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Battery Controller Unit

adfu

Aug 17, 2016
3
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Aug 17, 2016
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Hi!

I have a rather basic questions that I am trying to figure out for a (so far) purely theoretical project, but can't seem to find the answer to.

Imagine the following basic setup made up of four components:
A household that uses electricity, is connected to the grid, with a photovoltaic system on the roof of the house and an electricity storage unit (Li-Ion Battery) in the basement.
If a simple switch is used in front of the battery, this system allows for some basic energy management:
- When the PV system produces more than the household uses, surplus energy is either stored in the battery (relay on) or sold to the grid (relay off).
- When the PV system produces less than the household uses, energy stored in the battery is released to the household (relay on) or bought from the grid (relay off).

This is not, however, a satisfactory solution as there are many cases that are not covered by this simple setup. As an example let's assume that for some reason electricity prices are high at noon, when the PV system is producing a lot. There might still be energy stored in the battery from previous sunny days, and we might want to sell this stored energy at the same time as the PV system produces more than the household uses. This would require a way to have a controller on the battery that can actively 'pump' electricity out of the battery (one could easily think of a situations when it would be desirable to actively 'pump' electricity into the battery as well).

What kind of device would be required to control a battery in such a flexible way?

Thank you all in advance and please excuse any apparent silliness in my question.
 

oz93666

Dec 7, 2014
38
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Dec 7, 2014
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It's definitely not sensible to transfer electricity from a battery to the grid, the 'cost damage' to the battery would mean you loose ....

Batteries have a life span of about 500 cycles , so you can completely charge and discharge 500 times before a new battery is needed ....very expensive., and a battery doesn't hold much power ...and there are also loses in charging, and passing through the inverter.

Most PV(photo voltaic) systems that have a reliable grid (few power outages) , don't use expensive batteries , but transfer power , via a 'grid tie inverter' to the grid.

Better to think in terms of storing cold.... when electricity is cheap run freezers, fridges ... they can be off half the day and still stay fairly cold inside , also run washing machines when electricity is cheap.

If batteries are involved in a PV system you're electricity will cost more than from the grid power company , you only use batteries if the grid is unreliable/non existent.

Lithium batteries are most efficient (and most expensive), every 1KwHr you put it you get 0.85KwHr out

Lead acid efficiencies are about 70% if you put in 1KwHr , only 0.7KwHr comes out.
 
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adfu

Aug 17, 2016
3
Joined
Aug 17, 2016
Messages
3
Ok, thank you very much! So it is basically a bad idea to set something like that up.
But technically, what device would be needed? Does it even exist?
Say I'd like to throw away some money (i.e. ignoring economical feasibility) and would hook a battery to the grid. What device would I need to actively charge and uncharge the battery at my will?
 

oz93666

Dec 7, 2014
38
Joined
Dec 7, 2014
Messages
38
Ok, thank you very much! So it is basically a bad idea to set something like that up.
But technically, what device would be needed? Does it even exist?
Say I'd like to throw away some money (i.e. ignoring economical feasibility) and would hook a battery to the grid. What device would I need to actively charge and uncharge the battery at my will?

Not easy to answer because of the added complication of inverters ....there are two types , normal and 'grid tie' .

If running a house direct from solar panels(via batteries) you need a normal inverter...

If you want to sell power to the grid you need a 'grid tie' inverter... not sensible to buy two different inverter set ups .
What you want can be done with timers relays etc. .... but I think you need to be clear about what it is you want to achieve.
 

adfu

Aug 17, 2016
3
Joined
Aug 17, 2016
Messages
3
Thanks! Basically, I would like to be able to (remotely) control the current to and from the grid of this setup at any given time (Until the battery is either fully loaded or empty, at which point this flexibility would obviously be lost). The setup should then adjust accordingly by charging or uncharging the battery.
How would I be able to achieve this with Time Delay Relays?
 
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