question-am I on the right track

caesarsfish · July 2009

I'm building a house in Alabama and going solar and wind. I'm paying cash so I'm just adding as I go and not buying a complete system. So far I have purchased 12 200W solar panel and two 500 w wind turbines. I bought a 100 amp charge controller and a 4000W pure sine inverter. I plan to add six more solar panels. Question, is this system going to be big enought to power the house? It is a 24 volt system, how many batteries do I need? Can I use the deep cycle batteries from Wal-Mart? Any information would be appreciated. thanks, Caesar

nigtomdaw · July 2009

Re: question-am I on the right track

It depends on what you want to run in your house . You will need to calculated your total loads per day and factor for starters around a 50% efficiency rating from your panels STC rating dont know about yourwind turbines.

Some members on here get by on very frugal sized symtems without problems.

But if i suspect your looking initially for a ballpark figure of am I close ?

Well I am not offay with your weather or wind resource in Alabama but for starters your initial 12 x200w panels is exactly the same as my current set up. see signature at bottom of post.

I live in Sunny northeast Spain with 300 days sun a year on average and this is what I achieve. Off Grid

3 Double Bed House well insulated after major rebuild, 2 Reception rooms 2 Bath Rooms . Hot Water and all cooking is by LPG and Heating is by one woodstove. Lighting is either LED CFLs or standard Flourescent Tubes. Our main luxury is an American Fridge Freezer with ice and water dispenser, 1.5kwhrs a day rated . We have radio broadband internet on 24/7 1 laptop 24/7 . At least a half dozen wall warts for phones and chargers plugged in 24/7
We have a 40 inch LCD TV and satellite tv, on a max of 4 hours a day. We wash with a Automatic machine every sunny day at least once. Sometimes 3 or 4 times but we do not preheat the water via the machine.

I need between 3 and 4 hours sunshine a day to replenish our daily comsumption, after that we are dumping energy, which we try to avoid by extra washes, ironing hoovering.

There is currently only two of us and we are energy consious. We are spilling enough energy at this time or year that Im getting a small Inverter Style Air Con unit for one of our reception rooms. We also use ceiling fans and portable fans .

I have a large battery bank 2100 ah at 24v and on a no sun cloudy day it takes 3 hrs for a 6kw gas gen to replace the days usage. This year Ive ran my genny for about 30 hours to date . I have about three days of battery backup but I usually never go past one day unless the following days forecast is good.

Others will crunch number 4 you after you provide a lot more infomation, I suspect this real life explanation. gets you going good luck and welcome to NAWS, you couldnt hope to find a better resource for your project

HTH Nigel

Please note I no longer pump water as we have mains water connected now. Which you may have to factor in, and my array is fixed due south, optomised for spring/fall, with very short wire runs fromarray to system and batteries.

BB. · July 2009

Re: question-am I on the right track

CF,

As Nigel says--basically you are in a three step processes...

Conservation. Make sure that all of your appliances and home are the most efficient you can make them (Energy Star Rated, lots of insulation, etc.).
Measure/estimate how much power you will need per day in Watt*Hours / kWatt*Hours (by season).
Size your system to your daily loads.

Energy use is a very personal life style choice--and greatly influenced by your location.

Some people may choose to get by on 0.5 kWhrs per day (off grid cabin in snowy Canada). Me, I get by on ~8kWhrs per day (Grid Tied) in very temperate San Francisco Bay area (natural gas for heat/hot water/cooking). Other in the southern US get by on 80 kWhrs per day because of heavy use of A/C.

Where will you fall on that 100:1 range of power usage?

You are an Engineer and do not currently live in Alabama--so it may be difficult for you to estimate / measure your power usage... Do you have friends or family in the area that are "living the lifestyle" you foresee for yourself who can give you a year's worth of power bills and/or if they are already off-grid--there system size and experiences (much genset use, etc.)?

Also, you did not ask about about conservation techniques (insulation, double pane windows, heat recovery ventilators, lighting, turning off standby loads like DVR's, using laptop computers instead of desktop, etc.). You also did not ask about how to measure your 120 VAC 15 amp wall outlet loads (Kill-A-Watt Meter), whole house meter, and such.

In the end, you can probably cut your "city / on grid loads" by about 1/2 to 2/3rds and get a pretty cost effective off grid solar system (plus small genset backup) for your home.

However, if you are going to have high energy usage (for example A/C), and you have power near your home--even if it cost $20,000 or more to run lines to your home--You might be better of running the utility lines and paying for the poles to your property.

You did ask about how to "grow" a system... It is pretty difficult to do for various reasons. One of the fundimental issues is battery bank size. It is usually best to avoid adding battery capacitity to an existing battery bank. When you add new batteries to and existing bank (in parallel) the new batteries tend to take more of the load and "age" quicker until they eventually have about about the same "dead by" date as the original string (i.e., you have to replace your "new" and "old" batteries at near the same time).

So--you may wish to build out your battery bank to its final capacity--and just use the genset more until you have the cash/time to add the additional solar panels (and charge controllers+wiring+mounts as needed).

For your first battery bank--getting true deep cycle batteries (not marine/RV types) at Walmart may be a good idea. We sometimes call those "training" batteries as most people (including myself) will, many times, kill the first back quickly as we learn the system's limitations. Deficit Charging (too much load with to little solar panels/backup genset charging) is probably the number 1 killer of batteries. Over charging and not adding distilled water when needed (approximately once per month or so) probably are close behind.

For your system--get a Battery Monitor. It will probably pay for itself just to prevent you causing an early death of your first battery bank. Plus, if you have family and guests--it provides a very easy display to tell them when to stop using power and/or start the genset up.

In the end, you may be very used to paying $0.10 per kWhr for power--With off-grid solar, by the time you add up all of the costs and the maintenance requirements (battery replacement every 7-15 years, etc.)--you will be looking at ~$1.00 to $2.00+ per kWhr for your power. So you will want to understand your power requirements so you don't waste it--plus you will need to size your solar RE system to provide the power you will need (not too much, not too little) so as to not waste money on your RE system.

Some links:

Battery FAQ
MPPT vs PWM Charge Controllers
PV Watts Program (plus some world data too)
Solar Irradiation Data by city (US)
Inverters
Inverters + Water Pumps
Kill-a-Watt Meter
Example of whole-home AC monitor for Grid (cannot use with Grid Tied solar)
Battery Monitor
Heat Recovery Ventilator
Off-Grid Sanyo A/C system

Before you purchase anymore equipment--I suggest that you study your needs in detail--then start shopping.

For example, if you need 4kW of inverter power--I would have suggested that you go with a 48 volt version instead (unless you need lots of 24 volts DC for something else too)... the prices are almost the same, but the size of the wiring is much less (1/2 the current).

For larger systems (sounds like yours)--running everything off of your AC inverter (at 120/240 VAC) is usually the best decision. Running low voltage DC around the property has lots of its own issues (excessive voltage drop, heavy currents, large/expensive fuses and switches, equipment that cannot take the min/max battery system voltage--near 21 volts low to >30 VDC when equalizing, etc.).

Questions? Helpful? Too much?

-Bill

mike95490 · July 2009

Re: question-am I on the right track

caesarsfish wrote: »

So far I have purchased 12 200W solar panel and two 500 w wind turbines.

Unless you can see treetops that have a permanent bend at the tips (from wind), you are not likely to realize much harvest of wind power. Most wind power is a scam, wind speed is too low to be useful with any kind of turbine.

caesarsfish · July 2009

Re: question-am I on the right track

The weather in Alabama is moderate, A few cold weeks each year. The house or cabin I'm building is a two story, 1800 sq. ft. and will be well insulated. I have a large fireplace in the great room and one 24000 btu heat pump unit for extra cold nights and hot days. My father died on this old homesite when a gas heater blew up and the house burnt down a couple of years ago so I will have no gas, just electric. I've installed an on demand hot water heater.

I intend to install 18 200w solar panels (maybe more if needed) and I have the two wind turbines for overcast days when there is less sun and probably more wind, I hope this makes up the difference to keep the batteries charged. It is a 24 volt system, how many batteries will I need and can I use standard deep cycle batteries. thanks for your imput. Caesar

niel · July 2009

Re: question-am I on the right track

i'll put it in a general way to you here that the power you use in a day would need replaced plus all losses which will be anywhere from about 30-50% depending on circumstances and equipment used. you most likely will get about 5 full sun hours during a summer day with a reduction of course for winter production time. this is a decently sized system with 12 pvs now and another 6 to come. not sure of which controller you have, but i suspect that with 18 200w pvs that you'll be getting a second controller to handle the loads.
without knowing what pvs you do have i'll figure this out generically and mark each pv at 5.55a for 24v operation. at 12 pvs this is 66.6a and with the addition of another 6 this is now at 100a. the general plan is to have the pvs equal 5-13% of the ah capacity of the batteries. this puts the battery capacity range for this 24v battery bank at 769ah to 2000ah. i don't think you'll want to use walmart batteries with this large of a battery bank as walmart batteries don't last that long. 3-5 year guess. you don't need to go top of the line with you batteries either so you will need to shop around as to what will suit you best. if you go agm (a top of the line battery) there is a higher charge efficiency and smaller storage loss at a higher cost, but for first battery sets it may be better to not go top of the line for mistakes and accidents often happen with first battery sets.
you also made no mention of the grid and if it is off grid, you may want the higher ah capacity for the battery bank for any expansions of future power use (and there always is more power needed later) and to hedge any cloudy days. a generator too may be needed to make sure your batteries do not go below about 50% depth of discharge for those occasions of there just not being enough sun.
now if the system is to be a battery backed gt system the battery bank can be made to be more on the smaller side of the capacity range.
this is all pretty much general speak to aid you in your decision and what you decide will be up to you.

BB. · July 2009

Re: question-am I on the right track

Mike is correct.

I forgot to add anything about your wind turbines... You would probably be better off if you save the money to not even install them.

I am a "wind septic"--so take anything I say with a grain of salt (in all things Renewable Energy--do your research and double check all claims--and triple check all wind claims). Here is a thread with real data and experiences with wind:

Small windpower a scam ? Survey says SO

Regarding the Fireplace--Nice for ambiance--but for heat, you should be looking at a real wood burning stove.

A "typical" fireplace can actually use more heat (drawing cold air into the home) than it can produce.

Also, modern wood burning stoves are many times cleaner burning than a fireplace (much less particulates and unburned fuel up the chimney). If you will be burning a lot of wood for heat (and/or hot water)--look for gasification type stoves.

One of the posters here is a moderator on a wood burning forum--perhaps he can add some fuel to the fire ("Gooserider" for www.Hearth.com).

I understand your concerns about gas (natural or propane?) -- but for an off grid lifestyle--going with electric only for heating and other energy uses can really up your kWhr requirements.

What is the On-Demand hot water? Electric or propane/gas?

By the way, solar hot water (and space) heating is one of the best uses of Solar Energy out there... Much cheaper (per BTU vs solar electric) and more efficient.

Thread on solar hot water heating

Modern gas heating appliances generally don't blow up anymore. At least, in our area--I certainly hear more about electrical and cooking fires--few gas fires/explosions.

I live in earthquake country (San Francisco area, California). And we have several things that can be done to help prevent fires / explosions...

The first, may not apply to you... It is a valve that sits on the gas line--if there is an earthquake, the valve will shut.

The second, is to put a "slam shut" type valve in the point between the black iron pipe from the wall, to the flex line to the appliance (all appliances now have to have flex lines--stoves and furnaces, for example did not require flex years ago and earthquakes would break the lines). If the flex line tears open, the valve detects the increased gas flow and "slams shut".

Lastly, many (most) areas have outlawed un-vented gas heaters (which I understand to have been very common in the southern US). Besides the issues of fumes inside the home--proper venting does a pretty good job of preventing gas build up (natural gas is lighter than air, propane is heavier than air). You can add gas detectors, venting, placing furnace/water heater "outside" of the home.

Remember that batteries are their own issues... Sulfuric Acid, Hydrogen (and Acid) gas/fumes, huge amounts of current available into short circuits, etc. -- all add up to creating their own issues.

Even improperly made/approved solar array installations can catch fire on the roof of a home...

Regarding sizing of batteries... A good starting rule of thumb is to take your daily load requirements * 1/efficiency * 3 days of no sun * 1/50% maximum battery bank discharge.

For example, say you want 5kWhrs a day, have flooded cell batteries and an 85% average efficiency inverter:

5,000 Watt*Hours * 3 days * 1/(0.85) * 1/0.50 = 35,300 Watt*Hours of battery storage

Or, in Amp*Hours (assuming 24 volt):

35,300 Watt*Hours / 24 volts = 1,471 Amp*Hours (at 20 Hour Rate)

The amount of charging capacity (solar, wind, genset) should be in the 5-13% range (another rule of thumb--can be adjusted based on specific battery chemistry and usage profile). In rough numbers:

1,471 AH * 5% = 74 amps minimum
1,475 AH * 13% = 192 amps maximum

If you are looking for solar panel ratings (this is just based on battery bank size and cost effective use of $$$, not your power usage pattern and solar irradiation for your location--if you have a lot of sun, panel array can be smaller. Little sun, array should be larger, and if your summer/winter usage is different A/C no A/C things will adjust too):

74 amps * 34 volts (solar panel Vmp) = 2,500 watts min
192 amps * 34 volts (Vmp) = 6,500 watts max

-Bill

caesarsfish · July 2009

Re: question-am I on the right track

OK, this is really getting deep for an ole country boy but there is really some good information here. I think I understand about 70% but I'm picking more up every day. There is a few points that I would like to clarify.

The fireplace that I installed has two blower assisted ducts, one for the master bedroom and one for the great room, I thought this would help on heating. But I do remember the pot belly stove we had when I was a kid and I'm not above of putting one at the side of the great room near the open kitchen. This is where we will spend the first hours of a cold morning and I use to love the perk coffee in the morning. As for the warm evenings, I have three ceiling fans in the great room and one in the master bedroom. Also I am installing a 24000 btu cold/warm heat pump that is ducted to the great room and master bedroom for limited use on hot days.

Also about the wind turbines, I do not expect a lot out of them, but on a rainy cloudy day and most nights the wind does tend to blow quite hard and they would have to help some, and I have already bought them so I might as well put them up.

I will be on the local grid also but would like to keep the cost down. At the present, I owe no one any money, paying cash for all construction and will have a modest income when I retire so I understand that I will have to tighten my belt. The only problrm that I might have is keeping the car keys from my wife. lol

Caesar

BB. · July 2009

Re: question-am I on the right track

If you want to keep costs down... The only way to do that is with Grid Tied Solar PV (or also known as Utility Interactive Inverters).

You can get the overall cost of a GT system down to ~$0.10 to $0.30 per kWhr (depending on the amount of sun in your area, local weather and shading, and your ability to use the Federal tax rebate of 30% and other possible local incentives).

The cost for an off-grid system--will (very roughly) run you around $1.00 to $2.00+ per kWhr for the electricity you generate (many incentives do not pay for off grid systems).

If, however, you need/want solar power and off-grid capabilities for bad weather, ice storms, etc... Take a look at a Hybrid system (Xantrex XW is one good product).

It tries to mix the advantages of Grid Tied (lower losses when on grid power, uses the utility as a "giant AC battery" that can store power for a month to one year (depending on your local utility's net metering program)--And, when the power fails, the inverter automatically switches over to solar/battery backup (+generator if you have one). And, its cost per kWhr is somewhere between $0.30 and $0.75 per kwhr.

Off Grid and Hybrid systems become quite expensive because of the batteries and extra losses in the system (battery and "extra" inverter)--so you have to pay for more panels, batteries, and new batteries every 7-15 years or so...

Conservation--in the end, is the only way you will save money. The other stuff (off-grid power, solar power, emergency backup power, etc.) only really addresses other issues (no AC power available, high prices of heating fuel, etc.) that "grid power" cannot.

-Bill

PS: Please feel free to ask us to define terms... I try not to be to repetitive--but if you don't know what something is (like Grid Tied Inverter/Solar)--we will just confuse you more.

Solar Guppy · July 2009

Re: question-am I on the right track

Alabama has electric rates are very moderate , typically 9-11 cents a kilowatt-hour, even less if you on the TVA grid ( 8 cents is what I read using google ). Also AL does not have net-metering, as it makes little sense to have Gridtie solar for this state and they have no rebates. So that is not an option for you home.

Alabama also is NOT a temperate climate , the winters get into the low teens to high twenty's regularly, the typical house hold load is listed at about 1500 kWh for a residence per month, gas is the primary means for heating, being so close to the gulf and many major pipelines, anything else makes little economic sense.

Having a 2 Ton heat pump will require about 1.5kW for every hour it runs ( assuming its a SEER 15 ) unit , you would need a very sizable solar system to power just that alone

The "500" watt wind gennys will do little but make noise, the 1200 watts of PV might give you 3-4 kWh of electric or about 40 cents worth, but you'll have to spend a couple thousand every5-8 years to have battery's for storage.

The cost of what you have bought would pay for decades of electric with no maintenance, we all understand the "want" of being independent, but what you have will do very little to offset your grid usage and I for one don't recommend you spend another dime, it make no sense since you have cheap grid power available

nigtomdaw · July 2009

Re: question-am I on the right track

Un less you are off grid or is Alabama totally grid locked.................thought Alabamba was a big place like LUXEMBORG OR Litchenstein.................................................................................................................:D

caesarsfish · July 2009

Re: question-am I on the right track

The area that I'm building in is in north central Alabama and it gets a little colder than the mid twenties and there is snow. At the present I have a small farm in Florida and the rates are a lot less in Al. but they are rising there just as everywhere. I do not see any trend to reverse this. I also have a solar powered car on paper that I intend to play with when I get back to the states.

But back to Alabama, my brother lives in the area and although he is probably not as frugal as myself, his electric bill runs about $300 a month during the summer hours. This is way out of line to me. Any thing I can save is an asset to me and I think it will also enhance the value of the property in the future. Caesar

BB. · July 2009

Re: question-am I on the right track

Remodeling your home for conservation is probably an OK investment (generally, remodeling can give you ~$0.50 return on the $1.00 when the home is sold... ROI for solar system does not usually attract that sort of return because 1. If a person pays list price for the hardware, they are not saving any money over utility power; and 2. They are afraid of the hardware (believe it may structurally affect the home, or cause other problems).

If Alabama does not have Net Metered power--it even makes the ROI for a Solar GT system even worse (you may get wholesale pricing for your electric power which can be in the $0.03-$0.04 per kWhr for your area--if your local utility/co-op even allows GT systems.

18x 200 watt (3.6 kW) panels near Birmingham AL (using PV Watts Website), everything else for default (Grid Tied with 0.77 derating factor):

[FONT=Fixedsys]Results GT/Hybrid 3.6 kW system

Month
Solar Radiation (kWh/m2/day)
AC Energy (kWh)
Energy Value ($ at 7.6 ¢/kWh)

1      3.82          268        20.37   
2      4.27          269        20.44   
3      5.41          365        27.74   
4      5.77          366        27.82   
5      5.57          359        27.28   
6      5.65          345        26.22   
7      5.51          345        26.22   
8      5.66          355        26.98   
9      5.46          338        25.69   
10     5.17          339        25.76   
11     4.18          272        20.67   
12     3.51          246        18.70   
=====================================
Year   5.00 avg sun  3868 kWh  $293.97  

[/FONT]

Same thing, done as an off-grid system (derating = 0.52)

[FONT=Fixedsys]
Results Off-Grid 3.6 kW system

Month
Solar Radiation (kWh/m2/day)
AC Energy (kWh)
Energy Value ($ at 7.6 ¢/kWh)

1      3.82          176        13.38   
2      4.27          178        13.53   
3      5.41          243        18.47   
4      5.77          242        18.39   
5      5.57          236        17.94   
6      5.65          226        17.18   
7      5.51          226        17.18   
8      5.66          234        17.78   
9      5.46          223        16.95   
10     5.17          224        17.02   
11     4.18          180        13.68   
12     3.51          162        12.31   
=====================================
Year   5.00 avg sun  2550 kWh  $193.80   [/FONT]

Realistically, an GT system will cost around $6-$10 per installed watt (upwards $36,000 less 30% Federal Tax Credits)-- and an off-grid/hybrid system will cost almost 2x as much plus new batteries every 7-15 years (tax credit may or may not be available for Off-Grid system).

Even if you still decide you want some sort of Solar Electric power--Conservation (including energy efficient design and construction) and Solar Hot Water/Heating both offer much better ROI.

Take a look at Home Power Magazine--I don't always agree with their articles--but they do offer a lot of good information for a low energy lifestyle. Home Power offers one recent edition as a PDF download too plus a few articles online for review.

-Bill

question-am I on the right track

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