Utility Grid Intertie Systems

electricity from the sun by John Drake II | home

These systems connect to the electrical service entrance in your home or business and feed power directly into your wiring, any excess not used is either sold to the utility company or turns your electric meter backwards. This is probably the most popular photovoltaic system in use today as it qualifies for rebate programs in most states (currently in Calif. the rebate is either $ 4.50 per watt of output or 50% of system cost - whichever is lower.) These systems really do work.

Another reason these systems are so popular is that they are the most

efficient photovoltaic systems today. A photovoltaic array, when connected to

a battery, produces usable power only until the battery(s) are fully charged.

Then the controller disconnects the array from the batteries and little or no

power is produced. Much of the time, when the sun is shining, the array will

put out no power. With an inter-tie system, whenever you do not need power,

the array will feed power into the local power grid which is a plus for your

electric bill as well as to everyone on the grid. Also, without batteries to limit

the array output voltage, a grid-tie system will get the most power out of an

array.

NOTE: many systems are being installed by people who do not have any knowledge or background in either photovoltaics or low voltage direct current systems. Be cautious for a few reasons, some of these systems have to be rewired to meet National Electrical Codes (title 690 of the NEC handbook.) Many systems are not putting out the claimed power due to improper wiring, poor site assessment or just outright hot air from the dealer/installer. Few systems are installed with long term maintenance considered, you may pay a little more now, but you will save a lot more later in dollars and grief. ELECTRICITY FROM THE SUN IS A GOOD THING, LET'S USE OUR HEADS ABOUT IT. FOR MANY YEARS I WORKED WITH A MAN WHOSE MOTTO WAS "ONLY A FOOL STEPS OVER A DOLLAR TO PICK UP A DIME".

Back to Top

UTILITY INTER-TIE SUMMARY

What does it do?

A utility inter-tie (or grid-tie) system produces direct current (d.c.) power, changes it into 120 or 240 volts alternating current (a.c.) which is sent into the

building wiring.

How do I sell electricity to my utility provider?

Depending on the power company and state regulations a second meter may

be installed or the excess may turn your meter backwards. This is called "net

metering."

What is a photovoltaic (solar) inter-tie system made up of?

The utility intertie (grid-tie) system uses conventional photovoltaic modules which send d.c. current to a grid-tie type inverter. This inverter converts the incoming low voltage direct current to 120 or 240 volts a.c. and feeds it into the electrical service entrance (breaker panel) of the building. Whatever is not used is sent into the utility power grid. The excess can either turn your power meter backward or be measured on a separate utility meter. The intertie inverters are specifically set up to interface with the utility grid. They synchronize with the a.c. cycle on the grid and also monitor it to shut off if the grid power goes done. This is called anti-islanding. This means that when there is no power on the grid, your inverter will shut down so that it does not produce power and send it out onto the grid. This is done for safety.

How do I start?

First thing to do is to find a reputable dealer or dealer/installer. You will want someone who has experience in photovoltaics (solar electric panels and d.c. systems.) They will go over your recent utility bills and help determine what output size of system would be right for you. Also look for someone who carries the proper kind of insurance. Determine what type and size of system will work best for your needs and is within your means.

I have heard that some states will give a rebate to lower overall systems cost - what paperwork is involved?

In California there are three groups of paperwork requirements which must be fulfilled:

1st. Contact the state to request the rebate paperwork. Upon receipt, call to find out the current rebate rate (dollars per watt or percent of system cost - whichever is less.) Fill out and return or fax the form. NOTE, the system components must be on the state approved list to qualify.

2nd. Pull the appropriate city building permit(s).

3rd. Request, fill out and return the contracts (as a power generator) and agreement to your power company.

4th. When the system is installed, have it inspected by the city building department.

5th. Supply proof of inspection and a system cost invoice (with warranty, if contractor installed) along with your request for rebate payment to the state.

6th. Notify the utility company of completion and supply a building permit sign off.

7th. THE SYSTEM CAN ONLY BE CONNECTED BY (OR WITH THE PERMISSION OF) YOUR POWER PROVIDER.

What will a utility inter-tie system do for me?

From the outset you will lower your electric bill. You also may sleep better at night knowing that you are helping the environment by producing much, if not all, of the power your home or business requires. And this is being done on an ongoing basis without polluting our world. You are also making a statement that you are taking responsibility for your own needs. You will also reduce the strain on the power grid, which affects us all.

Are there limitations on what I can expect it to do?

Yes, in the event of a power failure (blackout) the system will shut itself down. Grid-tie systems can produce power only when they sense power coming from the utility - this is done for safety reasons. A secondary standby battery system is sometimes incorporated for continuity. The power production is reduced during the winter months but is usually highest in the summer when power is needed most. If you produce more power than you use (based on your monthly or yearly use) the excess will go into the grid but you will not receive compensation for it.

How much does it cost?

Inter-tie systems typically cost from $ 6.50 to $ 12.00 per watt installed (before rebate.) The larger systems have a lower per watt cost. Other contributing factors may include roof type and construction along with travel distances between modules and inverter/utility service entrance. The mechanical aspects of mounting the inverter and connecting to the service panel also require consideration in the installation costs.

Is it going to be difficult to maintain?

Maintenance consists primarily of hosing off the modules. Solar panels have life spans typically exceeding 20 years. The inverters (in Calif.) must have a minimum warranty of 5 years.

When will the system pay for itself?

Payback occurs anywhere from 6 to 10 years. This depends on current utility rates along with expected increases. It is difficult to see rates going anywhere but up. The costs to produce electricity (environmental, fossil fuels and political) continue to edge (for some - leap) upwards. Your system may also pay for itself much sooner by increasing the value of your property. An inter-tie system should only enhance the resale value of your home or commercial property.

Previous Page Back to Top Next Page

Home Page