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Sizing batteries and Solar


georgelza

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Hi all, some comments, input.

 

some logic/match checking quickly.

lets say i have a constant load of 600watt's.

For panels, so that means i min need 2 panels of 330w to cover that, more than that those 2 means i got excess and can load more, ie charge batteries also and cover spikes, looking at my consumption graphs, 9 x 330w should be a good spot for me (during day, with pool pump running I'm on a constant 1000w, pool pump eats 700w).

for batteries... bit more complicated:

a Pylontech, 3000 = 3000wh so

thats 3000*.8 (80% DoD) = 2400wh useable, and with the spikes thinking 2 batteries is probs desired, with a split board to isolate the 2 geysers off the battery feeds, and will most probable do the pool pump also (aka only allow pump and geysers onto utility and Solar feed)

= 4 hours / battery / best case

G

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Those panels only work at full capacity at midday. Other times not. So a rule of thumb is to multiply the rated capacity by 4.5 or 5 to get to the solar production over a sunny day.  In that case is is 3.3kWh on a good day. so you can run your 700W pool pump for about 5 hours, with batteries to even out the power supply at either end of the cycle. With inefficiencies of battery charging etc, you are probably looking at about 4 hours that you can run the load without discharging the batteries. 

I'm sure somewhere on this site, someone has written up all of these calcs for sizing systems.

I'm running 10x 300W panels and they make about 15 kWh per day.

Edited by DeepBass9
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4 minutes ago, DeepBass9 said:

Those panels only work at full capacity at midday. Other times not. So a rule of thumb is to multiply the rated capacity by 4.5 or 5 to get to the solar production over a sunny day.  In that case is is 3.3kWh on a good day. so you can run your 700W pool pump for about 5 hours, with batteries to even out the power supply at either end of the cycle. With inefficiencies of battery charging etc, you are probably looking at about 4 hours that you can run the load without discharging the batteries. 

I'm sure somewhere on this site, someone has written up all of these calcs for sizing systems.

I'm running 10x 300W panels and they make about 15 kWh per day.

... reading this that ye my idea of either 9 or 12 panels of 330w is a good plan.

G

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15 minutes ago, DeepBass9 said:

Those panels only work at full capacity at midday. Other times not. So a rule of thumb is to multiply the rated capacity by 4.5 or 5 to get to the solar production over a sunny day.  In that case is is 3.3kWh on a good day. so you can run your 700W pool pump for about 5 hours, with batteries to even out the power supply at either end of the cycle. With inefficiencies of battery charging etc, you are probably looking at about 4 hours that you can run the load without discharging the batteries. 

I'm sure somewhere on this site, someone has written up all of these calcs for sizing systems.

I'm running 10x 300W panels and they make about 15 kWh per day.

Even with set calcs for sizing systems, it doesn't always work out as you think it might.

@georgelza with the math you proposed I would get at least another 330W panel as you won't get 100% production out of a panel most of the time. One system that I recently inspected has 8x 275W panels, thus 2.2Kw, yet we never got more than 1.9Kw out of it. It's more than what the client needed, I think their max draw was 1.3Kw but it's nor constant. So there ample power left to recharge the batteries. It's an offgrid setup and been running 100% since 2015. The vision batteries don't show any sign of abuse or poor cycles, yet at least.

The Pylontechs you mention are made for daily cycling, so see if you can cause it to cycle daily. At 80% DOD they'll last 16 years.

9x 330W = 2970W. You'll probably get about 2.5Kw out of it at peak times, which could be between 10:00 and 14:00, or even 15:00, depending on your roof angle, obstructions, etc

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30 minutes ago, SilverNodashi said:

Even with set calcs for sizing systems, it doesn't always work out as you think it might.

@georgelza with the math you proposed I would get at least another 330W panel as you won't get 100% production out of a panel most of the time. One system that I recently inspected has 8x 275W panels, thus 2.2Kw, yet we never got more than 1.9Kw out of it. It's more than what the client needed, I think their max draw was 1.3Kw but it's nor constant. So there ample power left to recharge the batteries. It's an offgrid setup and been running 100% since 2015. The vision batteries don't show any sign of abuse or poor cycles, yet at least.

The Pylontechs you mention are made for daily cycling, so see if you can cause it to cycle daily. At 80% DOD they'll last 16 years.

9x 330W = 2970W. You'll probably get about 2.5Kw out of it at peak times, which could be between 10:00 and 14:00, or even 15:00, depending on your roof angle, obstructions, etc

I'm thinking I'm safe with the numbers atm... I'm not seeing anything over 3000w, (thats with the geyser on) my 3 biggest loads are pool pump at 700w and the 2 geysers.

otherwise everything seem ti hang together at about 400-500w.

if budget allows might up to 12 panels, rather have that little bit more to pull that extra W when the sun start dropping, big thing will be placement over the various locations of my roof.

G

 

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9 hours ago, georgelza said:

I'm thinking I'm safe with the numbers atm... I'm not seeing anything over 3000w, (thats with the geyser on) my 3 biggest loads are pool pump at 700w and the 2 geysers.

otherwise everything seem ti hang together at about 400-500w.

if budget allows might up to 12 panels, rather have that little bit more to pull that extra W when the sun start dropping, big thing will be placement over the various locations of my roof.

G

 

You can also replace your geyser element with a 2Kw, or even 1.5Kw element and let it run for a longer period. My 2Kw element runs about 2 hours to heat 35 degrees to 60 degrees. A 1.5Kw element would probably run an hour longer, but then you have more Kwh to use.

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If I have a limited supply (not enough solar pv,, then I can understand how this would help, but if I have enough panels to drive the larger element, how would this help.

I would never try and run the geyser of the batteries... but, ok, just reread your posting, by reducing the element i leave more of the cake for others device... meaning in the end I actually need less PV or a smaller Inverter.

thanks.

G

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You are only going to have max solar output for about 2 hours a day. Unless you shower at lunchtime, you will be running your geyser from batteries, or grid. I think you are a bit optimistic about the amount of power that will be produced.

Is your geyser solar (I.e solar heated) as that is way more cost effective than heating with PV. How big are the 2 geysers?

Edited by DeepBass9
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11 minutes ago, georgelza said:

If I have a limited supply (not enough solar pv,, then I can understand how this would help, but if I have enough panels to drive the larger element, how would this help.

I would never try and run the geyser of the batteries... but, ok, just reread your posting, by reducing the element i leave more of the cake for others device... meaning in the end I actually need less PV or a smaller Inverter.

thanks.

G

Yes. Differently put, in winter this helps a bit since you have less PV energy to begin with. I would not use a smaller inverter though as you don't know when you need the extra energy.

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our shower/bath times are 6-7pm, at which time a geyser timer would have it shut down anyhow, only prob going to switch on at 8am'ish (if i use a timer and not the sonof's to only push power to them when on solar. implying they will pretty much have the entire day to heat up.

G

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 But when are the batteries going to charge? I have a solar array about the size that you are contemplating, with probably lower loads than you describe, and I don,t have the spare power to run a geyser element. I think the system is too small for what you want to achieve. What is the intention, to go off grid, grid tie, loadshedding backup?

From the graphs you posted you are using about 25 to 30kwh per day, so you will need about at least 5kw of panels to drive that. My 3kw of panels makes 15kwh per day (in good solar conditions)

Edited by DeepBass9
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my panel "idea" is sitting at 4Kw at the moment, as TTT has also said, drive usage behaviour down, use what you need and not what you want. so I'm not under a false believe here... will have to reduce power usage.

It will be grid tied, as a backup, would prefer to be able to blend power sources but the Expert can't,  so might consider changing Geyser timers to maybe run during dark hours of night and safe the panels for everything else during the day, and then work from there.

Everything standing, whatever any of us do... it does initiate change in behaviours.

G

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3 hours ago, georgelza said:

... drive usage behaviour down ...
... it does initiate change in behaviours.

There we go!!!

First Rule of Solar: Reducing consumption even more is in your future. (from a fortune cookie)
Second Rule of solar: Behavioral changes you are going to make. (in Yoda's voice)
Third Rule of Solar: SWAMBO and her little ones are going to get upset with you. (just trust me on this one)
Fourth Rule of Solar: You are going to upgrade. (you'll see)

After having lived 1-3 above in real life we can call ourselves novice solar experts, for the journey has now begun with rule 4 the next level. 🙂 

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15 minutes ago, georgelza said:

SWAMBO and little monsters in JB, me in Jhb...

I wish you the best of luck - no matter what you buy. 🤣

Inverters and batts have the knack to trip at the least inopportune moment for SWAMBO coupled with the fright of all being in the dark with the little ones voicing their fright with an accompanying phone call in a very highly charged emotionally voice full or questioning ones decisions with accusations thrown in. 🙂 

Till someone has learnt the tweaks and what to do when it happens - and no amount of training helps - until they have had to sort it all out without you anywhere near available. 

From the 6 of us in the house, excluding myself, my daughter became the most logical person to switch things back on, parents, wife and son, not so much.

Not a negative either, just a fact of life going forward with YOU becoming "Eskom". We all have learnt to respect the engineers at Eskom. 😉 

Edited by Guest
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3 hours ago, The Terrible Triplett said:

There we go!!!

First Rule of Solar: Reducing consumption even more is in your future. (from a fortune cookie)
Second Rule of solar: Behavioral changes you are going to make. (in Yoda's voice)
Third Rule of Solar: SWAMBO and her little ones are going to get upset with you. (just trust me on this one)
Fourth Rule of Solar: You are going to upgrade. (you'll see)

After having lived 1-3 above in real life we can call ourselves novice solar experts, for the journey has now begun with rule 4 the next level. 🙂 

Replace the 20A  CB's with 13A CB's and just "oops, I don't know. Try switching some of the stuff off?" when it trips ;) 

Edited by SilverNodashi
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