Sizing a complete solar system

abudabi

abudabi

Expert Member
Joined
Aug 7, 2007
Messages
4,975
Reaction score
7,656
Location
JHB
Aim:
1) To use PV power during the day and batteries at night; using little to no eskom power (even during winter). I understand a week's worth of rainy/cloudy days will affect that and that's OK.
2) To not be the electricity cop; not have to make any lifestyle changes.

My current daily consumption is usually 30kWh but there's been a month or 3 that it's hit 35. Would the following system suffice?

12 kW inverter
6kW panels
15.36 kWh LiFePo4 Batteries

From the various calculators it seems that I should be OK... but do I have too much or too little of something?

https://footprinthero.com/peak-sun-hours-calculator tells me I have about 5.5-6 hrs of peak sun available and https://footprinthero.com/solar-panel-charge-time-calculator says I need 2.5 hours to fully charge the batteries from 80% DOD. Dishwasher, washing machine, pool pump etc. can be run during the day when there's sunshine.

I don't know what my evening base load is. I have outside lights, fridge, chest freezer, alarm system, smart light & plug switches, cpap machine... but if I put 1000 watts (which I'm hoping is overkill) into https://www.jcalc.net/battery-size-calculator it gives this:
1679429444575.png

So if I read that correctly I'll need 2 batteries just to survive 8 hrs? So considering I'll be using batts for evening usage, I'll either need to get 4 batteries or reduce my base load ?
 
abudabi said:
Aim:
1) To use PV power during the day and batteries at night; using little to no eskom power (even during winter). I understand a week's worth of rainy/cloudy days will affect that and that's OK.
2) To not be the electricity cop; not have to make any lifestyle changes.

My current daily consumption is usually 30kWh but there's been a month or 3 that it's hit 35. Would the following system suffice?

12 kW inverter
6kW panels
15.36 kWh LiFePo4 Batteries

From the various calculators it seems that I should be OK... but do I have too much or too little of something?

https://footprinthero.com/peak-sun-hours-calculator tells me I have about 5.5-6 hrs of peak sun available and https://footprinthero.com/solar-panel-charge-time-calculator says I need 2.5 hours to fully charge the batteries from 80% DOD. Dishwasher, washing machine, pool pump etc. can be run during the day when there's sunshine.

I don't know what my evening base load is. I have outside lights, fridge, chest freezer, alarm system, smart light & plug switches, cpap machine... but if I put 1000 watts (which I'm hoping is overkill) into https://www.jcalc.net/battery-size-calculator it gives this:
View attachment 1496237

So if I read that correctly I'll need 2 batteries just to survive 8 hrs? So considering I'll be using batts for evening usage, I'll either need to get 4 batteries or reduce my base load ?
Click to expand...

Its difficult to say without knowing your usage patterns and appliances. If you use most of your power at night then you will need a lot more battery. If you can keep things like geysers, washing machine, dishwashers on only during the day that helps a lot in terms of battery usage.

My gut says you will save somewhere between 50 to 70% of your current usage with that system but its tough to give a more accurate number without knowing all the information.
 
B-1 said:
.... If you can keep things like geysers, washing machine, dishwashers on only during the day that helps a lot in terms of battery usage.....
Click to expand...

Sorry, I thought I did put that in. Yes those kind of loads can be run during the day.
 
abudabi said:
Aim:
1) To use PV power during the day and batteries at night; using little to no eskom power (even during winter). I understand a week's worth of rainy/cloudy days will affect that and that's OK.
2) To not be the electricity cop; not have to make any lifestyle changes.

My current daily consumption is usually 30kWh but there's been a month or 3 that it's hit 35. Would the following system suffice?

12 kW inverter
6kW panels
15.36 kWh LiFePo4 Batteries

From the various calculators it seems that I should be OK... but do I have too much or too little of something?

https://footprinthero.com/peak-sun-hours-calculator tells me I have about 5.5-6 hrs of peak sun available and https://footprinthero.com/solar-panel-charge-time-calculator says I need 2.5 hours to fully charge the batteries from 80% DOD. Dishwasher, washing machine, pool pump etc. can be run during the day when there's sunshine.

I don't know what my evening base load is. I have outside lights, fridge, chest freezer, alarm system, smart light & plug switches, cpap machine... but if I put 1000 watts (which I'm hoping is overkill) into https://www.jcalc.net/battery-size-calculator it gives this:
View attachment 1496237

So if I read that correctly I'll need 2 batteries just to survive 8 hrs? So considering I'll be using batts for evening usage, I'll either need to get 4 batteries or reduce my base load ?
Click to expand...
Check my system again very similar usage. I would drop the inverter to 8kw and get a 20kw bat bank.

Just my 2c

Also maybe just one more panel to get 6.5kw

I avg 25kw but can push 35 if needed

1679464843500.png

Snyper's Solar Farm

Hi all, I am finally getting round to making this thread. After loads of research and another bout of load shedding I finally decided to pull the trigger and load shed Eskom. Prior to going solar I already had all the lights on LEDs, house is kitted with energy efficient appliances and...
mybroadband.co.za mybroadband.co.za
 
I have 12 panels West /East. And 10kwh battery that I set to 50% Soc during the day.
There have been 2 days so far in the month I have had the system where the battery didn’t charge all the way up to 100%. Got to 85 to 95%. They were cloudy, and we did use the tumble dryer, oven, stove and a few other things.

So I’d say 6 panels may be too little.
 
Pegasus said:
I have 12 panels West /East. And 10kwh battery that I set to 50% Soc during the day.
There have been 2 days so far in the month I have had the system where the battery didn’t charge all the way up to 100%. Got to 85 to 95%. They were cloudy, and we did use the tumble dryer, oven, stove and a few other things.

So I’d say 6 panels may be too little.
Click to expand...
6kw in panels Im assuming abt 10-12 panels.
 
abudabi said:
Aim:
1) To use PV power during the day and batteries at night; using little to no eskom power (even during winter). I understand a week's worth of rainy/cloudy days will affect that and that's OK.
2) To not be the electricity cop; not have to make any lifestyle changes.
Click to expand...
I suggest you switch all outside security lights to solar LEDs to reduce night-time electrical consumption.

There are some awesome units (30W, no PIR, in my case) that can supply up to 8 hours of light at night for as little as <R500 (remote control settings: on/off, auto, 3h, 5hrs) - the auto setting will switch light on at the time you switch it on, say 20:00, and will switch on at 20:00 every evening - looks like this:
hb78ca6ebb1244b989b90b96743f969e5z.jpg


Or, if you need a motion sensor, these:
2 x JD 3PC Solar Powered Human Motion Sensor Light Lamp with Remote Control
 
I average about 30 kWh per day but can go to 40 kWh+.

Can also reduce Eskom usage to zero if I don't top up from the grid due to load shedding, and push the batteries a bit deeper. Only bought about 40 kWh so far this month.

1679468225292.png
8 kW inverter, 6.3 kWp panels, 19.2 kWh batteries. Total cost around R240k...
 
There's lots of stuff you can do to reduce your consumption before you over-spend on solar. 30 kWh is a fair amount. What are the main culprits for pulling that amount?
There are various things that you can do for instance using heat-pump aircons instead of resistive heaters, making sure that the fridge's seals on the doors are in good condition (this is about a R500 fix and can save kWh if it wasn't in good condition), making sure that the roof is properly insulated, switching out geyser element for heat pump (down from 3.5 kW to about 800W as I've mentioned in another thread).

Ideally it would be good to shake these kinds of things down first before over-spending on a solar installation.

Edit: I'm currently eyeing one of these for use over the winter to get an accurate picture of my usage:
www.geewiz.co.za

Emporia Vue Gen 2 Energy Monitor - with 8x 50A Emporia Current Monitoring Sensors

Bundle includes Gen 2 Vue Energy Monitor Two 200A current sensors for service mains Eight 50A current sensors for individual circuits Wire harness Extra wire & wire nuts Wifi antenna & cable
www.geewiz.co.za www.geewiz.co.za
 
Last edited:
6kW of panels with 5.5hours of sunshine = 33kWh, so that's not enough panels to cover 30kWh average per day with 35kWh peaks. I would oversize the panels to account for 30% reduction in production for winter and slightly cloudy days. (35kWh/5.5)/0.7 = 9.0909kW panels.

My gut feel is that you don't have enough battery capacity. This depends on your use case though, how much of your usage is during sunshine hours and how much is outside of that. My use is about 70% outside of solar hours. In your case (35kWh * 0.7)/0.9 = 27.222kWh (the 0.9 is running the batteries down to 10% SOC remaining - adjust as necessary). [that also assumes perfect efficiency, etc. which isn't realistic, so I would round up, e.g. if batteries come in 5kW increments then get 30kW worth].

The calculation you used is for 8hours of runtime on battery. This is unfortunately not realistic. Imagine 8 hours that's say from 8pm until 4am, well both of those times are firmly in darkness and FAR from useful solar production. Solar production only picks up in the morning after sunrise and drops off in the afternoon before sunset. You're looking at closer to useful solar production from 7-9am on winter mornings and ending at 3-4pm in the afternoons. That's a lot more than 8hours.
 
1am7h30n3 said:
6kW of panels with 5.5hours of sunshine = 33kWh, so that's not enough panels to cover 30kWh average per day with 35kWh peaks. I would oversize the panels to account for 30% reduction in production for winter and slightly cloudy days. (35kWh/5.5)/0.7 = 9.0909kW panels.

My gut feel is that you don't have enough battery capacity. This depends on your use case though, how much of your usage is during sunshine hours and how much is outside of that. My use is about 70% outside of solar hours. In your case (35kWh * 0.7)/0.9 = 27.222kWh (the 0.9 is running the batteries down to 10% SOC remaining - adjust as necessary). [that also assumes perfect efficiency, etc. which isn't realistic, so I would round up, e.g. if batteries come in 5kW increments then get 30kW worth].

The calculation you used is for 8hours of runtime on battery. This is unfortunately not realistic. Imagine 8 hours that's say from 8pm until 4am, well both of those times are firmly in darkness and FAR from useful solar production. Solar production only picks up in the morning after sunrise and drops off in the afternoon before sunset. You're looking at closer to useful solar production from 7-9am on winter mornings and ending at 3-4pm in the afternoons. That's a lot more than 8hours.
Click to expand...
Yea you could even sacrifice aray size early on in exchange for battery size

Somehow everybody concentrate on getting aray size perfect to find that is idle big part of the day

Cause you don't have load the pull that in middle of the day and batteries is full by 10-12am

How do you know you have an optimum size/ratio ,

Either

you get the batteries full by the end of the solar output

Or
battery is close to your preferred discharge % just before solar kicks in again

Then you can add a bit more battery for bad weather/shedding reserve
 
Last edited:
At 30kwh a day I would suggest you add atleast 20kWh worth of battery storage or atleast get your consumption down.
Set your geysers on timers and lower your baseload usage.
 
leon.davibe said:
Somehow everybody concentrate on getting aray size perfect to find that is idle big part of the day
Click to expand...
For me I wanted to get it done once, otherwise if you want to upgrade later it can be a pain depending on your setup if you cannot find the same panels.

I wanted to get ~8kWp but could only realistically fit 6.5kWp on the ideal roof.
 
DrJohnZoidberg said:
For me I wanted to get it done once, otherwise if you want to upgrade later it can be a pain depending on your setup if you cannot find the same panels.

I wanted to get ~8kWp but could only realistically fit 6.5kWp on the ideal roof.
Click to expand...
Yea so true

Adding batteries later is a lot easier
 
1am7h30n3 said:
6kW of panels with 5.5hours of sunshine = 33kWh, so that's not enough panels to cover 30kWh average per day with 35kWh peaks. I would oversize the panels to account for 30% reduction in production for winter and slightly cloudy days. (35kWh/5.5)/0.7 = 9.0909kW panels.

My gut feel is that you don't have enough battery capacity. This depends on your use case though, how much of your usage is during sunshine hours and how much is outside of that. My use is about 70% outside of solar hours. In your case (35kWh * 0.7)/0.9 = 27.222kWh (the 0.9 is running the batteries down to 10% SOC remaining - adjust as necessary). [that also assumes perfect efficiency, etc. which isn't realistic, so I would round up, e.g. if batteries come in 5kW increments then get 30kW worth].

The calculation you used is for 8hours of runtime on battery. This is unfortunately not realistic. Imagine 8 hours that's say from 8pm until 4am, well both of those times are firmly in darkness and FAR from useful solar production. Solar production only picks up in the morning after sunrise and drops off in the afternoon before sunset. You're looking at closer to useful solar production from 7-9am on winter mornings and ending at 3-4pm in the afternoons. That's a lot more than 8hours.
Click to expand...
That production lines up - my 6kwp gets me on average 28-32kWh with the odd 35kWh day

1679494131460.png
 
Mzezman said:
That production lines up - my 6kwp gets me on average 28-32kWh with the odd 35kWh day

View attachment 1496661
Click to expand...
That's nice! A lot of my potential generation isn't seen as my batteries are normally fully charged by midday and my load isn't that high.

My max daily generation so far is around 23kWh. Really want to get a third battery.
 
I struggled to get my 10kWh batteries charged over the rainy weekend and had to top up with grid by late afternoon. This with 10x545w JA Solar panels facing true north.

Either you substantially need more PV (for the rainy days) or up your battery capacity to 30kWh to get you close to off-grid.

First stop would be to calculate your base load, from there you can estimate additional usage (& timing thereof) and spec a system.
 
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X