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Author Topic: please critique my solar ideas  (Read 793 times)

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Offline NCEric

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please critique my solar ideas
« on: March 17, 2021, 11:20:30 PM »
Other than heating my house and hot water with a wood fired water stove, I'm currently very conventional in my electricity use, but I'm curious about solar and wondering what my options are for using some solar without disconnecting from the grid. 

My main motivations would be (1) to have at least some power in the event of a power outage, (2) to defray some of the cost of the system by reducing my regular power usage, and (3) to get some experience with solar in case I decide to build a fully off-grid house in the future. 

The things that would be nicest to be able to keep going in the event of a power outage would be (1) two to three large chest freezers, (2) the well, enough to water a couple cows, some other animals, and for some limited household use, (3) a computer, and in the winter months (4) a small pump that circulates water from our outdoor wood fired water stove to the house and the fan in our blower unit to get the heat into the house.  I have less convenient back-ups for water and heat, and I can make do without a computer, but the freezers are the most critical thing if the power goes out long enough for them to start to thaw.

Since I don't so much need power at night, I'm wondering what a bare minimum of batteries would be just to make a system work.  I'm thinking if I can get my freezers really cold during the day, they could make it through the night without running.  And I can get by very well without water at night.

Any thoughts or recommendations (including books or other ways of learning more)?  Should I be thinking about DC systems at all?

Thanks!

Offline btulloh

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Re: please critique my solar ideas
« Reply #1 on: March 17, 2021, 11:30:03 PM »
For what you describe, a grid-tied system using batteries for storage and and inverter tied into your domestic power service would be best. It just needs to be sized based on your requirements. You may benefit from new freezers. Probably best to consult with someone who with expertise in those systems. 

Offline NCEric

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Re: please critique my solar ideas
« Reply #2 on: March 17, 2021, 11:36:29 PM »
Instead of a grid-tied system I could run certain loads off solar + a very limited battery bank and use the grid for a back-up battery charger, right?  Would that possibly make more sense?

Offline mike_belben

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Re: please critique my solar ideas
« Reply #3 on: March 18, 2021, 12:20:00 AM »
I think a decent generator will do you better for now.  It will not go unused if you end up building off grid.
Psalm 37:16

Offline Ianab

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Re: please critique my solar ideas
« Reply #4 on: March 18, 2021, 01:18:58 AM »
What you are envisioning is called a hybrid system. So basically a grid tied solar, with standalone battery backup in case of mains failure. 

With a system like that you normally have full mains power available, but may need to limit off-grid draw depending on the size of the inverter and battery pack. The inverter size determines how much stuff you can run, while the battery size limits how long you can power it for. 

Working out how much power you need is the interesting part. You probably want a watt-meter to connect to the various things and work out their peak power, and average daily power use. Things like water pumps and freezers are simple enough to work out the power draw when they are operating, but they are intermittent. Do they run 5% of the time or 50%?. Once you know your peak draw, and your daily watt / hours you can start sizing the system. 

A quite small inverter could keep 3 freezers cold and a water tank topped up if you ran each for 6 hours a day? It just means you don't have "regular" unlimited mains power where you can turn on everything and not worry if it's peaking at 10kW.  

And a standby generator isn't a silly idea no matter what other system you go with. Just it only solves issue one. It won't reduce your power bill, and you won't learn anything about solar power. 
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Offline stavebuyer

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Re: please critique my solar ideas
« Reply #5 on: March 18, 2021, 03:43:25 AM »
Building a system to power only the most critical needs makes perfect sense to me. Implementing the plan can get complicated. If you build a stand alone system you will need more batteries and independent wiring. If you use the grid for part-time or back up you will need an automated transfer switch and an electrician to tie it in.

I built a small system for an off grid cabin. Mines "hobby" grade and will power the lights and temporary higher drain items like a coffee maker, microwave, or 15 amp power tool. Its handy, didn't cost much, and I learned quite a bit. I also separated a few outlets to be powered by my gas generator if I want to stay overnight and run the air conditioner etc. because for occasional use it was much cheaper and easier.

You might start with a small stand alone system and put some lights and an outlet in an outbuilding. The education alone will justify the cost and provide some utility while you learn.

Offline Ianab

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Re: please critique my solar ideas
« Reply #6 on: March 18, 2021, 03:58:24 AM »
If you use the grid for part-time or back up you will need an automated transfer switch and an electrician to tie it in.


Can be an automatic or manual fallback. Manual just means that if the grid power goes down, then it's all "off", until you throw a manual switch to go off grid. 

The mains isolation is important as line crews could be out there trying to fix downed lines, only to find someone is feeding mains voltage back up an isolated feeder from their battery bank. 

So that isolation is important, but doesn't have to be automatic. Just "fail safe", as in if things go haywire, the lines are dead. Then you can throw a switch and change over to battery backup. 
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Offline mudfarmer

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Re: please critique my solar ideas
« Reply #7 on: March 18, 2021, 08:11:56 AM »
Lots of good feedback here that should keep you busy thinking for a bit!

I would not make my first system design/install one that is meant to power all the critical loads in my house, but there is nothing wrong with doing that if you have the time to research/implement and the money to pony up to make sure you get it right.

Quote
Instead of a grid-tied system I could run certain loads off solar + a very limited battery bank and use the grid for a back-up battery charger, right?  Would that possibly make more sense?
That will work just fine, but if you are powering several chest freezers, a well pump (what kind of pump?), boiler circulation pump and blower you should do as Ianab says and get a realistic measurement of your power requirements before thinking you can get away with "a very limited battery bank" ;D -- of course you can use a very limited battery bank and leave a charger connected to the grid all the time, this essentially creates a "UPS" like they use for computers, if the grid goes down you have a buffer of run time from the batteries and when it comes back up they will recharge with the added benefit over a traditional UPS of charging when the sun is shining. It would meet Main Motivation (1) and (3) but probably not (2).

Tying into the grid will likely require inspections, almost definitely will require disconnects and lockouts adding to the cost, probably a much more expensive inverter and it sounds like you don't care about feeding onto the grid so I would just avoid that part for this first go around.

Definitely buy something like a "Kill-a-Watt" meter and use it to get at least 24hr but preferably more time worth of data from each thing you want to power, and note the use conditions that might change these numbers. Properly sizing the system is the hard part, the rest of it is easy!

Offline peakbagger

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Re: please critique my solar ideas
« Reply #8 on: March 18, 2021, 09:40:19 AM »
What state do you live in?. Some utilities in some states are offering big incentives for batteries that they can remotely "borrow" on occasion. I think Mass is probably the best package of the bunch but havent researched other states. Some utilities in VT lease the batteries to those with the right equipment.  

In order to qualify for those programs you usually need specific hardware and communication with a firm that has a contract with the utility. Tesla is one of them and Solaredge is another. They can only borrow power when the grid is up so if the grids down their hybrid system works fine islanded. Worse case as has happened in VT at least once is the utility borrowed power from the battery and then the grid went down at night leaving folks with empty batteries in the dark. Battery tech is changing, Solar City (now Tesla) came out with a system designed to integrate with a Tesla Powerwall battery. Tesla stopped making that version of the Powerwall battery (High voltage DC coupled) and the Solar Edge gear was orphaned. The Solaredge 6 kw inverter is available cheap ($600) and folks are successfully running them off grid on YouTube without a battery but only if the loads are always less than array output. This is definitely a caveat emptor deal but the price may be right. No firm makes a high voltage DC coupled battery to match to it but my bet is someone is going to figure one out. I picked up one as it is supposed to work fine with grid tie and I wanted a backup for a couple of my aging grid tie inverters.  

From my limited research Outback, SMA and Sol Ark makes hybrid inverters that are far more flexible but may not have the utility borrowing capability (with its associated monthly payments to you for the privilege) . I dont think they need a big battery but battery size is linked to array size. If you have large array, the charge current may be too much for the battery and the system will have to throttle the array output going to the battery. If on the other hand you are using the power my guess is that its not a limitation. 

Think of the battery as balloon hooked to the system. If the panels are producing more power than you need the balloon fills up, if you are using too much power the balloon deflates. If the balloon is deflated by you or your utility and you need more power than the panels are putting out, then the system stops working. So a small balloon may work with careful control of the loads but not so good to replace a typical household demand where the the power company can seamlessly supply a whole lot more power if you need it.    

Offline mike_belben

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Re: please critique my solar ideas
« Reply #9 on: March 18, 2021, 10:34:14 AM »
 

And a standby generator isn't a silly idea no matter what other system you go with. Just it only solves issue one. It won't reduce your power bill, and you won't learn anything about solar power.
I do completely agree and this isnt an argument or defense.. Just a thing to consider.  


In 2012/13ish i cashed out of some things and chose to invest in durables of future need.  I ALMOST pulled the trigger on solar components and studied up pretty hard for months (on fieldlines.com, permies and midnight solar forum) in order to make wise purchases.  My conclusion was to wait on that stuff until the day it was needed because the technology improves and comes down in price so much with time.. So i made other investments that have proven quite good for me.  



In the learning process i devoured other people's problem threads and concluded that the biggest common problem averaged out to one issue.  Unreasonable expections of success on the first try with a limited budget using renewables alone.  
People were trying to build economical systems with an idealogical renewable only romance and no generator involved.  These systems seemed to almost always come out undersized, overdrawn, unreliable and in the end more expensive than they needed to be because of having to make gear changes to make it work.  and they were going without the amenities they insisted upon... until they gave up on the romance to have air conditioning or a washing machine etc... giving in to generator in the end to make it work.  Im not knocking their spirit here, that is their private right to choose any way they want.. My critique is only in the execution.



Had they been a bit more pragmatic and a bit less romantic.. Theyd have bought the small generator upfront like often advised by veterans, and simply incorporated it all into one plan from the start.   it all would have been more successful, economical and enjoyable.  This usually wasnt done until a battery bank was smoked or a well line ruptured because the heat tape didnt have juice.. Stuff like that. Catastophic fail that forced the romance back into a jack london book.



So i totally agree the genny wont reduce the power bill.. Other peoples experiences indicated to me that it will reduce the errors, failures, cold nights, discarded thawed food, bucket showers, dead battery banks, froze pipes and additional purchasing of components that can work with the genny and so forth.  It will provide an immediate backup for grid outages right now, and can be seemlessly built around as his renewable program is implemented in time.  Eventually the genset can just sit if he gets to that point of renewable generation.  



Anyways.. A very very good, cheap old used onan industrial 3ph diesel generator (to power my machine shop where 3 phase is unobtainable) and parabolic trough concentrators for solar water heating were the only components i have bought for the future zero grid home build because time will not make them much better or cheaper than what i got them for.   I am certainly content to wait for the best solar panels, charge controllers, batteries,  invertors and bulbs that the future has to offer.
Psalm 37:16

Online Al_Smith

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Re: please critique my solar ideas
« Reply #10 on: March 18, 2021, 10:42:01 AM »
As a general rule while it might be a noble thought it is kind of impractical to make your own electrical  power from a financial perspective .For 7.5 to 9 cents per KWH you can't make it yourself once you figure the initial cost of installation and factor in the life expectancy of either wind or photo cells . I use the KISS principle  on these things--keep-it -simple-stupid .Meaning a stand by generator with enough fuel to run for several days .--saying that good luck 

Offline NCEric

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Re: please critique my solar ideas
« Reply #11 on: March 18, 2021, 12:19:20 PM »
I want to re-read and further digest a lot of the information here -- the quality of information about solar power on a forestry forum is pretty amazing! thank you, all!  -- but one point I want to go ahead and respond about was a generator.  My initial thought was to get a generator without any solar, and I have used a borrowed generator a couple times with previous power outages, but power outages of more than an hour are pretty rare where I am in North Carolina (about 250 miles from the coast, so most hurricanes have lost most of their wind speed by the time they get this far inland -- ice storms are the most common cause of significant power outages), and the longest power outage I've had since I bought my current place in 2007 has been less than 48 hours, so mostly not so long that I can't get by okay without any power at all.  The trouble is that I never really know how long a power outage is going to last when I'm in the middle of it, and I don't necessarily want to plan on the power coming back on at the last minute before the inconveniences start turning into serious problems.  But I've heard that generators really ought to be cranked up and run for a while multiple times per year, and that's a chore I'm afraid I wouldn't be motivated to stay on top of.  I'd be a lot more motivated to invest time and effort in "free" energy.

Is it reasonable to think a solar system anything like what I'm envisioning could pay for itself over its useful lifetime?  Or even come out cheaper than a generator?  If it took decades to pay itself off but it would last long enough to do so, I'm pretty sure I'd want to make that long-term investment now.  I have a nearby friend that installed a grid-tied solar array about 15-20 years ago that said he's nowhere close to paying it off yet, though, so I don't know if it's reasonable to think solar systems will ever pay themselves off (in electricity saved, plus the cost of a generator...)

But I'm interested in possibly building a relatively primitive house in the future for which there might be other reasons to want to be totally off-grid, so gaining experience with solar now would also be of value to me.

And I've gotten by in my current place without a generator (at least not one that I own) or solar for over 13 years, so whatever the limitations of whatever solar system I might get, it would only be an improvement on what's sufficed for me so far.


The Solaredge 6 kw inverter is available cheap ($600) and folks are successfully running them off grid on YouTube without a battery but only if the loads are always less than array output.

That's definitely the kind of thing I want to look at more closely.  If I only had power when the sun was shining, little to no power when it was cloudy or in the early morning or late evening, and zero power at night, I think that would meet most of my present desires.  Most of my water usage is during the day anyway, so limiting it to when the sun is shining (particularly during infrequent power outages) wouldn't be very hard at all.  And if I could get my freezers really cold during the day while the sun's shining, it shouldn't be a problem if they don't run during the night.  And if I could power the pump and fan for my outdoor water stove during the day, that would greatly reduce how much propane I'd have to burn.

You probably want a watt-meter to connect to the various things and work out their peak power, and average daily power use.

Will a kill-a-watt tell me peak power usage in addition to total power usage over the time tested?  A kill-a-watt is no use with something like a 220 volt hard wired well pump, is it?

I've also wondered whether I should consider dropping a second DC powered pump into my existing well and configure my pressure switches so the AC pump only comes on after the DC pump has failed to keep up with demand.  Maybe add a larger pressure tank to my system, too, or a tank on top of the hill that I'd just use during the warmer months when I'm irrigating.  I basically have a really large garden that I mostly don't irrigate but that I irrigate as much as I can with a couple hoses and garden sprinklers running nearly continuously all day when we have an unusually long dry spell, which typically adds up to 2-5 weeks per year.

You might start with a small stand alone system and put some lights and an outlet in an outbuilding.

That's more like what I'm thinking: continue to rely on the grid for most of my electricity use but try to run the freezers and a well pump with a stand alone system (and maybe there would be a way to back up that system from the grid somehow like with a back-up battery charger.)


of course you can use a very limited battery bank and leave a charger connected to the grid all the time, this essentially creates a "UPS" like they use for computers, if the grid goes down you have a buffer of run time from the batteries and when it comes back up they will recharge with the added benefit over a traditional UPS of charging when the sun is shining. It would meet Main Motivation (1) and (3) but probably not (2).

I don't understand why such a system wouldn't accomplish my 2nd motivation of defraying the initial cost of a solar system.  Can you help me understand the point you were making there?

Tying into the grid will likely require inspections, almost definitely will require disconnects and lockouts adding to the cost, probably a much more expensive inverter and it sounds like you don't care about feeding onto the grid so I would just avoid that part for this first go around.

Yes, I would definitely like to avoid those sorts of issues and expenses.  I realize that will mean that I'll sometimes have more solar power generating capacity than I'll be able to use, but my goal (at least as best as I've figured out so far)
is only to generate a fraction of my total energy use anyway, just enough for my most critical needs.

From my limited research Outback, SMA and Sol Ark makes hybrid inverters that are far more flexible but may not have the utility borrowing capability (with its associated monthly payments to you for the privilege) . I dont think they need a big battery but battery size is linked to array size. If you have large array, the charge current may be too much for the battery and the system will have to throttle the array output going to the battery. If on the other hand you are using the power my guess is that its not a limitation.

That sounds like really good information that I'm going to need to understand before I buy anything, but it's pretty much all over my head at the moment.

For 7.5 to 9 cents per KWH you can't make it yourself once you figure the initial cost of installation and factor in the life expectancy of either wind or photo cells

In the most efficient set-ups, particularly battery-light or no-battery set-ups that also don't have the requirements of being off-grid, what is the range of cost per KWH of solar systems over reasonable expected lifetimes of those systems without subsidies?

Offline mike_belben

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Re: please critique my solar ideas
« Reply #12 on: March 18, 2021, 01:21:21 PM »
Im confident youll make a good decision.  


The ROI will differ for everyone based on how high their utility rates and consumption are, crossed by their savvy in implementing an effective system on the first try at the lowest expense.   Those who are against it will say it doesnt pay and those who are for it will say it does but only you will foot the bill and be able to tell us how it shakes out in the long run so the risk and burden are yours to bare alone.



If you dont need a generator thats fine. 

With a DC system in place you will have one parked outside on typically 4 wheels at all times. 12v systems are inneficient due to large wire gauge and power losses from component heating, but 12v batteries can be charged by the car sitting outside idling.  Run a jumper into the house and rotate the bank out individually if you absolutely must during a storm emergency to keep from losing the freezers or water in an off grid situation.  

I am fairly confident you could charge a single 12v battery that is wired into a 24v or higher array.. Pretty sure ive charged uo 24v equipment by chomping just one battery using a 12v charger..  I dont know if thatd cause grief with the other system gizmos however.  
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Offline Ianab

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Re: please critique my solar ideas
« Reply #13 on: March 18, 2021, 03:10:45 PM »
Quote
Will a kill-a-watt tell me peak power usage in addition to total power usage over the time tested?  A kill-a-watt is no use with something like a 220 volt hard wired well pump, is it?
Not your standard plug in unit. If the pump is 220 volt that suggests it's quite a large unit, the plate on the motor should give some idea of the current draw, then you have to allow maybe 2X that current to start the pump. From memory the pump we had on the farm was a 230v / 4 kW unit. Would take a lot of solar to keep that beast running, but it was watering about 200 cattle, 300ft up a hill, 

A smaller pump and decent header tank might be more practical, with that sort of setup you could even have the pump only run when the sun is shining, and have several days of water stored?
Weekend warrior, Peterson JP test pilot, Dolmar 7900 and Stihl MS310 saws and  the usual collection of power tools :)

Offline mike_belben

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Re: please critique my solar ideas
« Reply #14 on: March 18, 2021, 07:05:33 PM »
ped-gens and ped-pumps have been done.  just saying.. how bad do ya want it?   ;D
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Offline NCEric

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Re: please critique my solar ideas
« Reply #15 on: March 19, 2021, 04:25:58 PM »
Ped-gens and ped-pumps means bicycle powered generators and pumps?

Offline NCEric

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Re: please critique my solar ideas
« Reply #16 on: March 19, 2021, 04:28:43 PM »
There was a very fun article others here might enjoy, by the way, in Low Tech Magazine about 4 years ago titled
Could We Run Modern Society on Human Power Alone?
It's available for free online if anyone wants to search for it.  Lots of other great articles, too.

Offline mike_belben

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Re: please critique my solar ideas
« Reply #17 on: March 19, 2021, 07:58:28 PM »
You got it bub.  Pedal generation.  Theres a cordwood home builder in NY who has been pedal pumping his water up to a gravity feed tank (iirc) for a long time.. Name is escaping me right now. 
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Offline peakbagger

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Re: please critique my solar ideas
« Reply #18 on: March 20, 2021, 07:06:51 AM »
I missed the well pump part. If you have a deep well pump, you need a big system to overcome the current draw at startup. The rule of thumb is 3 times the running amps some go with 3 time nameplate. If you have pump with a external capacitor box (A small gray box usually in the basement where the wires go out to the well you can convert to variable speed pump. The pump controller is designed to ramp up slowly so no start up surge. Franklin Electric sells a "monodrive" conversion that replaces the capacitor. It will extend the life of the pump as it rarely if ever will run at full rated speed. It also does not need a big pressure tank. Three wire pumps are pretty much the standard these days. If you have an old two wire deep well pump without an external capacitor, its time to change the pump.  For most folks if they can get rid of the pump surge, they can run a much smaller generator. A variable speed pump in general is more efficient year round. The only down side is it adds complexity to what is pretty simple system. I recommend a good surge suppressor on the main panel to keep any surges from coming in on the power line as the well is frequently where surges head to. The best one I am aware of is the Midnight Solar SPD. Their initial clamp voltage (the point where the surge is bled to ground) is far lower than the old style Delta type that might keep the house wiring from melting but the electronics will be cooked.

Offline nativewolf

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Re: please critique my solar ideas
« Reply #19 on: March 20, 2021, 07:29:13 AM »
My advice might be a bit different but I'm a big fan of simple and low cost.  Nothing competes against a Tesla solar panel setup today in terms of price.  They are consistently 30% below competitors systems.  Not saying you could scrounge the internet and do better and do it yourself but I think after all that time you'd be way ahead to just get a small Tesla system.  Learn what they do during the install and see if this is moving you in the right direction.  They even lease the whole system in many states.  Just go on the website and get the quote online and you'll find out what your ROI looks like.

ROI does vary depending on your state power rules but with the systems guaranteed for 20+ years and the average panel putting out 300+watts today (even cheap 425 watt panels out there) the ROI is quite strong and the payback periods very short compared to even 5 years ago.

I'd be concerned about the inspections/code rules on a wiring system that is independent of the grid connected system.  Once connected to the grid you are going to need an ATS if you wish to continue to have electricity during a grid outage, sure you realize that.

Tesla Motor Club has an energy sub area with some very savvy folks that have built very impressive grid and off grid solutions.  Much of it is Tesla centric but plenty is not.  The whole electric car industry is vacuuming up the worlds lithium battery supply and that might be constrained another 2 years.  I'm staying with our propane generator until I see the prices falling instead of rising.  ROI of a battery pack is just not there for most people (unless you are determined to be off grid, which is my long term goal but I'm a forester and used to waiting).

Lots of comments on the pump.  It's a concern, there are special irrigation pumps meant to be driven off of solar in an off grid situation maybe take a look at those if the pump is a limiting factor.

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Offline mike_belben

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Re: please critique my solar ideas
« Reply #20 on: March 20, 2021, 02:17:42 PM »
Could a variable frequency drive be added to the existing well pump to cut start load amps? Thats how these super efficient ductless split AC compressors are doing it.  Someone with PLC experience could probably snatch a VFD from a scrapped minisplit and program it to run other things.  Im not that guy but maybe someone here is. 
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Offline peakbagger

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Re: please critique my solar ideas
« Reply #21 on: March 27, 2021, 06:05:16 AM »
You can add variable speed drive to an existing well pump. Franklin Electric sells a "subdrive" for 2 wire pumps and monodrive for 3 wire pumps. A 3 wire pump (actually 3 wires and a ground) has an external capacitor box while a 2 wire does not. Installing one means you switch the house over to constant pressure operation instead of high low. It also gets rid of pump surges on startup which really help it you are running on a generator. The pump rarely if ever runs at full speed so it lasts longer. The only downside is cost. I think the Subdrive is around $700 while the Monodrive is around $1,400. Strongly recommended is a whole house surge suppressor on the main electrical panel to protect the electronics. The surge suppressor that is used in the solar industry is a Midnight Solar SPD as it shunts power to ground at lower level than most of them.

One other comment is that many homes have real crappy grounding systems. If the ground system is not set up correctly, the well pump gets zapped. The well casing needs to be bonded to the house ground rods that the main panel is connected to with a heavy gauge wire located outside the wire conduit in the trench and it should be routed directly to the ground rods without going into the house.  


Offline mike_belben

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Re: please critique my solar ideas
« Reply #22 on: March 27, 2021, 10:45:11 AM »
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Offline tmarch

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Re: please critique my solar ideas
« Reply #23 on: April 19, 2021, 04:03:13 PM »
First I would get and install a solar pump system on preferably a separate well to irrigate your garden and have it coupled to you other uses so at least you would have water available when the power go's out.  This would be a relatively inexpensive project that will give you an Ida about how solar will help your usage.  Keep in mind that water is more important than a lot of things for life.
I installed that configuration on several of my pasture wells, when I saw how that worked I installed my grid tied system in 2012.  It is over half paid for in electric savings since that time so I consider it a good investment.  I can turn a valve and furnish water to homestead if the power does go out.
Retired to the ranch, saw, and sell solar pumps.


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