Jump to content

Cost per kw/h


Johny London

Featured Posts

I've been working on a formula for this... (In blue are my own figures)

 

Cost of fuel burned in 1 hr                 Engine service costs                                                           Engine wear and tear                       Running cost per hour         

(litres x price per litre)         +      (oil, filter, air filter, gearbox oil in £s / Service interval in hours)  +  (cost of engine in £'s / total hours ) 

         1x0.85      = 85p         +      (80 / 200)  = 40p                                                                         +  (5000 / 10000)   = 50p                     =           £1.75 

 

Then...

 

Ah generated (stored/used) in 1 hr                          Running cost per hour          Cost per Ah    (1000w/12v to get Ah per kw/h)

              10 (estimated average in my case) *     /                     £1.75                               17.5p     x         80                                             =      £14 kw/h

 

I'm not terribly good at formulas, infact this really is stretching my grade 4 cse maths, doubtless someone can correct/improve or tidy the whole thing up. I'm a bit surprised at the final figure - thought it would be around £2.

I suppose my point being, if you can increase what can be stored in a given time (ie with lithium batteries) then costs come tumbling down, so the lithiums would earn their keep much faster than some people think.

 

* but so often its more like half that!

Edited by Johny London
Link to comment
Share on other sites

That looks about right given your various assumptions - the only pedantic point is that the result is £14 per kWh, not £14 per kW/h.  You could increase the efficiency via a alternator controller of some sort, and obviously the cost comes down a lot if you are using the boat to move from A to B (where the extra diesel consumption for running the alternator is pretty minimal).

Link to comment
Share on other sites

Yup, I worked out something like this a fair few years ago. A big variable is the cost of the engine, do you include the labour costs for fitting it?, and also the labour costs for servicing? (even though you might be giving your own time for free?).

 

If you're running a big diesel using a litre an hour then it makes sense to have a bigger battery bank and bigger alternators. When I do a 2 hour engine run I would start charging at about 120 amps, and this might fall to 30 or 40 by the end, so an average of almost 80 rather than your 10. I do then have the extra cost of a long run once every two weeks or so when I spend some time only putting in 6 to 10 amps. My higher current brings your £14 down to about £2. I am also generating more electricity via the 240 Travelpower to drive the washing machine, and the engine is heating the back of the boat. I'm also irritating a few people who don't like the sound of boat engines and that's priceless ?

 

But Mr Gypsy is spot on, go boating!  All the "overhead" of just "rotating" the engine is then allocated to the boating budget and only a little bit of extra fuel is then used to generate the electricity.

 

..............Dave

Link to comment
Share on other sites

24 minutes ago, Johny London said:

I'm not terribly good at formulas, infact this really is stretching my grade 4 cse maths, doubtless someone can correct/improve or tidy the whole thing up. I'm a bit surprised at the final figure - thought it would be around £2.

I suppose my point being, if you can increase what can be stored in a given time (ie with lithium batteries) then costs come tumbling down, so the lithiums would earn their keep much faster than some people think.

 

I think your point is bang on despite the minor error in units. 

 

The rapid charging of lithiums is invaluable in more ways than money, too. The reduced time running one's engine is brilliant (unless one has a Whispergen, obvs ;) ) 

 

Lead carbon batts seem to have all the same advantages as far as I can tell, for half the price of lithiums and without the need for complex controls to 'protect' them

3 minutes ago, dmr said:

I do then have the extra cost of a long run once every two weeks or so when I spend some time only putting in 6 to 10 amps.

 

This could be substantially mitigated by splitting your 6 Trojans into two separate banks, as discussed in detail in another thread recently.

 

 

 

Oh hang on, I see a flaw in this!!

Link to comment
Share on other sites

Phew - was a bit worried posting that incase I'd made a massive blooper - I'd been working on it for some time. Just heard about the lead carbons on another thread and looked them up - the claims are good, but then so are they when you read the ads for just about any leisure battery. I suppose also the case with Lithiums.

In my case my batteries are knackered, so the figures are particularly bad for LA's but I see no point in replacing like for like as I know full well in 6 weeks I'll be back to the same situation.

I'm using a little genny now, and it "feels" a lot better not to be putting the hours on the engine, but I keep thinking that when I have finally pushed a few amps into those stubborn old lumps, I could have stored SO much more power if I had something that would just accept the current.

Link to comment
Share on other sites

I came across an interesting chart for the cycle life of a Lead Carbon battery. Although you can take them down to 60% DoD without too much reduction, the curve still tends to fall off a cliff below 50%. 

A9385588-347D-4404-B5B2-88222A3A05D4.jpeg.b0ed44c789716ab959c5306e6910d612.jpeg

Link to comment
Share on other sites

1 minute ago, WotEver said:

I came across an interesting chart for the cycle life of a Lead Carbon battery. Although you can take them down to 60% DoD without too much reduction, the curve still tends to fall off a cliff below 50%. 

A9385588-347D-4404-B5B2-88222A3A05D4.jpeg.b0ed44c789716ab959c5306e6910d612.jpeg

 

 

Indeed. 1,600 cycles at 100% DoD. PATHETIC.

 

Remind me of how many cycles a similarly priced Trojan is good for at 100% DoD every cycle....

Link to comment
Share on other sites

35 minutes ago, Mike the Boilerman said:

 

 

Indeed. 1,600 cycles at 100% DoD. PATHETIC.

 

Remind me of how many cycles a similarly priced Trojan is good for at 100% DoD every cycle....

500 cycles at 100%, but I don't know if the price is similar.

WotEver....what carbon batteries are these? can I have a www link please?

As for falling off a cliff at 50%   interesting!   If we replot this data in the more conventional manner (cycles on the vertical axis) then the falling off the cliff is no longer visible. Data presentation is a very interesting subject, something I used to work with quite a bit.  I believe Nick Norman did a spreadsheet to show there is NO 50% cliff, if you have half the discharge you get twice the cycles etc so the total amp hours over the battery life is pretty much independent of DoD.

 

..........Dave

Link to comment
Share on other sites

Here is my graph of cycle life vs DoD for various batteries, taken from data sheets on the www.

The lithium is a bit rough as there are not many points on the curve.

All battery types appear to follow the same basic shape but this might be because everybody uses the same equation to estimate cycle life from only one or two measurements?????

Note that nothing special happens at 50%.

 

Lead carbons look too good to be true, and we know what they say about that.......

 

.........Dave

 

 

Cycle Life.png

Link to comment
Share on other sites

3 minutes ago, dmr said:

Lead carbons look too good to be true, and we know what they say about that.......

 

 

I thought the same about BTL in 1995 and held back, then finally went for it big time in 1997.

 

Prolly cost myself, well, I expect you can work that out.....

Link to comment
Share on other sites

Victron/Battery Megastore (on eBay) say this:

 

Item description

Victron Energy. 106Ah C20 (10,8V). Tests have shown that our lead-carbon batteries do withstand at least five hundred 100% DoD cycles. (Several manufacturers of lead-carbon batteries claim a cycle life of up to two thousand 90% DoD cycles. ).
 
.............Dave
Link to comment
Share on other sites

4 minutes ago, dmr said:

Victron/Battery Megastore (on eBay) say this:

 

Item description

Victron Energy. 106Ah C20 (10,8V). Tests have shown that our lead-carbon batteries do withstand at least five hundred 100% DoD cycles. (Several manufacturers of lead-carbon batteries claim a cycle life of up to two thousand 90% DoD cycles. ).
 
.............Dave

 

Investment in these seems to be similar to s/h lithiums, but without the risk of farking them up or expense of the protection and bms electronics. 

 

On the other hand there is a much higher risk of as you say, "if its too good to be true...."

 

 

Link to comment
Share on other sites

46 minutes ago, dmr said:

the total amp hours over the battery life is pretty much independent of DoD.

Yes, I thought that was pretty well known. But only as long as you keep within the design parameters of course. Take some starter batteries down to 100% DoD just once and you’ll have pretty much killed them. A total of 100Ah life. 

Edited by WotEver
Link to comment
Share on other sites

1 hour ago, Mike the Boilerman said:

Indeed. 1,600 cycles at 100% DoD. PATHETIC.

Where did I say it was pathetic?  Halving the cycle life by discharging to 80% as opposed to 50% is pretty much falling off a cliff. I’d much rather have 4000 cycles than 1600. 

Link to comment
Share on other sites

13 minutes ago, Mike the Boilerman said:

 

Investment in these seems to be similar to s/h lithiums, but without the risk of farking them up or expense of the protection and bms electronics. 

 

On the other hand there is a much higher risk of as you say, "if its too good to be true...."

 

 

 

Have just wasted a bit more time on the www learning about these things. They do look pretty good and are based on good scientific thinking. Disadvantage appears to be a bigger voltage reduction as they discharge. Not many people making them yet so maybe prices will fall when there is a bit more competition. I suspect the specs might be a bit over optimistic, but for anybody thinking of lithiums I would suggest to wait a year and see how these lead carbons evolve.

 

................Dave

Link to comment
Share on other sites

54 minutes ago, dmr said:

WotEver....what carbon batteries are these? can I have a www link please?

Narada, I believe: 

http://en.naradapower.com/index.php/products/info/14?ctype=46

I came across that cycle life graph here: https://www.geekzone.co.nz/forums.asp?forumid=141&topicid=225720

Edited by WotEver
Link to comment
Share on other sites

 

An interesting comment made in one of the posts in that latter forum: “Because of the nature of her business the existing lead acid bank had been subject to partial cycling and sulfation.” which makes me wonder exactly how resistant to sulphation they actually are. 

Link to comment
Share on other sites

4 minutes ago, WotEver said:

 

An interesting comment made in one of the posts in that latter forum: “Because of the nature of her business the existing lead acid bank had been subject to partial cycling and sulfation.” which makes me wonder exactly how resistant to sulphation they actually are. 

 

 

I suspect the same, but I might yet put some money up to find out for sure. 

 

I'm constantly recalculating the risk Vs reward in my head, and it changes substantially every time.

 

 

 

 

Link to comment
Share on other sites

5 minutes ago, Mike the Boilerman said:

I'm constantly recalculating the risk Vs reward in my head, and it changes substantially every time.

As I see it, the only unknown is this mysterious ‘resistance to sulphation’. If it’s only a minor improvement over standard lead calcium then you’ll still have a problem if you can’t fully charge them daily despite their fast recharge characteristics. 

Link to comment
Share on other sites

The Leoch Lead Carbon is an AGM. I don't know much about these, so how much of the improved performance is from the carbon and how much from the AGM?

The link from WotEver is to sealed batteries of some sort. So in both cases if we do get sulphation how do we fix it if we can't equalise?

And I keep seeing mention of thin plates which sort of goes against everything we believe in.

 

Hopefully mtb is going to be the forum ginny piggy

 

..........Dave

Link to comment
Share on other sites

Read this:

 

https://www.victronenergy.com/upload/documents/Datasheet-Lead-carbon-battery-EN.pdf

 

I sort of trust Victron. I note that their cycles vs DoD figures are just about identical to a standard Trojan, and they are not exactly boating about the sulphation performance either.

 

.............Dave

Link to comment
Share on other sites

10 hours ago, dmr said:

The Leoch Lead Carbon is an AGM. I don't know much about these, so how much of the improved performance is from the carbon and how much from the AGM?

The link from WotEver is to sealed batteries of some sort. So in both cases if we do get sulphation how do we fix it if we can't equalise?

And I keep seeing mention of thin plates which sort of goes against everything we believe in.

 

Hopefully mtb is going to be the forum ginny piggy

 

..........Dave

 

I have Lifeline AGM's on my boat, and they get equalised periodically as recommended by the manufacturer. They are now 12 years old and still hsve about 60% of their original capacity. 

 

They are unfortunately not cheap and may be replaced with something else when they no longer hsve sufficient capacity for my needs.

Link to comment
Share on other sites

1 hour ago, cuthound said:

They are unfortunately not cheap and may be replaced with something else when they no longer hsve sufficient capacity for my needs.

But if the current set have lasted 12 years, wouldn’t it be false economy to change? Or are you thinking of changing boats in the next 12 years?

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
  • Recently Browsing   0 members

    • No registered users viewing this page.
×
×
  • Create New...

Important Information

We have placed cookies on your device to help make this website better. You can adjust your cookie settings, otherwise we'll assume you're okay to continue.