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Wind, solar, storage and back-up system designer - Page 7

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Posted by Scottish Scientist on July 9, 2019, 12:26 am
On Tuesday, 9 July 2019 01:14:46 UTC+1, Scottish Scientist  wrote:






ed for winter and on an average winter day, the solar panels (together with
 any wind turbine, though none are specified in the configuration quoted) g
enerate 5KWh.

or generating - very overcast - and the solar panels only generate half of  
what they normally generate of a winter's day - only 2.5KWh, that's a bit o
ver 100 Watts on average.

x 24h = 2.4KWh

system is generating 200 Watts+ - on a bad day.

m could supply the maximum usage of 4 KWh and add 0.9 KWh of energy to the  

, only solar power but at night there is none, there's no wind generators t
o take advantage of any wind, and the batteries start at flat and you want  
to run a 1 KWh heater for 4 hours at night and use no power for the next 20
 hours, so still technically you are only wanting to use a maximum of 4KWh  
a day, then under those very unusual circumstances the system will fail to  
meet the specified demand.  

fuels, for those worst-case scenarios.

es the system can supply the maximum daily usage specified, no problem.

 back-up power - in just 9 hours.

 mind the back-up power providing a majority of the energy consumed by the  
system and providing more of a "base-load" than a "back-up" then you might  
want to look at a Row H configuration.

It is past my bed-time and my typos are coming thick and fast.


"a 1 KW heater for 4 hours at night"
"an emergency stand-by legacy generator burning fossil-fuels"

Right I am off to bed!

Posted by Jim Wilkins on July 9, 2019, 1:38 am
On Monday, 8 July 2019 23:26:51 UTC+1, Jim Wilkins  wrote:

Let's assume for the sake of argument that the system specified is  
designed for winter and on an average winter day, the solar panels  
(together with any wind turbine, though none are specified in the  
configuration quoted) generate 5KWh.

5KWh on average but supposing however that it is a particularly bad  
day for generating - very overcast - and the solar panels only  
generate half of what they normally generate of a winter's day - only  
2.5KWh, that's a bit over 100 Watts on average.

The back-up power of 100W is on full blast so that day it generates  
100W x 24h = 2.4KWh

So the total generated that day is 2.5 KWh + 2.4 KWh = 4.9 KWh and the  
system is generating 200 Watts+ - on a bad day.


I monitor the raw solar panel voltage, current and wattage going into  
the controller as well as the net delivered to the battery or drawn by  
the inverter.

On an overcast day the panel output wattage may be only 10% of its  
rating, or less. Thin haze can cut it in half. They are  
polycrystalline Grape Solar panels, but I also have some amorphous  
ones on an older,smaller system that do no better.

One reason for watching the controller input is to detect battery  
voltage leaking back out at night, if a component shorts. That's  
already happened to me though it caused no problems.  

Posted by ads on July 9, 2019, 1:46 am
 On Mon, 8 Jul 2019 08:27:32 -0700 (PDT), Scottish Scientist

That answer just destroyed any credibility you may have had because it
points to your ignorance of battery chemistry and safe operating

Not even lithium cells are discharged that low - except by radio
control vehicle fans who have lots of money to spend on replacement

Reasonable discharge for AGM batteries (trade-off between useful
capacity and number of charge/discharge cycles is 50%.  Maximkum
discharge is 80%.  People do discharge them 100% - but very few times.

Lithium cells have the best life when not discharged more than 80% and
most electric/hybrid vehicles also use that value.

Flooded lead acid cells are more limited unless designed for deep
cycle use (fork lift, solar).

I'm tempted to say you're holding a newly minted degree and not much
real world experience.

I won't be watching for an answer.

Posted by Jim Wilkins on July 9, 2019, 3:12 am
 <ads> wrote in message  

This neatly summarizes the battery issues we've brought up.

Posted by Scottish Scientist on July 9, 2019, 7:43 am
 On Tuesday, 9 July 2019 02:46:49 UTC+1, ads  wrote:

If for technology reasons, you want a lower discharge percentage then add batteries to suit your supplier recommendations for maximum discharge.

The configuration species "Storage Energy Capacity: 4.48 KWh" but it doesn't specify "batteries" or "pumped storage" or "power to gas".

The numbers in the designer are technology neutral.

The numbers don't take account of any safety margin for the particular technology, so you have to add that yourself.

So if you wanted a 50% discharge maximum for your battery technology then you would select a battery capacity that would factor the configuration's "Storage Energy Capacity" as follows  

Storage Energy Capacity / 50%, or
Storage Energy Capacity / 0.5 or
Storage Energy Capacity x 2

So for the example quoted  
Storage Energy Capacity: 4.48 KWh

your 50% maximum discharge gives you 4.48 KWh x 2 = 8.98 KWh.

A minimum of 8.98 KWh in terms of 12V105Ah (1.26 KWh nominal) batteries would be 8 batteries.

8 x 12V x 105A x h = 10 KWh

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