Off grid solar system design

[Fisherus]

I'm surprised by your assumptions and comments, when you're here seeking advice on your project. The responses you've been given from these folks, who have been kind enough to help and advise you, have been spot on. My advice to you is to be smart enough to understand and use what you have been told, do some do diligence in research but, don't be argumentative with those who know far more than you. If you are sure of your design ( you must be to be so argumentative about what you were told) what is your reason for asking your questions?

[Kalintosh]

Your power consumption is too high for offgrid application. Either you make some changes to your lifestyle or you, simply, spend waaay lots of money on a very huge solar system

[Huru-ukko]

And totally agree with mike, make calculations properly and add50% extra - you will use it anyway...

[Huru-ukko]

And you should be able to connect your grid to your inverter and use it to charge batteries when you get grid electicity, but ask that from your dealer , at least multiplus has generatorsupport built in.

[Huru-ukko]

Hi Dialloljeri

I have been using wictron energy products for two summers now. I have 6 x285w panels , 150/70 mppt, 3000/24/70 multiplus. I dont have a possibility of grid. I hve 4 200ah ( c20?) cheap agm batteries . My daily consumpion when the sun is shining is between 1,5-4 kwh with no problems. When cloudy I dont use logging machine cook water etc. Normally the system goes to float at about 11-12 am. So When the aun is shining I can use the energy from the panels and the batteries are not ”used” but the mppt just raises the wattage used and still keeps floating.

So I’d say just go for it put more panels if u can and use the energy when its shining for example cooling the house.

But as said i have only been using the system for second summer now

[Mike90250]

Get a spreadsheet and put some numbers into it. don't do half the math in your head and half on paper !!

Power estimator load requirements.jpg

[SunEagle]

Thanks a lot,
The house is not going to be 100% off-grid because I will still have access to a grid whenever I need to, but it's just not anything like a grid-connected system in the States. I would just have to unplug my loads from the solar and plug into the grid. The bottom line is that I need to harvest from my system a minimum of 5KW/h. I just need the right information to make that happen. I can always arrange and adjust my consumption accordingly.

Makes sense. I would look into having your bigger loads connected to the grid because they will just greatly increase your battery needs. Try to keep the "off grid" loads as minimal as possible. That will help keep your costs down as you build your solar/battery system.

Based on some recent prices a solar/battery system can cost between $1500 and $2000 for each kWh it can safely deliver each day. So for a 5kWh system you may be looking at a cost of $7500 to $10,000 USD.

[Diallodjeri]

So all that data does not determine how many watt hours you will consume each day.

Try to remember that going off grid means you are relying totally on your batteries because the sun will not be shining every day. So your battery system will have to provide the entire amount of watt hours you plan on using.

So my question is what loads will you use each day and for how many watt hours. Once you total that amount you will come close to sizing your battery system. Once you have that determined you size your panel wattage.

Thanks a lot,
The house is not going to be 100% off-grid because I will still have access to a grid whenever I need to, but it's just not anything like a grid-connected system in the States. I would just have to unplug my loads from the solar and plug into the grid. The bottom line is that I need to harvest from my system a minimum of 5KW/h. I just need the right information to make that happen. I can always arrange and adjust my consumption accordingly.

[SunEagle]

I didn't actually forget to multiply the load wattage by the # of hours it will run, but I just assumed people will know these numbers are meant to be an hourly usage. I guess I did not make very clear my explanation. The big AC 2596*8 = 20,768W will only run whenever possible only during a day and the small one 1298*8 = 10,384W will run on the battery at night.

So all that data does not determine how many watt hours you will consume each day.

Try to remember that going off grid means you are relying totally on your batteries because the sun will not be shining every day. So your battery system will have to provide the entire amount of watt hours you plan on using.

So my question is what loads will you use each day and for how many watt hours. Once you total that amount you will come close to sizing your battery system. Once you have that determined you size your panel wattage.

[Diallodjeri]

You actually forgot to multiply the load wattage by the # of hours it will run.

That AC#1 calculates to 2596w x 8 hrs = 20768 watt hours = 20.8kWh
AC#2 comes to 1298w x 8 hr = 10384wh = 10.4kWh
Frig comes to 550w x 8 hr = 4400wh = 4.4kWh
Freezer comes to 230w x 6 hr = 1380wh = 1.4kWh
Fans comes to 250w x 6 hr = 1500wh = 1.5kWh
water pump estimated at 1-2kWh

Add all that up and you will come close to 40kWh so please run a calculation based on that number or higher since you didn't include any losses or small wattage loads.

I didn't actually forget to multiply the load wattage by the # of hours it will run, but I just assumed people will know these numbers are meant to be an hourly usage. I guess I did not make very clear my explanation. The big AC 2596*8 = 20,768W will only run whenever possible only during a day and the small one 1298*8 = 10,384W will run on the battery at night.

[SunEagle]

Thank you,
As a solar fanatic, you should know that array never produce the maximum wattage they are rated for, that's why I degraded their performance to 70% instead of leaving it at 100% when calculating the charge controller amperage. I think my math is right and I'm not sure about yours.

Here I tried to sum up my daily consumption from my array. The ACs are mini-split with an inverter.
AC#1: 220V, 11.8A => #hrs of use 8 a day => 220*11.8 = 2596W

AC#2 :220V, 5.9A => #hrs of use 8 at night => 220*5.9 = 1298W

Refrigerator: 110V, 5A => #hrs of use 8 a day => 110V*5 = 550W

Freezer 115V, 2A =>#hrs of use 6 => 115V*2 = 230W

4 fans with total consumption of 250W => #hrs of use 6 a day


I have don't know yet the consumption of the water pump but, I can safely assume it's going to around 1-2KWh and it will run for maybe 6 hrs. These are the heavy equipment I will have on the system and some of them are being used just during a day.

I can adjust my direct consumption from my array during a day to anywhere between 5 and 7KWh. My goal is to harvest at least 5 to 7KWh from my array.
I'm also planning to use only Victron products because I do have a local Victron dealer.

You actually forgot to multiply the load wattage by the # of hours it will run.

That AC#1 calculates to 2596w x 8 hrs = 20768 watt hours = 20.8kWh
AC#2 comes to 1298w x 8 hr = 10384wh = 10.4kWh
Frig comes to 550w x 8 hr = 4400wh = 4.4kWh
Freezer comes to 230w x 6 hr = 1380wh = 1.4kWh
Fans comes to 250w x 6 hr = 1500wh = 1.5kWh
water pump estimated at 1-2kWh

Add all that up and you will come close to 40kWh so please run a calculation based on that number or higher since you didn't include any losses or small wattage loads.

[Diallodjeri]

AC#1: 220V, 11.8A => #hrs of use 8 at night => 220*11.8 = 2596W. Actually, in this math, I just wanted to show that I will be using 2596W for 8hrs meaning it will be 8 x 2596W. Another thing is that I mixed up which AC would be used at night versus a day. AC#1 220*11.8 *8 = 20,768 would be used only during a day. AC#2, 220*5.9*8 = 10,384 would be used at night.

On the other hand, I'm assuming you agree with me on the deration rate of the panels output to 70% because of the high temperature and dust.

[Sunking]

As a solar fanatic, you should know that array never produce the maximum wattage they are rated for, that's why I degraded their performance to 70% instead of leaving it at 100% when calculating the charge controller amperage. I think my math is right and I'm not sure about yours.

My math is spot on perfect right out of engineering design best practices textbook. Your math is make believe. Every bit of it is wrong. Example

AC#1: 220V, 11.8A => #hrs of use 8 at night => 220*11.8 = 2596W

Is pure make believe math. WATT HOURS = Watts x Hours. 2596 watts x 8 hours = 20,768 Watt hours. More than most homes in the USA use in a day.

Now here is the reality. Just to run that AC unit on solar will require a 5000 Watt Panel System, 100 amp controller and a monster sized 48 volt 2000 AH battery.
I can't help you as your goals are not even realistic. You will fail if you proceed and loose a lot of money doing it. I am no Solar Fanatic, I am a professional engineer with 40 years experience.

[Mike90250]

A half HP water pump will pretty much consume about 1kw when running. That's what my XW logs my pump at. It is not 400w as simple math / hp cac would assume, because simple math leaves out motor losses and power factor, which the XW actually measures.

[Diallodjeri]

Thank you,
As a solar fanatic, you should know that array never produce the maximum wattage they are rated for, that's why I degraded their performance to 70% instead of leaving it at 100% when calculating the charge controller amperage. I think my math is right and I'm not sure about yours.

Here I tried to sum up my daily consumption from my array. The ACs are mini-split with an inverter.
AC#1: 220V, 11.8A => #hrs of use 8 a day => 220*11.8 = 2596W

AC#2 :220V, 5.9A => #hrs of use 8 at night => 220*5.9 = 1298W

Refrigerator: 110V, 5A => #hrs of use 8 a day => 110V*5 = 550W

Freezer 115V, 2A =>#hrs of use 6 => 115V*2 = 230W

4 fans with total consumption of 250W => #hrs of use 6 a day

I have don't know yet the consumption of the water pump but, I can safely assume it's going to around 1-2KWh and it will run for maybe 6 hrs. These are the heavy equipment I will have on the system and some of them are being used just during a day.

I can adjust my direct consumption from my array during a day to anywhere between 5 and 7KWh. My goal is to harvest at least 5 to 7KWh from my array.
I'm also planning to use only Victron products because I do have a local Victron dealer.