Pushing the limits of electric cooking

[GILow]

Originally Posted by krid2000

Thanks for sharing your numbers. So you've been using about 2100Wh per day including the electric cooking. Do you happen to know how much energy you've used per day before? That would give us a hint at how much Wh the electric cooking requires per day.



I'm currently calculating with 1000Wh/day for my electric galley planning, but have no real data points (except Delos mentioned they cook with 1.5kWh/day).



Thanks!

Dirk

FWIW, that figure from Delos seems pretty close to me. I found that when I converted my gas consumption figures they came out at a little over 1 kWh per day. That was for me when I was a solo cruiser.

[krid2000]

Originally Posted by GILow

FWIW, that figure from Delos seems pretty close to me. I found that when I converted my gas consumption figures they came out at a little over 1 kWh per day. That was for me when I was a solo cruiser.

Thanks, good data point!

Dirk

[Pete7]

Originally Posted by krid2000

Thanks for sharing your numbers. So you've been using about 2100Wh per day including the electric cooking. Do you happen to know how much energy you've used per day before? That would give us a hint at how much Wh the electric cooking requires per day.

I'm currently calculating with 1000Wh/day for my electric galley planning, but have no real data points (except Delos mentioned they cook with 1.5kWh/day).

Thanks!
Dirk

Hmm, tricky. Last year we were generating about 1.3kWh each day from 300w of solar in high summer and good conditions. However, this wasn't enough and we were about 0.3kWh short each day. Wasn't a problem for a weekend as the batteries had sufficient capacity. However, this prompted the switch to 600w of solar during the winter.

Just thinking about the 10 days away, we cooked meat and fish with new Jersey potatoes etc but served with lots of salad because it was really hot. We have 29'c today and England is melting, don't laugh

Had the weather been cooler, then more tea rather than soft drinks or wine and cooked vegetables rather than salads would have been on the menu. Off set by baking bread rolls regularly for lunch and made a cake one afternoon.

The other draw that i intend to change is the engine room blower. Currently the domestic bank runs all the instruments when at sea and includes the blower about 5A. Doesn't sound a lot but we did have to motor sail a couple of the days so that mounts up. Wasn't a problem because we were in float every afternoon. However, the only time we need the blower is when the engine is running, so makes sense to run that off the alternator and engine start battery. I will change the wiring and fit a new blower in the next couple of weeks.

We also used the kettle to make hot water for washing up once the calorifier goes cold, normally cold by the following breakfast.

From memory our usage isn't that different from Delos but its been a while since I watched their excellent video looking at the electrical loads on board.

A rough estimate taking into account last years numbers suggests we are using 1 - 1.5kWh for cooking. The problem is its so variable. A day at anchor means no autopilot, VHF 2 chart plotters and instruments etc but then I bake cakes and bread. If we have run the engine during the day, we have hot water, so no need to use the kettle. If its heavy cloud and cold we might make more mugs of tea and coffee whilst also trying to manage on far less solar power.

The good news is that turning one switch means the Victron Smart DC>DC charger is powered by the alternator to generate an actual 27A for the domestic bank. So a couple of hours of motoring makes a huge difference to the SOC of the bank, hot water and propels us too.

Pete

[rslifkin]

Originally Posted by Pete7

The other draw that i intend to change is the engine room blower. Currently the domestic bank runs all the instruments when at sea and includes the blower about 5A. Doesn't sound a lot but we did have to motor sail a couple of the days so that mounts up. Wasn't a problem because we were in float every afternoon. However, the only time we need the blower is when the engine is running, so makes sense to run that off the alternator and engine start battery. I will change the wiring and fit a new blower in the next couple of weeks.

Does your alternator charge the house bank while motoring, or no? If it does, I don't see an advantage to moving it. If not, then it's an advantage, but also carries a small risk in my mind. I'm not a fan of anything running off the start battery unless the power to it gets cut off when the key is turned off. I don't like having the ability to lose starting power because of a dumb mistake.

[Pete7]

Originally Posted by rslifkin

Does your alternator charge the house bank while motoring, or no? If it does, I don't see an advantage to moving it. If not, then it's an advantage, but also carries a small risk in my mind. I'm not a fan of anything running off the start battery unless the power to it gets cut off when the key is turned off. I don't like having the ability to lose starting power because of a dumb mistake.

Alternator only does the engine start bank, unless I switch in the DC>DC charger. All domestics currently wired from the house bank.

I plan to leave the blower switch (already in a great location on the instrument panel) and use the supply to run a relay. Then add a feed from the engine battery bus bar to feed the actual power to run the blower. All switches have red lights so easy to see if its been left on, in addition to the noise. Oh and turning the engine master switch isolates the bus bar too.

[krid2000]

Thanks Pete, very insightful!

Dirk

[Na Mara]

The techimpex horizon 2 micro compact installed and working.

It’s all been tested and the inverter and power assist function behaved impeccably all the way up to the full 3.75kW. It draws about 10W in standby but it’s better to leave it in standby as it’s start up sequence uses 100Wh, so if it’s switched off and on more than twice a day you land up using more power than just leaving it on.

I have to admit I hadn’t budgeted on the 0.25kW daily draw of just having it sit there. It’s about the same draw as each of my fridges individually. I recently fitted a colour GX aboard so I will be able to monitor the energy usage very closely from this Friday. We’ll use the summer to zero in on our realistic daily consumption with electric cooking and then put the necessary charging aboard to meet that.

I’ll report back once I have some concrete figures.

[Na Mara]

So we have been using our techimpex horizon 2 micro compact through our multiplus 3000 for over a week now and I have to say that it is a resounding success. Its all worked flawlessly.

The power assist mode when on shore power does what it should do and has given us unrestricted cooking even with only 10A shore hook ups. We have also cooked meals and boiled kettles on just the inverter both at anchor and underway and it was all really easy.

The hobs on the cooker took a bit of getting used to but once you allow for the fact that there is a bit of a lag between altering the temp control on the cooker and the heat on the hob changing (its a resistance hob), its all very intuitive and easy.

Microwaving, grilling and baking are a piece of cake though the grill is maybe a little less powerful than a domestic one and takes a bit longer to get the job done.

What was a bit of an eye opener is that with the electric cooker and kettle, without any economising of usage and with four people aboard, we are averaging 4kWh of electrical energy consumption daily. That is a good bit higher than I had thought would be the case. I had not accounted for the low level constant draw of certain items and I had not allowed for my mother's habit of running the kettle 10 times a day. The cooking is using roughly the amount of energy I had budgeted for. We are, however, going to have to come up with a way of generating 4kWh of energy a day on average.

[Na Mara]

So a little update on the new system.

The multiplus 12/3000/120 is worth its weight in gold! It has transformed life aboard Na Mara. Together with the 600Ah (8.1kWh) of LiFePO batteries it easily handles all we need for cooking and everything else aboard.

The cooker, as I have mentioned above, has two 1.2kW resistance hobs that cycle on and off to control the temperature (longer periods of on for hotter, shorter for cooler.). I had heard from some on these boards that the multiplus 3000 couldn't handle the official rating of 2.4kW in real life. Maybe that is true of older models, or maybe all of them can handle it for the short periods I'm exposing mine to, but for whatever the reason I can run both hobs fine without tripping the inverter! I wasn't expecting that. Indeed, I can run any two of my seven cooking appliances at any one time (hob1, hob2, kettle, toaster, microwave, grill, oven) simultaneously just fine.

It really is like cooking at home.

With the cerbo GX with colour touch screen I can easily monitor the energy usage exactly. Pasta carbonara for four adults used 0.5kWh and that is typical of our evening meals. Lunches when cooked (scrambled eggs on toast for example) use 0.2kWh on average. Running a full kettle uses 0.12kWh and toasting two slices of bread in the toaster uses 0.03kWh. In total we use about 0.8-1kWh a day for cooking and hot drinks for four adults. That is not me spit balling or calculating, that's me reading the meter.

On a plug we never have to think about how we are using the cooker and kettle thanks to the power assist.

In my post above I said that we were using 4-5kWh a day of energy. Whilst true, it was a truth with a modification. Unbeknownst to us, at some point in the past, someone had wired up the calorifier for the 40l hot water tank to the domestic AC circuit instead of having a separate circuit for it at the main breaker panel. That meant that when we wired up the inverter we inadvertently wired it with the calorifier as a load. The past three weeks the inverter has been heating our water for us. This is why our consumption was so high. Having removed the calorifier as a load I'm now seeing what we actually use at anchor and underway. At anchor its 2kWh a day (half of that is cooking and hot drinks), underway its 2.5kWh a day (less cooking partially makes up for all the instruments and autopilot). Again, these are figures off the meter and not theoretical.

As we have no sources of generation aboard aside from the alternator this gives us a three day charging cycle, which is what I was aiming for. The only thing is that with the alternator only being 100A and running at 80A on average, it takes 6-7 hours to fully charge after those 3 days. Bit of a drag, but where we are sailing we typically get to a plug within that 3-4 day window, so this isn't a serious limitation (yet!).

When we get to a plug we recharge at 100A. This is when the multiplus really puts out significant heat. Its gotten so hot that I have started to air the electrical cabinet in which the inverter/charge is housed when we first plug in until the batteries are fully charged. Its a bit of a nuisance but it only goes on for a few hours before the system goes into float.

On the whole, pushing the limits of electric cooking has been extremely successful for us. Everything finally came to together really well. You really don't need more than 2,4kW of inverter capacity to go electric as long as you have the right inverter and the right (lower powered) cooking appliances. We probably could have gotten away with 400Ah of LiFePO and settled for two days of autonomy, and if you have sufficient generation capacity aboard then you could probably get away with as little as 200-250Ah.

Our unplanned experiment with the calorifier was also interesting. On average it seemed to take between 2 and 3kWh a day to keep the water hot aboard. The big variation was due to whether people were showering or not. That's a lot of energy to meet from solar, we'd have to more than double the solar I am planning for next year, but a wind turbine on a windy day could easily do it and at the moment we've been stuck on the south coast of Sweden for a week due to almost nonstop 20+ knot winds.

Hmmm.

[Pete7]

A quick recap, we upgraded to 590w of solar last winter and added a second LFP battery during the summer giving us 220Ah of capacity plus a Trojan 85Ah FLA wired in hybrid.

The first big test was two weeks in June (covered previously in post 170) with no shore power only electric cooking powered by solar or, if needed the occasional top up from the alternator via a DC>DC Victron charger. Strong sunshine meant the solar was more than sufficient, indeed we were running out of electrical items on board to charge up and didn’t need to use the alternator at all.

Final tough test this year would be three weeks in September when solar output would be lower. We also fitted an analogue kW counter to the 2kW inverter to record what we used just for cooking and making tea etc.
During the 18 days we needed some 8 hours of alternator charging generating 2.9kWh whilst we were motoring or motor sailing to a new location. Solar providing the remaining 28.3kWh which also powered everything else on board as well as cooking.

I thought our cooking usage would be fairly steady but the results varied wildly depending if we were at sea or in port. Lunches at sea tend to be simple meals like salads, toasties or cheese/mushroom omelettes. In port we cooked more, baking cakes and used the portable washing machine via the inverter. The daily average for cooking and the portable washing machine over the 18 days was 0.9kWh.

We certainly ate well, with fresh fish featuring regularly which the Remoska cooks beautifully, the same with cakes. The double induction hob used for curries or steaks served with salads etc. Oh, and the odd fried breakfast, well we were on holiday.

Our average depth of discharge each dawn was approximately 50% of our 220Ah LifePO4 batteries suggesting plenty of spare power to cover inclement weather for a couple of days.

So, what happens if we go sailing in the depths of winter? Well, we do, indeed previously sailing across the Solent on Christmas Day with the turkey cooking in the galley. In winter we tend to stop each night in a marina at winter rates or harbours like Key Haven and Weymouth. There we plug in not just to charge the batteries but also use electric heating and the dehumidifier to make life on board comfortable.

Do we like cooking on sunshine? Yes definitely, kitchen gadgets like the toastie maker and electric hand whisk have now found a new life on board. Finally, no gas to consider. Whilst this won’t suit everyone, electric cooking makes a good supplement to extend those gas cylinders.

[sv_isara]

Great recaps everyone! Well I did my first outing - 4 days 3 nights. 840 Ah AGMs, 3kW inverter. Electric air fryer, AC hot water, induction cooking.

Everything worked great but a few notes:
My air fryer (ninja) is the biggest drain by a long shot. 168amps continuous for like 5+ minutes and cycling for 20 minutes! What then happened was the inverter would stutter (renogy), I believe when the battery went below 11v (didn't figure it out exactly, but that's what the manual says can happen). Unfortunately I didn't write down the Ah's consumed by everything, but the air fryer took well over 50Ah (168amps at 20 minutes calculated to 56Ah; it used at least that much).

I could see keeping a natural gas oven only, but cooking with the induction top was a no brainer. Low draw, no issues.

Hot water, because I'm dealing with some engine overheating problems currently, is AC electric only. That drew down my batteries to 11v or 10.9 under load by the end of the cycle. Used a LOT of Ah. Seemed like 80Ah but don't recall if I had other draws on it.

With 720 watts and AGMs in the SF bay in the fall, I'd need to have *plenty* of generator or engine daily use if I wanted to use the air fryer and AC hot water and keep the batteries at 95%. With a move away from the air fryer and hydronic hot water via diesel, I think I could reduce that to every 2 or 3 days.

With my planned lithium + 150 extra watts solar (total 870) and hydronic diesel for hot water, I think I'll fare much better with close to or zero generator useage needed. But I think that the pressure cooker will still be a much closer friend than our air fryer.

[sv_isara]

Also, at anchor/in the marina in early september, I was generating maybe 4600Wh from 720watts of solar (rigid). Under sail, I forget how much, but significantly less. Maybe 40% less (by memory).
Unfortunately I forget how much my induction stove used, but it was so small that I barely noticed it. Maybe 7ah to boil some water or something like that.

My fridge + freezer compressors are totally out of hand however. Almost 200Ah/day SMH

[Na Mara]

I had a similar experience with my setup. The BMS is set up to prevent my 600Ah LFP bank from going lower than 12.8V. If that happens it first sends a signal to the inverter to cut it off and if that doesn’t fix the problem it pulls the ATD signal low on all the loads cutting them off and if that doesn’t work it throws the contactor totally isolating the batteries.

The 2.4kW inverter is enough to run my two 1.2kW hobs simultaneously but it pulls the voltage down on the batteries by about 0.2-0.3V when it does it. Fully charged this isn’t a problem as I’m pulled down from 13.5 to 13.2. I’m even ok at the 75% charge mark at 13.2V. But as the batteries get down to 50% or lower charge, the pull down on the voltage from running both hobs results in less than 12.8V at the battery terminals and the inverter turns off.

There’s no drama, and the inverter restarts after 30s by which time I’ve turned one of the hobs off and it’s all fine. The situation should improve after I’ve fitted the 600W of solar Im planning (higher average state of charge, less pull-down whilst charging). Ultimately, I could also just add one more battery as well to reduce the pull down.

Discharging continuously at 0.3C + just is going to drop your battery voltage and with a good system that will lead to cutoffs to protect the battery under certain conditions. That’s just a fact of life with electric galleys without generator power supplies.

[JBP]

Originally Posted by Na Mara

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...

I only have a single burner. Most of the time it is no problem at all. Sometimes it takes a bit of planning. If I'm doing rice & fish for example, rice first, place it some where to keep warm wrapped in a tea towel while I cook the fish. Eminently doable albeit inconvenient.

The most obvious easy solution would be to get one of those portable butane burners for the occasions when you need an extra burner. They are very small and would store away easy. As a bonus you could use it in the cockpit or ashore.

Regarding power, the only thing I can add is that when it is hot and sunny with plenty of solar power, I find myself disinclined to cook in the galley. When it is cold and gray with little solar power is when I want to cook hot meals.

[Na Mara]

Originally Posted by JBP

Regarding power, the only thing I can add is that when it is hot and sunny with plenty of solar power, I find myself disinclined to cook in the galley. When it is cold and gray with little solar power is when I want to cook hot meals.

That is a good point well made. I also tend to eat cold alfresco meals for lunch in the cockpit if it’s hot. Maybe I shouldn’t count on solar charging helping out the batteries when I cook.