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Figuring out power for small, off-grid home

 
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Hey all!

I've been trying to figure out solar power for a little while now and it's been a struggle. There's a lot of lingo, a lot of equipment, and a lot of environmental considerations to take into account but I'm hoping that all you seasoned Permies will be able to help me through.

To start, we calculated that we will need about 1500 watts per day across all our electronics (phone chargers, iPad charger, DC fridge, lights, fans, television, wifi router, etc). From what I understand—and, please, correct me if I'm wrong—what we need is a battery bank that can provide that wattage, and an energy system that can efficiently produce the energy for those batteries.

Solar power seems to have a lot of considerations and plenty of opinions surrounding it. However, I did source this set from Renogy: https://ca.renogy.com/renogy-new-600-watt-24-volt-solar-premium-kit/?gclid=Cj0KCQjwiqWHBhD2ARIsAPCDzakZCwWR3iDLJRRFP0JWa_gJVOUBV2_NPXIEYfiTdLIBNrFNezC674UaAvdtEALw_wcB and it seems to make sense for what we need? Thinking this system can generate 600 watts per hour (give or take, once converted to AC) of pure sunlight, I would only need a handful of hours to fully charge batteries and be functioning comfortably within my total usage. I don't know if this is a good set, if my thinking is correct, or if this is a solar set that is meant to be a grid-tie system (which I have recently learned is very different from off-grid solar).

Additionally, we thought the use of a propane generator as a backup would be a good idea, however, I'm unfamiliar with the generators, if they are an efficient/cost-effective means as a backup, and if they would just charge the battery bank the same way as the solar panels?

Any other thoughts for producing this kind of power in a cost-effective way?

In short:

HELP!

Thanks, all!  
 
master gardener
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It would be good if we could get a better idea of your location both geographically based well as exposure to the sun in terms of land contour and trees.

A generator is a good idea as a backup. I would suggest a dual fuel.  
 
Brad Abdul
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John F Dean wrote:It would be good if we could get a better idea of your location both geographically based well as exposure to the sun in terms of land contour and trees.

A generator is a good idea as a backup. I would suggest a dual fuel.  



Yes, definitely! We will be moving to New Brunswick, Canada. We'll be close to the Maine border in a place called Howard Brook. I've tried to look at average sunlight hours and such, as well as wind speeds for a potential turbine down the line but I couldn't find any reliable resources to estimate those. If you have an idea of where I can leverage that info, that would be great!
 
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Buy twice as much as you need, solar panels now are cheap and last 30 years. Batteries are expensive but if you can buy more than you need then they last twice as long, and who knows what will come in the future. A top of the line charge controller will last long time as well as the inverter. Save you headaches down the road, I use Edison batteries, I call them the forever battery.
 
pollinator
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For estimating solar power, you need a "solar resource map" which you should be able to find for just about anywhere on earth. Here is an overview of all of Canada, https://ecosmartsun.com/solar-map-canada/#jp-carousel-1094 you can probably find a more local version with a little digging. It shows KWH per KW installed capacity per year. So the area you are talking about seems to be in the neighborhood of 1600 KWH/KW/yr. That means that if you installed 600Watts of panels (.6KW) then you would expect to get about 960Wh per day on average.

A quick reminder: Watts are a measure of power, and power is instantaneous. Energy is power over time, so when you are budgeting how much electricity you will need over the course of a day, you will be talking about energy; and likely using watt-hours. An energy budget of about 1500 watt-hours is a good ballpark for a simple household. So looking at the average solar power available, you would probably need to have at least 1000watts of panels. Since you are also pretty far north, you will likely need more in the winter time, so going up to 1500 or even 2000 watts would give you a lot more days where you were able to get all your power from the sun. Panels really have gotten cheap, so getting extra is not a huge step up in cost. Those little 100w panels are cheaper to ship, but the price per kw is a lot lower if you buy full sized panels. You can find stuff here in the states for around 0.65usd/watt - plus a few hundred bucks to ship them if you cant go pick them up somewhere.

There are several options for batteries, with their own pros and cons, but in general you want to aim for having enough capacity to get you through 3 or 4 days without sun. Lead acids should not really be discharged below 50%, so remember that you will need to double the rated capacity if you are going to get any sort of lifespan out of them.
 
Brad Abdul
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That's awesome, thank you so much for the info!  Do you have any suggestions on panels in the States that I can look into? I'm close to the Maine border, so it might be an option to pick up or have them shipped to a P.O box out there.
 
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In general, I would dissuade you from buying a kit, and now especially a Renogy kit, for two reasons.

1) There are rumors that Renogy is about to declare bankruptcy, and any warranty you get with them would go poof.  There are LOTS of complaints posted on other solar sites about their non-existent service, and lack of communication.  I myself have driven over to the Renogy headquarters in Ontario, Ca. and found their doors locked, and instructions to contact them via email.

2) I started with a Renogy cabin kit myself and over time have found their components to be amongst the lowest performers you can buy.

Don't buy panels or batteries through the mail.  For panels, you'll get the best deals on quality panels buying locally.  I've bought quality panels off of Craigslist and Ebay, with local pickup instead of shipping.  The highest quality, very best performing panels I've bought to date were used grid-tie panels pulled off of someone's roof.  Those used Astronergy panels that outperform my new Renogy panels by almost 10%.

For sure go with 24V for a cabin.  It's more expandable.  You could start with four Costco 6V golf-cart batteries.   They are 210Ah.  At 24V that's 210Ah X 24V =5040Wh, or 5.04kWh of power.  Assuming you never want to drain the batteries below 50% for extended life, that's 2520Wh.  Assuming you want to go two days in case it rains, that's 1260Wh each day.  Trojan makes a similar T-105 battery at 225Ah.  I started with that battery.  After 5 years of use, I passed them on to my neighbor, because I upgraded, but they weren't worn out yet.

You'll need to charge the batteries at up to 1/8C, which works out to be 210Ah X 0.125C X 25Vcharging X 1.175 fudgefactor= 771W.  The fudgefactor is the compensator to account for the panels never reaching their rated output in real-world conditions.  Three 260 grid-tie panels would match well.  I bought some 260W panels for a neighbor for 62$ each last summer.  240-250W panels would be just as good.  Assuming you only get 2.5 sunhours (SH) of light in winter, that would give you 780W X 2.5SH = 1950Wh of power per day.  In summer, expect >5 SH.  One string of three panels in series is described by the shorthand 3S1P.

The panels wired in series would be outputting around 90V, but the Voc (open circuit voltage) might be around 114VDC, so that would be higher than what the cheapest low-budget MPPT controllers can handle.  The cheapest controllers max out at 100Voc.  Take a look at Epever's Tracer5420AN controller.  It can handle up to 200Voc.  An MPPT controller can take the raw high voltage solar power and transform it down to battery voltage for charging.
https://www.ebay.com/itm/352541593982?hash=item52151dd17e:g:CQsAAOSwuWJbuH2K

Lastly, you will need an inverter for your AC loads.  For sure, get a Sine-Wave inverter.  A MSW inverter will make anything with an electric motor run hot, and fail prematurely.  Samlex makes a 1500W Sine-wave for 520$.
https://ressupply.com/inverters/samlex-pst-1500-24-pure-sine-wave-inverter
They also make a 2000W model for ~600$.

I have this inverter.
https://ressupply.com/inverters/schneider-electric-conext-sw4024-120240-invertercharger
This is a premium brand 24V inverter that provides split-phase 120/240V AC and also has a built in generator charging circuit.  You just wire a 120/240V gasoline generator to the ACin input terminals, and it will accept generator power directly to charge the batteries.  So, on a rainy/snowy day, you can start up the generator, feed the inverter the generator power, and it will charge the batteries.  It is designed to be hard-wired directly to your main electrical panel.  

Over time, you may want to expand your system.  You can replace the golf-cart batteries with larger L-16 off-grid batteries.  You can add another panel or three and wire them into 2S2P or 3S2P.  If you want to add even more panels, you'd have to upgrade your controller to handle more than 50A of current.  For my own 24V system, I have 2000W of panels, wired in 4S2P, but I have a Midnight200 charge controller that can handle higher amps.

Good luck!
 
Tom Berens
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When I purchased my batteries from Iron Edison there  engineers designed the kit all quality stuff, shipped in one shipment and I picked it up at the trucking depot, from the ground mount on up, all I needed was some pipe for the ground mount and some wire. Saved me a lot of chasing around making sure everything worked together and they were there when I needed.
 
pollinator
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Interesting situation with Renogy.
I guess social media has prevented a lot of people loosing money to dodgy outfits, since the word can be passed around quickly now.
 
Brad Abdul
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Holy smokes, this is all great info.

Thanks so much!!!
 
pollinator
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At your latitude you will see about 1.5 sun hours per day on average in the winter time. There was some good recommendations for gear above but keep in mind that most of the inexpensive equipment like renogy is consumer gear and is not rated for hard wired installation in a house. If insurance is involved or permitting it won't pass. Its a call you have to make do you want to just get going or do it once and not have to worry about it for 10 years.  The Schneider gear is good.
If I was designing your system
I would say 4 t105 batteries or 2 l16 batteries and surrette/rolls is in Nova Scotia so you are almost duty bound to use them.
I would want a good disconnect that meets code like the midnight solar  https://www.amazon.ca/dp/B00A0VVK9E/ref=cm_sw_r_cp_apa_glt_i_4QPPW9H3RD6WPXVW5VE6

Inverters are a tough one. I would only install a magnum, outback or Schneider as they all meet code and are designed for a long life of constant duty.

For a charge controller the midnight solar classic is a good choice as it has the ground fault and arc fault protection built into it which you will need for Canadian electrical codes.. I would match it with one string of 3 300 to watt panels and you would be good for year round solar only charging. Maybe a portable generator for occasional charging.
That is a bare bones design. If budget is less of an issue get a pre wired package like this one. The kisae is a good basic inverter, the outback is a good mppt charge controller.

http://www.cdnsolar.ca/product-category/kisae-power-panels/
Or fully code compliant like this one...
https://www.cdnsolar.ca/shop-wholesale-solar-products/magnum-energy-ms4024-power-panels-with-magnum-pt-100/

Cheers, David



 
Brad Abdul
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Thanks so much for the breakdown! 1.5 hours of sunlight in winter is a scary thought. Sounds like I'm going to have to consider some alternatives as well to make it more feasible.
 
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Yeah 1.5 solar hours per winter day is the average, consider that on an overcast day you might at best get 10-15% of the rated watts from panels, using the proper charge controller. It's those heavy overcast winter days that you want to account for, either with additional panels, additional storage, or generator backup, or a combo.
 
pollinator
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I would suggest the following:

1. 24v inverter, pure sine wave, 3000w minimum (120v ac plugs, plus wiring block ... gives you more wiring options)
2. two 12v 100ah to 300ah LiFePO4 batteries (no 50% penalty on usage, as lead-acid has), wired in series to 24v
3. generator (propane, if fuel is available in your area)
4. LiFePO4 battery charger (or get an inverter/charger combo)

If at all possible, stay away from lead-acid batteries, as you'll be moving to LiFePO4 sooner than later.

With just these items to start, you can run for however long you are out there, for whatever loads your generator is sized to run, and you anticipate needing to run (you always need more). The LiFePO4 batteries are a *buffer* between needing to run the generator all the time; with little to no penalty on how much you can pull out of these batteries (easily 80%, and many probably pull out 90% or more, with no ill effects) ... run all day on the batteries, charge them back up at a time convenient to you, and be ready for the next day. No maintenance whatsoever on LiFePO4, whereas lead-acid ate our lunch for many reasons until we finally switched.

The generator is a fine piece of backup equipment that every off-grid location should have, so just start with it. Propane generators are quiet(er), less maintenance-intensive (no carbs gumming up), etc.

At your leisure, add in solar panels, mppt controller, and whatnot ... if you determine that solar will work out for you in that neck of the woods. You can experiment with adding one panel and an inexpensive mppt controller, and see what you really get in that area. All the other required components are in place already, and immediately providing whatever power you need ... batteries first (as the buffer), generator second if some situation arises where you need *more power*.

We ran this way to start (gennie, batteries, inverter, charger), until all the solar stuff got sorted out and added in ... not as "permie-approved" at the beginning, but it really helped with all construction and large loads; as solar gets added in, the gennie falls back to "backup" mode, only as needed. We are off-grid, mortgage-free ... no power problems.
 
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