Final verdict on homemade GRID TIE inverters?

[arizonaguide]

I live in Arizona and I have been thinking that the GREAT batterybank that's in my friend's electric golf cart could be used as an alternative energy battery bank and charged with solar power, THEN fed through a GTI back into the grid/and used around the house as a suppliment (At least on days that it is not being used for Golf!)

It just seems like a waste to not use them except for 4hrs/once per week to golf!

Does anyone have advice a perfect (homemade) GTI/system for this application?

The golf cart parks in the garage (most of the week just sitting there!), and the solor cells could be put on the same garage roof, so it would not be difficult to setup a system around the garage area.

The Golf cart battery bank is a set of (8ea) 6volt cells.

Does anyone have a link to a good schematic for this application?
Any words of wisdom as to where to start?

IT just seems really cool to be able to use his alternate energy vehicle to also (help) power his house!!! But, I know that the "Inverter" is the key to that happening.

 

[picbits]

8 x 6 volt batteries = 48 volts
At a guess, around 12Ah capacity per battery

Total energy storage = 576Wh (i.e. 576 watts for 1 hour)

Cost in the UK (very expensive !) per Kwh = $0.20

So with switching efficiencies of around 80% you'd be able to feed back around $0.10 worth of power back into the grid from a full charge. Thats purchase price of the energy, I suspect the sellback value is a lot less (probably half that so around $0.05 per full charge)

Is it really worth it ?

 

[picbits]

Oh and after 1000-2000 full cycles (maybe less) you'll have to replace the battery pack at a large cost. The batteries will also be less effective as they get older with a lower capacity.

 

[magickaldan]

Look on the side of the batteries and tell us what the AH rating is.

 

[arizonaguide]

I'll check with him and find out what the AH are for sure. I believe they are 6V/210AH.

It may not be worth it as an attempt to "sell back" wattage to the utility, but it may be worth it to know that he would have emergency backup power available if he needed it, simply by having the system preinstalled and working. We have a tremendous amount of solar available to us here in AZ! But you do bring up a good point about the costs-vs-the costs on the photovoltaic system.

I guess the main thing I should do is design a Solor hot-water system, and start with cutting the hot-water expense out of the loop.
Current electric bill average = $300/mo, so anything that is one step closer to getting off the grid is a good planning/learning exercise if nothing else. HUGE air conditioning costs in the Summer monthes.

So, he (in fact we all) needs to figure out lifestyle changes to change expenses, and converting to an electric vehicle as much as possible has been one step. (using the golf cart for short trips, getting off of dependance on $2.50/gal+ gasoline, etc). And it bugs him that his battery-bank just sit's there idle the rest of the time, when it at least could be used as "backup household power" in an emergency, if not actually tied into the grid.
He would of course like to get completely OFF the GRID if possible.

And I know that a good inverter is one of the major expenses in this type of system, so being able to build it myself would not only cut costs, but be a great learning exercise as well.

 

[picbits]

You're better off first identifying where your $300/mo is spent on Electricity and see if you can can work out alternative methods of reducing that amount.

For example, if you spend $100 of that on heating water, consider solar heated water (or partially solar heated water).

Air conditioning ? Just open the windows

On a more serious note, how about some kind of evaporative cooling system ? Pump the interior air through a set of old car radiators which have water dripping over the outside and a low power fan to aid the evaporation. If you have a ready source of water available (i.e. a lake or stream) then you have plenty of cooling there as well.

Solar electricity power is fairly expensive for the initial setup. The cells don't last forever as well and you lose a fair bit in converting from DC to AC so using solar to heat water is a much better idea (and cheaper !)

 

[arizonaguide]

Yup, for sure I'm thinking of a solar hot water (supplimented) system. That's pretty easy, and I just need to build it.

And the idea of a evap-cooler is good for MOST of the summer...except aug/sep when the humidity jumps and the evap cooler is almost useless. For those 2 months it HAS to be air conditioning.

But, I am looking at trying to design/setup a solar evap-cooler also, for the months of APR-JUL.
I guess for that I really need a good high efficiency DC motor, and some serious photovoltaic cells...and I imagine that puts me into the $600-800range to get a whole solor supplied fan motor/water pump system built. THAT'S the trouble with all this...the HUGE initial cost outlays.

The problem with just opening the windows is that on a typical AUG day...that just lets in the 112-115deg F ambient air temp.

THAT'S the whole thing that bugs me about Arizona! We pay to cool the house by having the air-conditioner exchanging and venting the heat outside...then we pay more to heat hot water in the hot water heater inside...
Just recapturing the waste heat from the air-conditioner would heat all the hot water we would use in the summer...but the solar H20heater will do that also with less trouble.

But wasting all that air-conditioning heat seems silly. It ought to be used to power something/somehow.

I would like to design ONE UNIT that acted as Air-conditioner/Refrigerator/Water Heater so that by the time it was done there would be very little heat wasted to the atmosphere.

That way, the heat from the refrigerator exchange could be used also, instead of currently just venting into the kitchen like it does...(which in turn doesn't help the AirCond bill!). In other words pay what I have to for air-cond/refrigeration...and let the waste heat from that be used to heat water and other energy uses.

Solar "cooling" is what we REALLY need here! That was kinda the thought behind the solar charged-Golf Cart Battery Bank running the air-conditioner and evap cooler systems.

With the right inverterand system capacity, I could use a standard 120v. EvapCooler and our current AirConditioner...and not have to get a special DC Fan Motor system, etc...
which would leave more $$$ to buy the solar cells themselves!

 

[summitville]

Why do you need Golf Cart Batteries to use Solar Panels with a Grid Tie Inverter? Many Grid-Tie systems can run directly from the Solar Panels. The newer Grid Tie Inverters incorporate Max Power Point technology to squeeze Maximum Wattage from the Solar Array under all sunlight conditions. When the sun shines the Grid Tie Inverter will reduce/offset the energy used by your home. Charging Batteries will just cause another 10-20% Energy LOSS in the system. Batteries are only usefull if you have Inverters to run important appliances during AC black-outs or you are Off-Grid.

Geothermal Heat/AC is the way to go! It is 10 Degrees outside and my house is warm and toasty. There is 50 Degree water deep within the earth. My Geothermal Unit gets that heat, concentrates it and makes 80-85 Degree warm air. And it uses very little electricity doing it.

In the summer the reverse happens. The 90 Degree heat in my house is moved deep into the earth where it is still only 50 Degrees. Also, it moves heat into the the Hot Water Tank as a bonus.

Based on MY COSTS, Geothermal is way Over-Unity because it just moves heat from one location to another. It can move way more heat energy into my home in the winter than it consumes in electrical power. Of course, if you consider the Energy from the Earth + the Electrical Energy used then Geothermal is less than Unity but for ME the Heat Energy from the earth is FREE just like Solar Energy is FREE and Wind Energy is FREE !!!

I have an ALL Electric 2,800 Sq Ft Ranch home with a 2,800 sq ft heated basement and my Electric Bill is $166.00 / month. I have figured out how to live without Natural Gas (which I cannot make) and not "break-the-bank". Although propane gas is a requirement for the Grill. I also have the propane hooked-up to the Sealed Fireplace in the Great Room for "back-up heat" when the AC Grid is down and for the occasional ambience.

Wind Energy is the cheapest way to create electricity if you live in a consistently windy area.

If you live in the South-West, USA then Solar Panels can create more useable energy per year especially if the winds are calm.

Given the current State Grants and Tax Credits, now may be the time to install enough Wind Turbines and Solar PV get my Utility Bill as close to $0.00 / month, as possible. Every KW-Hour that I can create is a KW-Hour I do not have to purchase at FULL PRICE! It will be a long time before I can make more Electricty than I use. So, I am not concerned with the issue of "Selling-Back" excess Electricity at a discount.

My friend's next door neighbor finished installing a 10KW Wind Turbine on a 100' Tower in late October. It is the biggest residential Wind Turbine in the county. We are going to visit my friend's neighbor in the Spring to see how much electricity his Wind Turbine has ACTUALLY generated after 6 months.

 

[arizonaguide]

Why do you need Golf Cart Batteries to use Solar Panels with a Grid Tie Inverter?

Nighttime. Summertime here in Arizona, you even have to run the AirConditioner at nighttime (from MAY-SEP). Part of the problem with geothermal is that the water table is so deep here, combined with what is called calichi clay "soil" (cross between hardplastic and concrete). Just beneath the consistancy of Bedrock.

 

[itsapplied4]

yes GTI is a problem however..

Hello All...

The idea of building a GTI is very entertaining ..IGBT's in H-bridge configuration seem to be the acceptable way to accomplish this. However the constraints of part selection , layout, as well as failure rate and not to mention certification for utility backfeed ...All these seem a huge problem . Realisticly they have already been solved by many of the pre packaged GTI builders and can be broken down into several blocks of responsibilty.

1. Frequency Syncronization - I'm sure that the torroid coil application to couple the freqency is well understood so I won't go there. But to get a clean sinosoidal 60hz +/-1%thd thats derived from a square head DC is another matter so lets just glean from the others who have already done this. Freqency and pure sine outputs have been around and are old hat for Trace engineering/Xantrex ...Use the charateristics from one of them to hold it online. Oh yes another company call Basler I believe has been making a paralleling device for generators for years... Gensets maintain frequency by varying RPM so getting two sine wave ito sync is not much harder than changing the lead/lag of the monitored systems.

2. This block of concern is one of Permanent Power being monitored so as to sync the two and if interupted downstream backflow is stopped. Here again the problem has a solution in the existing GTI's on the market .This control section is no more than a voltage sensing circuit which operates the devices' internal switching system. One can easily gleen from The smaller ...lesss costly .....units (250w) and use the control section to operate a much larger amperage device. Another idea that worked well for me was using two stacked one as a ext-ref for my scope.

3. The hardest part of this entire project is not the generation of "pure sine interuptable output " but to gain the Utility Companies blessing for this. They do not like any backfeed from any system be it you or another Utility company. In fact one of their biggest worries is that the grid tie breaker from another generator (utility owned portable) grid will be left closed . If you put yours online maybe no one will know. However there are exceptions like this...Example : During the ice storm of 2008 i checked the output of a dead ckt and was surprised to get 96 volts even more surprising was the freqency was 400hz. Someone had a military genset on line and was totally unaccountable for the backfeed...so your liability is self imposed by the safety factor and the responsibilty of ones actions...

Not making this type of project sound impossible is a little hard to do...In some of the very early posts one of the writers mentioned why re-invent the wheel. Thats true but experimentation is the key to the door of the future. I do feel though that using the information/circiutry/modules or whatever to accomplish you goal is as if you had started from scratch with the idea and nothing else.

I am a new poster to this forum and will be showing up from time to time.
Happy New Year to All....Itsapplied4

 

[arizonaguide]

So, does anyone have an advice on the best OEM inverter/GTI that would handle the type of load that an AirConditioner would require.

 

[magickaldan]

Well if you do the math with 210AH then you get quite a bit of power storage. 6v*210AH=1260Watts
1260 watts * 8 batteries = 10,080 Watts/hr. So you have around 10KW of power sitting there.

Also how many KW are you using in one month for $300? Does that include natural gas, water, sewer? or just electric.
Before I changed out all the lights in my house to low watt fluorescent my bill was over twice as high as it is now.

Right now I pay $0.12/KW and my bill is $61.09/month and I use around 484KW's month, if you break that down to hourly average it is like this (484KW/bill cycle my case is 29days)=16.69/24hrs in a day=0.695 KW/hr or 695 watts per hour on average. Which is basically a old fridge, microwave on occasion*, 2 laptops, clock, maybe around 4 42watt fluorescent lights. So that battery pack based on my average would run my house for 10,080/695=14 hrs or would offset my bill by 10.080KW*$0.12=$1.20

So your better off going for solar hot water. Also how hot do you run your hot water heater? And is it located in a heated room if not maybe find some way to help insulate the tank better. Also the refrigerator is another major appliance that sucks up a lot of juice

I'll check with him and find out what the AH are for sure. I believe they are 6V/210AH.

It may not be worth it as an attempt to "sell back" wattage to the utility, but it may be worth it to know that he would have emergency backup power available if he needed it, simply by having the system preinstalled and working. We have a tremendous amount of solar available to us here in AZ! But you do bring up a good point about the costs-vs-the costs on the photovoltaic system.

I guess the main thing I should do is design a Solor hot-water system, and start with cutting the hot-water expense out of the loop.
Current electric bill average = $300/mo, so anything that is one step closer to getting off the grid is a good planning/learning exercise if nothing else. HUGE air conditioning costs in the Summer monthes.

So, he (in fact we all) needs to figure out lifestyle changes to change expenses, and converting to an electric vehicle as much as possible has been one step. (using the golf cart for short trips, getting off of dependance on $2.50/gal+ gasoline, etc). And it bugs him that his battery-bank just sit's there idle the rest of the time, when it at least could be used as "backup household power" in an emergency, if not actually tied into the grid.
He would of course like to get completely OFF the GRID if possible.

And I know that a good inverter is one of the major expenses in this type of system, so being able to build it myself would not only cut costs, but be a great learning exercise as well.

 

[tcmtech]

As your seeing when you break down a simple $300 a month electric bill and even at higher KWH cost rates it still adds up to a very large amount of energy. And in realistic terms it is not actually continuous usage rate but rather goes up and down over the period of a day.

When designing AE systems doing an honest energy audit of your place and finding what uses the most power and by what way can you decrease that power usage can decrease your costs substantially.

Making more energy is expensive but often times just finding out how to use less is the cheaper and more cost effective method.

Home made GTI is not all that hard. Getting it certified and legal will be far more work in most places. I am lucky being my local power company is a very strong supporter of customer owned AE and are openly willing to work with me on my designs when I need them too.
Unfortunately most utility companies feel that anything that the customer does them selves to conserve energy is like money being taken out of their pocket and should be discouraged or prevented by all means possible.

 

[summitville]

" ... So, does anyone have an advice on the best OEM inverter/GTI that would handle the type of load that an AirConditioner would require ..."

There is no "Best".
But Xantrex is one of the leaders.
Check out this website ..
Affordable Solar - Solar Panels, Kits, Residential Solar , Inverters, Charge Controllers
$6,000 for a 1KW Solar Grid Tie System that will save you a whopping $0.10 per hour when the sun shines.
How many YEARS is that before you break-even on that "investment" ?
About 20 years?

Read this horror story about the Power Jack 3500 Watt Inverter ...
The Power Jack 3500 Watt inverter - buyers beware!
This device was not a lemon ...
It was down right fraud.
It would eventually electrocute you if it would actually "operate" for more than a few hours before releasing the magic smoke.

 

[arizonaguide]

Yup, this whole thing has been bouncing around in my mind for awhile, trying to think creatively "outside the box" and "off the grid"...and yet when you start to look at the cost/benefits (as you folks have mentioned) it's just hard to justify at today's prices. If photovoltaics and replacement batterys were MUCH less expensive, it would be a lot easier to justify. And then you DO hear the related horror stories.

I also have considered just setting up a single room as an emergency (well insulated) 12v room, something that could be fallen back upon for "emergency" light and A/C in the event of a prolonged power outage...and powered copmpletely by a 12V system. But if that actually happened we would probably just get in the car and head north. Self Sufficiency sounds great...but it's a long way from realistic in the 115deg summer heat of PHX, Arizona. That is, until we come up with inexpensive and effecient Solar Cooling somehow.

 

[smanches]

Couldn't you setup solar cooling the same way they make Propane refrigerators?

 

[Oznog]

So, does anyone have an advice on the best OEM inverter/GTI that would handle the type of load that an AirConditioner would require.

Well, you've got to clearly state your criteria. Do you hope to somehow save money doing this?

A large air conditioner could not be run off a 12v system at all. Same for any large loads- the current required becomes impractical and ohmic impedances alone kill the usefulness. Say you just need 1KW continuous (that might be an ~7000 BTU room unit). Assuming 10% inverter loss, that's 92.6 amps needed. The long cables off the roof and the connections, say they're a total of 50 milliohms, that drains 4.63v right there.

Quality deep cycle lead acid batts realistically have a ~300 cycle life expectancy under the BEST conditions, and that's rather optimistic, frankly. High-rate usage, or other "rough conditions", is MUCH less. And don't be surprised if a battery just conks out early on for no apparent reason. Lead acid tends to do that.

LiFePO4 now costs only about 3x-5x more that quality lead-acid, BUT it's a more efficient cycle (for solar, that's important!), typically lasts 1000+ cycles (maybe much more), and categorically supports much faster charging and discharging than lead-acid. And the cost comparison is actually better when you consider the amount of "usable" lead acid capacity vs LiFePO4, which is 100% usable:
When it's cold, lead acid battery capacity drops
If you want deep cycle lead acid batts to last longer, you wanna limit discharges to 50% or so (so, what, we buy twice as many batts at double the cost?)
At high currents, lead acid batts' usable capacity drops as per Peukert's effect

 

[Oznog]

Couldn't you setup solar cooling the same way they make Propane refrigerators?

That's an ammonia-hydrogen Servel Cycle refrigerator, a type of Adsorption cooling. IIRC the thermal efficiency is poor, and the amount of equipment needed to cool a house and the volume of chemicals would be quite high. There are other types of adsorption which are more promising than the Servel cycle for cooling a building. A particularly difficult factor however is the range of ambient temperatures at which heat must be rejected. A traditional HCFC compressor system loses efficiency when pumping heat out of a 70F inside to a 110F outside- BUT it can do it. Some technologies like water evaporation have a fixed temp differential they can generate, and past that it just can't pump any colder regardless of how big the system is.

 

[arizonaguide]

So, it sounds like the Solar Charged-Golf Cart Battery Bank running the air-conditioner and evap cooler systems idea is JUST not practical with our current technology and prices.

I still may be onto something in designing ONE UNIT that acted as Air-conditioner/Refrigerator/Water Heater, where I pay what I have to for air-cond/refrigeration...and let the waste heat from that be used to heat water and other energy uses, with very little heat wasted to the atmosphere. That way, the heat from the refrigerator/AC exchange could be used productively.
But, excess heat is not really in a shortage here...so even that becomes questionable.

An efficient way to take that heat (from both solar gain and other household waste heat) and create energy to run a cooling system is what we REALLY need here! Our attic gets so hot in the summer, I could heat our water to comfortable "shower temps" just by moving a passive tank into the 150deg F attic!!! Let alone building a collector.

There just ought to be a good way to efficiently use that excess heat to create energy for other houshold uses (ie: cooling!)...without the complexities of a solar-steam engine or whatever. Perhaps some type of "fuel cell" or something. More research, I guess.

 

[Oznog]

Well, you're going to have to consider heat quality.

Say the attic's 90 deg. That's not enough for a hot water system, and if you boost the system with a gas or electric heater to 120F, any heat exchange with the air will be COOLING the water, not heating it.

BUT, it can preheat incoming cold water. For every gallon you take out, a gallon of cold water enters the heater. If you could warm it, great, but water movement is sporadic and fast, leaving little time to preheat.

A refrigerator or air conditioner loses efficiency- significantly- when operating in high ambient temps. Ideally, if it's 70F inside and 90F outside, the expansion valve inside yields very cold coolant, the evaporator inside absorbs enough heat to get the coolant near the 70F ambient, it send the coolant outside to the compressor where it gets very hot, then the condenser cools it back to near 90F ambient.

IF you tried to cool that condenser with water being heated, and it got to 100F and returned 100F coolant, the AC efficiency and overall cooling power decreases. BUT, if you intercept the coolant right out of the compressor where it's very very hot, use some of the heat to heat water, THEN let the precooled coolant go through the condenser and get back to the 90F, YES. That's free. Assuming the condenser was already big enough to do a good job and getting the coolant within a few degrees of the 90F ambient anyways, the coolant won't get significantly colder so it's not going to create any GAIN per se in the AC system.

Using waste heat is all about the "quality" of the heat. High temps are usable. A-bit-warm may be useless- as described above in the attic hot water heater, if it's not hot enough for the water, how MUCH hot air you have is irrelevant because the water will never get hotter than the ambient temp.