Grid intertie has several advantages, it`s cheaper, simpler, greener than stand alone PV. I know personally 7 off grid households, they all have run thru several sets of expensive, toxic, heavy batteries, they all use dirty, noisy, PIA backup generators for the cloudy periods we get, they all only get 80-85% of the energy they put into batteries back from them, they all fill their battery banks when they have two sunny days in a row, then any more solar energy produced is wasted. With a grid intertied PV system, 100% of any electricity that you produce but don`t need immediately, goes into the grid, in the seven states TVA serves, I get paid 12 cents a KWH MORE than TVA charges. This way your neighbors can use your excess
solar electricity, and you get a credit, if you run a surplus you get a check.
http://www.tva.com/greenpowerswitch/partners/
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My grid tied 4.6KW system produces more than my home uses, so we have no electric bills, 100% of the Green energy it produces gets used, and I get paid about $800 a year for the clean energy I put into the grid for my neighbors to use, displacing the carbon based energy they would of burned.
http://www.builditsolar.com/Projects/PV/DougEnphase/DougEnphase.htm
https://enlighten.enphaseenergy.com/public/systems/dpBj53033
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http://www.txses.org/PVgrid.php
One increasingly popular way of using photovoltaics is what is known as "grid-attach". In this configuration, the consumer stays attached to the electric company (the "grid"). The PV system forces whatever it produces directly into the building's AC lines. If the PV system is producing more than the building uses, the meter runs backwards. If the building is using more than the PV system is producing, the difference is made up by energy from the electric company.
This type of attachment has a number of advantages:
It is cheaper, because there is no need for batteries.
It needs less maintenance, again because of the lack of batteries.
It makes the most effective possible use of the energy that the PV generates: because the grid is always able to accept any surplus, the PV panels can always be operated at their most efficient point.
A Utility Intertie System Without Batteries
This is the simplest and most cost effective way to connect PV modules to regular utility power.
All incoming PV-generated electrons are converted to household AC power by the intertie inverter and delivered to the main household circuit breaker panel, where they displace an equal number of utility-generated electrons. That’s power you didn’t have to buy from the utility company. If the incoming PV power exceeds what your house can use at the moment, the excess electrons will be forced out through your electric meter, turning it backward. If the PVpower is insufficient, that shortfall is automatically and seamlessly made up by utility power.
Have you considered going completely energy independent with a
solar power system? That is, do you long for going off-grid,
free from the expensive rates of utility companies? I had always thought that off-grid was clearly the way to go, until I did a bit more research.
There are a number of pros and cons for you to consider when implementing a solar power system that will take you off-grid. First, let’s review the three types of solar power systems:
On-Grid Battery Solar Power System
On-Grid Solar Power System without Battery
Off-Grid Solar Power System
With an on-grid battery system, a back-up battery is included as part of the solar power system. Batteries can store excess energy generated by the solar panels, and even send the surplus electricity out to the grid. Of course, the system is connected to the electricity grid which is why it is called “on-grid.” The solar panel system includes solar panels, a charge controller, battery, inverter, AC service entrance and AC subpanel, and a utility meter.
You can still stay on-grid without a battery, however. These solar power systems are the simplest and least expensive to set up. All that is included is the PV array, an inverter, AC service entrance and utility meter. Your system is connected to the grid, but there is no battery back-up. The obvious drawback is that when power goes out in your area, your solar power system will also shut down.
Finally, there is the off-grid solar power system. There is no tie-in to the electricity grid. Batteries are required as part of the system in order to store excess energy.
Turning to a comparison of on-grid vs. off-grid solar power systems, there are clear advantages and disadvantages to each of these.
Off-grid systems are the only way to go if you live in a remote area where there are no utilities. In fact, you can get a better deal on rural properties that are not connected to the grid because of the expense of running lines out to the home.
But, if you have the ability to connect to the grid, why wouldn’t you? First and foremost is the idea of independence from utilities. No more worries about rate increases. If the power goes out, your
lights and refrigerator (and television and radio) are not affected. Second, due to the cost of an off-grid system, many homeowners find themselves forced to conserve energy rather than expand the system to generate more power. This is very appealing to the environmentally-minded.
What are the down-sides for going off-grid? Instead of the utility company maintaining your system, you’ll be doing it all yourself. Batteries will have to be replaced (about every 5-15 years) at a cost of at least $1000. In addition to the cost of the batteries is the inefficiency, which increases as the batteries age. They start out at about 90% efficiency. Moreover, when you’re not connected to the grid, excess energy that is generated is not fed out to the utility to give you an energy credit (this can happen with on-grid systems). Off-grid systems must use the surplus or lose it. Finally, most off-grid systems include a back-up generator, which can be very expensive.
For an on-grid system, the primary upside over off-grid is that you can draw on grid-based electricity when necessary, rather than either go without power, or use a fossil-fuel based generator. You still get a great deal of independence and cheap electricity, but it may be more reliable in many ways.
The biggest question for you is whether you will include a battery or not. Battery-based on-grid systems cost about 35-50% more than without, but you lose the opportunity for back-up without a battery. Also consider the cost of utility line extension for grid-ties. If you are close to the line, it may cost you nothing. But if it will be a major extension, it could be very expensive and you may decide that staying off-grid is the best way to go for your home. If you tie into the grid, be sure you are clear about the question of net metering (when you can sell back excess energy to the grid for credit).
Fortunately, there are many solar power system options for homeowners. No matter your circumstance or where you live, you can find a way to use solar energy to power your life!
Library of State-Specific Interconnection and Net-metering documents-
http://www.irecusa.org/index.php?id=30
If money were no object, I’d opt for a grid-tied system with batteries. While such a system provides the best of both worlds, it is also the most costly. A grid-tied system with batteries must be able to automatically disconnect from the electrical grid when the power fails. If not, it could be dangerous for utility workers in the area. As a major advantage of such a system, it uses all of the free-power available, only switching to costly grid-supplied power as a last resort. Switching is automatic, based on setup parameters. The system can be set to be very gentle on the batteries, extending their life, or be set to use them to a greater extent, resulting in a lower electric bill. It must be great to have choices like that!
I think it’s reasonable to assume that while grid reliability problems may increase in the future, the grid is never going to disappear completely. As long as it is there part of the time, those attached can take from it and contribute to it. And those who supply power to the grid are paid, or at least credited, for their contributions. So unless electric rates or grid-connection charges are prohibitively high, being grid-tied makes more sense from a financial standpoint than an off-grid system does. And since an off-grid system with batteries efficiently uses the energy generated by the sun, it’s a good “green” choice.
While a batteryless grid-tied system is efficient and cost-effective, it must be embarrassing to have a large PV array, but no power when the grid goes down. What would the neighbors think? Still, this type of system is the best “green” choice, and it requires the least maintenance.
Efficiency – When your batteries are full, they’re full. No matter how hard the wind blows or the sun shines, you can’t harvest anything more. A grid connection allows you to harvest all the power from your system. When you have extra, you sell it to the grid so someone else can use it. When sun or wind is scarce, you tap in and buy some back.
Cost - Solar equipment is expensive. You can run a few lights with a car battery, but if you’re serious about powering your home you’ll probably want a set of good-quality deep-cycle batteries. These can set you back $300-$1,500 apiece. You can expect to have to replace them about every 7 years – maybe longer with good care. If you have batteries you’ll also need a charge controller – another $150-$600 or more. Connecting to the grid allows you to dispense with batteries altogether if you choose.
Convenience – Off-grid systems require constant monitoring. Flooded lead-acid batteries are long-lived and cost-effective, but they need frequent maintenance. Living off-grid also requires you to adjust your energy consumption according to available power. If you have a few days without much sun or wind, you may have to ration your power use or supplement with a generator.
Self-reliance – No doubt about it, when you’re off-grid you’re not at the mercy of the power lines. There is something to be said for being able to offer your neighbors water, for instance, after a tornado goes through and they have no power to their pumps.
Politics – You may have strong feelings about your power company. You’re entitled to them; just don’t let them act against your own best interests.
Ask nearly any PV installer, and they’ll tell you it makes sense to connect to the grid. But at the end of the day, it’s a decision you need to make for yourself. And don’t forget – it’s not an either-or decision. You can grid-connect and have an
emergency battery back-up, too – the best of both worlds!
With grid tie and battery backup, you will take about a 10% hit on overall
efficiency of your system. That being said, it is still about 20% more
efficient then an off grid systems where you are drawing off the battery
every day and having to recharge them. Batteries are only about 80%
efficient meaning you have to put 20% more energy into them then you can
take out.
Outback is a very good brand for this. the thing to know tho, is that the inverter is complicated and more expensive if it charges batteries too. That means that when the batteries are full, the inverters efficiency is still lower because of it's use as a charger, your not getting the full benefit of a grid tied inverter, it's less efficient.