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most efficient generator and solar battery set-up for portable kitchen

 
Posts: 129
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Hi,

We have just purchased a food cart that we want to take to the beach and run on portable power during the summer for 4-6 hours a day.

Longer term, we want to have enough solar panels at home and batteries in the foot caravan to have it running from these and also to provide the remainder of our energy needs in winter (we have just installed a wood fire / hot water boiler, and so our electricity usage is currently about 5kW a day average usage (my husband is not playing with his big power tools in the garage). This could decrease when we make an outdoor stove/oven as part of our greenhouse. (So need to buy batteries and an inverter at some stage.) We are on 8 acres with various building plans, and could always use a portable power source as well.

We looking at the cheapest short term option to get started that would also be useful for our long-term plans.

Our caravan has:
- A 2.9kW pizza oven and pie warmer on the top. (plugs into a power point)
- A normal house-sized fridge/freezer that is rated 550kW a year. ? About 200W an hour in summer?? (?Probably as its own plug?)
- instant hot water heater (hard-wired into the wall)
- 4 soup bain maries with unknown Wattage (will probably not use in summer) (hard-wired into the wall)
- A cash register (has its own plug)
- lighting (hard wired into the wall)
- various other items will be plugged in at times - e.g. 300W ice shaver.
- a 4-element gas stove

I am not sure if the 2.9kW rating on the oven is it is maximum pull when on or its average pull over an hour of use. Also, with the fridge/freezer, I am not sure what its maximum pull when on is. I am guessing my total maximum pull to be at around 5-6kW.

What I am wondering is how much "wasted running energy" a large generator would use compare to a small one. Also, does a larger inverter use more battery power than a smaller one to run the same items?

I am also wondering if it is worth paying double the cost for a diesel generator. (We are in NZ, so can only look at options here, but diesel petrol is about 3/4 the price of petrol here as it does not include road taxes).

Finally, what would happen if I had a 2.9kW appliance plugged into 2.8kW generator?

I am looking at the following options:
- Buy a 6 kW generator and just run it

- Buy a 4 to 6 kW generator - as soon as I can afford it, have the extra power going into a small battery bank, and turn the generator off when there is enough battery charge to run things from this using a 5 or 6 kW inverter.

- Buy a 2.8kW to 4 kW generator, and have it powering just the oven. Have extra electricity running into the batteries, and have the batteries running the rest of the cart with a smaller ?2kW inverter.

I could later look at putting in a gas oven and/or stove, but do not have the extra money at present.


Thanks for any help you can give with that. I will also put the question on Yahoo Answers, if anyone finds the double post - I hope that is not bad forum etiquette.


 
pollinator
Posts: 2793
Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
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forest garden solar
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You dont need a battery bank for your setup.
You get the most watt/fuel if you run your generator at 50%.
So if you use 4kw/h and buy a 8kw/h generator you get more watt per fuel than a 5kw/h generator with battery.
Your setup has a constant non-variable load for 6 hours. no need for a battery.

If you could somehow get free energy somewhere else and not have to use a generator. you would need
at least 4kw x 6hr x 1.2 for battery loses x 1.2 for partial discharge so around 32kwh or 32 golf cart batteries.
I am not too sure how much ton that would be are you going to be pushing this up any hills?
 
Annie Hope
Posts: 129
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Hi,

Sorry, I was speaking kiwi, not American. A food cart here is usually a caravan that is towed, or a motorised vehicle, not a push cart.

Power here is 33c kW and 22c kW off peak, while diesel is $1.50 and petrol over $2 per litre ($8 per Gallon). A 6.5kW petrol generator rates at 18L fuel tank, and 6 hour run time @ 50% load. That is $6 per hour or $2 per kW. It seems power is a LOT cheaper!

How much electricity is lost charging 24v batteries with 220V electricity, and then taking it back to 220V with an inverter?

Does a larger inverter take more power than a smaller one?

Thanks


 
S Bengi
pollinator
Posts: 2793
Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
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forest garden solar
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The charger and inverters are probably USD700 each and each kwh battery is USD500 so
T=700+3700+(32x500)
T=4400+16000
T=USD20,400

You could get the batteries for alot cheaper If you get them in bulk or used or free.

I found a site check it out. http://www.cellpower.co.nz/shopping/pgm-more_information.php?id=277&=SID
If you could run everything off DC you would not need a inverter.
You could find a DC fridge and LED and it seems possible that the "heater" could run off DC.
Luckily you seem like the DIY type of person.
 
pollinator
Posts: 583
Location: Southwest U.S.
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I cringed at the thought of using a battery/inverter system in this application. Use a genny. Period.

I say go with a Diesel generator, like a Yanmar. You pay less for Diesel fuel as you stated, and the Diesel is going to use 30% less fuel or better than the gas engine generator for the same power generation. Your fuel costs with a Diesel vs. gas engine generator will be cut in half. Also, Diesels are more likely to outlast the gas engine all else equal. If you are likely to power only very small loads for extended periods, then it makes some sense to get a modest battery system with inverter and give the generator a break. However, if you're gonna pull 1500 watts plus at all times, then please forget the idea of a battery bank. Keep us posted, I'd love to see the end result.
 
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If it is a motorised caravan then you dont need a dedicated generator you could use a generator powered by the motorised caravan engines hydraulics.
 
Posts: 1400
Location: Verde Valley, AZ.
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Definatley the diesel Yanmar is the way to go.

I would still get some panels, batteries, and a smaller inverter, just so the refrigerator could be run on down times, without having to fire up the generator all the time tho....
 
Posts: 600
Location: Michigan
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Some items could be switched to propane or other gas. The oven and any other heat sources used for cooking or warming.

With the much reduced load,  a battery based electric system for lighting, ventilation, refrigeration, communications, entertainment, etc., would require a more practical size/cost generator, battery and inverter.

Then you might even be able to fit the array on board.

The yanmar is supposed to be a fine machine. There are waste heat recovery units available for these. This way the generator can heat water for potable use and even space heat, if needed, while running large loads or supporting/charging the battery.
 
S Bengi
pollinator
Posts: 2793
Location: Massachusetts, Zone:6/7, AHS:4, Rainfall:48in even Soil:SandyLoam pH6 Flat
239
forest garden solar
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I recommend running the pizza oven, instant water heater, warm water bath, 4 element gas stove directly from gas. The rest you can off a $1000, 2kw honda generator, it's about 30lbs and super super quite. It is easy to set it up to run off gas too.
 
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