Battery bank capacity

[David HK]

Can you help?

I am planning a battery bank to receive power from a wind turbine and solar panels. The system is planned to be 12 volts at the moment.

My electricity bill is sent bi-monthly and the breakdown is as follows:-

Kilowatts billed        Rate        Cost

400.             $0.862        $344.80
     
600.             $0.932        $559.20
     
800.             $0.996        $796.80
     
784.             $1.082        $848.29
     
     

I do not intend to go off the grid but I would like to generate enough renewable energy to offset (replace) the last two figures in the bill 800 + 784 + 1,564 Kilowatts over 61 days. This averages 25.63 Kilowatts per day.

I may not have supplied sufficient information but could any of you clever people on the board have a stab at working out what sizecapacity of battery bank would be required plus a 10 or 20% spare margin.

If you need more information please let me know what is required.

Thank you

David HK

[wpowokal]

David it's too big an ask for a 12v system it's somewhere like 550 amps / hour for full 24 hours.

allan down under

[wpowokal]

I have an Excell spread sheet which is interactive for all system paramiters, but I have no idea how to make it available other than 'e' mail.

allan

[David HK]

Alan down under.

Well at least thats a helpful contribution and I am grateful. So can I crank up the voltage to 24 or even 48 volts?

My e-mail is strltdATnetvigatorDOTcom

Change the obvious if you wish to send me the Excel file. I am sure I would find it useful.

Well done!

David HK

[David HK]

Amps =     Watts ÷ Volts

Let me see if this is how it works

26 Kilowatts = 26,000 Watts

Therefore:-

26. ,000Watts ÷ 12 volts = 2,166 Amps    Divide by 24 hours =  90.25 Amps per hour
    
26. ,000Watts ÷ 24 volts = 1,083 Amps     Divide by 24 hours =   7.62 Amps per hour
    
26. ,000Watts ÷ 48 volts = 541 Amps      Divide by 24 hours = 22.5  Amps per hour
    
    

I have looked at these figures and they seem quite impressive!

Perhaps someone could forge on with the battery aspect.

Am I going around the twist?

David HK

[David HK]

Sorry, a correction in the mathematics.

B   26,000Watts ÷ 24 volts = 1,083 Amps     Divide by 24 hours =  45.12 Amps per hour

David HK

[Darren73]

David,

check your tariff information, if it's the same as mine the more expensive rates apply first, so any reduction in usage will come off the lowest rate first, i.e. the savings will not be as great as they first appear. The other reason for the multiple rates could be a change in tariff part way through the bill, that happened to me this time around with gas and electricity prices going up.

regards

Darren

[David HK]

Darren,

Thank you for the interesting prompt. Yes, I will follow up your suggestion tomorrow and let you know the outcome.

David HK

[wpowokal]

Yea but add in losses, etc and the margin you suggested, anyway look at the spread sheet it allows you to interperate all this info.

allan

[Nando]

David:

Is the KWH cost in USA dollars ?.

If the cost of the energy is so high in Hong Kong, then a good energy management is due, to reduce the KWH usage.

Greater the voltage easier to work the energy.

48 or 108-120 volts battery bank may be a good solution.

With 48 volts You may be able to get DC/AC inverters to supply the AC power and using MSW ( Modified Sine Wave) inverters the price would be lower, though some electrical equipment may not operate well.

You need to determine what loads You have ON and at the same time and for how long, to give an idea of the power of the inverter.

There are a few DC/AC inverters that work with 108 Volts.

Nando

[David HK]

Nando,

As always your contribution is most welcome. There are some good chaps in this forum and my little question is turning out to be very intersting.

Yes the costs are in Hong Kong dollars - NOT American dollars than goodness. I believe I could easily work a 48 volt system but, after that, I am doubtful since higher voltage RE systems seem to be rarely discussed in the forum.

This is all good stuff, lets see how it all turns out.

Thanks to all.

David HK

[wdyasq]

1 Hong Kong dollars = 0.128594208 U.S. dollars

In North Central Texas I'm paying about $0.15kWh. I am told this is the highest rate in the US. The politicians de-regulated the utilities to "Lower the rate the consumer paid for electricity".

Ron

[dinges]

I'm sure I'm telling you nothing new, as you're a regular contributor on this board.

But, the most important thing to do first, before investing in an RE system, is reducing your power consumption. 25kWhr/day is a lot. I use less than half that, and even that is a lot for an RE system.

If this old hat to you, then just ignore it (maybe you've already reduced your power consumption down to 25kWhr/day, who knows?  ). But it was a remark I felt needed to be made.

[Nando]

David:

48 volts is a "forced" standard by many in the industry, because a relationship of watt hours storage time, and cost of the multiple battery banks, as well as, the concept that higher voltage is EXTREMELY dangerous.

Most of the forum grows out of people "crying" for help that many times have electrical power knowledge limitations, I have not searched for other forums to see if there are some for 24 / 48 / higher volts, there is one for 12 volts that I visit more or less periodically to see what is going on, 12VDC_Power@yahoogroups.com .

Higher voltage is ideal to get higher efficiencies, better inverters, over all reduction of the wire sizing, specially now days that the copper has increased its value due to the the great demand of it.

You really scared me with the dollars you input -- and for some time, I said WHAT is going on with that power source, then I discovered you were in Hon Kong, and a very heavy weight came Off -- then I was able to move my body.!!

I do not know the relationship of energy and income there, to see what would be a good way to develop a system with a good ROI (return on investment).

Energy reduction is the issue here and if You have a place for a wind mill and/or Solar Panels, then a solution for the battery voltage depends on the distance between the sources and the battery banks as well as where the loads are and how the energy requirements are.

I have, always, assumed that 12 Volts is for emergency use, of course there are the die hards that say 12 Volts period .. !!!!! and the system is a total compromise with constant miseries ( many times ) for those that really do not have a good electrical know how.

24. volts is, for me, still a compromise that came from the 1890's with the wind mills in USA that run 24, or 36 volts and a few 48 volts, as well as, the small 24, 36 or 48 volts gas generators --- which have permeate up to this these present 2006+ years.
    
48. volts,from my point of view, would be the minimum to use -- though I have made 120 volts battery banks, because in the countries that use 120 AC GRID power there are too many electrical products that can use 120 Volts DC, in case the inverter fails.
    
    

I have designed a very in-expensive MSW inverter using 120 volts battery bank, capable of many Kilo Watts that is very easy to build, and my circuit has protection included, (there is one that does not have such protection, that the plans are sold in Ebay for around USA 40-50 dollars -- I have been unable to find it in Ebay).

Maybe, You could include some other parameters You may have, like the place where you can install your Mill and/or the panels, the distance to the battery bank and loads, and what type of loads you have, and their use.

Regards

Nando

[The Crazy Noob]

Do you want to share the circuit with us please?

[veewee77]

I have an online calculator that will figure this for you.

I ran your numbers through it and got the following:

This is figured with a 360amp-hour, 6V battery.

12V (nom) solar panels at 10 amps each (120W)

Are you sitting down?

This calculator already has built-in losses in inverters, charging losses and discharge losses.

Keep in mind that this calculation was based on your daily average watt-hours.

Conservation is the FIRST thing you need to learn to do before even considering trying to make up the power with alternative resources.

(results from the calculator are below)

The total Watt-Hours average used per day is 25630. (25.63KWH)

Based on data acquired on the preceeding pages, this system is sized for a maximum of 1 days with little or no sunsine, cloudy, or overcast.

The batteries are less efficient the colder they are so there is a battery efficiency factor of 1.11 figured into the capacity of the batteries which will change based on the temperature where the batteries will be stored in the wintertime.

The batteries chosen have an Amp-Hour rating of 360 and a Voltage rating of 6 and it takes 2 of the selected battery to add up to the DC System Voltage of 12 Volts.

Solar Panels convert sunlight to electricity and the chosen Solar Panels for this system have a Voltage Rating of 12 and Peak Optimum Amp Rating of 10.00.

It takes 1 of the selected Solar Panels to add up to the DC System Voltage of 12 Volts.

4.2 is the average Sun-Hours per day as entered on the preceeding page.

Given all these factors, the System being calculated based on this information is described as follows:

Solar Panels Required: 62

Batteries Required: 12

(end of results)

If you want to play with the calculator, visit:

http://dsjscrd.gotdns.com/calc

If you want to run the numbers yourself, go to that site and just scroll to the bottom and click Study It! and that will take you to the second page, click Calculate on the top one of the two and then it will take you to the page that requests information about batteries and panels and etc. Enter the projected watt-hours (not KWH) per day at the top of that page and follow the rest of the information to calculate for yourself. If you had already filled in the first page, the watt-hours would have already been there for you.

In order for the bottom of the two to calculate properly, you have to complete the first page so it can calculate everything correctly, and even then, the conservative calculations are just an estimate at best and for reference only.

Doug

P.S. I found an error while looking at this. . . this set of parameters will allow a 50% drawdown on the batteries. . . It is supposed to figure no more than 80% (80% remaining) so I have to go look at the math, but you get the idea.

[veewee77]

Also, I should have noted, for a system of that capacity, go to 48V. You will be much more happy with it!

Following is the same calculations using a 48V system.

(calculation results for 48V system), 24Volt panels at 5A each (120W)and a 360AH battery at 6V.

The total Watt-Hours average used per day is 25360.

Based on data acquired on the preceeding pages, this system is sized for a maximum of 1 days with little or no sunsine, cloudy, or overcast.

The batteries are less efficient the colder they are so there is a battery efficiency factor of 1.11 figured into the capacity of the batteries which will change based on the temperature where the batteries will be stored in the wintertime.

The batteries chosen have an Amp-Hour rating of 360 and a Voltage rating of 6 and it takes 8 of the selected battery to add up to the DC System Voltage of 48 Volts.

Solar Panels convert sunlight to electricity and the chosen Solar Panels for this system have a Voltage Rating of 24 and Peak Optimum Amp Rating of 5.00.

It takes 2 of the selected Solar Panels to add up to the DC System Voltage of 48 Volts.

4.2 is the average Sun-Hours per day as entered on the preceeding page.

Given all these factors, the System being calculated based on this information is described as follows:

Solar Panels Required: 62

Batteries Required: 16

I know this uses more batteries, however it calculates the batteries based on how many it takes to make the nominal system voltage and rounds the actual battery count up to the next multiple.

Example if the system is 48V, that is 8 batteries.  If your system beeds 9 batteries, it rounds up to 16 because it takes two sets of 8 to make enough to cover 9 batteries.

Hope this all helps!

Doug

[veewee77]

Yup, my calculator got the same 22 amps per hour (or close) so it is working pretty good. . .

Doug

[electrak]

Got you beat, $.165 in Maine, about $.085 to make it and $.08 to deliver it.  I can run my diesel genny for about $.20 plus upkeep to make all the power I need, just need to get it hooked up. But I only use about 6kwh a day with electrons heating the water. So as soon as I can scronge up some exchangers the diesel should heat the water good too.

Dave

[David HK]

Gentlemen,

Thank you very much indeed for your comments, they are most welcome and a great eye opener.

My next step will be to visit the Head Office of China Light and Power to ascertain the order of their billing costs - cheapest leading to expensive, or, expensive leading to cheapest. This will be an important influence on planning.

Whichever way it goes, it looks as if a 48 volts system will be a yardstick to follow.

I take the point that energy reduction and conservation is a good starter so that's another area destined for a fresh look.

After living in Hong Kong for 36 years I can say that the place is getting warmer/hotter and this has become more noticable in recent years.

The biggest power monsters in my home are air conditioners, although when I came to Hong Kong in 1969 these were only in the homes of the rich and everybody else used oscillating pedestal fans. Such is progress!

After chewing over the above I will probably start a new forum entry because this one is getting rather long.

David HK

[BigBreaker]

I pay $0.22/kWh in Manhattan, so I have you beat by a mile.  The funny thing is that New York is next to Ontario and they pay $0.03-0.04/kWh.  It just doesn't make sense.