Jeff,

I came across an add for the Power Save 1200. Electricity flow “cleaner” with a 1K solar panel to connect without batteries. We are on the grid and looking to waste less and minimize our “footprint”. http://www.power-save1200.com/1200.html. They have an assortment of interesting products.

Donna

Donna,

Even if we installed wind and solar equipment for free, no labor charges at all, just the hardware costs for either system would easily exceed many thousands of dollars, so anyone that claims they can do this for $299, tells me there may be more to the story. For example, the web site you referred me to is very interesting as it discusses in detail their solar grid-tie system, but no costs or sizes are given, and a grid-tie wind system, but no costs or sizes are given, then the ad goes into describing this power saving product with a $299 price, as if it included all the solar and wind features that were also listed as if this was all the same product.

Based on the very limited information provided as to how this “black box” can save up to 25% of your home’s utility usage, a figure I highly doubt, it appears to me this is just another capacitor bank with an added whole house surge suppressor. Yes, there are times when large motor or transformer loads on an electrical system can cause the voltage and current to be out of phase more than 90 degrees as required for maximum power conversion. However, I do not know any utility companies that measure this power factor penalty except for large commercial clients since this requires installing a separate power factor meter. It is highly doubtful that even if you had an extreme case of all kinds of motor and transformer loads in your home, odds are this is not being metered or is not enough to cause the type of added savings being claimed by this device. The only time we install equipment like this is for a large retail store with thousands of fluorescent lights, or a large industrial facility with all kinds of large motor loads.

As far as the mentioned benefit for having a surge suppressor, yes this can save your appliances from damage if there is a major voltage surge on the utility line like lightning nearby, but you can buy a whole house surge suppressor at Lowes for about $40.00.

I suggest that you first contact your local utility to see if they even measure power factor on their residential meters, and if they do, ask them what this added utility cost is. If it is not metered by the utility, the only benefit I can see to adding a capacitor bank would be if your power factor was so bad that it was increasing the actual VA metered usage, and for that you would need a whole house-full of motor and ballast loads to realize these kinds of savings.

I say read the small print on anything like this since the basic information being offered before the sale is too limited to actually know what you are buying, how it works, and how they are measuring their very high utility savings. Odds are this sample case is nothing like your home.

Buyer beware,

Jeff Yago

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Hi there.

Tom Stepien

Tom,

I’ll make it simple for you – there is no such thing as wiring inverter outputs in series. You also do not wire different groups of modules to more than one inverter input. You are mixing up how this really works. When we were finally allowed to legally do a grid-connect solar system, the inverters used were designed for higher voltage solar arrays than the battery based inverters using solar arrasy in the 12 to 48 violt DC range.

With a high voltage array, the wire sizes connecting the solar modules are much smaller and have a much lower line loss due to the high voltage. Its not unusual for these systems to have an open circuit voltage in the 400 to 450 volt DC range. Lets say you have a 4 kw array. You could wire this to a 4 kW inverter, or two 2 kW inverters each wired to the house panel which would be a parallel output arrangement.

Now if this 4 kW array was going to be used with the two inverters, you would wire half of the array, or 2 kW of array to each 2 kW inverter. It is important to understand that in this arrangement, each half of the array only has wire runs to one inverter, they cannot be wired together.

When deciding how to wire an array together, you can only wire in series the number of modules that will not exceed the high voltage input limit of the inverter. This means you may have ten modules at 100 watts in one string, in parallel with another string of 10 modules, making a total of 2 kW feeding a single inverter.

When we have more than one string, there are several things we do to avoid the balance problem you mentioned. For example, on a long east-west roof, we could wire all 10 modules of each string side by side in single rows east to west. However, if there is some side shading, we may have the last few modules in each string in the shade while the rest are in full sun, which means none of the strings will be providing very much power due to the shading of the end modules. If we had wired the 10 modules in series in a 2 X 5 arrangement on half the roof and feed one inverter, then do the same for the other half of the array and feed the second inverter, then at least one inverter will be near full power output if the other half were being shaded, since side shading in the early morning or late afternoon usually only affects half of the roof. Of course if there is no shading, then it would make little difference how we arranged the modules.

Finally, you are also correct that no two modules have the same exact voltage-current output curves, so during installation we usually try to place groups of modules on the ground facing the sun and quickly take output readings before the sun or clouds change. This cheap and dirty method will still tell you which modules have the higher and which have the lower outputs. I usually mark the backs with my readings, which makes it much easier to “balance” the separate strings when we start installing them. By balancing the strings that are in parallel, we are minimizing the balance problem you mentioned, as we want each parallel string to produce the same voltage or the inverter will not properly “track” the maximum power point of the array and we will have a lower overall solar output.

Hope this helped,

Jeff Yago

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Jeff,

Mark

Mark,

As I see it, you have 2 possible reasons for this problem. You indicate the charging voltage is around 14 to 15 volts during charging which would seem to be good, but you did not say what the charging current was. For example, your inverter could be producing the right voltage output, but little or no current flow which would mean the batteries are getting little or no real charging amps going into them. My first check would be the generator and checking the amp loading of the charger.

Many low cost generators have a voltage regulator that drops the peak to peak voltage of the output waveform when more loads are added to the generator as their way of controlling overloading. Although this method of load control does not affect lights and motor driven tools, most battery chargers and inverters in charging mode will stop charging completely. These chargers are designed to use the full 169 peak to peak volts (120 VAC is the average of this voltage) of the generator. In other words, battery chargers only use the “peaks” of the voltage waveform and if these peaks are cut off or reduced, there is a major drop in charging amps output.

My second guess is the batteries. If these batteries are either old in age, or are newer, but have experienced many extreme total discharge cycles, or go long periods with only a partial re-charge, then what you describe is a classic indication of a failing battery bank. Assuming you do have a good charging process, when a battery is in the condition I just described, it will get what we call a “skim charge” and shuts down the battery charging because the battery voltage goes up real fast which tells the charger to stop charging. However, the aging battery plates usually have very little lead remaining in contact with the acid as most of the plate area is covered with calcium buildup and no longer in contact with the acid. This in effect is like making your batteries much smaller, which causes the battery voltage to rise very fast under the heavy charging, yet little real charging is taking place. As soon as the charging process stops, the battery voltage will drop almost down to a totally discharged level of around 12 volts since it was never really re-charged, and will quickly drop even lower when a load is connected, which also is what you have described.

I would not only suggest replacing these batteries, but I would switch to a deep discharge type of battery like a 6 volt golf car battery or larger L-16 battery. This will give you more amp-hours of capacity with fewer batteries wired in series. Its always better to have only 1 or 2 battery strings in parallel, as one string will always end up getting most of the charge and most of the discharge when you have 3 or more strings in series.

Good luck,

Jeff Yago

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Hello Jeff,

Steven

Steven,

This might surprise you but the inverter size has nothing to do with the size of the solar array or the amount of sun. First decide what electrical loads the inverter must power during a power outage. If off-grid, determine what electrical loads will be on at the same time.

For example, you have a well pump, microwave oven, refrigerator, TV, and some lights you want to power from an inverter. Normally not all of these loads will be operating at the same time, so first decide what is the most likely worst case and that will determine to inverter size. Odds are the larger loads of the well pump and microwave oven will not both be on at the same time, but the refrigerator could cycle on while the well pump is pumping. You also would not normally have every light turned on at the same time so you might only count half of the lighting load.

Since most high quality inverters can handle a very large overload for a few seconds, there will be times when the well pump or other load might kick on but only last a few seconds. This is not as critical as it seems and should not harm a quality inverter, but could occasionally trip a circuit breaker.

After you know your peak electrical load and inverter size, check the inverter specifications and this will give you the highest battery amp draw, which will help size the wiring and battery bank. If you now add how many hours per day these loads will operate, this will determine how many amp-hours will be removed from the battery bank, which in turn will tell you how many amp-hours the solar array must put back per day. Most designers use a simple spreadsheet for this calculation.

For week-end cabins, you take the total amp-hours that will be used for the weekend visit, then consider that you will have several days of solar to make up the battery drain so you could actually get by with a solar array that is smaller than the actual daily usage.

I usually figure 4 hours of sun during the winter and 6 hours during the summer which when multiplied by the array size will give you solar amp-hours per day, but I suggest multiplying this answer by 75% to account for system losses, array losses, weather losses, etc. It is very rare that any solar array will produce 100% of its nameplate rating.

Good luck,

Jeff Yago

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Jeff,

Thanks

Bill Wilson

Bill,

I saw an ad for a car that can go 120 miles per hour, but that does not mean I can drive it down the Interstate at that speed if I buy it. In other words, the ad you reference may say you can turn your meter backwards, but you cannot do it legally unless you install all of the required safety dis-connects as required by your local utility, you complete their application form, and then they replace your existing electric meter with a model that records each in and out electric flow separately. Some states have other requirements like providing the utility with a copy of your homeowners liability insurance policy and having a lockable handle exterior disconnect switch for their use.

Although this company is known for their quality wind products, I don’t like having the inverter mounted 75 feet up a pole and subject to all the weather extremes. The inverter is the weak link in most of these systems and I want a system where this is at ground level and have as few electronic components as possible up on a tall tower and in the weather.

Most small wind systems generate DC power for battery charging. What they have done is mounted a DC to AC inverter inside the wind turbine to convert the DC electricity from the turbine into 120/240 VAC which can feed back into the utility grid. However, you cannot legally just plug this into the wall outlet and “turn your meter backwards”.

On another note, for those readers wanting to do something like this, please understand that the power output from any wind turbine is “wild”, in that it jumps constantly all over the place as the wind changes direction and flow rate. You cannot use a standard DC to AC inverter with a wind turbine since the voltage and current goes to such extremes every few seconds. Most inverter manufacturers make a “modified” version of their solar inverters to work with wind turbines, and most are designed for ground mounting in a protected area.

Also note that there are very few areas of the US with enough wind to make these worth the cost and the easiest way to tell is if there are already other wind turbines nearby. Those areas of the US with lots of wind year-round are usually already covered with wind turbines. Although you might be the first in your area, you may want to check a wind resource map for your state first before paying out $6000 plus.

Good Luck,

Jeff Yago

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Jeff,

Richard Heiser
Sacramento, CA

Richard,

A solar charger is sized based on the following –

First, total short circuit amp rating of solar array X 125% .    Note- Under extreme cold and sunny days, its possible for a solar array to reach 156% of short circuit amp rating for short periods and this is used to size solar array wiring.  If your charge controller does not have this temporary surge capacity, you should use the larger multiplier .

This calculation will determine the “amp” rating of the charge controller.

Next, select voltage for charge controller.  This will be total voltage for battery bank.  For example, two batteries of 12 volts in series would require a 24 volt controller.  Four batteries of 12 volts in parallel would require a 12 volt controller.  Four batteries of 12 volts with 2 in series and 2 in parallel would require a 24 volt controller.

The controller doesn’t know or care how many batteries you have or how they are wired, as long as the controller design voltage matches the voltage of the battery bank.

Now that you know amp rating and voltage for controller, select a model with the options you need, like digital meter, low voltage dis-connect, and/or temperature sensor.

Good luck,

Jeff Yago

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Jeff,

Thanks for offering this service.

Mark

Mark,

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.

Jeff Yago

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Jeff,

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,

Rick Conaway

Rick,

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.

Good luck,

Jeff Yago

Jeff,

Rick

Rick,

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.

Good Luck,

Jeff Yago

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