Questions on off grid systems

Hi all, I am trying learn more about solar. I am looking at 10) 24v 240watt panels for a 24v system, wired in series for 240v 10amp to keep from using large wire. Is there a pwm, or mppt controller to convert the 240v to charge a 24v battery bank? Or any other ideas? The system will be solar, and hydro combined. Thanks

1 Like

Do not go with 24 volts, I would look at a 48 volt system for the efficiency gains.

1 Like

I agree, and thought about going 48v, but, I can’t get the rpms to get 48v with the stream flow I have.

2 Likes

Hello Al,
Why not have a grid-tied system, too, so you can use the power from all those solar panels? Connect the batteries to the hydro from the stream, and if you need more current to charge the batteries, then use a regular battery charger. Here’s a photo of what my system was producing a few days ago. The power below the graph horizontal axis is what I was not using on that day. (Not charging my electric car, not using any tools in the workshop, because I was mostly working on the wood supply and cutting up trees that Harvey blew down.)
Bluebonnet_Sept12_2017

2 Likes

Thanks Ray, what did you have to do to grid tie, as far as the power co.? What grid tie inverter will handle 240v? I just checked, in WV we have to have $100,000 in liability insure. to grid tie

2 Likes

I put my panels on a ground mount rack made from steel pipe that I welded up. They wanted a diagram of Proposed Renewable Energy Generation Facilities including:
a. Inverter(s) or Generator(s)
b. Lockable Disconnect
c. Fusing or Bi-Directional Breaker
d. Manufacturer’s Specifications for the Inverter(s) or Generator(s)
I used the Enphase Microinverters that work on 240 volts. (Without the 240 volts, they don’t work.) The M215 and M250 are available on eBay for less than $70 each. You put one below each panel. The M215 will handle the 240 watt panel, and the M250 will take care of up to 265 watt panels. Both of these are not the newest ones, but neither are 240 watt panels. My neighbor just bought a pallet load of Chinese made 240 watt panels for about $90 each.
Look carefully at the fine print in the grid tie agreement. Mine specified Liability Insurance, but only for very large installations producing over a Megawatt. Here is a screen shot of that portion of the .pdf:
Bluebonnet_Liability_Ins
After I put up the array, and the switch box disconnect, I hand dug a trench for the underground conduit to my pole circuit breaker box, and then I called them for an inspection. Once their Engineer signed off, they installed a dual register smart meter, and we turned on the power.

4 Likes

Thanks for the replies, but I am hoping some one can help with my original question. I would really like to go off grid.

4 Likes

Hi Al,

Look into Hybrid inverters, ( the way i am heading is similar )

as per example this article, but more can be found on the net

https://www.solarpowerworldonline.com/2015/01/hybrid-inverters-used-solar-projects/

2 Likes

The enphase m250 is a good unit if you are net metering. They 190 and 215 have lots of waranty replacements so beware of used. The only mppt charge controller for off grid that I know that will do 240 volts (it’s not 240 more like 270 or 280 voc) is the morningstar 600volt units. They only come in 48 volt size though. Better to cut it in half to 120 volts, make 2 strings and use a midnite solar classic 150. It will take all of them at 100 amps and the money you save on using one charge controller will pay for the thicker wire. Depending on your run and the voltage loss you are allowed probably 8 gauge 2 wire tech cable… or go to aluminum tech cable one or two gauges bigger at half the money of copper.
Cheers. David

4 Likes

That’s a heck of a pile of power for off grid. How have you calculated you power consumption, and what will you be using for a battery bank?

Personally I aim for efficiency reductions, I think the best power is power you never had to use to get the same effect.

For grid tie it makes sense, we seem to have reached a roughly 8 year break even, but the battery bank will will delay the break even point significantly.

2 Likes

We installed a 10 kw array for a private battery based system this spring. The arrays are growing in size as solar panel prices drop. People are getting creative like switching to electric hot water to use the extra capacity in the summer then back to propane in winter… electric hotplates next to the propane stove airconditioners that store cold in ice form and use it later, anything to use that extra solar when you have it. Most full sized systems are going to close to 5kw arrays as a standard. So much so that the charge controllers will probably grow soon…
Cheers

4 Likes

Wow, that’s a lot of power. DC LED lighting produces 60w equivalent with 8 watts of power, so roughly 80w should provide peak illumination for a house. An LED tv might consume roughly 120 watts plus conversion losses of inversion. But you can buy direct DC tv’s now, for not much of a premium. A satellite receiver might consume 40 watts AC, but some are made to run on 12v…

I can see fit to use an induction cooktop, if there’s excess power, or the propane ran out. Water can be heated with greater efficiency in summer with a flat plate collector. Or for year round use, why not just use a converted gas hot water tank? Here’s a commercial model. Makes sense to me, as most of the world never got access to endless cheap energy in a pipe or electrical service, and this is a highly efficient use of abundant biomass.

I am leaning towards using compressed air to move water, the air compressed by a windmill, and stored in 100 lb propane tanks.

A microwave might be in the energy budget, but use of that appliance is usually for minutes at a time at 1,000 to 1,200 watts.

What else does a house really require? A clothes washer. Then what? Toaster, coffee maker, each for very limited use.

Edit; fridge…

For welding and power tools, given the periodic nature, I feel a stand alone, or PTO generator would be more practical.

1 Like

Al, We are on a 1kW solar, 24 Volt system for 2 years now. We use 6 volt batteries currently with 2 banks. This cost about $10K. When I can afford it I want to add another 1kW of panels and 4 more batteries. This would be enough to last us about 2 days.
As Garry suggested, I have a separate generator for welding.
If you want, I can put up pictures of what I have for a controller and inverter. I bought this system with the intent to add a wind generator in the future.

2 Likes

Another thing I was thinking about is rather than regulate power run it to a dc water heater dump load. Not sure how to do that without running low voltage to the batts. When I ran windmills the power(12v)
ran directly to batts., then dumped excess to heating element, or light bulbs.

1 Like

Built into the mppt charge controllers is an adjustable auxiliary relay that you can adjust to a set voltage. Connect it to a solenoid, connect solenoid to batteries connect to a heating element and poof… instant dump load.

3 Likes

Thanks Dave, Is that feature on all the mppt’s

1 Like

It’s on the midnite solar the magnum energy and outback units. Probably on the schneiders as well. One of those 4 should be your go to charge controller. I’m partial to the magnum and the midnite solar.

1 Like

I haven’t setup a solar system here myself but I have seen a few. And working in industry I really liked schneiders components they are one if the better electronic supply companies in industry. I am willing to bet any of the manufacturers David mentioned would work well.
I would suggest spending some time at alte store online they have a decent website with alot of different opetions. And sizing tools.

2 Likes

I do not have your direct answer either Al.F.
Here I chose to keep the primary residence house on-grid. Have one by one pulled all of the out-building off-grid.
Here with our Public Utility in the state of Washington they stack on $,$$$. hurdles for anyone trying to tie in micro-wind, micro-hydro. My old Drupal/DOW photo album shows a man with a private 20 kW wind turbine rig bled out of $100,000. step by step jumping demanded hurdles. Bird folk got an injunction to force him into locked-rotor for his “potential eagle killing machine”.
PV solar is allowed grid-tied and even encouraged . . . BUT only if you do it their way. They get green-energy carbons reduction credits from the Feds for every PV solar kW brought into the grid. 90% of our grid power is Fed BPA supplied. So the big-dog must be kept happy. Or he will growl and bite.
NO battery banks allowed. Only grid depend tie-in from only certified PV solar are ever possible to tie-in.

So fellows regardless of some quoted federal law - local grid suppliers decisions rules.

Now if I was not a married man. Wanting to stay married to this very Steve U-understanding woman . . . I’d say . . . Grid-Freedom at any effort or sacrifice.

GaryT. sometimes a fellow can chase the energy-use reductions too, too far. A Smart car owner. I have had many, many four door small sedans able to haul four people and modest luggage that can energy-use kick any Smart(for Two) cars ass. Silly oldsters buy into this garp. Forgetting about grandchildren! And where do you put the child safety seats?!
This same thing applies to all energy uses. A rural property growing it’s own fuel wood trees for heat and power will beat the snot by any true measured matrix, out of deliver-to clean-blue-flame propane trucks, Big-Grid for heat and power.
Tiny house all the new craze out here Portland and Seattle. 300-400 square feet is consider a large-Tiny.
Same. Same. Where do you put the two children?
Where do you put the aged out 'Ma? The aged out 'Pa unable to live alone anymore? Unable to navigate stairs safely, let a lone a loft ladder. ALL-of-these; the wife and I have had to accommodate. Can-do, have-done, will-do again this weekend with 1200 square feet and throw in couple of dogs and cats too.
Doing this with 40, 7.5 watt actual LED lights.

Keep on getting with it AL. Do not be put back by anyone, ever.
tree-farm Steve unruh

4 Likes

I like your thinking Steve. I’m not in the granola munching, turbines kill eagles crowd. :slight_smile:
From my experience, as you say, a small 4 door sedan has greater functionality, and with mechanical reliability and lower price, much greater efficiency. Especially if Japanese made or designed… :smiley: (I believe Toyota Echo, Yaris, or Corolla hold the high places for economy and mechanical robustness). Anyone else miss mechanical window winders?..

My above comments were largely regarding the report of a 10kw home system. I just can’t imagine a practical way to use that much power. Unless grid tied, then a whole other dynamic. If we figure on 3 hours daily average at 80%, that is still a tremendous amount of power. You have to waste it by design into space or water heating, maybe hydrogen split from water? Using the C10 figure for charging, the battery bank will have to be gigantic, and carry significant costs. I also am probably guilty of considering our insolation, we tend to get decent winter sun exposure, so you don’t need to overbuild so extremely for the winter.

I can’t imagine what a house with modern efficient appliances would do with 30kwh per day, though I guess that isn’t too far from average north American consumption. I just think it is following down the path of the affluent dream we have been so fortunate to grow up with. Our ancestors would have thought they were in heaven with electric light and tv, maybe a couple of appliances.

Some times it’s better to re-examine than recreate a life from another place or time.

Regarding the tiny homes, there should be room for another tiny home for old folks beside the first one. And our definition of acceptable personal space mushroomed with consumerism post WWII, so I feel it’s open to examination too.

Regards,

2 Likes