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Planning solar array for home and yard

 
pioneer
Posts: 198
Location: Chesterfield, Massachusetts, United States
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I'm trying to figure out what I need to know about how solar energy is produced and stored so as to determine what my energy needs are both on average and at peak. My electric bill says I use 15kWh/day on average and about 22kWh/day on the highest use months.

So I can do easy math and say 31 days in the longest month means I'm looking at a system that can produce 682kWh/month. But that's cutting it too close, of course. I know I will have a great many overcast days, I know I'll need (well, want) to run stuff at night, etc. So I know I need battery storage and I know I need to produce an excess of solar power over and above what I need so as to not have brown outs.

So... When a system touts itself as, say, a 15,000kWh system but then says it can produce between 2,000 and 3,000kWh per month.... What? Is that saying that were the sun shining 24/7 the system would crank out 15,000kWh per month, but since in reality I probably have 5-6 really good peak hours per 24 hour day, realistically I'm going to generate 2,000-3,000 kWh?




My next question pertains to two categories of usage. I have two plots of land, one with my house on it, my refrigerator, lights, computers, fancy internet nonsense, etc. That's what is drawing 14-22kWh/day. Some of that draw is an always-on radon remediation pump for our well (low voltage DC line, 1/2HP). Some is the well pump itself when it kicks on. Some is stuff like a microwave or a computer. I imagine these all have really different surge energy ranges. So how much is enough to use power stably without the lights flickering like a mad scientist is at it in the lab?

The other plot of land is totally undeveloped with pristine wetlands on three sides and a quiet country road on the fourth. I want to put in a small pond. So I need the power system over there to be able to run a pond pump (24/7 running is my understanding of what's needed for a pond to keep out pondscum and god$&#@ mosquitoes), a well pump, and a small shed with just enough juice to run a couple lights, charge up a cell phone or two, maybe charge a couple Bluetooth speakers so I can get my most brutal, heavy metal jam on while digging hugelkultur mounds for days.

So that's two very different power needs. I've got schematics for the 2kW power station from the recent permies freebie (thanks, Paul!), but I imagine that is going to be GRIEVOUSLY too low an amount of power supply because <b>maths</b>.

I do not expect anyone to sit here and compute the requirements I'm going to need to get this done right, though if someone has the wherewithal to do so that would be stupendous. Rather, given what I'm looking to do and the complexity (or maybe it's simple?) of my setup, can somebody recommend a sort of "Idiot's Guide to Solar for Dumb-Dumbs 101" book? There are so many options out there and so many charlatans because of Peak Capitalism™. And I am a dumb-dumb with respect to solar power (and a non-zero number of other subjects, excluding of course dry, acerbic wit).



Lastly, how often do solar panels need swapping out? How useful do batteries need swapping out? Am I just chasing my tail on this?   Am I likely to spend the rest of my natural life swapping out parts on this infernal system and have way higher of a cartoon footprint than just burning the stupid oil and coal?


Thanks and happy trails, folks!
 
pollinator
Posts: 1633
Location: Victoria BC
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That is a lot of power.

I have no idea what sort of system specs you are looking at, they sound rather misleading.


There are 3 main things to worry about with a solar system.

1) The batteries. First because they are the biggest limiting factor and ongoing expense.

2) The panels. Pretty darned cheap these days. Ought to last a couple decades easily, but it is hard to test for longevity up front!

3) The inverter/s. Quality is key here.


I left out a bunch; charge controller/s, panel mounting setup, fusing, battery monitoring systems, wiring. But, these are all things that follow naturally; they must be specced to correctly support the key items above.

Once you know how much peak power you will draw, you can choose your inverter/s, to prevent the mad scientist effect, or more realistically, a blown fuse or failed inverter.

Once you know how much power you use over time, and how much sun you can reasonably count on, you can size your battery bank and panel array.

While it is possible for a battery bank to not be able to provide enough current to support the inverters specced, with the sort of major power usage you are talking about this is an unlikely issue.


For example... I live on the wet coast. In CDN$, my chinese LiFePo4 bank cost about $1000 per usable Kw/H, ... It has effectively no manufacturer support and I am not super confident in longevity. A reputable brand with good support might cost 2-3 times this.

I spent 6k+ for batteries, around 4K for a pair of Victron 3000VA inverters, and less than 3K for 10x 300@ panels. Wiring, breakers, charge controllers add up fast, but under 2K for everything. So around $15,000, of which the batteries were 40%. IF you DIY it all, which you certainly should not on a system of this scale without significant experience.


Note that I've only got 2100W of the panels currently mounted.

In summer, I run a 3/4hp pond pump for livestock and garden irrigation, charge a LOT of cordless power tools, use slow cookers and a dehydrator, run my tinyhouse exhaust fans 16 hours a day, and don't worry about running my power hungry laptop all the time. I still have to be a bit careful if I run a big sprinkler for several hours with the pump going the whole time.

In mid winter, I run the small DC fridge, carefully charge up all the powertools on the rare sunny days, and ration my laptop time. These is no surplus to be had.



This system would obviously not have a hope in hell of running your loads, especially in my area.

If I assume your 1/2HP load is about 350W continuous, this system would handle that OK, on sunny summer days. 8.4Kw/H per day.. no sweat, I can make 25KW per day easy.. I just can't store that much. But the 6KW usable is more than enough to get through a night. One night. As long as the next day is also fairly sunny.

I don't want to do the math on running this in winter, because it is just plain depressing. At a glance the consumption described looks like a 6 digit bill to me..


To start figuring the cost, decide how many cloudy days you want to be able to last. Size the usable capacity of your battery bank to be equal to the average daily consumption for that season times that many days, and start looking for prices. Lead acid is cheapest, but doesn't last nearly as long as lithium based stuff, nor can you discharge it as deeply; 50% MAX vs 80% or more.

This is the single biggest system cost; might as well figure out if it's at all practical before carrying on!
 
D.W. Stratton
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Location: Chesterfield, Massachusetts, United States
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D Nikolls wrote:That is a lot of power.

I have no idea what sort of system specs you are looking at, they sound rather misleading.


There are 3 main things to worry about with a solar system.

1) The batteries. First because they are the biggest limiting factor and ongoing expense.

2) The panels. Pretty darned cheap these days. Ought to last a couple decades easily, but it is hard to test for longevity up front!

3) The inverter/s. Quality is key here.


I left out a bunch; charge controller/s, panel mounting setup, fusing, battery monitoring systems, wiring. But, these are all things that follow naturally; they must be specced to correctly support the key items above.

Once you know how much peak power you will draw, you can choose your inverter/s, to prevent the mad scientist effect, or more realistically, a blown fuse or failed inverter.

Once you know how much power you use over time, and how much sun you can reasonably count on, you can size your battery bank and panel array.

While it is possible for a battery bank to not be able to provide enough current to support the inverters specced, with the sort of major power usage you are talking about this is an unlikely issue.


For example... I live on the wet coast. In CDN$, my chinese LiFePo4 bank cost about $1000 per usable Kw/H, ... It has effectively no manufacturer support and I am not super confident in longevity. A reputable brand with good support might cost 2-3 times this.

I spent 6k+ for batteries, around 4K for a pair of Victron 3000VA inverters, and less than 3K for 10x 300@ panels. Wiring, breakers, charge controllers add up fast, but under 2K for everything. So around $15,000, of which the batteries were 40%. IF you DIY it all, which you certainly should not on a system of this scale without significant experience.


Note that I've only got 2100W of the panels currently mounted.

In summer, I run a 3/4hp pond pump for livestock and garden irrigation, charge a LOT of cordless power tools, use slow cookers and a dehydrator, run my tinyhouse exhaust fans 16 hours a day, and don't worry about running my power hungry laptop all the time. I still have to be a bit careful if I run a big sprinkler for several hours with the pump going the whole time.

In mid winter, I run the small DC fridge, carefully charge up all the powertools on the rare sunny days, and ration my laptop time. These is no surplus to be had.



This system would obviously not have a hope in hell of running your loads, especially in my area.

If I assume your 1/2HP load is about 350W continuous, this system would handle that OK, on sunny summer days. 8.4Kw/H per day.. no sweat, I can make 25KW per day easy.. I just can't store that much. But the 6KW usable is more than enough to get through a night. One night. As long as the next day is also fairly sunny.

I don't want to do the math on running this in winter, because it is just plain depressing. At a glance the consumption described looks like a 6 digit bill to me..


To start figuring the cost, decide how many cloudy days you want to be able to last. Size the usable capacity of your battery bank to be equal to the average daily consumption for that season times that many days, and start looking for prices. Lead acid is cheapest, but doesn't last nearly as long as lithium based stuff, nor can you discharge it as deeply; 50% MAX vs 80% or more.

This is the single biggest system cost; might as well figure out if it's at all practical before carrying on!



Thank you for the response. I understand what you're saying, I just don't understand how to figure out the details your saying I should figure out. I guess I should consult a solar installation expert in my area and keep trying to find a good book that discusses specifics. Thank you for the candor though. 6 figuretd to get it up and running? Oof! I hope that's not right but fear it might be.
 
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My new system has been online for three years now, and I produce about 20kwh a day on days I'm pumping well water.  Keep in mind that I say 20kwh, because that's what I actually use.  It's likely that it "could" produce 25+kwh, but I've never yet actually consumed that much power.

My system consists of eight Trojan L-16 batteries wired for 48V, a Schneider XW6848 inverter, Midnight200 charge controller, and 15 300W grid-tie panels, wired in a 3S5P configuration.  The solar arrays are single-pole ground mounts made of welded unistruts.  They can be rotated by hand (hillbilly solar tracking) east and west to track the sun over the course of the day.  With this system, I can power my 2000W wellpump from about 8am till 4pm.

It powers the well pump, the kitchen refrigerator (standard 120VAC) and all the usual home appliances.  The system performs so well, that I'm shortly adding an air-conditioner.  During the night, I restrict myself to just lights and TV, and can wake up in the morning to batteries still at 90% charge.  That most likely will go down once I start running the air con.

The key to good solar utilization is to plan your activities around when output is highest.  You want to wash clothes?  Sure, but wait till after 9am.  Want to use the toaster oven?  OK, but just at noon.  Don't make toast at 9pm for a late-night snack.  What you will find is once you are making the power yourself, you'll become far more conservative in your power use.  I get out of the cabin before sunrise to go to the utilities room to monitor the incoming watts in the charge controller.  Watching that is better than television.

As the first responder said, panels are now the cheapest component.  I can now get a kw of panels for 220$ from a local Craigslist seller.  Don't buy panels through the mail.  Shipping costs as much, or more then the panels themselves.  Batteries even more so.  Buy name-brand components from an established company.  There are many fake products being sold on ebay and Amazon that lie about capabilities.  They'll slap a "MPPT" label on a cheapo PWM controller and make you think you're getting a good deal.  You aren't.  Still with name-brands and you'll be OK.  Buy products with names like Schneider, Midnight, Outback, Magnum, and MorningStar.
 
pollinator
Posts: 3114
Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
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Usage = 22,000WHr per day
Production = 30,000WHr per day to account for power losses
Estimated Cost = $30,000

Solar Array size = 30,000WHr divided by 3hrs or 4hours = 10,000W or 7,500W
Charge Controller = 12KW,
Battery = 12KWHr for LiFePO4 or 24KWHr for lead batteries.
Inverter = 8KW, this will handle your appliances demand (surge up to 20KW)
Backup = Propane Tank(You probably already have one) and Propane Generator (12KW for $4,000)

Solar Array = $7,000 for 10,000W (excluding railing support and wires, etc)
Charge Controller+Inverter = Sol-Ark All in One 12KW for $7,000
Battery = I recommend LiFePO4 batteries, $12,000 for 12KWHr (You can get 48KWHr if you get lead acid batteries, but they can only be discharged to 40% vs 80%, and they only last 1/4th the time)

Here are some package:
https://www.wholesalesolar.com/1893128/wholesale-solar/complete-systems/10.24-kw-gridtied-battery-backup-solar-system-with-outback-power-center-and-32x-heliene-320-panels

https://www.wholesalesolar.com/1892311/wholesale-solar/complete-systems/the-ranch-9.6-kw-30-panel-heliene-off-grid-solar-system

 
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