All Electric?

[Bee]

2 minutes ago, MtB said:

 

You'd need one of these on your foredeck!

 

Hmmm, well its still at the development stage, I wonder if a composting loo would produce a worthwhile amount of gas? I think sitting on the loo and smoking a fag might not be too good though. I can see there's still a bit of tweaking before I exhibit the first all gas boat at Crick. Might need to build a blast wall around it as well Ho hum, back to the portable nuclear reactor then.

[IanD]

22 minutes ago, MtB said:

 

I'm not entirely convinced on that point. A 12v lithium bank spend most of time in the range of 12.8v to 13.6v AIUI, and that broadly equates to float charge for LA batts. So if the new LA is fully charged in the first place before connecting it up, it is unlikely to deviate much from 100% SoC for an awfully long while.

You might very well be correct. But I still don't really see what the LA is giving you -- if you want the lithiums to take all the charge/discharge strain then they have to be big enough to support all your power needs, if the LA bank is big then it's a waste of space because it does nothing, if it's small then what's the point? I just don't see what it's bringing to the party, apart from maybe some "last-gasp" capacity if the lithiums hit 0% SoC and shut down, in which case I'd have said money would be better spent on an effective battery monitoring system and possibly a small standby generator...

 

It seems that the main driver is the desire not to "throw perfectly good LA away", when they're effectively now redundant.

2 minutes ago, Bee said:

Hmmm, well its still at the development stage, I wonder if a composting loo would produce a worthwhile amount of gas? I think sitting on the loo and smoking a fag might not be too good though. I can see there's still a bit of tweaking before I exhibit the first all gas boat at Crick. Might need to build a blast wall around it as well Ho hum, back to the portable nuclear reactor then.

Rolls-Royce are working on SMRs (Small Modular Reactors), sound like just the job 😉

[nicknorman]

2 hours ago, IanD said:

Just be *very* careful about internet videos telling you how easy it is to either install lithium batteries or add them in parallel with lead-acid, because a lot of them frankly don't know what they're talking about and the end result is dead batteries -- there are *loads* of cases of this happening in the much bigger yachting and RV communities.

 

This one isn't too bad, and most of what he says about lithium is correct -- which begs the question, why make things more difficult by keeping the lead-acids, why not just switch to 100% lithium?

 

Some suggested reading, if you haven't already...

 

https://marinehowto.com/lifepo4-batteries-on-boats/

https://nordkyndesign.com/category/marine-engineering/electrical/lithium-battery-systems/

Nope, the numbers say exactly the opposite -- which is why I provided some... 😉

 

And they were optimistic -- typical alternator efficiency is 60% maximum, and more typically 50% (or lower!) at cruising rpm, and diesel efficiency is about 20% under the same conditions:

 

https://electronics.stackexchange.com/questions/96051/what-makes-automotive-alternators-so-inneficient-relative-to-other-applications

https://www.hybrid-marine.co.uk/index.php/hybrid-info/hybrid-efficiency

 

So fuel-to-amps efficiency while cruising is about 10% for main diesel engine compared to 25% for a generator:

 

https://www.victronenergy.com/upload/documents/VE_Marine_generator_test_RVA_07-jan-2008.pdf

I’m sceptical about your claims for alternator efficiency for an already-running engine. An already running engine already has the alternator fan spinning and other frictional losses (belt, bearings, winding windage etc) not to mention the frictional losses in the engine. What we need to know is the marginal increase in fuel consumption between an engine running at say 1300rpm propelling the boat and with zero load on the alternator, versus ditto with a big load on the alternator. It seems highly unlikely that the marginal efficiency is worse than a dedicated generator running, since for the latter you have to take into account all the frictional losses of the generator engine and it’s alternator cooling fan.

 

If the marginal efficiency of an alternator is 50%, that means that when I’m putting out 175A from my Iskra, it is also putting out about 2kw in heat. Yes it does get hot, but nothing like that hot.

 

I think you are over-egging your pudding!

Edited November 15, 2021 by nicknorman

[nicknorman]

1 hour ago, Bee said:

I have a somewhat mischevious desire to promote an all gas boat and bin the ferociously expensive electrics. When you add up the industrial processes, mining, ecological and political disasters, the raw materials, copper, lead, lithium, valium and all the other rare and expensive stuff in a modern electric boat it all seems to be the worst of every world. Gas heating, lighting, cooking, fridge, and diesel engine running on gas seems to me to be a whole lot simpler and cheaper and a simple dynamo off the engine charging a lorry battery (just the one) that runs a telly and radio looks like something I could live with and  understand and reduce the chances of electrical fires to zero. The last plus point is that you could keep a canary or two and if one fell off the perch you would know you had a gas leak. I am only half joking.

I’m disappointed. I thought you were going to propose a gas powered telly! Could be done, eg with a peltier device and a gas flame!

[IanD]

9 minutes ago, nicknorman said:

I’m sceptical about your claims for alternator efficiency for an already-running engine. An already running engine already has the alternator fan spinning and other frictional losses (belt, bearings, winding windage etc) not to mention the frictional losses in the engine. What we need to know is the marginal increase in fuel consumption between an engine running at say 1300rpm propelling the boat and with zero load on the alternator, versus ditto with a big load on the alternator. It seems highly unlikely that the marginal efficiency is worse than a dedicated generator running, since for the latter you have to take into account all the frictional losses of the engine and alternator cooling fan.

 

If the marginal efficiency of an alternator is 50%, that means that when I’m putting out 175A from my Iskra, it is also putting out about 2kw in heat. Yes it does get hot, but nothing like that hot.

 

I think you are over-egging your pudding!

Look at the efficiency curves for a diesel engine, and work out the marginal efficiency, it's what I did. The problem is that a diesel running at about a tenth of maximum power (typical on a narrowboat) has terrible efficiency, typically about 20%. For every bit of extra load you add on the power has to come from somewhere, and that needs more fuel. Whether you think it seems unlikely doesn't affect the result, the numbers don't lie 😉

 

A generator is more efficient because it's running at close to the maximum efficiency point, and the AC alternators used in them are much more efficient than an accessory alternator, typically 85% or more. The 25% overall efficiency from fuel in to AC out is measured, and it's what the suppliers data sheets also show.

 

The alternator efficiency I quoted was an actual curve; when I looked at high-power alternators (like the 175A Iskra) I found similar figures, 60% at best but this is when running close to maximum speed, 50% really is typical at cruising rpm. Again, if you don't believe me, go and dig into the manufacturer's data.

Edited November 15, 2021 by IanD

[Tacet]

2 hours ago, IanD said:

 

Nope, the numbers say exactly the opposite -- which is why I provided some... 😉

 

And they were optimistic -- typical alternator efficiency is 60% maximum, and more typically 50% (or lower!) at cruising rpm, and diesel efficiency is about 20% under the same conditions:

 

https://electronics.stackexchange.com/questions/96051/what-makes-automotive-alternators-so-inneficient-relative-to-other-applications

https://www.hybrid-marine.co.uk/index.php/hybrid-info/hybrid-efficiency

 

So fuel-to-amps efficiency while cruising is about 10% for main diesel engine compared to 25% for a generator:

 

https://www.victronenergy.com/upload/documents/VE_Marine_generator_test_RVA_07-jan-2008.pdf

It's tricky questioning someone who knows what they are talking about.  But let's put some numbers I (perhaps) understand, assuming lead acid batteries, please.

 

100ah drawn off the a batteries overnight - say 1.5kWh to be returned in, say, 4 hours running a modern diesel with a chunky automotive alternator.  At (round about) 1 litre diesel to a notional 10kWh, it would take an additional 1.5 litres of diesel to recharge the batteries at your 10% overall efficiency.  Possible but seems a bit high on the marginal basis since maybe only 5 litres used altogether including propulsion - and doubt  that it would drop to only 3.5 litres for the next four hours once the batteries have been charged.  But who knows without testing.

 

And at 25% efficiency with this generator, it should only require 0.6 litres for the full four hours.  Really?

 

If you have wonder-batteries where you can stuff all the coloumbs required in five minutes, I can see the greater efficiency of the generator will begin to win. 

 

 

 

  

 

   

[IanD]

8 minutes ago, Tacet said:

It's tricky questioning someone who knows what they are talking about.  But let's put some numbers I (perhaps) understand, assuming lead acid batteries, please.

 

100ah drawn off the a batteries overnight - say 1.5kWh to be returned in, say, 4 hours running a modern diesel with a chunky automotive alternator.  At (round about) 1 litre diesel to a notional 10kWh, it would take an additional 1.5 litres of diesel to recharge the batteries at your 10% overall efficiency.  Possible but seems a bit high on the marginal basis since maybe only 5 litres used altogether including propulsion - and doubt  that it would drop to only 3.5 litres for the next four hours once the batteries have been charged.  But who knows without testing.

 

And at 25% efficiency with this generator, it should only require 0.6 litres for the full four hours.  Really?

 

If you have wonder-batteries where you can stuff all the coloumbs required in five minutes, I can see the greater efficiency of the generator will begin to win. 

 

 

You can look up the fuel consumption figures for any generator or read the Victron report, the answer always comes out very close to 25% efficiency. The diesel and alternator numbers are also for real equipment, not just pulled out of thin air.

 

Yes really, a decent size LiFePO4 battery bank (no point having a small one on an all-electric boat...) will happily accept the full charge current from a generator, or even more, and still have very high cycle efficiency since you'll normally be charging below 1C rate -- usually below 0.5C, which is 2 hours for 0% to 100%.

Edited November 15, 2021 by IanD

[Tacet]

1 hour ago, MtB said:

 

You'd need one of these on your foredeck!

 

 

 

Or one of these.  Speak to Bizzard

 

 

 

[nicknorman]

1 minute ago, IanD said:

Look at the efficiency curves for a diesel engine, and work out the marginal efficiency, it's what I did. The problem is that a diesel running at about a tenth of maximum power (typical on a narrowboat) has terrible efficiency, typically about 20%. For every bit of extra load you add on the power has to come from somewhere, and that needs more fuel.

 

The alternator efficiency I quoted was an actual curve; when I looked at high-power alternators (like the 175A Iskra) I found similar figures, 60% at best but this is when running close to maximum speed, 50% really is typical at cruising rpm. Again, if you don't believe me, go and dig into the manufacturer's data.

But you are not really addressing the issue. The issue, for an engine that is already running, is the marginal efficiency ie the difference between the engine propelling the boat with no load on the alternator, vs the same with a big load on the alternator.

 

You are right that a Diesel engine is pretty inefficient especially at low power. But what is the MARGINAL efficiency of adding a (relatively small) additional load at the same rpm. I think you will find it is much better than 20% you mention. I just can’t see how it can be worse than a dedicated engine /alternator (aka generator) because with the latter, all the losses of the engine and alternator have to be allocated to the efficiency calculation, whereas with the marginal propulsion engine case, only the additional losses created by the slight increase in load for the engine, and electrical efficiency for the alternator, have to be allocated to the marginal efficiency calculation.

 

Yes I know alternators are not efficient but a major source of loss is the mechanical ones created by the spinning fan, belt etc. But when running the engine to propel the boat, these losses exist anyway. It is only the addional electrical efficacy that comes into play. As I said, if you choose to say it’s 50% marginal efficiency then by conservation of energy, for every kw of electrical energy produced, another kw is lost as heat. And that simply doesn’t stack up.

[IanD]

1 hour ago, nicknorman said:

But you are not really addressing the issue. The issue, for an engine that is already running, is the marginal efficiency ie the difference between the engine propelling the boat with no load on the alternator, vs the same with a big load on the alternator.

 

You are right that a Diesel engine is pretty inefficient especially at low power. But what is the MARGINAL efficiency of adding a (relatively small) additional load at the same rpm. I think you will find it is much better than 20% you mention. I just can’t see how it can be worse than a dedicated engine /alternator (aka generator) because with the latter, all the losses of the engine and alternator have to be allocated to the efficiency calculation, whereas with the marginal propulsion engine case, only the additional losses created by the slight increase in load for the engine, and electrical efficiency for the alternator, have to be allocated to the marginal efficiency calculation.

 

Yes I know alternators are not efficient but a major source of loss is the mechanical ones created by the spinning fan, belt etc. But when running the engine to propel the boat, these losses exist anyway. It is only the addional electrical efficacy that comes into play. As I said, if you choose to say it’s 50% marginal efficiency then by conservation of energy, for every kw of electrical energy produced, another kw is lost as heat. And that simply doesn’t stack up.

 

There are two cases to consider here; one is engine running while stationary, the other is added load while running -- and as you say, this will be better, and I'm not ignoring that, see below.

 

Standard alternators are inefficient because of voltage drops in the diodes (typically about 2V for 2 series diodes) and winding resistances (limited by winding area and copper cost) and excitation current, which is why 12V ones are so bad. Cooling fan losses are small in comparison to the electrical ones. Really, you're doing very well to get 60% efficiency and 50% is more typical, and even the manufacturers admit this if you go and dig deeply enough. High-voltage DC alternators are better because the diode losses are smaller, AC alternators in generators don't have these at all -- and also winding losses are lower because much more copper (and money) are used.

 

Here's a diesel efficiency curve from Hybrid Marine. Let's say you're cruising at 3kW at about 1300rpm (19% efficiency, 16kW fuel energy) and you add on 3kW load for the alternator, pushing the efficiency up to about 25% at 6kW (24kW fuel energy). You've added 8kW of fuel energy in exchange for 1.5kW of electrical output, which is 19% marginal efficiency -- which is indeed higher than the figure for running when moored, but still lower than a generator. This is for a pretty heavy alternator load which would very likely cause alternator overheating problems if sustained; the bigger the added load is, the more efficient the diesel gets and the better the marginal efficiency is, which is exactly what Hybrid Marine point out, and also what Integrel rely on at even higher power levels (9kW!) -- and prices 😞

 

So you're right, charging while cruising is not as disastrously bad as charging while moored. But given the use most people (not you!) seem to put their boats to, charging while moored is far more common -- when I walk or ride along the canal, I pass far more boats moored with engines or generators running than I pass cruising along.

Edited November 15, 2021 by IanD

[Tacet]

1 minute ago, IanD said:

 

You can look up the fuel consumption figures for any generator or read the Victron report, the answer always comes out very close to 25% efficiency.

 

Yes really, a decent size LiFePO4 battery bank will happily accept the full charge current from a generator, or even more, and still have very high cycle efficiency since you'll be charging well below 1C rate -- usually below 0.5C, which is 2 hours for 0% to 100%.

If the generator is always very close to 25% efficiency, there is no advantage in charging at high rates.  It seems odd that propulsion diesel engines are inefficient when at reduced power - but diesel generators are not even though the latter tend to run at constant rpm, which you might have thought would count against.

 

[IanD]

1 minute ago, Tacet said:

If the generator is always very close to 25% efficiency, there is no advantage in charging at high rates.  It seems odd that propulsion diesel engines are inefficient when at reduced power - but diesel generators are not even though the latter tend to run at constant rpm, which you might have thought would count against.

 

No, they're only close to 25% efficiency running between 50% and 100% power, read the Victron report. So if you run one for charging batteries, you run it at high loads/currents not low ones.

Edited November 15, 2021 by IanD

[nicknorman]

2 hours ago, MtB said:

 

For me, it was a simple way to use the existing engine alternator for charging without fear of it getting *ucked (technical term) should the lithium BMS decide to emergency disconnect. 

Modern alternators tend to have zener diodes as the main rectifier diodes. This means that they break down (temporarily and gracefully)at some abnormally high voltage and absorb the transient created with a sudden load dump and before the field current can subside. My Iskra for example has this in the data page:

so the diodes should gracefully limit the voltage spike to between 19 and 25v (depending on what the field current was when the load was disconnected, presumably). Which is of course is quite high for a 12v system, but nothing like as bad as the 100 or more volts one might get with an old fashioned alternator’s load dump transient.

 

But no, I haven’t actually tried it! And yes I have just sent away for some small boards from China onto which I’m going to mount some transient absorption diodes. belt and braces!

 

I also have communication between BMS and alternator so not only does the alternator know the individual cell voltages, but if the BMS is going to disconnect on high cell voltage it will give the alternator a few seconds warning and tell it to shut down. Double belt and braces!

Edited November 15, 2021 by nicknorman

[Up-Side-Down]

2 hours ago, Bee said:

I have a somewhat mischevious desire to promote an all gas boat and bin the ferociously expensive electrics. When you add up the industrial processes, mining, ecological and political disasters, the raw materials, copper, lead, lithium, valium and all the other rare and expensive stuff in a modern electric boat it all seems to be the worst of every world. Gas heating, lighting, cooking, fridge, and diesel engine running on gas seems to me to be a whole lot simpler and cheaper and a simple dynamo off the engine charging a lorry battery (just the one) that runs a telly and radio looks like something I could live with and  understand and reduce the chances of electrical fires to zero. The last plus point is that you could keep a canary or two and if one fell off the perch you would know you had a gas leak. I am only half joking.

You're almost there! An all diesel boat fuelled by HVO is the probably the closest you'd come to the  KISS approach to sustainability. You do have a very good point there.

[Tacet]

16 minutes ago, IanD said:

No, they're only close to 25% efficiency running between 50% and 100% power, read the Victron report. So if you run one for charging batteries, you run it at high loads/currents not low ones.

Which comes largely back to battery types.  Running a large generator to charge a lead acid battery bank will typically be inefficient.

 

In the example I raised of putting 100ah into lead acid batteries, using the alternator whilst cruising will be likely be more efficient than running a generator.  Not so with batteries that can accept a high charge rate close to the sweet spot of the generator.

 

 

 

[IanD]

8 minutes ago, Tacet said:

Which comes largely back to battery types.  Running a large generator to charge a lead acid battery bank will typically be inefficient.

 

In the example I raised of putting 100ah into lead acid batteries, using the alternator whilst cruising will be likely be more efficient than running a generator.  Not so with batteries that can accept a high charge rate close to the sweet spot of the generator.

 

 

Of course if you're bothered about efficiency/emissions then LA are a non-starter anyway, due to the combination of high Ah in vs Ah out, big voltage difference between charge and discharge, and engine fuel needed to run for hours to get to 100% charge while accepting little current -- again, if you get 70% round-trip efficiency you're doing well, and it'll be even lower if you allow for charging to 100% to prevent sulphation.

 

If you want cheap and easy then use the engine alternator to charge lead-acid batteries and put up with the inefficiency/emissions/fuel consumption/long running hours.

 

If you want an efficient but expensive solution for an all-electric boat with short running times then install lithium batteries and a generator. Costs a fortune but gets rid of gas...

 

Nothing in between really makes much sense...

Edited November 15, 2021 by IanD

[Up-Side-Down]

I accept that you make a 100% watertight case for lithiums, whatever way one comes at it.

 

There will be many of us, though – probably driven by cost – that will hang our noses around the compromise solution hence, for instance, my introducing the hybrid battery set up into this thread. My reason was simply that the bulk of the energy storage would be in LA technology (lead carbons in my mind) with an expensive lithium up front. I also accept your perceived shortcomings in this concept as more than a possibility but it looks like the guy in question has made a success of it.

 

What I would like to see explored further in this thread is LA technology (and its hybrid forms) in relationship to a decent PV array where absorption and float is left to the sun and does not depend on highly inefficient and lengthy periods of generator running. As and when navigation authorities instal regular charging points for electric craft there is a second option for getting absorption and float more efficiently.

 

I'm certainly familiar with one electrically-powered nb that although he cycles his LA batteries on a daily basis when cruising, he's happy to let his generator provide the bulk charge and looks for absorption/float once or twice a week from shore power. Throw in a wee bit of equalisation from time to time and this battery bank is still looking very happy on this regime after 5+ years extensive cruising throughout the system. There is no PV in this set up, just reliance on that once or twice weekly marina hook up that hopefully will be replaced over time by more and more bank-side 32amp outlets. I suspect that Lead carbon would be even more amenable to this regime which has proved itself to be effective with little capacity loss due to sulphation.

[dmr]

1 hour ago, nicknorman said:

But you are not really addressing the issue. The issue, for an engine that is already running, is the marginal efficiency ie the difference between the engine propelling the boat with no load on the alternator, vs the same with a big load on the alternator.

 

You are right that a Diesel engine is pretty inefficient especially at low power. But what is the MARGINAL efficiency of adding a (relatively small) additional load at the same rpm. I think you will find it is much better than 20% you mention. I just can’t see how it can be worse than a dedicated engine /alternator (aka generator) because with the latter, all the losses of the engine and alternator have to be allocated to the efficiency calculation, whereas with the marginal propulsion engine case, only the additional losses created by the slight increase in load for the engine, and electrical efficiency for the alternator, have to be allocated to the marginal efficiency calculation.

 

Yes I know alternators are not efficient but a major source of loss is the mechanical ones created by the spinning fan, belt etc. But when running the engine to propel the boat, these losses exist anyway. It is only the addional electrical efficacy that comes into play. As I said, if you choose to say it’s 50% marginal efficiency then by conservation of energy, for every kw of electrical energy produced, another kw is lost as heat. And that simply doesn’t stack up.

 

If we set aside the fixed losses attributable to just rotating the (diesel) engine (oil pump, belts, ring friction etc, the engine equivalent of the quiescent current in an inverter 😀) then as we put extra load on the engine does it actually become more efficient?, by how much?, and due to what physical or thermodynamic mechanism????)

 

and a bonus question.......

 

Is this the same in a petrol engine and if not why not?

[IanD]

9 minutes ago, dmr said:

 

If we set aside the fixed losses attributable to just rotating the (diesel) engine (oil pump, belts, ring friction etc, the engine equivalent of the quiescent current in an inverter 😀) then as we put extra load on the engine does it actually become more efficient?, by how much?, and due to what physical or thermodynamic mechanism????)

 

and a bonus question.......

 

Is this the same in a petrol engine and if not why not?

The graph I posted should answer all your questions...

 

Petrol engines are less efficient than diesels at full power, and the gap gets even bigger at lower power outputs because of throttling losses.

Edited November 15, 2021 by IanD

[nicknorman]

5 minutes ago, dmr said:

 

If we set aside the fixed losses attributable to just rotating the (diesel) engine (oil pump, belts, ring friction etc, the engine equivalent of the quiescent current in an inverter 😀) then as we put extra load on the engine does it actually become more efficient?, by how much?, and due to what physical or thermodynamic mechanism????)

 

and a bonus question.......

 

Is this the same in a petrol engine and if not why not?

It does become more efficient at higher loads, for the same speed. Simply because the fixed losses you mention remain more or less the same, and thus become a smaller proportion of the engine’s useful output. Ditto for petrol, until you get to the point where the fuel system needs to over-richen the mixture to avoid knocking.

[IanD]

21 minutes ago, Up-Side-Down said:

I accept that you make a 100% watertight case for lithiums, whatever way one comes at it.

 

There will be many of us, though – probably driven by cost – that will hang our noses around the compromise solution hence, for instance, my introducing the hybrid battery set up into this thread. My reason was simply that the bulk of the energy storage would be in LA technology (lead carbons in my mind) with an expensive lithium up front. I also accept your perceived shortcomings in this concept as more than a possibility but it looks like the guy in question has made a success of it.

 

What I would like to see explored further in this thread is LA technology (and its hybrid forms) in relationship to a decent PV array where absorption and float is left to the sun and does not depend on highly inefficient and lengthy periods of generator running. As and when navigation authorities instal regular charging points for electric craft there is a second option for getting absorption and float more efficiently.

 

I'm certainly familiar with one electrically-powered nb that although he cycles his LA batteries on a daily basis when cruising, he's happy to let his generator provide the bulk charge and looks for absorption/float once or twice a week from shore power. Throw in a wee bit of equalisation from time to time and this battery bank is still looking very happy on this regime after 5+ years extensive cruising throughout the system. There is no PV in this set up, just reliance on that once or twice weekly marina hook up that hopefully will be replaced over time by more and more bank-side 32amp outlets. I suspect that Lead carbon would be even more amenable to this regime which has proved itself to be effective with little capacity loss due to sulphation.

There have been plenty of analyses done on this forum about solar vs. generator as power sources. A narrowboat has limited space so you can't get much more than about 2kWp of panels on, which give about 7kWh/day average in summer and 1.5kWh/day in winter. Sounds a lot but that's only 60W average in winter (less on some days), a fridge and a few other power-sippers (LED lights, small TV, Wi-Fi router) will probably exceed that.

 

So depending on power budget, in summer solar can probably provide all the domestic power you need -- but don't use LA and throw 30% of it away.

 

In winter solar is very unlikely to meet power requirements, another power source is needed which means either plugging in or an onboard generator.

 

What fraction of the year solar can keep up with demand obviously depends on power consumption -- for a gas-free boat probably only the sunniest few months (or maybe not at all if power use is very high), a very electric-frugal boat might just get through the winter, for most people it would be somewhere in between.

 

Bankside charging would change all this, especially with boats with electric propulsion, but no sign of this happening yet in the UK. Lead-carbon promises a lot but some people who've tried it have found it delivers much less, and it's roughly double the cost of LA, which when you take lifetime and 100% charging and usable capacity into account gets it close to LiFePO4 costs (or higher) over lifetime -- cheaper to buy but shorter life ans still takes hours to trickle up to 100% regularly.

Edited November 15, 2021 by IanD

[dmr]

12 minutes ago, nicknorman said:

It does become more efficient at higher loads, for the same speed. Simply because the fixed losses you mention remain more or less the same, and thus become a smaller proportion of the engine’s useful output. Ditto for petrol, until you get to the point where the fuel system needs to over-richen the mixture to avoid knocking.

 

But I said lets set aside the fixed losses, because as per your argument these have been attributed to the "cruising budget" rather than the "battery charging budget",  so in your terminology I am asking about the "marginal" efficiency, how much does this improve as load is increased?

 

Petrol is not good at lighter loads due to the pumping loss but its less obvious with a diesel.  Losses go up quite a bit with speed but what is the load effect at fixed speed?

[IanD]

2 minutes ago, dmr said:

 

But I said lets set aside the fixed losses, because as per your argument these have been attributed to the "cruising budget" rather than the "battery charging budget",  so in your terminology I am asking about the "marginal" efficiency, how much does this improve as load is increased?

 

Petrol is not good at lighter loads due to the pumping loss but its less obvious with a diesel.  Losses go up quite a bit with speed but what is the load effect at fixed speed?

I answered exactly this question a few posts back, with numbers... 😉

 

(the post with the engine efficiency graph at the bottom)

Edited November 15, 2021 by IanD

[Up-Side-Down]

18 minutes ago, IanD said:

There have been plenty of analyses done on this forum about solar vs. generator as power sources. A narrowboat has limited space so you can't get more than about 2kWp of panels on, which give about 7kWh/day average in summer and 1.5kWh/day in winter. Sounds a lot but that's only 60W average in winter (less on some days), a fridge and a few other power-sippers (LED lights, small TV, Wi-Fi router) will probably exceed that.

 

So depending on power budget, in summer solar can probably provide all the domestic power you need -- but don't use LA and throw 30% of it away.

 

In winter solar is very unlikely to meet power requirements, another power source is needed which means either plugging in or an onboard generator.

 

What fraction of the year solar can keep up with demand obviously depends on power consumption -- for a gas-free boat probably only the sunniest few months (or maybe not at all if power use is very high), a very electric-frugal boat might just get through the winter, for most people it would be somewhere in between.

Sorry if I'm being dense (or just plain ignorant) here but please could you explain the relationship between a winter output of 1.5kWh/day and the figure of 60W average you go on to quote?

[IanD]

Just now, Up-Side-Down said:

Sorry if I'm being dense (or just plain ignorant) here but please could you explain the relationship between a winter output of 1.5kWh/day and the figure of 60W average you go on to quote?

1.5kWh = 1500Wh, divided by 24h is 60W...