over time. Also, I live in Tennessee and my power company doesn't do grid tie. They don't want me feeding power back into the grid. I don't know if that's a technical decision or a political decision

This is really easy to answer. It is both a Political and a Technical issue. If you do not want to go off grid which would be very foolish if you have commercial power, and the POCO will not allow you to grid tie, then no solar PV for you. It is that simple. Only solar you can do is thermal hot water, but PV is out of the question.

On the Political side if your local government does not mandate Net Meterting, then no POCO is going to connect you as there is no reason for them to do that as it only cost them money and being a biz is not in biz to loose money. On the technical side if the POCO will not allow Grid Tie you only have one option to go off-grid. If you go off grid battery will cost you roughly 10 times more for power then buying it from th ePOC for th erest of your life with constant battery replacement cost.

So you are pretty much done.

[Trevarthan]

Is there no such thing as a diode for ac current? No way to ensure the electricity I generate does not make it back onto the grid?

I was looking at the enphase m215 micro inverter today. Looks ideal for what I want to accomplish.

Or is it just that simple? No net metering, no grid tie? Apparently I'm in one of four states without net metering in any form. Unlucky.

netmeteringmap.gif

[Mike90250]

I know the XW series will do Grid Support, which is what you want, without backfeeding the grid, but it will still be connected, and you may need PowerCo buy-in to hook it up. And they may not allow that even. If you bootleg it in, your meter will flag FRAUD, and they will come out to bust you, thinking you ARE backfeeding.

[Trevarthan]

Yeah. I guess I could split the circuits in the house and run high current appliances on grid and the rest on solar, but I'll still need batteries for that, just not as many. Well, kwh are dirt cheap here for now. Guess I'll wait until Tennessee gets past it's typical 10 year tech lag. Lame.

[Sunny Solar]

Is there no such thing as a diode for ac current? not quite ready yet.. santa claus is working designing one now. and the easter bunny has promised to deliver them ASAP..

[Mike90250]

Is there no such thing as a diode for ac current?

Nope.

[Sunking]

Yeah. I guess I could split the circuits in the house and run high current appliances on grid and the rest on solar, but I'll still need batteries for that, just not as many. Well, kwh are dirt cheap here for now. Guess I'll wait until Tennessee gets past it's typical 10 year tech lag. Lame.

You just do not know how blessed you are, and complaining about it. That is not lagging, that is forward thinking. Tennessee is an exporter of energy and a conservative state. What you are asking for is to be an importer, higher prices and liberal policy asking your neighbors to pay for your daily needs.

States with Net Metering laws do so at the consumers expense. State regulators allow the electric companies to raise electric rates on all customers to recover the losses they incur from Net Metering. States also raise taxes to pay for the incentives they offer. States without Net Metering laws like where I am from allow Grid Tie connections, but the Electric Utilities are not required to pay retail for energy produced by customers. Instead they pay wholesale prices and works something like they pay you 6-cents per Kwh for any excess you generate, and charge 10 cents for any you buy from them. What that ends up doing to the customer is makes them bear the burden of the cost because they can afford it, plus they never achieve a ROI doing so at rate and tax payers expense. So be careful what you ask for, because you are asking for your loss of freedom and your money.

[mapmaker]

I don't want batteries. They just add additional cost and complexity to the system, especially over time. Also, I live in Tennessee and my power company doesn't do grid tie. They don't want me feeding power back into the grid.

This doesn't exactly meet your criteria since there are batteries involved, but perhaps you might be interested in Outback's "grid-zero" technology:

http://www.outbackpower.com/downloads/documents/APP_NOTE_RADIAN_GridZero_ABC_2-18-14.pdf

--mapmaker

[inetdog]

I don't want batteries. They just add additional cost and complexity to the system, especially over time. Also, I live in Tennessee and my power company doesn't do grid tie. They don't want me feeding power back into the grid. I don't know if that's a technical decision or a political decision, but essentially it means I want to generate the bulk of my own power, draw the rest from the grid, and not feed any surplus back into the grid.

Nobody makes an inverter that can sync to the grid and share your local loads between itself and the grid and not use batteries.
A Grid Tie Inverter does not have any energy storage, so it will take all the power that the panels can produce and output it as AC. That AC will go to your local loads and/or back to the grid depending on how what you produce compares to your current local load.

If your POCO will allow you to make a grid connection as long as you do not export power, you have two possible paths:

1. You can use a conventional GTI along with a circuit that detects when you are about to export power and turns on additional local "opportunity loads" like water heating without a thermostat to use up the extra power.
2. You can use a hybrid inverter with batteries to stabilize it so that it can produce only a much power as you are using locally (or less) and import power from the grid as needed but not export power back out.

[mapmaker]

If your POCO will allow you to make a grid connection as long as you do not export power, you have two possible paths:

If you're not exporting power, why involve POCO at all? As far as POCO is concerned, your system is just an energy consuming appliance.

--mapmaker

[inetdog]

If you're not exporting power, why involve POCO at all? As far as POCO is concerned, your system is just an energy consuming appliance.

--mapmaker

Well, the UL listing for a GTI includes all sorts of things like anti-islanding which are required to prevent the unit from becoming a hazard to POCO linemen in the event of a malfunction of the grid.
Implicit in that is the need for POCO approve the interconnection based on the listing and conformance to their various requirements.
Under the POCO tariffs as approved by state regulators, any form of co-generation, even if it does not export power back to POCO must follow POCO approval procedures.

[mapmaker]

Under the POCO tariffs as approved by state regulators, any form of co-generation, even if it does not export power back to POCO must follow POCO approval procedures.

I'm not on the grid but if I were... would I need POCO permission to hook up a standby generator (with a transfer switch, of course)?

--mapmaker

[inetdog]

I'm not on the grid but if I were... would I need POCO permission to hook up a standby generator (with a transfer switch, of course)?

--mapmaker

No, because there is no possibility of interaction between the generator and POCO as long as you use a UL listed transfer switch, installed with a permit and inspected to conform to the NEC.
But if you did not get a permit for the generator and transfer switch installation, POCO would be justified in yanking your power till you conform.
And if no permit and inspection are needed in your locality, then POCO may add to their boiler plate contract that you will have them inspect any generator and transfer switch you install. Lives are at stake if this is done incorrectly.

[Trevarthan]

You just do not know how blessed you are, and complaining about it. That is not lagging, that is forward thinking. Tennessee is an exporter of energy and a conservative state. What you are asking for is to be an importer, higher prices and liberal policy asking your neighbors to pay for your daily needs.

States with Net Metering laws do so at the consumers expense. State regulators allow the electric companies to raise electric rates on all customers to recover the losses they incur from Net Metering. States also raise taxes to pay for the incentives they offer. States without Net Metering laws like where I am from allow Grid Tie connections, but the Electric Utilities are not required to pay retail for energy produced by customers. Instead they pay wholesale prices and works something like they pay you 6-cents per Kwh for any excess you generate, and charge 10 cents for any you buy from them. What that ends up doing to the customer is makes them bear the burden of the cost because they can afford it, plus they never achieve a ROI doing so at rate and tax payers expense. So be careful what you ask for, because you are asking for your loss of freedom and your money.

Are you saying I'm blessed because my grid kwh price is so low? I agree. It's nice. However, I'd prefer to have net metering, even if it raised the cost per kwh a point. Is that unethical because it forces a cost on my fellow consumers? I think that depends on how you look at it. In the short term, I understand how this would anger some people. However, in the long term, solar will only become more viable. It's coming. Sticking your head in the sand won't stop it. Might as well get experience managing and implementing it now.