I live in Wisconsin, which is prone to ice storms similar to what shut down the power grid in the Northeast and across Indiana this winter.
I am considering a battery backup system using four golf cart batteries wired to 12v and a 1500-2000 watt inverter to power lights, fridge, gas furnace, or wood stove blower [separately, of course].
Since I don’t have the budget yet for solar or wind, I was wondering if using my Honda Odyssey’s alternator with a battery isolator installed to recharge the battery bank would be a good idea. Any thoughts would be appreciated.
Thank you in advance,
Frank Falzon
Frank:
We have many projects with batteries and inverter for emergency power that did not include solar. However, I would not use the car to re-charge the batteries as this will be a major load on the small alternator and will use more gas than you think as you will probably need about 3 hours of charge time per day which is like driving 200 miles each day.
Keep your idea, but buy a generator. Most high quality inverters will include a high capacity battery charger which will allow re-charging for about 1 or 2 gallons per day. The only caution is you need a good quality generator in the 6 kW or larger size range, and having a good voltage regulator. Low cost generators drop their peak to peak voltage as they get loaded up and any battery charger will stop charging altogether when this happens.
We recently had our home completely remodeled from top to bottom. As part of the construction we had all new wiring, panels, and associated electrical work done brand new. Additionally we had a 3.2 KW solar array mounted onto our new metal roof. This solar array is grid inter tied with a 8 gel battery backup connecting 3 circuits in our home. We moved in on December 15th 2007 and have lived without any issues until June 7th, 2008.
On June 4th, 2008 we had a violent wind storm that dropped a tree limb on the power line serving our street. The power went out, our battery back up kicked on and all was fine. On June 6th the power company restored power to the street and we were back running on AC power from the power company with the solar array supplement.
Starting from June 7th through the date of this letter my wife and I have been experiencing physical discomforts such as intermittent “electrical shocks” and what feels like a mild electrical current running through our bodies. Additionally we have been getting recurring dull headaches where neither of us have had them before.
We have had our electrician, solar company, city inspector and power company out to check things out and all have said that they cannot find anything wrong.
The only time that we find complete relief from these physical symptoms is when we shut down the power at the utility junction breaker.
I am reaching out to you to see if you have any ideas of what may be causing these physical symptoms. We are both sane individuals in our early 40’s with no history of mental or physical ailments of this type.
I hope to hear from you soon.
John N
John:
I am not a doctor and don’t play one on TV either, but I can provide some information that may at least rule out some things.
I won’t insult you about how many of these type problems can be psycho-somatic, as I am sure you already know that and still feel there is something physical involved.
You did not describe your system but said it was grid-tie and battery based. From this I can only guess that it is a 48 volt DC system which would hardly give you a shock even if you touched the battery terminals unless you were standing barefoot in water! Of course many grid-tied solar arrays are wired for over 400 volts DC which can give you a severe shock.
You said the solar array was installed on a metal roof and you had a recent strong storm, and all this started after the storm. I have seen bad wind and rain storms cause one or more of the array wires to short out on the array frame or rub a bare spot on a array wire touching the metal roof. Normally this would trip the array ground fault breaker, but you may not have one. Also, if the metal roof has a poor ground or the ground fault circuit was wired wrong, if the array is now energizing a metal this may not trip the ground fault breaker.
I am not sure how even a metal roof could cause the problems you are experiencing even if it is energized, but this is easy to check. Did the service installer do a “meg-ohm” test of each array down lead in reference to ground? We do this for every installation to make sure there is no dead short or electrical “leakage” to ground or to the metal roofing.
Are you near high voltage power lines and could your metal roof be acting like an antenna? Again, making sure the solar array frame and metal roof are grounded to an earth ground would keep this from happening. Does your solar array have lightning arresters installed? These can fail after a severe lightning storm and may allow electrical path to the metal roof since they are wired to both the positive, negative, and ground wires. These are also easy to dis-connect and check for shorts.
Some inverters can develop a very high frequency “hum” that can be very annoying and can act like a dog whistle that most people cannot hear. This type of high frequency noise has caused headaches in some test subjects, but I have not heard anything specific related to an inverter. This can be checked with a sound pressure meter which can be purchased at Radio Shack. It can check sound levels in many different frequencies, and I would expect you are concerned with those frequencies just above normal hearing range or ultra-low.
If these checks prove negative, then shut the system down for a few weeks and see if anything changes.
With all the rebates in Florida, we decided we should put in a grid tie system. We went to a local home expo already committed. When we talked to the man selling solar systems, he told us that in Florida, you cannot use your grid tied system when the grid is down. This is supposed to be a safety requirement. It seems to me, it’s just another way the power company discourages people from installing grid tied systems.
Is it true that some states, especially Florida, have this “safety” requirement? Do you really think this is a necessary safety requirement? Isn’t there some kind of safety switch used that will disconnect my solar panels from the grid when the grid is down?
It’s always sunny after a hurricane, or ice storm, when the power can be off for days or weeks. For us, one of the major benefits of such a grid tie system would be that we would have power for at least 4 to 6 hours a day even when the grid was down. That would allow us to run the well pump, the freezer, the hot water heater. Those 4 to 6 hours of electricity would make life a lot more bearable while the grid was down.
Thanks,
Allyn Uptain
Allyn:
Funny you ask. I just had an article on this subject in a solar trade magazine but it is for those in the business and I doubt you can find it at a book store.
Yes, all grid-tie systems shut down when the grid fails but this is not a utility scheme, it is required by the design of all grid-tie inverters. The only way the grid-tie inverter can sell solar power back into the utility grid is to match the grid’s sine wave and voltage and cycles perfectly. If any of these do not match, there will be no flow out to the grid. This means the inverter is constantly taking these measurements which it uses to make this perfect match and cause the flow from the solar power back out to the grid.
However, almost all battery-based inverters designed to also sell power back to the grid first put the solar energy into the battery bank, then this stored battery energy is converted to grid power and sent out on the grid. In other words, battery based inverters have no problem providing power to your emergency loads when the grid fails, but this means you will need a large battery bank, a room for these batteries, and a higher cost inverter.
I have found that many of the newer solar dealers just entering the solar business have never installed a battery based solar system as they are harder to design, harder to install, and cost much more so they have very few people interested in buying this type system.
Those of us who have been installing solar systems for years have no problem installing battery systems because at one time NONE of these solar systems sold power to the utility grid and they all had batteries. I recently had a client tell me another solar dealer told them the manufacturer would void the warranty if they installed a battery based system. Keep in mind both systems use the same size and type solar modules. The only difference is a grid tie system will wire 10 to 12 modules in series and use a high voltage DC inverter which allows using smaller wire to connect the array. A battery based system will have the solar array wired for 24, 48, or 60 volts DC to match the battery bank voltage. This requires a different wiring arrangement but can use the exact same module.
Having recently bought some land in Missouri that is located out the the sticks and very much at the end of the power grid. I have pretty well deduced that I will need some back up power.
Recently I have discovered the backwoodshome.com website and a number of your articles. As one who is not totally familiar with alternative power like wind and solar, everything I read seems only to confuse me more.
With interest I have read about l-16 industrial batteries for a battery bank in some articles. In an article about adding a solar cell to a truck camper a RV/marine battery is recommended. Since RV/marine batteries are easy to find and will take to repeated charging wouldn’t they be logical choice for a battery bank vice the harder to find L-16?
I have noticed too that with wind power most often suggested is a dc wind generator that requires upwards of 6 or 7 knots of wind to operate. In searching around I have found a source for a AC wind generator that begins operation in the sub 7knot range. AC generators have to best of my knowledge a big advantage over DC generators and that is in size of the cable between the transmission line from the tower to the battery bank. An ac generator can use a standard ac power cord and suffers no loss in current between the tower and batteries.
I have to admit that my understanding of the way a ac generator works is taken from the following website: http://www.tlgwindpower.com/default.htm On the opening page there is a photo of a customer using 9 ac wind generators on his farm in Wisconsin. Although wind power as such is confusing to me I believe that this ac system must be quite good or the farmer who had added to it and bought these generators would not be doing so if they weren’t efficient.
Perhaps you can give some insight into battery banks and DC versus AC generators in a future story. Also the battery bank issue of l-16 versus marine batteries is very confusing to a novice seeking information like myself.
Any information you can provide along these lines would be greatly appreciated.
Thank You
Keith McElroy
Keith:
Lots of questions! Actually you are talking about “L-16″ batteries, not “I-16″. When I suggest using an RV/Marine battery, you will find that it is for a small 12-volt DC system that does not have a large load that would fully discharge it each day. These batteries are much heavier duty than a typical car battery, and most have re-combiner caps and do not need to add water. However, they will NOT hold up to a daily deep charge/discharge cycling like a solar powered home or cabin. For these larger loads and system sizes, the lowest cost battery designed for a heavy charge/discharge cycling each day is a 6-volt golf cart battery ( T-105 size). These are less than $100, and can be found at most big box stores during the summer months. They are about the same size as a car battery, but because they are 6-volt, the plates are very thick and very heavy.
For a 12-volt system you will need two 6-volt batteries wired in series, and for larger systems you will need 4, 8, or 12. When you start getting above 8 batteries of any size, its better to switch to a larger amp-hr battery and stay less than 16, as this can cause problems with un-even charging and dis-charging when you have multiple strings of parallel batteries.
I think you are caught up in the AC or DC debate as a marketing ploy. There is no engineering difference in the amount of wind it takes to turn a wind turbine based on AC or DC output voltage. Wind energy is a “cubic” function of the area of the blades, and below around 7 MPH I think you will find most small-scale generators will not provide any real power, although the blades might turn. There are now both AC and DC wind turbines and each has its advantages, but only in wiring and additional equipment that will be required.
A 24 or 48 volt DC output wind turbine is very easy to add to an existing solar-power system, and some models have built-in charge controllers and can be hooked directly to the batteries. Yes, this will require a larger wire size since the voltage is lower, but the ease of wiring is its real advantage. Also, unless you are talking about some huge wind machine on a 150-foot tower, the difference in wire costs would most likely be less than 50 cents per foot for the larger wire caused by using a lower voltage DC model. An AC wind turbine can use a smaller wire size since the voltage is higher, and these are usually designed for grid-connect systems without batteries. There are a few other issues, but you cannot say an AC unit works better than a DC unit having the same size and blade design, and the reverse is also true.
I have a Fronius 5100 inverter on a grid tied solar system. When the grid goes down, I lose all power to my house even though the solar panels are working.
Is there a way to simulate the grid so that when power goes down I can still utilize my solar energy?
Thanks
Mike Emmons
Mike:
I can’t believe this was a surprise to you, and I sincerely hope the installer made it very clear that ALL grid-tie solar inverters are designed to shut down in the event of the loss of grid power.
If they continued to operate after a power outage, they could be energizing a downed power line that the utility crew would not realize power was being supplied from the wrong end of the line which they may not check. Keep in mind that any power you are sending back to the grid at 240 volts AC goes through the transformer on the power pole in reverse and will go out onto the power lines at 480 or higher voltage which is deadly.
All inverters must pass a very strict testing process to make sure their design will not allow this to happen, and proof of meeting this safety requirement must be provided to the local utility before they will allow you to install the inverter on their grid. The equipment label will note – “UL 1741″ and “IEEE 929″ to indicate this.
Yes, there is a way to make a grid-tie inverter “think” the grid is still operating and not shut down, but this requires a second inverter with battery backup. In addition, since the first inverter is now being fooled and continues to operate, your system must isolate the output from the utility grid, and include enough electrical loads in your home that are operating to consume this excess power being generated or you will have a system error in the inverter that will shut the system down.
I do not want to give out too much information on this subject as you really need to work with an experienced solar installer to make this conversion due to several safety concerns, but it can be done.
