Your Ideal Solar Setup

TrevorDav · January 2016

Good afternoon all,

The wife and I are looking at constructing a house in the next year or so, very preliminary stages, so specifics will be hard to come by.

My question regarding a solar system is, if you were in my position, what would your ideal setup look like? 24v? 48v? LIFEPO4 battery bank?

We would be looking at an off grid installation with our current energy usage running somewhere around the 750-850kwh/month mark. Would it be feasible to replicate that energy usage for around $30k? Am I just scratching the surface with the info that would be needed to answer this question? Please bear with me as I'm fairly new to the world of solar. 2500sqft or so house.

Thanks!

Dave Angelini · January 2016

Where you live, how many people, and your ability to conserve in winter when solar is harder to harvest are things that need to be addressed. Your budget is good but while you may be able capture 800 KWH 9 months a year it will be much harder in winter. Answer the questions, I do not think you are scratching the surface. It can be done and you are smart to be doing this now.

TrevorDav · January 2016

Oklahoma: 4.5 hours of sunlight or so according to maps. Just the wife and I for now. I'm thinking of a mini split system with an alternate form of heating for winter months as well. Possibly a well pump mixed in their also, haven't quite got that far. I'm mostly wondering I suppose, what VDC I should be gearing my system towards? Appliances and all. I'm sure there are many schools of thought but a little hand holding would be much appreciated.

Thanks!

BB. · January 2016

Trevor,

Sorry, I forgot to post the link to HomePower Mag:

http://www.homepower.com/

Just to give you some math as a starting point using "nominal" off grid rules of thumb (lead acid battery bank--We can talk about the Li-Ion battery stuff later):

850 kWH per month / 30 days per month = 28.3 kWH per day
28,300 WH per day * 1/48 volt battery bank * 1/0.85 inverter eff * 2 days of storage * 0.50 max discharge = 2,775 AH @ 48 volt battery bank

A set of forklift batteries (which can last 15-20+ years) would run around:

2x series * 3x parallel strings Crown Industrial Battery - 24 Volts, 935 Amp-hours $4,561.00 = $27,366 @ 8,640 lbs

Next, the solar array... Two types of calculations, first based on size of battery bank: 5% to 13% rate of charge, with 10%+ for full time off grid home:

2,775 AH * 59 volts charging * 1/0.77 panel+charge controller deratings * 0.05 rate of charge = 10,631 Watt array minimum
2,775 AH * 59 volts charging * 1/0.77 panel+charge controller deratings * 0.10 rate of charge = 21.263 Watt array nominal
2,775 AH * 59 volts charging * 1/0.77 panel+charge controller deratings * 0.13 rate of charge = 27,642 Watt array "cost effective" maximum

And based on the amount of sun you get in your area... Assuming a fixed array around Oklahoma City Oklahoma

http://solarelectricityhandbook.com/solar-irradiance.html

Oklahoma City
Average Solar Insolation figures

Measured in kWh/m2/day onto a solar panel set at a 54° angle from Vertical:
(For best year-round performance)

Jan	Feb	Mar	Apr	May	Jun
3.97	4.23	4.98	5.47	5.38	5.59
Jul	Aug	Sep	Oct	Nov	Dec
6.03	5.70	5.32	4.79	4.05	3.71

Toss the bottom three months (bad weather) and use genset to make up when needed (minimum array suggested):

28,300 WH per day * 1/0.52 off grid system eff * 1/4.79 hours of sun per day = 11,362 Watt array minimum (Oct "break even month")

So, somewhere between 11 to 21 kWatt array, or around $11,000 to $21,000 for solar array (at ~$1 per watt for solar panels)--Mounts, wiring, etc. will be a significant amount of costs too (used to be ~$1 per watt--not sure now, hopefully less).

Solar Charge controllers:

21,000 Watts (recommended) * 1/59 volts charging * 0.77 panel+controller derating * 1/80 amps per typical controller = 3.4 ~4 controllers

4 controllers * ~$600 each = $2,400 for charge controllers.

A 4-8 kWatt AC inverter-charger would run around $4,000 or so...

Backup genset around 10-20 kWatt (diesel, propane, gasoline, etc.)...

Roughly, you can see where your major costs are. The above pricing is based on US materials. You can save money on less expensive hardware in some cases (but many people come back to "brand name" products after problems with the inexpensive stuff).

Power usage is a highly personal set of choices... I am not questioning your choices--But I do suggest you look at your power needs and think "what would you do if your present utility bill went up by 10x"--Effectively what happens when you go off grid.

Also, look at the options for utility power to your property. In many cases, the value of the property and ease to sell later will be higher if there is utility power on-site already. Plus, as decades pass, utilities are charging more and more for new power connections in rural areas.

-Bill

vtmaps · January 2016

One of the balances you find is system size vs. generator. In my location there is no practical way to build a solar powered battery based system without a generator.

OK, so I got a generator. I build my solar system to run lights, radio, laptop computer, small RV pump, ultra efficient fridge and freezer. No electric heat or hot water or air conditioning.

For laundry, power tools, vacuum, etc we use the generator if the sun is not shining bright. For us, the cost of avoiding the generator for a night time laundry would be a doubling of the battery bank. Of course, a larger battery needs more charging resources ... so add in the cost of a larger solar array and controller, and a larger generator. All to avoid 30 hours a year of generator use.

IMO, living off grid is all about batteries. The less battery the better. My simple 120 volt, 3500 watt Outback Inverter draws 20 watts just being turned on and doing nothing (tare loss). That's as much energy as my refrigerator uses in a day! When you get into 240 volt split phase dual inverter systems you will have higher tare losses, need bigger batteries, a 240 volt generator, and all the rest.

Watch out for defining loads. These are loads that stand out and by themselves require a larger system than would otherwise be needed. Example: Well pumps can be huge loads. I've seen quite a few systems where, except for the well pump, the system could be half the size. In those circumstances, I think it is wiser to buy a more expensive ultra efficient, low surge pump than to consign yourself to a lifetime of twice the battery.

You are wise to be working this all out in advance... do more research into ways of avoiding electrical energy use. Do some generator research. good luck

--vtMaps

Dave Angelini · January 2016

TrevorDav said:

Oklahoma: 4.5 hours of sunlight or so according to maps. Just the wife and I for now. I'm thinking of a mini split system with an alternate form of heating for winter months as well. Possibly a well pump mixed in their also, haven't quite got that far. I'm mostly wondering I suppose, what VDC I should be gearing my system towards? Appliances and all. I'm sure there are many schools of thought but a little hand holding would be much appreciated.

Thanks!

This tells me that you are reasonable and there are many ways to reduce the 800 KWH and still be very comfortable. You would be looking at a 48V inverter charger and the ones I use are on my webpage in my signature.

The equipment now is very easy to use and living offgrid is one of the sweet things in life to me and many of the people I know.
Good Luck!

WaterWheel · January 2016

TrevorDav, Keep in mind that you did ask for the "ideal setup" so they are suggesting systems like we all dream of owning.

I am the least knowledgeable of the people to reply to your thread but if you had...

6500+ watts in panels and about 1000 amp/hr in 48v batteries (a bit larger would be super nice) with a 6000+ watt inverter and 2 80 amp charge controllers. You'd be impressed at how rarely you ran the generator or the battery bank got below 50%, especially if you did laundry and dishwashing mostly on sunny days or on evenings when you knew the sun would be out the next day.

Without the items listed below assuming energy efficient devices and being a little mindful about power use two people should be able to live comfortably on 360 kw/hrs per month. That number assumes that items like a toaster oven, microwave, well pump, and occasional hair dryer stay on the solar system.

My 1700 sf home has 2 people and a deep well; we need to supplement the panels energy about 2-3 times a month this time of year (December and January) since the items listed below are either gas or on the grid, not on the solar system. We have 4500 watts in panels and a smaller (395 amp) battery bank with a 6k inverter but average 5.4 hrs sun per day here in GA. This time of year the small battery bank SOC rarely gets below 68%.

Clothes dryer, stove, water heater, and home heating would need to be off the solar system, AC would also need to be off the solar system although you could probably get away with a 9000 btu mini split or two on sunny days, especially if you added a few panels and enlarged the battery bank a bit.

mike95490 · January 2016

1st - if there is any chance of getting Grid to the site, you can do Grid and have GT solar to offset the bill. Much less cost then periodic battery maintenance and replacements.
2nd - LFP batteries are still quite young, and charge/discharge regimes are still being developed. At least 2 more years before I would make a decision.
3rd - 48V based system is going to give best performance, And a backup genset, Cloudy weather here for the last 5 days, and 10 more days forecast. Learn with a manual start genset, You will become well acquainted with load shifting to sunny days, Knowing you have to go outside to start if you want power in the AM. Auto-run systems are fine till the oil gets low, or the fuel runs out because you forgot to check it. While I run the genset, I check water levels in the batteries,
4th - Buildings. Batteries & protected electronics in one, Generator in a different one, Don't want 1 accident to take out everything

TrevorDav · January 2016

This is all really great advice, and it's certainly appreciated!

My takeaways thus far is 48v system is going to be the most efficient. I'm going to need a larger than 10kw solar array panel. And batteries are expensive as all get out.

It looks like to me, and many of y'all have already mentioned this, I'm going to have to get energy consumption down to AT LEAST 700 kwh if I'm going to make this even kind of feasible.

The part where I'm having the most trouble is with the battery bank. I'm just not even close to knowledgeable enough to put one together. I asked a question on another post about the Tesla Powerwall. Is the main reason it's not really feasible to use is because of the discharge rate? At least I think that's what people were saying.

Also, would the solar panel array need to be set up a certain way for the 48v system?

Again, y'all have been very helpful and I appreciate your time and effort.

vtmaps · January 2016

TrevorDav said:

I asked a question on another post about the Tesla Powerwall. Is the main reason it's not really feasible to use is because of the discharge rate? At least I think that's what people were saying.

Also, would the solar panel array need to be set up a certain way for the 48v system?

The powerwalls are not shipping yet. They are designed to work with very high DC voltage... there's not yet much equipment available to utilize them. Do you want to be on the expensive bleeding edge of a new technology?

You will get much more bang for the buck with flooded lead acid batteries. Lithium technologies have some advantages over lead acid, but most of the advantages won't make a difference in a large off grid system. The one off-grid advantage they do have is the ability to work at PSOC (partial state of charge) without degradation. They also have many disadvantages over flooded lead acid (cell balancing and monitoring).

How you configure your array, depends in large part on how far the array is from the controller. There are advantages to keeping your string voltage at 80-100 volts for a 48 volt system. If your array is far from your power center, then you might consider higher string voltage which requires some expensive charge controllers. Another option if your array is far from the power center is to put the power center near the array and transmit AC to the house.

One more thing... if you have the space, I recommend NOT putting the array on your roof. Do you have any electrical codes you must conform too? There are new rules, not yet adapted in all jurisdictions, that may complicate a roof top array (e.g. module level disconnect).

--vtMaps

Ethan Brush · January 2016

TrevorDav said:

Oklahoma: 4.5 hours of sunlight or so according to maps. Just the wife and I for now. I'm thinking of a mini split system with an alternate form of heating for winter months as well. Possibly a well pump mixed in their also, haven't quite got that far. I'm mostly wondering I suppose, what VDC I should be gearing my system towards? Appliances and all. I'm sure there are many schools of thought but a little hand holding would be much appreciated.

Thanks!

May we ask why you want to go off grid? Is it values, assumed high cost due to distance from power lines, both ?

zoneblue · January 2016

It looks like to me, and many of y'all have already mentioned this, I'm going to have to get energy consumption down to AT LEAST 700 kwh if I'm going to make this even kind of feasible.

Uhu, keep going. The system you are contemplating would be one of the largest in the off grid community. What you have done is take a just slightly on the lower side of the average amercian lifestyle and say what would it cost to do off grid? Another approach would be to say, well what would an off grid lifestyle actually look like? That answer is most often something like 3kWh/d, and not only does that not require a football field sized solar farm but a budget more like 10K. As Bill says, each to their own, but just suggesting that an average lifestyle needs an average grid supply. Off grid is about conservation. We do things differently because we see that the worlds resources are finite and being rapidly depleted. Using 3kW/d is a first step in being part of the solution. But it can also be cost effective. Power companys (here at least) obviously dont like iddy biddy 3kWh/d customers. They tend to charge outrageous line charges. And that helps pay for the batterys.

And batteries are expensive as all get out.

Yes.. and die every 5-10 years. So if you were dreaming of a one off "upfront cost" with no more power bills, well thats quite how it is. Its more like you pay your power bills in large lump sums.

My takeaways thus far is 48v system is going to be the most efficient. I'm going to need a larger than 10kw solar array panel. ... about the Tesla Powerwall. Is the main reason it's not really feasible to use is because of the discharge rate? Also, would the solar panel array need to be set up a certain way for the 48v system?

System voltage relates to system size. If you are seriously contemplating designing and building this system yourself, you have some serious research ahead of you. Be patient and just start reading, theres enough stored wisdom on this forum alone to learn to do it, if you have the time and aptitude. I did ours, but honestly if i was to do a 30kW/d system i would be reaching for the yellowpages. The mistakes i know i'd make would more than pay for the professional assistance.

Mangas · January 2016

We are powering off grid a 4,000 sq ft house, wells, two three ton central A/C high efficiency compressors, multiple major appliances and so on.

Batteries probably every 6+ years (with latest flooded cell technology.)

Cost is not always the dominant factor for everyone who decides to build an offgrid system. First conservation and then how you plan to live.

zoneblue · January 2016

Absolutely. Sucessful off grid systems usually have a person in the household for whom renewable energy is a hobby slash passion. In that respect its a much cheaper hobby than formula 1 or transoceanic yaght racing.

We have a friend who just sold their off grid place, and after two changes of ownership in quick sucession the latest owner, threw his hands in teh air saying "i cant stand it, sign me up for the grid."

Mangas · January 2016

Simply a matter of privacy and preserving our majestic landscape and valuable ranching heritage.

For our way of life the grid can stay where it is.

Our electric utility bills would run over $25k in 5 years. Set of batteries in 5 years about $21k. Of course, I've got to water them 3 or for times a year. . .

Dave Angelini · January 2016

Definitely privacy and sustainability! Rainfall the blue oak woodland and good soil! The lack of utility power was always our main goal.

Your Ideal Solar Setup

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Oklahoma CityAverage Solar Insolation figures

Oklahoma City
Average Solar Insolation figures