Pushing the limits of electric cooking

[Na Mara]

The gas system on my boat is not up to code and needs changed. The costs of upgrading including a new oven and stove is about 1200 euros give or take. I love cooking with gas but I am not a fan of the space it takes up in my cockpit lockers, the sourcing of the gas, and the (albeit minimal) ever present danger of blowing oneself up.

As it happens I am presently upgrading my electrical system and in that upgrade is included 600Ah of lithium batteries, a 2400W inverter, and 600W of solar. Roughly the inverter is big enough to run a single hob on full power, 2 hobs on two thirds power, a minioven at full power, a minioven and a hob at two thirds power, and so on.

So here is my thinking. What if, instead of upgrading the gas system, I put a combi electric microwave oven and dual induction hob onboard and ditch the gas completely. On shore power cooking would be totally unrestricted but away from a plug we would have to restrict ourselves in how we cook. Basically, the rule would have to be no more than one cooking appliance on at any one time. One hob, or the other, or the oven, but no combination of the above.

This would require some getting used to and some planing but it should be eminently possible to do without too much sacrifice on the cuisine front.

So I have two very different questions, one is an electrical question while the other is cuisine question.

1. Using a standard rule of thumb the solar panels should deliver about 2.4kWh of energy a day on average. Will that meet the needs of an electric galley plus domestic loads on a typical cruiser? How long do we really cook for anyway? What is the average power used on a hob when cooking? Is it about 1 kW and do we use that for about an hour each day or is that guess way off?

2. Could you live with serial cooking, where only one hob/oven can be used at any given moment, when away from shore power? What would cooking be like then? Are there meals you couldn't make or make as well? Would you miss them?

If the answer to 2 is no, then there is a fairly easy solution, which is to buy another similar inverter and to parallel couple it with the existing one. But that is money and complexity I would rather do without (also it was hard enough finding space for the first monster inverter, finding space for a second would be challenging).

[Adelie]

How big is you propane tank and how long does it last? From that you can make a guesstimate of how much electricity you will use daily for cooking.
See attached graphic.

Why not get a 4500-5000W inverter?
Make sure whatever inverter you get is pure sine, modified sine wave doesn’t get along with induction.

[wholybee]

tldr; I think you will need more solar. Another 200W-300W might be enough. Of course that depends on your other electric loads.

I have 700W of solar, 300Ah LFP. If I cook one quick single pot meal, about 15 minutes or so, it works ok. If I cook more than that then every other day I need to add charging with some other method (run the engine in my case). This is with good sun. If it's cloudy I need to supplement charging every day.

Induction cooking works very well. I never use it at full power. So you should have enough battery and inverter capacity to run a couple hobs at one time, or one hob and a microwave, provided you have enough solar to replace the power used.

I still have my propane, and use the induction when I can. The induction has better temp control and doesn't heat the cabin.

[Na Mara]

Hi Adelie,

It was a space issue. The 5000W inverters are about 25cm deep and otherwise huge and that would have messed up my neat electrical installation in a suitable cupboard. The 2400W inverter was the largest that would fit and, as I said, it can be paralleled later if I need 4800W, or 7200W or watt ever. Also, if I'm being honest the electric galley idea just hit me. I was like, owww I've spent all this money making a kick ass electrical system, maybe its kick ass enough to do an electric galley..... The inverter is a victron top of the line thingy so its pure sine wave all the way.

Wholybee, so with twice your capacity and nearly the same solar I should be roughly twice as long between supplemental charges. So every third or fourth day I'm looking at a supplemental charge if cooking is kept minimal. Every second day or so if I go heavier on the cooking or its cloudy. Does that sound about right?

I did consider the whole thing of using both hobs on low power. A normal dual hob cook top is 3.5kW, so if neither hob is used at over 5 on a 9 point scale (2 kW), or if I impose a rule that the hobs together can't add up to more than 10, then I should be able to use the hobs together. With lids on most things cook well on 800W or less on an induction cooker. The inverter alarms if its overloaded before shutting down AC for 30 seconds and restarting. It not a disaster if I push the limits and get it wrong.

Of course you don't have to cook everyday. I'm partial to salads and fruit when its really hot out. One can also budget the cooking.

[s/v Jedi]

Originally Posted by Na Mara

Hi Adelie,

It was a space issue. The 5000W inverters are about 25cm deep and otherwise huge and that would have messed up my neat electrical installation in a suitable cupboard. The 2400W inverter was the largest that would fit and, as I said, it can be paralleled later if I need 4800W, or 7200W or watt ever. Also, if I'm being honest the electric galley idea just hit me. I was like, owww I've spent all this money making a kick ass electrical system, maybe its kick ass enough to do an electric galley..... The inverter is a victron top of the line thingy so its pure sine wave all the way.

Wholybee, so with twice your capacity and nearly the same solar I should be roughly twice as long between supplemental charges. So every third or fourth day I'm looking at a supplemental charge if cooking is kept minimal. Every second day or so if I go heavier on the cooking or its cloudy. Does that sound about right?

I did consider the whole thing of using both hobs on low power. A normal dual hob cook top is 3.5kW, so if neither hob is used at over 5 on a 9 point scale (2 kW), or if I impose a rule that the hobs together can't add up to more than 10, then I should be able to use the hobs together. With lids on most things cook well on 800W or less on an induction cooker. The inverter alarms if its overloaded before shutting down AC for 30 seconds and restarting. It not a disaster if I push the limits and get it wrong.

Of course you don't have to cook everyday. I'm partial to salads and fruit when its really hot out. One can also budget the cooking.

Which inverter do you have in mind? Do you have a link? A unit like Victron is less Watts than it’s number which is in VA.

I recommend using just one induction cooktop, plus a separate rice cooker which doubles as steamer and a microwave/convection combi oven to replace the propane oven.

[Adelie]

I would not get a separate appliance for cooking rice if I had a microwave. There are a number of microwave rice cookers. I got one to try. Works fine.

[JPA Cate]

Na Mara, forgive me, because this is not a direct answer to your question, but a response from half of a couple who have used propane for cooking aboard for roughly 36 yrs. Where you are, and where you said you want to go, are very poor for solar powering electric cooking. You would probably be looking at a genset install, which will lost not only space, but involve you with another engine to maintain and carry parts for. I don't know your style of cooking, but having two pressure cookers has made it possible for us to cook everything we wanted to and in sufficient amounts. It would also allow you to preserve foods in jars. We have had 2, 4, and 3 burner stoves in this time, all with ovens. Since you like cooking with gas, I'd stay with it. You can learn to re-heat foods efficiently with a gas stove, too, thus lessening the need for a microwave.

Over the years, we've noticed that people's energy needs/wants seem always to increase. It will be challenging to provide enough power for your boat for all the high latitude sailing you want to do in any event. Plus you will probably want warm water for bathing/showering...even if it is only once a week. (You can do a lot of cleaning with 1 cup of warm-hot water, if you have short hair.) In the tropics, one can keep very clean, just by swimming every day. I'd be chicken to try it where you're going. Our shower is supplied by a "flash heater", an on-demand propane-fired burner heats the water, and one adjusts the temp by adjusting the height of the burner flame.

Our 9 k. propane tanks last roughly 3 months in normal usage, but we consume more in winter (takes longer for water to boil, because the water starts colder).

We visited some friends on their boat one time, and that boat used the genset for a lot, including running a 20 gal/hr water maker (they had so much pure water, they'd wash the boat down before entering harbor)--and he worked on the genset 8 days of 12 during that visit.

Ann

[fxykty]

We have a dual induction hob and an electric oven (didn’t bother with a microwave). Also an electric kettle, pressure/slow cooker and coffee machine. We have a 700Ah bank (12V) and a 230V 5000W inverter (VE Quattro). We are two adults full time live aboards.

General cooking (two meals a day) takes between 50-100Ah daily. Add in baking or roasting and that adds another 80-150Ah.

However, we frequently pull >3KW when cooking. We generally stick to 1 full power and 1 or 2 half power (hobs plus oven plus electric kettle), but one of the challenges with electric appliances is once they’re at temperature they cycle 0-full power. If we’re not careful we trip our inverter.

Your 2.4KW inverter will be enough to run one galley appliance at a time, but I’m sure you will be tripping it occasionally even then. Pulling 1C current will cause voltage sag unless you’ve got a strong charging current at the same time, heck, even 0.5C drops the voltage, especially at lower SOCs.

We have 2.6KW of solar and on sunny days that’s way more than enough and on grey or rainy days it’s not enough. You’re definitely going to need an off-grid charging source, whether that’s your engine(s) alternator(s) and/or a generator.

[Na Mara]

Adelie, the inverter is a multiplus 2 12V 3000VA 120A inverter charger. It will reliably put out 2400W of AC continuous and can boost all the way up to 5500W for short periods. Usually a dual hob unit is one hob with 2000W capacity and one with 1500. Using one hob at a time should be fine and having two is convenient when on shore power. I was already there with the microwave- convection oven combo, I would just need to find one that is no wider than 45cm to fit the available space.

fxykty, I'm a one hot meal a day (lunch is alfresco bread and salad and breakfast is museli and yoghurt) plus one-two kettle boils a day kind of guy. I never bake or roast. The oven is mostly for heating pies and pizzas. I am likely to use less energy than you for cooking. Maybe half, so 50Ah a day, so including kettle boils we should be at about 600-800Wh a day on cooking. 600W of solar deliver 4 times that in Wh on average so 2400Wh on average. So my math says we will use a quarter of our production in cooking. That should be fine no? My understanding is that lithium batteries don't voltage drop even at high C. We are talking here about drawing 200A from a 600Ah bank. That shouldn't cause a voltage drop on a lithium bank.

Hi Ann, as you know our cruising will be european west coast in the summer of 2023, in the Med from autumn to spring 2023-24, and then up to Svalbard via Iceland and the Azores for summer of 2024. Having looked at Uniteck's site our worst solar performance will be in January where we will only be getting about 1,2kWh a day on average from the cells. I plan to be on the north african coast then. We may indeed have to engine charge more and plug in more around that time. The wife is also suggesting that we fit a hydrogenerator to charge the bank between stops. We will see, but solar works great in northern latitudes during the summer as the days are so long. Indeed, when we will be is Svalbard the sun will never set so we will be generating 24/7.

I presently carry 12kg of propane and it lasts up to half a year for us. the problem is that the system is not up to code and to get it up to code will cost me time, money and one of my three cockpit lockers. If I did it, I could carry 24kg and so be set for propane for the full year we plan to be away. Propane is great to cook with (ignoring the condensation issue), and the idea of having less strain on my electrical system is nice. But electrical cooking is just so convienient and, if we are being honest here, it is the future.

[Na Mara]

So for the cook top I'm thinking something like this (sorry its in swedish)

https://www.klarstein.se/Vitvaror/Ko...0W-Silver.html

Its 3000W. I found a useful site that suggests that the power levels step down in 200W steps on the 1800W hob and 100W on the 1200W hob. So I should be able to run the two hobs up to level 7 together without overloading the inverter (6 would give me a 300W margin.). Being long and thin this will definitely fit the space for a cooker. Now I just need to find a suitable microwave oven combo.

[Dockhead]

One question -- do you have a way to make up power if you run low? Generator or large alternator?


If you do, then I wouldn't worry about plus or minus a couple of hundred watts of solar.


Some comments to your plan:


1. People I know who switched to electric cooking seem to all say that they use less power than they expected and, with a variety of systems, don't seem to have much trouble powering the cooking.


2. Without any single exception everyone I know who has switched to electric is very pleased with it.


3. My gas system works (most of the time) but I do probably 90% of my cooking on a single NuWave induction hob. If you don't have gas at all then I do think you need two induction burners, but I don't think you will ever need to use two burners on full power at the same time. What you call "serial cooking" is entirely doable in my experience; main cooking on one, simmer on another.


4. Baking however is a different matter. You might want a separate inverter for electric baking if you do much of it and don't want to be barred from the cooktop whenever the oven is on.



5. Beware of overrated Victron inverter output. I have nearly the same unit and it doesn't like to put out more than about 2kW continuously. Note also that this is temperature related and I'm in a cold climate. In hot weather I guess even less.

[noelex 77]

The real problem is that on average the energy in will not exceeded the energy out.

600w of solar is too little to rely just on electric cooking even if you don’t cook a great deal. At best you will be restricted to only cruising areas and seasons with excellent solar insolation. This is too limiting on a sailboat where plans are written in sand at low tide.

Unfortunately, a large battery bank cannot solve the problem of not enough energy on average.

The inverter size is only a small issue. If you are determined to go ahead, start with your present inverter. If you find it limiting it is an easy component to upgrade. As the appliances will not often be used at full power I think you will find this aspect less of a problem than you imagine.

If you can bring the propane system up to a safe state and preserve this option to cover some of your requirements then having an electric cooking can be very worthwhile even with just 600w of solar. It means your bottles will last a very long time, which removes one major hassle of propane. The propane can remain turned off at the bottle for much of the time reducing any danger (although personally I think propane is very safe). You also gain redundancy (if for example your inverter, or solar regulator fails you can continue to cook normally. Finally you will have the versatility to use the best tool for the job depending on your cooking requirements, energy state etc.

[Dockhead]

Originally Posted by JPA Cate

Na Mara, forgive me, because this is not a direct answer to your question, but a response from half of a couple who have used propane for cooking aboard for roughly 36 yrs. Where you are, and where you said you want to go, are very poor for solar powering electric cooking. . . .

Actually the OP is posting from the Land of the Midnight Sun (just across The Sound from where I am writing this in Denmark actually). Solar production is really good in the summer up here -- better than in the tropics. Days are much longer and cooler temperatures make solar panels more efficient. He might get 3 or 4 kWH a day in sunny weather in the summer there. We presently have 17.5 hour long days and brilliant sunshine. Winter of course is a different matter . . .

I know several people using solar powered electric cooking up here and all are very happy.

I do think it's important to have some kind of backup source of power, however. A school bus alternator on the main engine would do it.

[Dockhead]

Originally Posted by noelex 77

The real problem is that on average the energy in will not exceeded the energy out.

600w of solar is too little to rely just on electric cooking even if you don’t cook a great deal. At best you will be restricted to only cruising areas and seasons with excellent solar insolation. This is too limiting on a sailboat where plans are written in sand at low tide.

Unfortunately, a large battery bank cannot solve the problem of not enough energy on average.

The inverter size is only a small issue. If you are determined to go ahead, start with your present inverter. If you find it limiting it is an easy component to upgrade. As the appliances will not often be used at full power I think you will find this aspect less of a problem than you imagine.

If you can bring the propane system up to a safe state and preserve this option to cover some of your requirements then having an electric cooking can be very worthwhile even with just 600w of solar. It means your bottles will last a very long time, which removes one major hassle of propane. The propane can remain turned off at the bottle for much of the time reducing any danger (although personally I think propane is very safe). You also gain redundancy (if for example your inverter, or solar regulator fails you can continue to cook normally. Finally you will have the versatility to use the best tool for the job depending on your cooking requirements, energy state etc.

The benefit of a large battery bank is that he can store a lot of power when it's abundant, which will be every time he starts the main engine if he has a heavy duty alternator.


Unless he's spending weeks at anchor without moving, I wouldn't think this would be such a problem. And if he finds he's often short of power, he can add some panels, right?


That being said, having BOTH electric and gas as you suggest (and which is what I have) gives maximum flexibility. But the problem with that in the OP's case is that he would have to replace the entire system together with the appliances. That's why he's thinking about ditching the gas altogether.


Another benefit to the OP's plan is safety. Opinions of course vary on how actually dangerous propane is on board, but prudent sailors with gas on board spend a lot of time and effort keeping their installations safe. Ditching gas means forgetting about this problem and saving all that time -- I think a huge plus.

[GordMay]

Originally Posted by Dockhead

... And if he finds he's often short of power, he can add some panels, right? ...

Aside from expense, isn’t suitable real estate is one of the primary drawbacks, for PV/Thermal solar panels, on a boat?
At some, not-too-distant, point, where does one put more panels?