There has been a lot of discussion about using grid tie inverters (GTIs) with wind turbines to connect to the grid. Here we go trying to do our best to answer some basic questions about GTIs, their use with wind turbines, and to summarize trends we see emerging. Most of the information here is accumulated from the many discussions we have with the amazing members who frequent our Community Forums!
(Almost) Everyone needs an inverter
Inverters take direct current (DC) power and change it into alternating current (AC) power. For most small-scale do-it-yourself power generation (like what folks are doing with WindyNation's products), the power coming out of your wind turbine or solar array is DC power.
When you charge a battery bank, your batteries are ready to put out DC power. In order to use this power with normal household appliances and lights, you need an inverter to invert the current to produce AC power. This is true unless you have wired your house to use all DC appliances and light bulbs or if you're powering DC appliances (which are found on some RVs or sailboats, for example).
In summary, the need for an inverter with most small-scale household systems holds whether you are using a battery bank or connecting directly to the grid because, at the end of the day, what you need is AC power.
What are grid tie inverters?
Like any inverter, grid tie inverters change DC power into AC power. The grid-tie component of a GTI allows transfer energy from a renewable source into the grid. Being connected to the grid has the obvious benefit for small-scale renewable energy producers of balancing out your load (e.g. you don't need to produce all of your power all of the time).
With a grid tie inverter, you can either tie directly to the grid (without batteries) or elect to charge a battery bank and be connected to the grid. Though more expensive due to the cost of batteries and a grid tie inverter, the advantage of charging a battery bank is having energy in the event of a power outage. With or without batteries, tying to the grid makes it possible to reduce your utility bill by generating some of your own power. In some states and provinces, you may even be paid for the surplus power you send to the grid as you watch the meter run backwards.
What are the main considerations I should think about before investing in a GTI?
Watching the meter run backwards is sexy. However, a GTI is not for everyone.
First, in order to use a GTI, the grid needs to be accessible (i.e. close), so this type of inverter is not appropriate for those of you who live beyond the grid, as you would then be faced with trenching lines to the nearest part of the grid which could cost thousands of dollars (or more!), depending on the distance to the grid and on rates charged by the utility company nearest you.
Second, at present many people connecting their wind turbines to the grid are using GTIs that have not been approved by the Underwriters Laboratories (UL). The primary reason that many small-scale wind energy folks are using GTIs that are not UL-approved is that, at the moment, most UL-approved wind turbine GTIs are set to cut-in at relatively high voltages (>30 volts) and consequently, are not very compatible with most small-scale (<1000 Watts) wind turbines. As a result, UL-listed GTIs are pricey, and blow a big hole in a small-scale wind or solar project budget.
If you are using a GTI that is not UL-approved, it is likely that you are also connecting to the grid without notifying your utility company. While various forum users have discussed the possibility of getting "in trouble" for connecting to the grid without telling their utility provider, the real risk of connecting to the grid without advising your local utility is that, in the event of a power outage, you could be putting line workers in danger of electrocution from the electricity your system is pumping into the grid when the lines are down. Bottom line: if you plan to connect to the grid, you should first notify your utility company.
What are the benefits of connecting to the grid?
Said clearly by WindyNation forum contributor, Larry (leamywind1), you have to consider your main goal for your wind turbine(s). Is your goal to:
- Charge batteries?
- Tie into the grid to reduce your electric bill?
- Tie into the grid to get paid for it?
A) Charging Batteries
If you live off the grid, charging batteries is currently the most viable way for you to harness energy from the wind. For you, a battery bank and inverter system is going to be the right fit. Some RV drivers and sailboat operators also elect to charge a battery bank using renewable energy sources (typically solar) so they can avoid using gas generators to charge batteries when they are parked without access to electrical hook-ups.
This article, however, is focused on grid tie inverters. The main advantage to coupling batteries with a connection to the grid through a GTI is having electricity in the event of a power outage. As with other grid connections, you can also reduce your utility bill by generating some of your own power.
There are also some drawbacks to batteries. They eventually wear out (lifetime is related to usage patterns and storage), they contain a variety of toxic chemicals, and charging and discharging batteries reduces the overall efficiency of the system. You also have to carefully consider which type of battery is appropriate for your system.
B) Tying into the grid to reduce your electric bill
When you are tied into the grid, your meter runs backwards whenever you are producing a surplus of energy. This is called net-metering, which is summing the kiloWatt-hours (kWh) you are drawing from the grid and subtracting the kWh you are giving back to the grid.
This reduces your utility bill because whenever you are producing your own electricity, you are saving the amount you would otherwise be spending on that power from your utility company. The downfall of this option as compared to batteries is that you don't have storage capacity. The advantage is that you don't have any batteries to worry about.
C) Tying into the grid and getting paid for it
If you are giving back more power than you are using (e.g. you are a net producer of energy), you can potentially get paid for it. Utilities across the world and across the U.S. vary in the way they compensate you for the electricity generated by renewable sources that you contribute to the grid. If you want to go this route, you will need to contact your utility company to find out if and how much they will pay you for surplus electricity. You can find some basic information about how utilities in various parts of the U.S. incentivize residential energy producers at: www.dsireusa.org.
You also may have heard about renewable energy certificates (RECs) as a compensation mechanism for the wind-energy you are producing. Making money by selling the renewable attribute of the power you are producing is a complicated process that varies dramatically from state-to-state. You can read some of the basic ideas behind RECs here.
What are the different types of grid tie inverters out there?
For your consider, we have compiled a few reviews from our Community Forum members. We attached Member names to specific reviews so you can contact the reviewer directly if you have questions. Links to information about other GTIs has been provided (thanks to Forum Member Minnesota for the links to the UL-approved GTIs listed here). Although this list is not exhaustive, it is a compilation of the GTIs mentioned most regularly by our most active Forum members.
Please note that our lawyer has asked us to remind you:
WindyNation does not endorse the practice of using unapproved GTIs or of tying into the grid without notifying your utility company.
Two further notes of caution related to GTIs:
- It is important to use GTIs designed for WIND applications, not solar, as they are built to handle the voltage fluctuations endemic to wind as an energy resource.
- Be sure that you have something set up (extra capacity, battery clamping, etc) to deal with over-voltage if the GTI you are using does not have overvoltage protection
As Minnesota, a Frequent Flyer on the Community Forums explains, "The world still lacks an affordable wind GTI under 1000W and $500. That would sell."
> Check out Grid Tie Inverter Prices & Reviews