Off Grid Design questions

BleuSoleil

Hello,

Been lurking and learning awhile but would like to draw on expert opinions on system design for my solar cottage pictured below. My wife and I will be using this as our full time residence and I have collected load estimation data for the six months we have lived there and verified much of it with Kill a Watt.

Verified load estimation range between 16-19kWh/Day.
Orientation 190 degrees
29.97 latitude
Standing Seam Metal Roof zee lock double fold 50ft E to W , 17ft eave to ridge.
Roof Pitch 22.5 degrees
0% shading

I'd like to design a hybrid off grid using PV, battery bank and propane genset but I find myself overwhelmed with design choices. I know I am supposed to start with training batteries but with a generator as back up I'd like my system to run on auto pilot other than regular battery maintenance. Since I am in Louisiana and have 80% tax credit, Ihave the luxury of considering premium batteries either AGM or Crown forklift. The goal is minimize day to day monitoring and maximizing design life(to 12 or more yrs).

I'm totally confused as to what inverter/charge controller would be best or how best to configure my strings.

I'm interested in using the Sanyo HIT 215's but will defer to more experienced opinions on equipment choices to meet my objectives.

Thanks to all.

Cariboocoot

Re: Off Grid Design questions

Welcome to the forum!

Let's start with that "16-19 kW hours per day".
The three rules of off-grid living are 1). Conservation, 2). Conservation, 3). Conservation.
I don't know what you're planning on running, but that's a huge kW figure for an off-grid system. Not impossible to achieve, but it will be very expensive.

To determine what you need for an inverter you need to know your maximum load at any given time. If the most you have to supply is 1 kW @ 120 Volts you would be able to do that with a 12 Volt, 1-2 kW inverter. If on the other hand you need 4 kW @ 240 Volts for something then you're looking at a 48 Volt system and a 6 kW inverter. Above that and you will be stacking inverters.

Just to give you some idea of supplying that kilowatt hour figure you mention:

19000 Watt hours @ 48 Volts = 395.8 Amp hours * 2 (50% max DOD) = 792 Amp hour battery bank.
Charging: 79 Amps @ 57 Volts = 4503 Watts minus derating factor (77% typically) = 5848 Watts of panels. That's roughly $18,000 in panels, at least one Outback FM80 controller @ $600, and about sixteen L16B's @ $330 each for $5280. Not including wiring, fuses/breakers, hardware, or inverter. One of those big inverters will set you back roughly $3,000 too.

Sorry to hit you with the sticker shock, but see why we say "Conservation" over and over?

Maybe you could list your intended loads and we'll all have a look to see how they can be reduced. Off grid living demands a minimalist attitude. Loads always grow over time!

niel

Re: Off Grid Design questions

the power used might indicate a very large system to be needed. rounding up to 20kwh/day and you get about 4hrs of full sun per day then you need at least a 5kw system. accounting for efficiencies and real world outputs may place you more into the 8kw system area.

as to the roof angle, that would not be ideal for the pvs in winter when you have less sun available so a higher angle of at least your latitude would be in order and maybe a tad more. if it were me i'd figure between 40 and 45 degrees. the 190 degree orientation is only about 10 degrees off of true south so i would not think that to be too critical unless you know you get more sun in the morning hours. a site survey may be a good idea.

for the batteries agms fair better as there is not normally any gassing and they charge more efficiently. you could still use a forklift battery, but they also have quite a bit of weight to them and the agms would be smaller batteries that one could series/parallel and would be easier to move. it will be a very large battery bank for 20kwh/day. you may need to upsize it to keep from going below 50% dod and have extra for more than 1 day's use.

as far as pvs go, they all produce electricity. if you feel you will need more room than the roof allows then the higher efficiency pvs may give you a bit more power for their area at a higher cost. if the roof still doesn't fit the numbers of pvs you may need to ground or pole mount some too.

maybe you could reduce the power needs somewhat through conservation and i might suggest you get someone to look over what you have and give you better ball park ideas on what could be done and even a rough idea of those costs.

BleuSoleil

Re: Off Grid Design questions

Thanks for the quick and helpful replies.

I am most certainly aware of the conservation argument knowing that a watt saved is priceless compared to the cost of PV generated ones. That said, it is harder to get the spousal unit on board with doing away with the washing machine etc. We do have ultra high efficiency appliances.

I am not necessarily in sticker shock because in my state if i spend $50,000, my final cost is $10,000 (30% tax credit, 50% state tax rebate) but I want to be smart about how that money is spent.

My assumptions are that since I am using a propane generator as backup to the battery bank that I can perhaps consider reducing days of autonomy to 2 and have a smaller battery bank. I do not want a huge bank of flooded batteries to maintain so that is why I would be looking towards either AGM or using large forklift batteries. I don't see weight as an issue as I would plan on pouring a pad.

mikeo

Re: Off Grid Design questions

Let's start with that "16-19 kW hours per day".
The three rules of off-grid living are 1). Conservation, 2). Conservation, 3). Conservation.
I don't know what you're planning on running, but that's a huge kW figure for an off-grid system. Not impossible to achieve, but it will be very expensive.

I live in Arkansas so not so far away. Your AC loads will be your biggest requirement in the summers, I suggest looking into zone cooling with ductless split units and only cool the spaces as needed. Use propane or put in a solar hot water system, its best solar bang for the buck in your location. No resistance heating strips, they are hard to supply with solar. Gas cook stove and aux heat. Try to get the consumption down without giving up too many comfort items. How about wood heat in the winter months, shouldn't require more than a cord of wood per winter?
Mike

BleuSoleil

Re: Off Grid Design questions

Thanks all. Great suggestions.

The building was designed with the lower than latitude roof pitch anticipating that our biggest energy hog would be AC. We have a Sanyo 09KS71 9,000 BTU ductless mini split which can run on low power consuming 300watts and SEER of 16. Our living space is 1150 sq ft but we are spray foam sealed tight slab to ridge(with an ERV for ventilation, 35 watts running 50% duty time). This is an intentionally undersized AC but since we are sealed so tight and will be running one of the most efficient dehumidifiers on the market(Ebac Triton 200 watts -variable run time) having constant 45% Relative Humidity and ceiling fans should allow us to keep the set point on the AC at 82 and still be fairly comfortable. We also have two 5000 lb interior adobe block walls for thermal mass but they also absorb excess humidity.

I am at my office as I reply so I don't have my load estimation spreadsheet in front of me but from memory our washing machine is an ASKO W6222 rated at 100kW per year. We have a propane gas clothes dryer and use propane for a range and cooktop. We have a Closed loop glycol solar hot water system that feeds a tagaki Jr. tankless propane water heater.

As you can see, we have a passive solar architecture design so we have no mechanical source of heating. This winter has been colder than average so when it has gotten down to 19 degrees outside in the morning our interior temp went down to 62 but that will improve when I install more inuslation.

ggunn

Re: Off Grid Design questions

BleuSoleil wrote: »

Thanks for the quick and helpful replies.

I am most certainly aware of the conservation argument knowing that a watt saved is priceless compared to the cost of PV generated ones. That said, it is harder to get the spousal unit on board with doing away with the washing machine etc. We do have ultra high efficiency appliances.

I am not necessarily in sticker shock because in my state if i spend $50,000, my final cost is $10,000 (30% tax credit, 50% state tax rebate) but I want to be smart about how that money is spent.

You might want to check those numbers before you write the cheque. The way rebates usually work (and although I am from Louisiana I don't live there any more) is that they are applied to the out of pocket expense after the 30% federal tax credit has been applied. If that's the way it works there (and the 50% number is correct) then for a $50K system it would be $50K - (.3)(50k) - (.5)(.7)(50k) = $17.5k.

BleuSoleil

Re: Off Grid Design questions

the way rebates usually work (and although I am from Louisiana I don't live there any more) is that they are applied to the out of pocket expense after the 30% federal tax credit has been applied

Actually, the 50% is applied to the total cost of system including installation with a $25,000 limit per system however, the solar industry here lobbied the legislature and was able to get favorable definitions and clarifications so that a PV installer can classify an inverter as a "shared component" and that way each string can be invoiced as its own system so essentially it is without limit if your paperwork is correct. It is also my understanding the IRS has written a letter of determination that the state rebate is not considered taxable income by the Feds.

Louisiana is great for renewables. The company I work for does solar thermal here.

Cariboocoot

Re: Off Grid Design questions

"Tax rebate" and "tax credit" are two terms that don't translate into Canadian.
You Americans are lucky that your government actually walks the walk of green (if a bit wobbly) and doesn't just talk the talk.

Now, do these tax incentives apply to off grid? Hard to imagine when you live up here in the land of "hand over your income". :roll:

I still think you should be able to get those usage figures down, even with a spousal unit. We get by on less than 3 kW hours per day and Tony (icarus) is the champ at not using power. Rough estimate, I'd think 6 kW hours per day would be comfortable. Maybe 10 if you have to run AC.

Derik

Re: Off Grid Design questions

I had a 1750 sq foot home built last year, it was finished in May 2010. I had to be off grid because of the distance to the nearest utility line. I didn't want to sacrafice anything and live like I was in a "solar" home. The details of my system are listed here.

I made no sacrafices in regards to appliances or anything else for that matter. I have a full size fridge, washer, dryer, dishwasher, propane heat and water heater with an H20 pilot light, 36 inch propane range, 52 inch LCD.. anyway I am living like a king (by my standards) & my energy use is 4.5kwh to 13kwh depending on what I run that day.

The only sacrafice I made is I don't run the dishwasher, heater, microwave or washer and dryer at night or evenings or days when it's cloudy.

My AC is not hooked up yet but I have central air a 4 ton unit, I am not even going to try to run it on solar but use a generator when I need ac. It's cost prohibitive to run ac on solar for me anyway. Last summer was cool but I will get a propane generator this spring and hook the ac up directly to the generator.

I do have a Fireplace Extrodinaire wood fireplace that will heat up to 2,500 sq feet that I use every night. It has a fan that blows air out the front that's about 150 degrees.

When shopping for applinaces I used the Energy Star listings and chose those appliances that were the most efficient, but didn't sacrafice anything as far as size or quality. I have Kenmore Elite kitchen appliances & LG washer and dryer. Even my LCD (Sony) is efficient using only 100 watts.

My houses has 10 foot walls and 16 foot ceilings so it has a lot of volume but I can still heat it with the wood stove and it stays cool in the summer with ceiling fans but we have little humidity here and at 3,300 feet it cools off most nights of the summer.

icarus

Re: Off Grid Design questions

Derik,

How much PV? What sort of battery bank?

Nice job on getting consumption down as low as you have. It will be curious to see how that works with the A/C going. Good idea of time shifting loads for when the sun is out, an automatic ~20% increase in efficiency right out of the gate.

Tony

Derik

Re: Off Grid Design questions

Oh, I thought my info was listed but I guess not. I have 9-215 watt panels that put out than what they are rated for. I see 2300 watts during the winter. I have the outback Flexware 500 with twin inverters, hub, mate, FM 80 charge controller and 12 Trojan RE L-16 B batteries all wired in a 24 volt systen.

My panels are off the roof on a rack system and I can easily turn them or tilt them during the seasons.

It is just me there most of the time but my girlfriend was there for three days with me a few weeks ago and our power use was still less than 8kwh, and I was running the dishwasher, disposal, doing laundry, and running the fan on the fireplace 24 hours a day, and she was watching tv for about 10 hours a day

Today I noticed my system went into absorb as early as 10:45 so my power use on the batteries is only about 10-15% of capacity probably due to the fact I don't run anyting but lights, tv and the fireplace fan at night.

Now if I could only get firewood cheaper!

icarus

Re: Off Grid Design questions

Using my napkin calc (panel capacity/2*4=wh/day average) not counting your load shifting, your system is ideally suited for your ~4.5 kwh daily consumption. I would be a bit concerned it you begin to routinely use your stated 17 kwh/day. It will be curios to watch it as your A/C loads increase while your heating loads decrease.

Tony

LagoonFarm

Re: Off Grid Design questions

Derik wrote: »

My AC is not hooked up yet but I have central air a 4 ton unit, I am not even going to try to run it on solar but use a generator when I need ac. It's cost prohibitive to run ac on solar for me anyway. Last summer was cool but I will get a propane generator this spring and hook the ac up directly to the generator.

How big genset do you plan to get for your 4 ton AC? What's the start load and run load specs for your unit?

I've got a 3 ton unit that I have not finished hooking up yet. I'm curious about how you'll get yours going.

Thanks

Derik

Re: Off Grid Design questions

Icarus, I think it was the original poster who was going to use 17kwh. Maybe your responding to him. If so sorry to intervine, I just wanted to post my house size and amenities to show you can live off grid and not spend a fortune on solar or sacrafice much if you buy efficient applinaces.

I never get close to using that (17kwh) . I did use 13kwh one summer day testing the system with a lot of stuff running including a small portable ac unit.

My typical use is about 4.5kwh to 6kwh with a 8kwh or so thrown in now and then with heater, laundry, dishwasher, and lots of tv.

The 4 ton ac unit will be all powered by the generator. I believe that the heater fan/ ac fan is the same that operates the flow through the ducts so that will draw the same as the heat fan. (same unit) 600 watts. (the reason I heat 95% with wood) When I do get the ac up and running I will only use it an hour or two a day. My house stays 20 degrees cooler inside than the outside temp.

LagoonFarm: I am not sure what size unit I'll need to get. The Kohler guy told me to get the off grid warrenty I needed a 14KW. I know that's over kill but I may get it anyway for the warrenty.

icarus

Re: Off Grid Design questions

Derik,

My mistake, I misread a couple of things including the fact that you would run the A/C off the genny. Sorry for the stupid questions,, carry on.

T

Mangas

Re: Off Grid Design questions

I am not an engineer nor a solar expert but we actually live with a "real world" large off grid system much like you are contemplating in a very remote area. It was professionally designed and built 5 years ago. While the people on this site are far more knowledgeable than I am, I can give you my life's experiences living off the grid with a dependable system.

To do it right costs money but the comfort return quotient and confidence is well worth it. I prefer making an initial higher upfront investment than trying to "jury rig" retrofits and fixes later. I counsel people who ask me about it as follows:

Cannot stress enough careful conservation measures and site planning with expansion potential.

Regardless of cost, I used the best quality solar components and wiring available.

I overbuilt my system by a factor of about 35% and still used a lot of it after judicious conservation measures (RASTRA insulated block house construction, triple pane windows, metal roof, heavily insulated walls, 3/4 " drywall throughout, insulated garage doors, high seer efficiency variable speed propane furances and central air conditioning) while splurging on creature comforts. We work hard for them.


Given the system's output, I oversized the charge controllers to Outback Flexmax 80s' replacing the smaller 60s'. Same for the inverters. I wanted plenty of surge capacity well beyond the actual peak start/running loads. I figure I've got 50%+ surge capacity above and beyond what the actual loads generate (e.g . air handlers and A/C compressors).

Carefully match the number of panels with the battery banks. My system is set up in two zones i.e. one battery bank and two 5,500 W inverters per zone for each air handler, A/C compressor powering up half the house. Our philosophy right or wrong was to assure redundancy if one zone goes down we still can live in the other half of the house until repairs are made.

Probably would have gone with the new industrial Onan 1,800 rpm 20 kw propane fueled genset instead of my SG 15 kw Generac that was available back then. In my experience, for people building a large off grid system they need to spend the money and install a top of the line interfaced Genset equipped with sound accentuated weather cover, block heater, battery charger to back the system up. It may kick on only 40-100 hours a year but it will make the difference of living comfortably and confidently or not. Finally, annually service it by the book.

If using flooded cel batteries (we do) plan on replacing then in 5-6 years. They might last longer but peace of mind is worth it. We budget for that.

Finally, find experienced solar and licensed electricians to do the work.

My two cents.

Derik

Re: Off Grid Design questions

Dang Mangas your power hungry there in Arizona. Is most of your power use the AC unit? I do understand that you have some extreme temperatrues there and you have to run your ac much more than we do here. For me spending all the money on solar to run one thing (ac) for a few weeks a year didn't make sense but I understand your probably running yours way more than a few weeks and a few hours a day.

What else are you powering? with all those panels you could make about 44,000 watts a day here or more! Is that about what you make or do you lose a lot due to the heat?

One therory I have is that solar is a lot about location. I experience non of the losses most do here expecially those who are way up north & maybe those in Arizona. I know my panels can make 15% more when it's cold.

I like your idea of splitting your system in two just in case.

How big is your home? Do you have energy efficient appliances? I would guess with all the power capabilities you really don't care kind of like Jay Leno.

My system was geared towards what I use at my on grid home minus some for all the efficient appliances. Were you using that much power on grid?

With your system I would have it installed by a professional. A system like mine can easily be installed by the home owner & I don't know about Arizona but here in S. California there are no professionals, just pretenders.. I found that almost nobody here knows anything about off grid solar.

Mangas

Re: Off Grid Design questions

All that money is relative when the grid is a long way away. Besides the ranch is in conservation and we want it to stay that way. We do care how much energy we use it's just that we work hard and enjoy our creature comforts.

Exluding the garage the home is about 4,000 square foot heated/air conditioned space. The solar system powers the house, central air conditioning (2 x 220 V compressors) and variable speed air handlers (2 x 110 V) pushing propane fired furnaces (2). Hot water heater is propane. System powers water supply to house's 500 gallon pressure tank supplied from two 1700 gallon underground water storage tanks each powered by a 1/2 hp 220 v submersible pump.

Well located 1/2 mile away and manually run to fill the underground storage tanks.

Yes we have extreme temp ranges i.e. can experience 115* summer and 0* winter.

I've found most of the power usage occurs from running the furnaces' air handlers in winter because of short sun days. We set the house winter thermostats at 66*. In summer A/C compressors and air handlers together seem to have plenty of power through the night except on multiple overcast days when the genny has to pick up the slack for two hours in the overcast morning usually between 4 and 6 am. During inclement weather this is when you want the genset to run to boost the batteries getting the most out of the panels during the day.

Yes, we have energy efficient appliances but they won't replace judicious conservation measures as posted. We have a propane stove and dryer.

As you say there a lot of "pretenders" out there claiming "they know solar". My experience is there are only a few who really do and have the real world references to prove it. Theory is one thing and real world practice is another.

Sounds like you're doing your homework before getting too far into it. This site is an excellent resource for you to ask questions. There are some very knowledgeable people who post and I am still learning a lot myself.

Derik

Re: Off Grid Design questions

Yes water pumping uses a lot of power as well. I was lucky in that my land made it possible to put my 10,000 gallon storage tank up on a hill about 1200 feet from my well. PVC is fairly inexpensive, I ran the line up the hill from the well and then ran a 2 inch line back down to the house.

I use a generator to pump the tank full and then add to it a littl once a week or so to keep the water fresh. Solar didn't make sense to me for the well pump since it's a 2hp two phase 220 volt pump. I can pump 8 gallons a min. so it doesn't take long to pump water.

So my solar is not relied on for everything where it sounds like yours is other than your propane.

Derik