Using batteries to lower the load peaks without solar/wind energy?

[Delly]

Hi Martin

I'm currently a university student working on a research project for company. The purpose of the project is to find a way to help reduce the load peaks or averaging the load throughout the day in winter seasons. Since where I live is very north in this universe (Norway) there is a lot of snow.  Now I don't have much experience or knowledge compared to others about PV, but from what I've read and gathered there is almost no point in installing these here. The electricity price here varies a lot from day to night in winter. Generally more load = higher electricity price.

Since solar energy is kind of useless (not sure how wind turbines work in snowy weather) the idea that I've been given to research is to store the energy during low load, mostly during the night, through the main grid and then use the stored energy to push down the load peaks during the day. I've hoped that one of your videos could explain how this could be done, but so far I haven't seen any.

My idea so far is like this:
main grid -> inverter -> *(solar/wind ->) charge controller -> batteries -> inverter (same or new, not sure what's best/possible yet) -> main grid.

* The government is planning to install AMS (advanced measuring instrument) in all the houses before 2020 and they are considering the "sell back" option as well. Therefor there should be the possibility to install solar panels and or wind turbines for those who wish to do so, even though it is quite rare here.

Does this sound reasonable, and are there smarter ways to do this?

Thanks in advance!

[SeanB]

Battery charger direct to the battery bank, and an inverter to feed the house load. That way you only have to have a timer to connect the charger to mains when cost is low, then turn it off when power prices are high ( or a half hour after the low point and a half hour before the high point to account for clock drift in either system). Then you decide what loads you will power from the inverter side and have it running all the time to power the house side. That will shave demand peaks but then you will definitely need to look at your energy budget so that the battery bank is going to be discharged no more than say 10-20% during the largest period it has to supply power, and size the charger so that it can handle both the charge current of the battery and the load side demand via the inverter. If you are charging at night then the current demand will likely be less as there will be little load, so the charger does not have to be capable of doing both at full current at the same time, it just has to keep the battery at float voltage with the draw but still charge it.

Martin did have something similar in his house in SA, as the solar arrays charged a battery bank during the day and drew at night from it, you would be doing something similar, but with a simple battery charger ( transformer, rectifier and voltage stabilisation by some means along with current limiting with a time switch to turn it on and off) in place of the solar panels.

[Delly]

Thank you for your answer.

I'm not sure how your solution will work. From what I know I can't connect the main grid directly to the battery charger (I assume here it is a different name for a charge controller) and then from the battery charger to the battery? I must have an inverter to convert from 230V to e.g. 24V or 48V, isn't that correct? I'm the system is able to reduce the peaks by 20-25% then I think that is sufficient for a good time.  I've seen and heard of many DC/AC inverters on forums and youtube, but haven't seen any AC/DC inverters or perhaps an inverter with both ways. Are there any good and cheap brands out there?


The timer is it's own project since they want to remote control the charging/discharging. I guess it is the utility company which will be the guys controlling it. In this case I'm considering GSM, z-wave and ZigBee. There is also the possibility to remote control it through the AMS based on price  and/or time (only utility company can do that a far as I know).

Also Martin, in your video how to solar power your home #1, you explain the on/off grid systems. There you say you have a system which your power goes from the PV through the GT and to main grid. The excess power goes to you batteries. The thing is, the way you have drawn the system, the excess power goes through the inverter and then to the batteries. Then from that thought the inverter, again, and to the main grid. That means you energy goes through 4 components before it reaches the main grid. Isn't that more insufficient than going through the CC, battery and inverter (only 3 components)? I also dont understand why you would want to convert the power twice when the power goes from PV to the batteries as you stated. @ 13:00 http://www.youtube.com/watch?v=bzcTFUcXwIY&feature=c4-overview&playnext=1&list=TLQcHrx3Mm4MU

[MJLorton]

Also Martin, in your video how to solar power your home #1, you explain the on/off grid systems. There you say you have a system which your power goes from the PV through the GT and to main grid. The excess power goes to you batteries. The thing is, the way you have drawn the system, the excess power goes through the inverter and then to the batteries. Then from that thought the inverter, again, and to the main grid. That means you energy goes through 4 components before it reaches the main grid. Isn't that more insufficient than going through the CC, battery and inverter (only 3 components)? I also dont understand why you would want to convert the power twice when the power goes from PV to the batteries as you stated. @ 13:00 http://www.youtube.com/watch?v=bzcTFUcXwIY&feature=c4-overview&playnext=1&list=TLQcHrx3Mm4MU

I understand your concerns but the power comes through the grid tie inverter (GT) and then through the main inverter to charge the batteries. Then at night it goes back through the main inverter to feed the house...that's 3 components not 4.

There is another scenario that I elude to in a later video that I have not yet mentioned that can add efficiency in certain situations.

If your house does not use much AC load during the day and you want the energy stored for night time use then a charge controller would be better than the grid tie inverter. So instead of going PV -> DC -> GT -> AC -> INV -> DC to charge battery...you go PV -> DC -> CC -> DC charge battery.

Hope that makes sense.

Cheers,
martin.

[Delly]

Also Martin, in your video how to solar power your home #1, you explain the on/off grid systems. There you say you have a system which your power goes from the PV through the GT and to main grid. The excess power goes to you batteries. The thing is, the way you have drawn the system, the excess power goes through the inverter and then to the batteries. Then from that thought the inverter, again, and to the main grid. That means you energy goes through 4 components before it reaches the main grid. Isn't that more insufficient than going through the CC, battery and inverter (only 3 components)? I also dont understand why you would want to convert the power twice when the power goes from PV to the batteries as you stated. @ 13:00 http://www.youtube.com/watch?v=bzcTFUcXwIY&feature=c4-overview&playnext=1&list=TLQcHrx3Mm4MU

I understand your concerns but the power comes through the grid tie inverter (GT) and then through the main inverter to charge the batteries. Then at night it goes back through the main inverter to feed the house...that's 3 components not 4.

There is another scenario that I elude to in a later video that I have not yet mentioned that can add efficiency in certain situations.

If your house does not use much AC load during the day and you want the energy stored for night time use then a charge controller would be better than the grid tie inverter. So instead of going PV -> DC -> GT -> AC -> INV -> DC to charge battery...you go PV -> DC -> CC -> DC charge battery.

Hope that makes sense.

Cheers,
martin.

Hello Martin

I'm sorry, but to me, that doesn't make sense at all. As you're saying:

"the power comes through the grid tie inverter (GT)" = 1 component
"and then through the main inverter" = 1 component
"to charge the batteries" = 1 component
"Then at night it goes back through the main inverter to feed the house." = 1 component

That equals to 4 joints. Using cc on the other hand, the power goes through  only 3 components. CC = 1, batteries = 1, main inverter = 1.

Also, I can't seem to understand why would you want to convert from DC to AC then to DC just to store the power in the batteries. Wouldn't it be better to go from PV to CC to Battery, then from Battery to INV to main grid?

For the prototype system that I'm researching I've decided that i need 500wh for 2 hours which equals to 1kwh/h -> 1kw.
So in a 24V system I would need 1000/24 = ~42Ah.

Taking into account 80% battery efficiency and 50% discharge I get 105Ah.
24*105 = 2520
Charging time @ night = 7.5 hrs
This means i need: 2520/7.5 = 336Wh.

I would be very thankful if someone could guide/tell what sort of inverter/CC I would need for the system above.

PS. I've heard that it is possible to use (super)capacitor instead of batteries. Anyone knows/heard of this. It uses farad instead of ampere so i don't know how to proceed with the calculations.

[MJLorton]

Ok..so my mistake for not counting the battery as a component so yes..it is 4. Using a charge controller does use less components if you primary goal is to store energy in the batteries for later use.

However, as the main load (in our case) is the house grid during the day it does not make sense to go from PV -> CC -> INV / BAT -> House. Rather PV -> GT -> House.

I'm also interested in storing energy in super / hybrid capacitors...but at the moment the cost and energy density does not make it viable for the general public. The best efficient (mainsteam) storage at this point in time is lithium iron phosphate batteries (LiFePO 4).

I have posted a spreadsheet you might want to try size your system and highlight any issues you might find.
http://mjlorton.com/forum/index.php?topic=239.msg2883#msg2883

Cheers,
Martin.

[Delly]

Ah, ok. Well now I understand, thanks for the help.

How good do the LiFePo4 do against a deep cycle battery like lets say trojans? Also, if I remember correctly, you said in your video that you used led crystal batteries. Are they good? I'm mostly concerned about life span vs price.

Greetings
Delly

Edit: Let's say I chose this solution. Would it be best to choose MPPT, PWM charge controller or a regular 3 step battery charger? Choosing the regular battery charger I could skip the inverter from AC to DC since they have built in inverters.

[MJLorton]

Hi Delly,

Sorry I missed your reply so this is a little delayed.

The  LiFePo4 batteries should provide many more cycles than traditional deep cycle batteries...however...if they are mistreated (under / overcharged) they could be damaged very quickly.

Lead crystal apparently have a lower internal resistance than traditional deep cycle batteries and from my testing (and manufacturer claims)  are very robust if mistreated. They claim more cycles too...but I've not had enough time to evaluate that...it's some future testing I have planned.

At the moment if you can afford  LiFePo4 and have the correct charge controller...it's the way to go.

Whatever your setup is, you want to use MPPT...MPPT is not directly related to battery charging. It's an efficient way of getting the maximum power from the solar panels.

Cheers.