Battery Back up hours in solar power for day timing or night?

[AJK]

Hi,

It is pleasure to communicate

I will be really thankful if someone can guide me in the following;

During sizing of the battery backup in solar power system, conventionally or mostly I come across the designer who are sizing the battery according to the daily usage of the KWh consumption. For example;

Total Appliance power is = 770 W
Daily usage is = 6 hours/day
Solar panel Wp = 1500 W

In the above case, suppose the usage in the night is 3 hours/day then what usage we should consider in the sizing of the battery, whether we should consider 6 hours/day or 3 hours/day in the sizing of the battery backup?

Because most designers says that we have to consider all the 6 hours usage in the sizing of the battery backup,
I am concerning why should we consider all the 6 hours in the battery backup sizing as I think in the sunshine hours we don't need big batteries, only small battery will be enough to power the inverter and load, like in the above case don't we consider 3 hours in sizing of the battery backup instead of considering all the 6 hours?

and also when the battery is charging during the sunlight and when it becomes fully charged, is it happening at that time that the load is taking power from the battery and at the same time solar panel charges the battery or instead of both only one process works?

Really appreciate for any response

Thanking you

AJK

[Mike90250]

If you only want lights and fridge to be active for 3 hours in the night, put a timer on them and go for it. But my wife won't. Wants the lights to work at night and not just days. Wants cold milk in the AM for her hot coffee (propane stove)

But it's not 12hr sun, 12 hr night, in winter months, it's more like 4 hours sun (charging) 4 hours partial power production, and 16 hours of no production that has to be dealt with. And a couple cloudy, rainy days to run the generator too.

[Wy_White_Wolf]

What happens if you have a cloudy day with a small battery bank? The bank needs to be sized to carry the full load when the sun don't shine.

WWW

[paulcheung]

I use generator and grid power when I have rainy or long cloudy day. I only have one day battery can discharge to 25 to 30% DOD.

[AJK]

What happens if you have a cloudy day with a small battery bank? The bank needs to be sized to carry the full load when the sun don't shine.

WWW

Basically, most of the days in a year are sunny and few days like 30 to 45 days in a year are cloudy and also our inverter is capable to do 3 actions like when the solar power is available the controller will charge battery, if grid is available it will supply to the battery and as well as to the load, if both are not then the battery will supply power to the load.

Here my concern is all about the charging of battery, is it happening that when the sunlight fully charged the battery and then load starts taking power from the battery, what happen at this time in the solar charging, will the charge controller still allows solar panels to charge the batteries if the sun is available and at the same time the load is taking power also from the battery or just only one process works?

AJK

[AJK]

Basically, most of the days in a year are sunny and few days like 30 to 45 days in a year are cloudy and also our inverter is capable to do 3 actions like when the solar power is available the controller will charge battery, if grid is available it will supply to the battery and as well as to the load, if both are not then the battery will supply power to the load.

Here my concern is all about the charging of battery, is it happening that when the sunlight fully charged the battery and then load starts taking power from the battery, what happen at this time in the solar charging, will the charge controller still allows solar panels to charge the batteries if the sun is available and at the same time the load is taking power also from the battery or just only one process works?

[russ]

I use generator and grid power when I have rainy or long cloudy day. I only have one day battery can discharge to 25 to 30% DOD.

When you have grid power why in the world are you playing with batteries?

[AJK]

When you have grid power why in the world are you playing with batteries?

There are many places in the world where there is a load shedding of 12 hrs to 18 hrs and people are now going towards alternate solutions because of the unavailability of grid power for the last 10 years

[russ]

I worked in India for many years - same problem for most people.

Charging batteries off the grid may be practical - cheaper and easier than solar by far

[AJK]

It is right that the UPS system is the cheaper option but in those areas where the load shedding timing is not too big like more than 10 hours. Here one other problem also exit and that is the voltage supply, the grid supply which exist, most of the time it is under rated due to which most of the inverters deteriorate and its lifetime reduces. Here due to this problem these UPS types are also now loosing its popularity.

[Mike90250]

If you have grid, then a robust, hybrid inverter with internal battery charger, is the way to go, and only have a small solar array. The grid, even when not in spec, will still be used to charge batteries. With the XW inverter like I use, it will accept input voltage from 80-150VAC and use that to charge batteries, much faster than a solar array can.

[paulcheung]

When you have grid power why in the world are you playing with batteries?

Because we are paying 45 to 65 US cents per kwh and the rate are going up on June this year again for 20% more, also we don't have net metering policy. With off grid setup I will be forced to conserve and behave my self for energy consumption.

[russ]

Because we are paying 45 to 65 US cents per kwh and the rate are going up on June this year again for 20% more, also we don't have net metering policy. With off grid setup I will be forced to conserve and behave my self for energy consumption.

Pakistan doesn't have those kind of power costs. You really need to learn where all that money goes - politicians stealing it?

[paulcheung]

I am not sure if Jamaican Government is the only one in the plant Earth Tax electricity. WE have 16.5% general consumption tax on business electricity include factories shops and plant. and they complain we can't get investor come to Jamaica. WE only have one power company in the island and a lot of people can't afford the electricity so they steal it. So the power company have to make profit. you know the answer.

[paulcheung]

The funny thing is the one of the reason for June this year rate increase is a lot of their good customer (the power company customers) are going off grid, for them to stay in business they have to increase the rate. Talking about Monopoly!!. Well thank GOD we have sun shine in Jamaica and no Winter!