diy solar

diy solar

Looking for Guidance on Basic All-in-One Solar System for Cabin

distant55

New Member
Joined
Jun 3, 2021
Messages
20
Hi All,

I'm hoping to get some guidance on a project I'm looking to build for my cabin. Right now we have grid power that we use, which works fine, but we are interested in setting up a backup solar system should the need arise. Its a small cabin, 800 square feet, with two bedrooms and 1 bathroom. We have a septic and a well and typical devices including, 7 lights, two laptops, 1 55 inch TV (not a necessity), PS3 (again not needed), microwave (not used often), fridge, electric water heater (probably won't put this on the solar system) and a pump (I believe it is a 1/2 HP, but I'll double check). I have been watching Will's youtube channel trying to learn as much as I can and based on my expertise level (low) I'm thinking about an all-in-one set up. Below is the set up I am considering, I would like your feedback on if this is feasible or not even close. And if I'm way off any suggestions would be appreciated.

1. Growatt 24V SPF 3000TL LVM
2. 2000 watts of solar panels (10 x 200 watt panels)
3. 2 x AGM Batteries (VMAX MR127-100)
4. ECO-WORTHY 6 String PV Combiner Box & 63A Circuit Breakers for Solar Panel
5.All needed cords and accessories

I'm going for a budget build and trying to follow the guide below.


Thoughts, suggestions?
 
Did you budget for a charger to make sure that prior to putting the batteries into use, each one is individually charged properly? Doing so from solar-only first time out can be less than effective.

If you want to stick with Vmax, they make a line of chargers that will do this job. Don't cheap out and use the cheapest option if you do. Their model BC8S1215A looks like it will do a fine job.

Agm's don't like being tickled-to-death. Use this to set up initially, and perhaps for use as a PM measure every once in awhile if needed.
 
I did not, but I will add it to the list, thank you! Anything else I should consider?
 
Honestly, you're doing it backwards, but that is common.

To spend the least amount of money, before you buy anything, you invest in tools to measure exactly how much power you are actually using daily. Kill-A-Watt meters, clamp-on ammeters and such are quick tools to ballpark it.

Then you multiply that figure, by the amount of days of backup you need.

Then you figure out how many hours of solar-insolation you have based on winter months. Solar insolation is far different than mere sunrise to sundown. It is based on your geographical location, modified by possible local sun-blocking conditions nearby. (Trees, buildings, and so forth)

Now you can figure out how much battery capacity you need to purchase to support your power draw. Secondly, how much panel-power you need to keep those batteries charged based on your solar-insolation. Because you indicated that you'll be using AGM's, that calculation will be much more critical, than if you did so with LFP - since sulfation from lack of enough charge is not an issue with LFP.

NOW you can start buying all the solar goodies. :) It sounds like me trying to be a buzz-kill, but this is the cheapest way to do it. Otherwise you may either over-spend upfront, or end up repurchasing items modifying the system as you go.
 
I don't think that inverter will have the capacity to start your wellpump. Assuming your pump is half the size of mine, then half the starting wattage would be ~4500-4600W. Once started, the pump might draw about 1000W running.

For high-surging equipment like pumps, you are likely to need a low-frequency inverter like a Radian or a Conext/XW.

I would also recommend a larger battery than 2AGMs. Assuming you have 100Ah at 24V, and you want to charge at no more than 0.2C, the math works out to be...
100Ah X 0.2C X 25V charging X 1.18FudgeFactor= 600W. So, 2000W is far to large for this small battery.

For 2000W what you would put out is (2000W/25V) X 0.85FF =68A. That many amps would be good for a 340Ah battery, about triple of what you are planning now. Look at Trojan L-16s as an appropriately sized battery.

All in all, very imbalanced. As Substrate indicates above, you'll end up spending more money down the road as you find out what you randomly assembled doesn't work and you need to replace, replace, replace.
 
Yup, and the advice here changes on whether this cabin is in Stockholm, or Tucson.
 
Thanks guys, this the kind of advice I was looking for to see if I am lost, which is seems like I am. Hopefully you guys won't mind a few more dumb questions to get me on the right path.

1. What if I were to remove the pump from the equation, would what I have above make any sense? Based on what you said the batteries I selected aren't going to cut it. How many Trojan L-16s would I need for a 24v system?
2. As far as a solar pump system, does it make any sense at all to have a solar pump all in one system separate from the above scenario? Or does that only add costs? What about if its a DC powered pump versus AC.

Sorry for the really basic questions, but if I don't ask I'm probably going to make the mistake you guys mentioned above of buying stuff until I figure it out. This would be for a cabin in Wisconsin just FYI.

Also if you have any ideas on some reading or something I can look into on this topic please let me know so I don't waste too much of your time.
 
I did some more research tonight and I think I can rule out both of these at this point. So if I am understanding both of you correctly, the Growatt is not going to work for my purpose. I'll have to get an inverter that supports higher starting wattage. Do you have any suggestions on the inverter? Also if you could help on the number of Trojan L-16s that would be helpful as well.

Thanks for being patient with me.
 
Good question, I'm not sure. If anyone knows of an alternative pump with lower start up power requirement, I would love to see it.
 
Trojan L-16s are 6V batteries, so you need four of them to equal 24V. There are many combinations that you could look at. I myself only work with lead-acid, so that's what I would recommend. Going cheap, and getting the 99$ Costco golf-cart batteries, you could buy eight of those and wire two parallel strings of four batteries to get about 420Ah at 24V. You could also wire four 6V Trojans, or three 8V Rolls, or six 4V Rolls. You could even buy twelve 2V Trojans or Rolls, but you won't have enough amps to charge those at the density they like.

My recommendation is to build a system to run the pump you already have in place, instead of installing a pump your system can run. I have pulled a pump 400 feet out of the ground, and can tell you that pump replacement is nothing to look forward to. The added benefit will be if you build a system robust enough to run your pump, then it will be robust enough to run anything else.

Here's what you need to do. Get a clamp meter like this one that can measure "inrush current".
Measure the actual startup current of your unit, then select an inverter that can support that current. For the sake of design, lets pretend that your pump uses 20A at 240VAC for startup.

Here are the specs for one inverter I would recommend, I have the Conext 4024 myself. Looking at the 5 second surge capacity, it could potentially handle 7000W for 5 seconds. That should be enough to start your pump.
1622827864205.png
 
This is great info, thank you Michael! I will order that device and start working on this.
 
The Direction your headed , I see no reason not to just jump to a 48 volt system.
I use outback equipment and it’s great , but if I was buying today I mite switch over to the conext 40/48 .
I use the sams club golf cart battery’s and have no problem with them at all .
I have 16 battery’s in series parallel for 430 amp hours .
I have 4500 watts of 295 watt panels 3 series and 5strings .
I wanted to run a GSQF solar pump off just solar panels but decided to just add 15 more panels to my system and run it from the inverter , the pump will be set at 700 feet .
 
Here is one more bit of info to help persuade you. My system is much like Wellbuilt's, with 4500W of panels wired 3S5P, with a XW+6848 inverter.

When I used my generator (AC-Delco 6500W) to power my wellpump, the pump draws 10.0-10.1A at 240VAC and pump produces on average 275gph.

With my XW+ solar system, the same pump draws only 9.4-9.5A at 240VAC but produces 300-305gph.

This means the pump is running better off the cleaner electricity of the inverter, producing more water at lower power consumption.

In the real-world, besides just getting more water, this also means my pump is being fed cleaner electricity which will make it last longer.

Get a quality inverter like a Radian, or a Schneider, and you will sleep better. You'll remember the quality long after the price is forgotten!
 
That's good to know! You all have given me a bunch to think about. I'm going to order the tool that was recommended and go back to the drawing board on my design. I will come back with any questions that I can think of. Thanks again!
 
Back
Top