All Electric?

[Up-Side-Down]

1 minute ago, IanD said:

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

Ah, as in 60W an hour! I've always just thought of it in terms of the amount of leccy that goes back into my batteries in the average winter's day. Thank you.

[IanD]

5 minutes ago, Up-Side-Down said:

Ah, as in 60W an hour! I've always just thought of it in terms of the amount of leccy that goes back into my batteries in the average winter's day. Thank you.

You can't have "60W an hour". 60W is already a rate of energy consumption (it's 60 joules per second).

Edited November 15, 2021 by IanD

[Tony Brooks]

29 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 would venture to suggest that the marginal efficiency of an INDIRECT injected diesel definitely reduces as speed increases (not load) because of the extra pumping losses in the throat. If the speed stays the same I suspect the efficiency will as well until the swirl is no longer enough to ensure all the extra fuel droplets are burned. When that happens incompletely combusted f, be it CO or C, will leave via the exhaust so the efficiency must suffer.

[IanD]

3 minutes ago, Tony Brooks said:

 

I would venture to suggest that the marginal efficiency of an INDIRECT injected diesel definitely reduces as speed increases (not load) because of the extra pumping losses in the throat. If the speed stays the same I suspect the efficiency will as well until the swirl is no longer enough to ensure all the extra fuel droplets are burned. When that happens incompletely combusted f, be it CO or C, will leave via the exhaust so the efficiency must suffer.

<sigh> See the graph I posted which shows exactly this, with actual numbers (for an indirectly injected Beta 43). Look, here it is again...

Edited November 15, 2021 by IanD

[Up-Side-Down]

19 minutes ago, IanD said:

You can't have "60W an hour". 60W is already a rate of energy consumption (it's 60 joules per second).

Point taken Ian ......... and pretty much understood. In a past life, as a plumber, I'd regularly turn up on a job to find the same electrician there. He never tired of repeating that electrics worked in exactly the same way as water flowing through pipes. I wasn't convinced then ........ and I'm not convinced now. He also used to insist that the reason that I couldn't find myself a reliable mate was that my tool box was far too heavy. There might have been more truth in that!

[nicknorman]

9 minutes ago, IanD said:

<sigh> See the graph I posted which shows exactly this, with actual numbers (for an indirectly injected Beta 43). Look, here it is again...

So just for clarity (since my interpretation of Tony’s post is the opposite) this shows that at a fixed rpm, increasing the load from a small value to a medium value at constant rpm increases the efficiency. Ok the overall efficiency doesn’t increase hugely with say a 3kw additional load, but if you break down the graph into fixed propulsion load and losses (which remains the same as before the extra load was added), and the marginal increase in load and losses from the 3kw load, the marginal increase in load vs losses (the marginal efficiency) is much better.

Edited November 15, 2021 by nicknorman

[IanD]

18 minutes ago, nicknorman said:

So just for clarity (since my interpretation of Tony’s post is the opposite) this shows that at a fixed rpm, increasing the load from a small value to a medium value increases the efficiency. Ok the overall efficiency doesn’t increase hugely with say a 3kw additional load, but if you break down the graph into fixed propulsion load and losses (which remains the same as before the extra load was added), and the marginal increase in load and losses from the 3kw load, the marginal increase in load vs losses (the marginal efficiency) is much better.

Yes, that's what I gave numbers for a few posts back -- marginal efficiency (when already cruising) for an added 3kW alternator (1.5kW electrical) came out to 19% (double the figure for charging when moored), but it will be worse than that if the charging happens while passing moored boats or in locks when the engine load is lighter.

 

With a bigger added load still this goes up further, see Integrel (9kW output at 1200rpm) -- assuming the alternator won't fry itself in the process which many will, they don't like providing high output currents at low rpm...

 

It's easy to work out numbers for any case from the graph -- look up the efficiencies with and without the added load, work out the difference in the incoming fuel energy, divide this by the alternator output (assume 50% alternator efficiency for standard 12V alternators).

 

The numbers are *much* more attractive for a high-power high-voltage alternator like the Integrel, IIRC this outputs 8.5kW (10kW input) at 1200rpm. When cruising this moves the engine load up from 3kW/19% (16kW fuel) to 13kW/30% (43kW fuel), so 27kW extra fuel for 8.5kW output which is 32% marginal efficiency -- which as Integrel point out is better than a generator. The big increase compared to the 19% above is because of much heavier engine loading and much higher alternator efficiency.

Edited November 15, 2021 by IanD

[nicknorman]

Here's some figures from the graph. I chose 1500rpm and 5kw for propulsion, plus another 5kw load for alternator - which is a bit excessive, admittedly, but saved me interpolating between axis gridlines.

	1500rpm	load(kw)	efficiency%	total energy in	loss
		5	21.5	23.3	18.3
		10	27	37.0	27.0
	marginal	5	36.2	13.8	8.8

 

Sorry, formatting from excel not great but you can see that the first 5kw wastes 18.3kw, the second 5kw wastes another 8.8kw massively increasing the marginal efficiency. Iskra quote my alternator as being 65% efficient but that is not the marginal efficiency since it takes into account the fan and other no-load frictional forces. I'd say probably 75% is a reasonable figure for marginal efficiency. So overall, 36.2% and 75% gives us 27.15%. I cant see it worth having a separate generator, or at least the payback time is going to be very long.

Edited November 15, 2021 by nicknorman

[IanD]

4 minutes ago, nicknorman said:

Here's some figures from the graph. I chose 1500rpm and 5kw for propulsion, plus another 5kw load for alternator - which is a bit excessive, admittedly, but saved me interpolating between axis gridlines.

	1500rpm	load(kw)	efficiency%	total energy in	loss
		5	21.5	23.3	18.3
		10	27	37.0	27.0
	marginal	2.5	36.2	13.8	8.8

 

 

I think you forgot to allow for alternator efficiency -- 5kW load on the engine only gives 2.5kW output with a standard 12V alternator...

 

(also 5kW on the engine is a lot, 3kW is a more normal figure for a narrowboat, or even less if you go more slowly than "normal"). I think the correct numbers are:

 

	1500rpm	load(kw)	efficiency%	total energy in	loss
		5	21.5	23.3	18.3
		10	27	37.0	27.0
	marginal (Pout)	2.5	18.1	13.8	8.8

Edited November 15, 2021 by IanD

[nicknorman]

5 minutes ago, IanD said:

I think you forgot to allow for alternator efficiency -- 5kW load on the engine only gives 2.5kW output with a standard 12V alternator...

 

(also 5kW on the engine is a lot, 3kW is a more normal figure for a narrowboat, or even less if you go more slowly than "normal")

I'd made it "submit" accidentally whilst trying to tweak the formatting. Now included comments about the alternator efficiency. 5kw is a fair bit - 1500rpm is too much for our boat on a narrow canal, but fine on a deeper canal and absolutely fine on the north eastern waterways or rivers. But my point was to show the difference between overall efficiency and marginal efficiency. Using the figures at 1300rpm would give slightly different results, but the principle would be the same.

Edited November 15, 2021 by nicknorman

[IanD]

5 minutes ago, nicknorman said:

I'd made it "submit" accidentally whilst trying to tweak the formatting. Now included comments about the alternator efficiency. 5kw is a fair bit - 1500rpm is too much for our boat on a narrow canal, but fine on a deeper canal and absolutely fine on the north eastern waterways or rivers. But my point was to show the difference between overall efficiency and marginal efficiency. Using the figures at 1300rpm would give slightly different results, but the principle would be the same.

They did, just as I said -- for 3kW engine + 3kW alternator load (1.5kW out) marginal efficiency was 19% when cruising compared to 9.5% when moored.

 

Payback time for a generator is indeed huge, and makes no sense unless you also go lithium on an all-electric boat -- and even then the money side makes no sense, unless you happen to already have all this for a boat with electric drive...

 

(which also makes no sense monetarily speaking...)

Edited November 15, 2021 by IanD

[nicknorman]

1 minute ago, IanD said:

They did, just as I said -- for 3kW engine + 3kW alternator load (1.5kW out) marginal efficiency was 19% when cruising compared to 9.5% when moored.

You seem stuck on the 50% alternator marginal efficiency, but without any evidence. And in fact as I've pointed out, clear evidence to the contrary.

[IanD]

Just now, nicknorman said:

You seem stuck on the 50% alternator marginal efficiency, but without any evidence. And in fact as I've pointed out, clear evidence to the contrary.

So put it up to 65% and re-run the numbers... 😉

 

(but do check the figures from Iskra, because they'll be peak efficiency, probably at much higher rpm than you're looking at -- and may also be cold not hot...)

[nicknorman]

Herewith figures from your graph for 1300rpm, 3kw load to prop, 3 kw to alternator. Marginal efficiency marginally better, though it could just be graph-reading inaccuracy.

 

1300 rpm	load(kw)	efficiency%	total energy in	loss
	3	19	15.8	12.8
	6	25	24.0	18.0
marginal	3	36.54	8.2	5.2

 

times 75% for marginal alternator efficiency gives pretty much the same as before - 27.4%

 

5 minutes ago, IanD said:

So put it up to 65% and re-run the numbers... 😉

 

(but do check the figures from Iskra, because they'll be peak efficiency, probably at much higher rpm than you're looking at -- and may also be cold not hot...)

but the 65% is the overall efficiency taking into account the fixed losses from it spinning along with no load. The marginal efficiency will be much better at high loads.

Edited November 15, 2021 by nicknorman

[IanD]

3 minutes ago, nicknorman said:

Herewith figures from your graph for 1300rpm, 3kw load to prop, 3 kw to alternator. Marginal efficiency marginally better, though it could just be graph-reading inaccuracy.

 

1300 rpm	load(kw)	efficiency%	total energy in	loss
	3	19	15.8	12.8
	6	25	24.0	18.0
marginal	3	36.54	8.2	5.2

 

 

 

Marginal efficiency is 36.5% * 65% (alternator efficiency) = 23.7% -- has to be measured at alternator output...

 

(and do check Iskra figures at actual operating conditions, that's what I did...)

Edited November 15, 2021 by IanD

[nicknorman]

Just now, IanD said:

Efficiency is 36.5% * 65% (alternator efficiency) = 23.7%

You don't seem to grasp the difference between overall efficiency and marginal efficiency.

[IanD]

1 minute ago, nicknorman said:

You don't seem to grasp the difference between overall efficiency and marginal efficiency.

Yes I do. It's electrical output divided by added fuel energy. Alternator efficiency has to be included. 3kW load on the engine gives 2kW output.

Edited November 15, 2021 by IanD

[nicknorman]

5 minutes ago, IanD said:

Yes I do. It's electrical output divided by added fuel energy. Alternator efficiency has to be included. 3kW load on the engine gives 2kW output.

Of course alternator efficiency has to be included, but only the marginal efficiency, which disregards the losses from the alternator spinning whilst producing no output. There is quite a bit of mechanical drag from an alternator so if the max overall efficiency is 65%, the marginal efficiency is going to be much better, especially at moderate loads.

 

Incidentally of course one source of alternator losses are the fixed voltage drop (times 2 because it's full wave rectification) in the rectifier diodes. Around 1.5v, let's say. And of course 1.5v out of a 12v system is a much greater (twice the) percentage than it would be with a 24v system. 4x for a 48v system.

[IanD]

5 minutes ago, nicknorman said:

Of course alternator efficiency has to be included, but only the marginal efficiency, which disregards the losses from the alternator spinning whilst producing no output. There is quite a bit of mechanical drag from an alternator so if the max overall efficiency is 65%, the marginal efficiency is going to be much better, especially at moderate loads.

 

Incidentally of course one source of alternator losses are the fixed voltage drop (times 2 because it's full wave rectification) in the rectifier diodes. Around 1.5v, let's say. And of course 1.5v out of a 12v system is a much greater (twice the) percentage than it would be with a 24v system. 4x for a 48v system.

You can't have it both ways. The Iskra numbers include losses from the fans, so the numbers are correct with the alternator charging. If you don't do this the parasitic losses on the engine increase when not charging which consumes more fuel -- but this is a consequence of you fitting the big alternator, you can't turn it into a "better efficiency" number unless you also decrease the efficiency of the raw engine!

 

Higher voltage alternators ahve lower diode losses, as I said earlier. Best of all is a high-voltage AC alternator with active rectifier, which is what Integrel use (and maybe Travelpower?).

Edited November 15, 2021 by IanD

[nicknorman]

7 minutes ago, IanD said:

You can't have it both ways. The Iskra numbers include losses from the fans, so the numbers are correct with the alternator charging. If you don't do this the parasitic losses on the engine increase when not charging which consumes more fuel -- but this is a consequence of you fitting the big alternator, you can't turn it into a "better efficiency" number unless you also decrease the efficiency of the raw engine!

 

Higher voltage alternators ahve lower diode losses, as I said earlier. Best of all is a high-voltage AC alternator with active rectifier, which is what Integrel use (and maybe Travelpower?).

No I only want it one way. I was looking, as I thought you were, at the difference between running the engine to propel the boat without charging batteries, vs ditto with charging the batteries. I didn't imagine a situation where the alternator would be removed for cruising when not charging the batteries since it's unrealistic.

I presumed the graph you published for the Beta 43 was in a standard configuration as shipped from Beta - ie with a 175A alternator (and smaller engine alternator)

Edited November 15, 2021 by nicknorman

[IanD]

6 minutes ago, nicknorman said:

No I only want it one way. I was looking, as I thought you were, at the difference between running the engine to propel the boat without charging batteries, vs ditto with charging the batteries. I didn't imagine a situation where the alternator would be removed for cruising when not charging the batteries since it's unrealistic.

I wasn't suggesting that -- but if you're comparing to a generator then you have to include all the losses with your "big alternator" solution, which includes the alternator parasitic losses whether charging or not, so you actually have an extra fuel cost in both cases -- I believe the Beta 43 efficiency curves are for a bare engine with no alternators.

 

You should still check whether your 65% efficiency figure from Iskra is correct for the actual use (lowish rpm, hot), I suspect it's peak efficiency going by what I found when I was looking at 24V Iskra alternators...

Edited November 15, 2021 by IanD

[nicknorman]

2 minutes ago, IanD said:

I wasn't suggesting that -- but if you're comparing to a generator then you have to include all the losses with your "big alternator" solution, which includes the alternator parasitic losses whether charging or not, so you actually have an extra fuel cost in both cases.

 

You should still check whether your 65% efficiency figure from Iskra is correct for the actual use (lowish rpm, hot), I suspect it's peak efficiency going by what I found when I was looking at 24V Iskra alternators...

 

I wasn't considering a big alternator solution, just the standard alternator solution (which is quite big!).

 

65% is the quoted figure but no doubt it is their best figure and reality will be worse. But as I said, I am only interested in the marginal efficiency which is much better, especially at lower outputs (when its running cooler)

 

Interestingly if the overall marginal efficiency is 27% and 1 litre of diesel is 80p and contains 10kwh of energy (which apparently it rather conveniently does) then for your additional 1 litre of fuel burned charging the batteries as you cruise, you get 2.7kwh, ie aroud 30p per kwh which is actually pretty good considering household electricity is up to 20p a unit these days. Of course that is massively better than if you were running the engine solely to generate power and using LA batteries!

[IanD]

1 minute ago, nicknorman said:

 

I wasn't considering a big alternator solution, just the standard alternator solution (which is quite big!).

 

65% is the quoted figure but no doubt it is their best figure and reality will be worse. But as I said, I am only interested in the marginal efficiency which is much better, especially at lower outputs (when its running cooler)

 

Interestingly if the overall marginal efficiency is 27% and 1 litre of diesel is 80p and contains 10kwh of energy (which apparently it rather conveniently does) then for your additional 1 litre of fuel burned charging the batteries as you cruise, you get 2.7kwh, ie aroud 30p per kwh which is actually pretty good considering household electricity is up to 20p a unit these days. Of course that is massively better than if you were running the engine solely to generate power and using LA batteries!

I don't think you'll get 27%, probably 20% is closer to the mark including all losses so you end up around 40p/kWh -- which is still not too bad, and is half the 80p/kWh of running the engine while moored.

 

LiFePO4 should really be part of the solution though; using LA you not only have the low round-trip efficiency but the need to run for at least a couple of hours regularly to get to 100% SoC. I'd be surprised if these don't put the cost per unit up by al least 50%, probably more than that...

[nicknorman]

5 minutes ago, IanD said:

 

LiFePO4 should really be part of the solution though; using LA you not only have the low round-trip efficiency but the need to run for at least a couple of hours regularly to get to 100% SoC. I'd be surprised if these don't put the cost per unit up by al least 50%, probably more than that...

On that, we definitely agree! And I would say “run for at least a couple of hours…” is a massive understatement.

 

Edit: although of course if the boat is mostly used for cruising, getting the LA batteries to 100% isn’t an issue. I fitted Li just for the fun of it really (although they are awesome) but our usage pattern is mostly to cruise for 6-8 hrs a day, or be on shore power in the Marina so they are a bit wasted!

Edited November 15, 2021 by nicknorman

[IanD]

1 minute ago, nicknorman said:

On that, we definitely agree! And I would say “run for at least a couple of hours…” is a massive understatement.

I know -- and every extra hour drinks more fuel...

 

I know you're well aware of this, but an external alternator controller is also a must to get anywhere close to the efficiencies and charge times we've been talking about 😉