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Archive for the ‘Grid-tie’ Category
Wednesday, April 8th, 2009
First of all, thank you for offering a place where the rest of us can ask power questions! We really appreciate what you are doing.
We are looking to both test our location for wind potential and in the meantime fractionally lower our monthly bills – especially our overall peak electricity usage – by way of self generated power and better home efficiency.
After doing some research and checking prices we have come up with what we hope to be good theoretical plan to produce a little energy and perform our test. Unfortunately, we cannot get straight answers on how the proposed system might perform, if at all. We have found similar all solar solutions, but we really like the idea of harnessing the wind – we have a ton of wind, but only so many hours of light.
The proposed Hybrid test components are as follows:
Wind – 200W VAWT (specs below)
Solar – 50W solar panel
NC25A/12volt charge controller
Smart Sine Wave Inverter-250W (sadly, not UL listed but the next version in April 09 will be)
5 x 100 watt bulbs (temporary diverter load)
All plugged into an existing dedicated 20amp GFCI outlet, left over from landscaping.
I wanted to ask specifically is this even worthwhile to attempt to do this project. Will this configuration cause components to die a premature death? Will these components work together? And possibly what other pitfalls, if any?
The only issue I could really easily identify is the inverter start-up voltage was pretty high, which doesn’t take full advantage of any low speed wind energy. Because of this I opted to additionally use a solar panel to jump start the voltage, which may help during daylight hours anyway. But again, this is why we are writing you as it is all a little out of our league.
We know this isn’t much power to produce or save, but I think it will make us more aware of what we are using and it will likely knock us down a tier or two on our power bill while additionally helping up plan for our next steps. That and we feel buying a “wind survey” or wind survey equipment isn’t likely going to supply us with all the practical knowledge we are sure to gain playing around with our own working model!
Charlie and Sara
Charlie and Sara,
If you guys want to “play around” with this proposed system as a learning experience then go for it but remember, a 20 amp circuit could easily kill you under the right grounding conditions. However, I can offer you some warnings if you ignore that advice.
If you check a recent email question from another person wanting to do this same thing, I pointed out that most wind turbines cannot be connected directly to a standard solar inverter because the output power is “wild.” A grid-connected wind turbine requires a special, modified solar inverter designed specifically for a wind turbine, and if you go the way you are going I am willing to bet you will quickly burn up your inverter which is NOT designed for this type application.
You also cannot connect a solar module and a wind turbine together to “jump start” the system as you describe. Each will require their own charge controller type device to prevent reverse charge flow and coil damage.
If you want to know wind potential at a site, you can purchase a recording wind meter for $74.00.
I don’t see how your approach will teach you anything useful except how fast you can fry electrical equipment, as a real wind turbine installation will not have the same performance issues of your experiment.
Also, you have not describing any safety disconnects, fuses or circuit breakers, and have not discussed the fact that it’s against utility regulations to make this connection to the grid without written approval, and this requires evidence that your inverter is both UL listed, and certified for grid backfeed applications.
Again, I am not against experimenting as a learning process, but I am afraid all you will discover with this approach is how fast you can burn up several hundred dollars worth of equipment.
Be very careful,
Monday, March 30th, 2009
Thanks for offering this service.
I am building my own wind turbine for the home. This will be a grid-tied system that will plug into an outlet to supplement the grid. Can you recommend an affordable converter? I saw the Smart Sine Wave Inverter, but that costs $300. Is there a less expensive alternative?
I think its great that you want to tackle a project like building a wind turbine. If you are going to use it to charge a set of batteries for a backup power system then that would be the way to go, but you will not be able to connect it to the grid.
Just a small point, a “converter” is used to convert AC to DC, and “inverter” is used to invert DC to AC.
First, the voltage and current output from a wind turbine is all over the chart as the wind keeps changing by the minute, which requires a very special DC to AC inverter designed for this type power input, plus be certified to feed power back into the grid. The lowest cost inverter I have seen that is designed for this type application and certified for grid connection costs around $2,500.00, plus circuit breakers and wiring. Your local utility will not allow you to feed power back into the grid unless the inverter has these UL and IEEE certifications, and you will not find this level of quality in any $300 inverter..
Sounds like you are on a tight budget, so I would stick with charging batteries and powering some emergency DC lights.
I will point out that many who ask me these type questions totally ignore my advice and go on and waste a lot of their time and money to find out the hard way, so either way, good luck with your project.
Monday, March 23rd, 2009
Is there a UL product out there similar to a DC grid tie in inverter that would work for an AC generator?
I am aware of how the DC is converted with an inverter to AC and the phase angle is adjusted as well as the phase voltage to maintain proper alignment of electric main power. I have seen wind generators plugged directly into a breaker in the main panel as a grid tie in and initially was confused on how this was causing a dead short. However, I understand how it is possible now (there is an inverter in the wind generator head which adjusts Phase angle and Phase voltage to allow simultaneous feeding), but, haven’t been able to find anything for AC generators.
What I am looking for is something that will go between my AC generator and the main panel that will allow me to directly connect to the panel without a dead short, and allowing back feeding to the main line. Also an automatic shut off or transfer switch that would turn off the generator’s power supply from pumping electric back into the power grid when the main power goes out.
I am looking for an AC grid tie in device that will not cause a dead short.
Your thoughts would be appreciated,
I can’t imagine why anyone in the world would want to do what your are suggesting, although it is technically possible. Yes, there are special “in phase” monitors that will sync a generator with the grid, but this is only dome with very larger generators like you would find in hospitals or military bases. The main reason they do this is they are on a time of day rate and if they are approaching a peak demand period, by running their generators in sync with the grid they can save hundreds of thousands of dollars per year because these rates usually carry over the high penalty for the next 11 months. In addition, this switchgear to sync the generator with the grid costs more than your house and requires all kinds of coordination between the utility engineers and your installer. You will also be required to carry a huge liability insurance policy listing the utility as the insured in case something goes wrong and your power feeds back into a down line and kills a lineman.
Inverters for solar and wind systems have special circuits that make sure power is not fed back into the grid during a power outage, and the inverters must supply this power within a very narrow window of voltage and cycles. Most smaller generators are not that easy to maintain a constant output under varying loads.
Now that you know the legal issues involved with doing this, I will give you the simple reason why nobody in their right mind would ever do this:
If you count the cost of fuel, generator maintenance, repair parts, added oil changes, and annual service, you will be paid about 20% of what your actual costs will be, because you can never ever generate electricity cheaper than a utility. The only reason many of these solar and wind systems are doing this is either they are receiving some type of grant or tax credit, or they have been given a special feed-in tariff rate.
Many people still install solar systems as some systems also offer emergency backup, or at least do not need constant fueling or make noise like a generator. The national average cost today to generate electricity from a solar system is 35 cents/kWh. The national average for grid electricity is 9 cents per kWh. You figure it out.
Thanks for the insight and your knowledge on these subjects is amazing. Everyone at times has an idea and can’t figure out why the situation is the way it is; until they ask an experienced individual.
Thank you again. So if I wanted to have some sort of “economical” unit (and I use that term loosely), we would be best off using a UL device DC based unit (solar, wind, hydro) with an inverter monitoring the phase angle and voltage back to the main panel which would shut off when the main power goes out? If we wanted any sort of power when the main power goes out we would be using a battery system or a separate backup AC generator/transfer switch which would not back feed to the main power until main power comes back on. We would then turn off the generator and manually switch the transfer switch back to main power?
I guess I am in the same boat as most people trying to figure out what will work best for my individual circumstance. Oh, yeah I’m not a millionaire so the in phase monitoring for an AC generator would be out of the question.
I will probably be investing in a solar or wind powered DC unit with an inverter for my needs. Would you recommend any companies that you have had a positive experience working with for these devices. Probably, a 2KW-5KW max output would be what my financial situation will allow.
Jeff I can’t thank you enough,
Any inverter designed for grid tie in the US should have the automatic transfer function built in. If you select a battery based inverter, it will also include a built-in transfer switch to disconnect from the grid. Some battery based inverters include a “second” transfer switch to allow also connecting a generator and the grid, and will switch to the generator when the grid is down and the battery charge is low. If you select an inverter that does not have the second transfer switch, then you will need a generator that includes its own transfer switch panel.
Monday, March 2nd, 2009
Putting together an off-grid system, I am inquiring as to how best choose/purchase the solar panels for optimal efficiency in relation to their voltage output. There are panels that put out similar wattage, however the vp/imp can vary greatly.
Let’s imagine for example the system objective is approximately 2kw using a 24v to 110v inverter with battery back-up.
Which would be the best solar panels to use for maximum efficiency?
* 12 – 160w panels @ 24vp/6.80imp
* 10 – 190w panels @ 26.7vp/7.12imp
* 10 – 190w panels @ 17.8vp/10.96imp
* 10 – 200w panels @ 53.8vp/3.16imp
As we say on the web site, we cannot answer specific design questions because there are too many variables we would not know about your specific application, and we are trying to keep this a free service. However, I can provide some general answers that should help you narrow down your choices.
First, there are many things that go into the design process and the first is inverter input limits if grid tie, and solar charge controller input limits if battery based. In other words, if your solar charge controller has a limit of 75 volts DC input, this will require the number of solar modules wired in series to be well below this high limit. The NEC Article 690 provides more specific design guidelines related to safety multipliers that you must use.
The maximum input amp rating of the solar charge controller (or inverter if grid tie) will determine the maximum number of parallel strings and total amps from the array after the required NEC design multipliers are added.
Once you know the maximum voltage and maximum current your system can safely handle, this will define the solar array that your system can handle. Once you know this maximum total array wattage, you want to select the highest quality module you can buy that has the lowest cost per watt.
Take the total delivered price of a specific module and divide by nameplate wattage to get the $cost/watt.
If this process does not give you the solar array you want, then you will need to make changes to the inverter if grid tied, or the solar charge controller if a battery based system. Normally I first select the exact solar array wattage and physical size I want for a specific budget, then I select the inverter if grid tie, or the solar charge controller if battery based, but it sounds like you are working backwards and trying to base you design on comparing output voltages and amp ratings of the modules to fit a specific requirement.
In other words, its like taking a car and trying to replace the engine with a bigger engine to get more power. However, if you do not also upgrade the transmission, tires, drive shaft, fuel system, exhaust system, and brake system, then the vehicle cannot take advantage of the higher horsepower.
Hope this helps,
Monday, January 26th, 2009
Not wanting something for nothing, I just became a subscriber to backwoods home. I found the website most helpful and your answers also. More I read, the more confusing it gets. So much info is out there.
Eventually I want to put whole house on either solar or wind power or both (gridtied). I will discuss that when I get to that point in my remodeling. But that appears to be one or two years away.
But for now, just to start small.
I would like to power my LCD tv (200 watt), vcr /dvd combo (30 watt), the surround sound amp (135 watt), two laptops (max 120 watt combined), internet radio antenna (14watt), and wireless router (10 watt) from a small solar panel and a battery backup. They add up to about 540 – 550 watts
Both laptops have built in batteries for shut down purposes, and one is on a battery backup for longer grid interrupts, along with the internet radio antenna and router. But will probably use the UPS battery as the backup for the router and internet radio antenna and leave it hooked to the grid as is for now and remove the laptop from it.
When we are home or not everything runs constantly. Tv, vcr, amp are off, but have the keep warm circuit. I would like to put a manual (for now) switch in the system, so I could manually switch these items back to grid if needed. I know I could save energy by turning everything off when not in use with a power strip, but for now that’s not my point in this matter.
I live in Rocky Mountains at about 41 /42 degree latitude.
Could you give me an idea of the size solar panel, batteries, and inverter I would need to support running these items?
Does a charge controller just interrupt the power the panel produces to the batteries so a “dump” is not needed as would be needed in a wind generator?
Would I still need the GFC between the panel and controller, and the circuit breakers between the controller and batteries?
I know sounds like a lot of work and expense for a little gain. But every little bit helps down the line. And I could move these components later on out to the work shop, when I get it built.
Nobody is home all day, and split shift at nights.
We get many questions like this and the answer is – you can do this but the cost will be out of sight. It’s just not a good return to buy a solar power system dedicated to a few specific electrical appliances when still on the grid, as the solar system’s output would be totally wasted for any time periods when solar was available but these loads were not operating. Since you lose about 15% in efficiency when charging a battery, and another 10% when converting it back to 120 VAC, its not economical to charge a battery to power a load later in the day.
If you want to reduce your electric usage, install a small grid-tie solar system that feeds back into your house electric panel where it can off-set part or all of the electric loads that are operating at the same time.
If you want a battery backup system, add a battery bank to the grid tie system. Once the battery is charged, all of the solar power is sold back to the grid and the battery stays full until the next power outage. This way you will not have these charge/discharge losses during normal utility power.
Sunday, January 18th, 2009
Interested in knowing the economics comparison between a grid-tie v. off-grid system.
For simplicity, let’s imagine a 2Kw grid-tie system can be installed complete for $12,000, with no battery back-up. Also an off-grid system can be installed complete for the same price of $12,000 inclusive of battery bank.
In the course of 10 years, in comparison, which system will normally provide higher dividends?
If more details are needed for the overall scenario, please ask.
You are comparing apples and oranges so this choice makes no sense. If your goal for installing a solar system is to provide the most utility cost savings for the lowest initial cost, then any grid-tie system without batteries will have the lowest cost and will provide the shortest payback. For comparison purposes, inverters designed for grid-tie sell-back without batteries are usually a little more efficient than inverters designed to charge a battery bank, but this is not the real reason you would choose one over the other.
Any solar system with batteries cost more for the inverter and switchgear, costs more for the batteries, requires battery maintenance, takes up valuable heated interior space that could be used for other purposes, the costly batteries must be replaced every few years, and as stated above, the inverters are less efficient in sell-back mode. Yet, there are lots of battery based solar systems sold each year and the reason is very simple. People buy a more expensive battery-based solar system because it provides peace of mind. If you are in an area without grid power, it provides peace of mind of having reliable power without running a generator 24 hours per day. If you on the utility grid but in an area where there are lots of power outages, it provides the peace of mind that your freezer, lights, and other appliances will continue to operate during brief power interruptions. If you live in an area that has gone weeks at a time without power due to yearly storm damage, you have the peace of mind that any future storm will have only a minor impact on your lifestyle or perhaps your home-based business.
People place a high value for this peace of mind and do not calculate this in terms of payback or return on investment, just like you would not purchase a fire extinguisher or security system based on a cash flow analysis.
Hope this helps,
Wednesday, November 19th, 2008
Can I hook up a engine driven generator to the grid in a net metering arrangement? Can I do this with an AC generator head? Can I do this with a DC generator head? How would I go about it and what equipment would I need?
If your state allows net metering then you can do this, but I do not know why you would want to. By every measurement I have seen, you cannot generate electricity with a generator cheaper than what you are paying the utility for power. The only way this might work out would be if the utility has very high rates and you ran the generator on waste methane gas from a large refuse pile or other source of free gas. Still, the wear and tear on the generator and replacement cost usually still makes this not a very good economic process.
If you do try this, most utilities will NOT under any circumstances allow a direct connect between your generator and the grid. You must separate with a power inverter that has been tested and approved for grid inter-connect. Without this separation the grid power will blow out your generators windings if the grid is energized, and if you did try this during a power outage, the 240 VAC backfeed from your generator will go through the utility line transformers “backwards” and be stepped up to thousands of volts that could kill a utility worker repairing the power lines down the street.
Thanks. I understand that much. I have already been in contact with the Utility Company and New Jersey DEP. I qualify for net metering. I also have a source of free or cheap fuel that I plan to burn, so that has been thought through. My question was about availability of equipment that would allow me to use an AC generator head to grid connect. Alternatively, if I use a DC generator head, can I simply hook it up to the inverter the way I would do for an array of solar panels? Thanks, and I appreciate your time. I had tried getting answers from the inverter-companies, but got no-where.
If you connect a fuel-driven generator to back-feed the utility grid, it is not only illegal, IT WILL BLOW UP YOUR GENERATOR!
One way you can make this work is by using an inverter certified for grid-tie application and designed to operate with a DC battery bank. The inverter serves as the “translator” between the DC battery bank and the utility grid to match the grid voltage, current, and 60 cycle wave form. The battery serves as a “buffer” . One manufacturer recently introduced a grid-tie inverter that can take the straight output from a DC wind turbine without using a battery bank, but you most likely would need to have a high voltage DC head on your generator to match the DC input required for this inverter.
In the battery-based system, the generator is separately connected through a battery charger to charge the battery bank which means you can use either a DC or AC generator depending on the battery charger. If this system will be under 8 kW, you might check into the several grid-tie inverters that are available that have connection for a generator input and include a battery charger. With the proper sizing of the generator, battery charger, and inverter, the batteries should never become discharged since you are supplying battery charging into the battery bank at the same rate the inverter is taking battery power out of the batteries at the other end.
Large utility size mega-watt co-generator plants and gas fired peaking plants do connect their generators directly into the the utility grid without first charging batteries, but they use custom designed power conditioning equipment and extensive safety equipment to prevent all of the many power and safety problems that can occur. I assume you do not have several million dollars for this equipment and do not want to spend another $100,000 for the utility permit and inspection process to allow direct inter-connection.
Check these links -
Xantrex XW System
Windy Boy 6000U
Thats all you get for free!
Sunday, October 26th, 2008
Is it possible to run one of the less expensive high voltage grid tie inverters (e.g. the Sunny Boy 1200U needs 130-400 VDC input) with just a few 12 volt panels through the intermediary of a DC to DC converter (hopefully the rectified output of a cheap 12 volt inverter)?
I’d like my three 75 watt panels to do something useful when they are finished charging batteries and irrigating the garden.
The SunnyBoy and similar grid-tie inverters need a solar input well over 240 volts DC or they cannot put out 240 volts AC to grid, and normally have solar inputs above 300 volts.
Yes, it is possible to custom design and build some kind of DC to DC converter that could take the 36 volt solar array you have and convert this to 240 volts AC, but the resulting current amps would be very low and may not be enough to overcome the efficiency losses involved. Nobody I know makes anything like this and there is a good reason for that.
In real world terms, your 75 watt solar array is so small it would best be left doing what you are already doing – charging batteries and running small pumps or fountains.
Hope this helps,