Cost per Kwh using a generator

[Robbo]

Just done some quick figures on charging my batteries and how much it costs per kwh that some people may find useful.

 

Using a 4kw diesel generator that uses about .7litre at 25% load.

Diesel cost - 84.9p

 

I run the batteries down to around 65% before charging, and do a full charge once a week. With running the generator about 3 times a week, total around 8hrs, most of this is to get the batteries to 100%, other times it's 65%-90% which doesn't take long.

 

Ah's used is from a Victron BMC602, and I take the readings before and after charging so I know how many amps I've used in between charging.

 

I've calculated around £1.26 per kwh.

 

I may unhook the generator from the main tank and run from a jerry can as I'm guessing from the tech specs the average load usage the generator uses at the moment.

 

Anyone else done similar calculations?

Edited January 15, 2014 by Robbo

[Alan de Enfield]

So - About 10x the cost of 'mains' electric and that doesnt take into account depreciation, oil, & servicing of the generator

[Robbo]

So - About 10x the cost of 'mains' electric and that doesnt take into account depreciation, oil, & servicing of the generator

 

 

Yep, another calc is that I get an average of around 40ah's into the batteries per hour when charging from 50% to full (charger goes into float, takes around 6hours) although the bulk charge is charging at 75amp which is around 17% of total ah's of battery bank (450ah)

[Chalky]

That's why combined heat and power installations are attractive - you get to use the "waste" for something useful. If I run my engine it uses about 0.7 litres/hr. I get the batteries charged, a tank of hot water, cabin heating and it also moves the boat. The electricity is in effect cheaper since I've used the waste heat to heat water and the cabin. If your generator waste heat could be used else where it'd help.

[DeanS]

we use solar for battery charging or shorepower.

we use the gennie to run the washer when cruising, and at the same time the heat from the gennie drys the clothes which we put on a hanging rack next to it.

[Justme]

I have done a long term cost analysis & over a 2 year period out cost per kWh has averaged at 70p if I exclude the effect of the solar panels. With the solar panels it drops to 40p.

 

For me its all relative as we get paid FIT's on our solar power & that more than pays for our winter genny fuel.

[Paul C]

I am personally amazed that many boaters don't know how much the cost of the various energy sources, or fuels, cost, on a comparable basis with one another.

[blackrose]

Well, I didn't know that power from a generator cost 10x as much as the mains - and that's a diesel generator which I imagine is likely to be cheaper on fuel than a petrol generator.

I am personally amazed that many boaters don't know how much the cost of the various energy sources, or fuels, cost, on a comparable basis with one another.

 

It's not going to be such a simple calculation, especially if you're taking costs of equipment into account - which you must do if you want truly complete and comparable results. For starters, you'd have to make some assumptions about how long the equipment is going to last over its lifetime and costs of servicing so that you can allocate those costs correctly - and how would one know that? Then if you want to compare costs with someone else you've got to make sure you're both working on the same set of assumptions.

Edited January 15, 2014 by blackrose

[bassplayer]

If you are a CC'er who moves the boat most days, it isn't an issue....

Edited January 15, 2014 by bassplayer

[Robbo]

That's why combined heat and power installations are attractive - you get to use the "waste" for something useful. If I run my engine it uses about 0.7 litres/hr. I get the batteries charged, a tank of hot water, cabin heating and it also moves the boat. The electricity is in effect cheaper since I've used the waste heat to heat water and the cabin. If your generator waste heat could be used else where it'd help.

 

This is planned, it's raw water cooled via heat exchanger (so quite quiet!) so I'll need another heat exchanger and run them in series, one for water heating the other for canal water.

Well, I didn't know that power from a generator cost 10x as much as the mains - and that's a diesel generator which I imagine is likely to be cheaper on fuel than a petrol generator.

 

I'm going to see what the difference is if I only do a full charge every other week, and then do the same experiment but taking the fuel from a jerry can so I know exactly how much I've used. I think it would be a lot less (hopefully!).

 

Also it's not the power from the generator costing 10x much (14 amps @220v uses 1.2 litres, this is at it's max efficiency), but running the generator to get the battery from 90% to 100% charged takes so long and uses so little from the generator that it's really inefficient.

Edited January 15, 2014 by Robbo

[peterboat]

Thats where my wispergen wins I only use it in winter when the solar cant produce enough leccy. But on a sunny day the wispergen reduces its output as the batteries are fairly well charged also it heats the water and the central heating. The cost is a negative as it cost secondhand £3500 however it can run on kero or diesel and kero is much cheaper than diesel

 

Peter

[Alan de Enfield]

To get the 'last 10%' into the batteries you could try this

 

Switch on your inverter, plug the battery charger in and let it charge the batteries, no running the engine or generator, no diesel used and 'no losses, perpetual motion proven'

[station tug]

we are using a lister ld running at 500 rpm driving an alternator which produces 25 amps the engine uses 1 ltr of fuel per 6 hrs.....we also use a lister cs running a washing machine its water cooled so this heats some water as a secondry bonus....in summer we never run the engine as the solar takes care of everything

[kris88]

i do the same run a small lister not shure if its an ld though, and its running a 50amp alternator. Reckon i get the same 5-6 hrs per lt not bothered to work it out exactly. Dont run it in summer because of solar

[Ex- Member]

 

This is planned, it's raw water cooled via heat exchanger (so quite quiet!) so I'll need another heat exchanger and run them in series, one for water heating the other for canal water.

 

I'm going to see what the difference is if I only do a full charge every other week, and then do the same experiment but taking the fuel from a jerry can so I know exactly how much I've used. I think it would be a lot less (hopefully!).

 

Also it's not the power from the generator costing 10x much (14 amps @220v uses 1.2 litres, this is at it's max efficiency), but running the generator to get the battery from 90% to 100% charged takes so long and uses so little from the generator that it's really inefficient.

 

 

That's why we use a small 1kva generator.

 

We bulk charge with 1 to 1.5 hours engine running most days. Gives us a tank of hot water too.

 

We then let solar do the rest until daylight ends. Depending on the weather that day will depend on how long we run the wee 1kva genny for. If it's a Sunny day then usually only an hour. But of course it's also supplying ur 240v needs as well. If it's been a poor solar day we need to run it longer, sometimes up to 3 hours to reach a full SOC.

 

The Honda holds 2.5L of petrol that costs £3,25 and runs on average for 6.5 hours on a single tankful, so costs about £50p per hour to run. Might sound a lot but on sunny days we only need to run it for an hour, a couple of days this month so far it's not run at all. We've had 4 days exceeding 100amps since 01 Jan as well.

 

I worked out the engine diesel cost based on 1.5l diesel per hour.

 

Taking all the fuel costs over this winter period so far from boat engine running and generator running. We calculated on average over the entire year our fuel cost to produce energy is about £3.60 per week. And we don't exactly skimp on what energy we use either.

 

We did post this info somewhere a couple of weeks ago but I can't find it, I'm sure the £3.60 figure was correct though.

Edited January 16, 2014 by Julynian

[churchward]

I am personally amazed that many boaters don't know how much the cost of the various energy sources, or fuels, cost, on a comparable basis with one another.

Perhaps you could offer a more constructive contribution and educate us?

[Robbo]

I'm going to do a better calculation (well using a known quantity of fuel instead of the manufactures figures), just done some research and a no-load generator uses around 10% fuel of a full load, so mine would be around .17litres at this figure. I've re-calculated using a bit of a guess on average consumption when doing the 100% charge and the cost has come down to around 54p-84p per kwh so quite a vast difference to my initial thoughts.

[Robbo]

Thats where my wispergen wins I only use it in winter when the solar cant produce enough leccy. But on a sunny day the wispergen reduces its output as the batteries are fairly well charged also it heats the water and the central heating. The cost is a negative as it cost secondhand £3500 however it can run on kero or diesel and kero is much cheaper than diesel

 

On research the Wispergen can only reduce it's consumption to just under 50% of full which is around .3litres, and at full output is around 800w at .7litres, mine does 1100w for the same consumption. I can see the advantages in one, size and quiet been the main ones but for generating electric for battery charging it's not any better. To generate the same heat a normal diesel heater such as a Eberspacher uses around 0.62litre (5kw).

[Proper Job]

I am personally amazed that many boaters don't know how much the cost of the various energy sources, or fuels, cost, on a comparable basis with one another.

 

Sometimes life is to short

[Willber G]

To get the 'last 10%' into the batteries you could try this

 

Switch on your inverter, plug the battery charger in and let it charge the batteries, no running the engine or generator, no diesel used and 'no losses, perpetual motion proven'

You are Dave Payne AICM £5!

[Hawkmoth]

 

On research the Wispergen can only reduce it's consumption to just under 50% of full which is around .3litres, and at full output is around 800w at .7litres, mine does 1100w for the same consumption. I can see the advantages in one, size and quiet been the main ones but for generating electric for battery charging it's not any better. To generate the same heat a normal diesel heater such as a Eberspacher uses around 0.62litre (5kw).

Hi Richard,

Long time, no see.

I thought that Ebersplutters were rated at .82 ltr @ 5Kw.

Bob

[Robbo]

Hi Richard,

Long time, no see.

I thought that Ebersplutters were rated at .82 ltr @ 5Kw.

Bob

hello, how's tricks up the river?

 

I got the figure from http://www.eberspacher.com/products/heating-products/water-heating/hydronic-5.html

 

.82litre sounds more like the consumption of a 7kw heater.

[Hawkmoth]

I got the figure from http://www.eberspacher.com/products/heating-products/water-heating/hydronic-5.html

 

.82litre sounds more like the consumption of a 7kw heater.

I stand corrected.

PM on it's way.

[Paul C]

Perhaps you could offer a more constructive contribution and educate us?

 

Apologies, yes, I could have added a bit more info.

 

I worked out a typical cost of generating electricity from running the engine; and from solar power (capital cost but pretty much zero running cost) for our boat, using best-guess (or adequately researched) estimates for things like fuel consumption, alternator efficiency etc to arrive at approx. £1/kWh from the motor. We don't have shoreline, or a place to plug it into (not in a marina) so that's not an option, but if we did then I'd revisit the calculations to take into account its capital and running costs, to see how long the "payback" would be. I also did a bunch of comparable calcs between a 240V fridge/freezer and 12V equivalent.

 

The figures are never going to be exact (because you're guessing efficiencies) but a ballpark figure is useful.

 

Our boat has very few gas powered items, if you have the option to eg heat water via gas heater or engine or something else, then its worth doing the calcs for that too. We had only the one source of water heating (calorifier) and 2 sources of space heating (solid fuel stove and engine coolant-fed radiators), obviously the solid fuel stove wins on the cost calculations because we're burining a free supply of logs.