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Can my system support an electric oven?  RSS feed

 
Robert Sigvaldason
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When it comes to electricity and solar panel talk my brain fries. Watts, kilowatts, kilowatt hours, amps, volts, DC, AC, aaaaaaahhhh! Lol

I've tried to google this but can't find anything that breaks things down into solar-idiot chunks. I would much appreciate any help.

I have a 2400 watt system in Costa Rica. Per day I run a mini fridge 24 hours, two LED bulbs 6 hours, two fans 12 hours, one laptop 6 hours, two iphones 2-3 hours each, and one burner of a two-burner stovetop once a day for at most an hour a day. Maybe once or twice a week will use a blender and/or food processor for a few minutes.

I want to buy an electric stove/oven and want to be sure my system can handle it. The estimates I've seen for one hour for an oven are 3000 watts. I would be using the oven maybe once or twice a week, but mainly using the stovetop. I saw somewhere that my system would produce around 10,000 watts per day, but don't know if it can handle the oven?

Many thanks
 
allen lumley
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Robert Sigvaldason : I expect that someone will explain this better, but at least I will end on a positive note ! Your system should be tested for the amount of kilowatts

it actually produces on a clear brite sunny day. The manufacturers claims can easily be inflated by 20%. Subtract from that the efficiency reduction of an additional

20% starting at about year 3 and your available power will have dropped off some. These rates are not carved in stone but they are real !


Now the next question is the health of your battery bank, if you have lead acid batteries -by now you should have heard that you should never draw off enough energy

to drain them below (the figure varies ) 70% - and never below 80% if you are trying to make your batteries last into the 20 year range ! (Batteries should be tested

and regularly maintained to promote the health and potential strength of all of your batteries individual cells !


So unless you have a Gi-normous bank of healthy batteries -the answer to your original question is - - - probably NO !

What can you do? There are about three things, 1) learn to tend to your batteries health weekly, never discharge your batteries below 70% - 80% and have a fund for

replacement batteries, a couple of batteries with weak cells can trash some or all of your other batteries !


2 ) Most Minifridges - like are ubiquitous in college dorms use as much or more Electricity than a regular full-sized fridge ! Investigate high efficiency chest type fridges!

There are alternatives that use a chest type freezer and replace the built in thermostat to create a chest type fridge - Google it !

3) Solar cooking together with Hay box cookers- Google it ! This is practically free energy and implementing it should cost you little or nothing beyond time to assemble

simple materials !

Finally there will be sunny days where direct sunlight will do all of the things that you have gotten used to- AND will also allow the use of the humble crock pot - using the

Haybox Cooker as your primary cooker will make a Crock-pot seem like a miraculous device indeed !

I hope that you take this as a positive message, and take personal responsibility for learning more about the health of your solar package and how to protect it !

Remember- the greenest dollar is the one that you do not spend ! For the Good of the Cause ! Big AL

 
Su Ba
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By a "2400 watt" system, I'm assuming you mean that your inverter is a 2400 watt inverter. Ok then, the answer is no. The inverter will go down every time you turn on the oven that is asking for 3000 watts.

As Allen pointed out, the amount that your battery bank is storing has a bearing upon how long it can supply the power that is being called for. An electric oven draws a lot of power for a long period of time. Most small home systems cannot meet that demand.

If your heart is set on using an oven, you could consider using a big enough generator. Just be sure to get one well overrated for your needs. They degrade over time and put out a lot less electricity two years down the road. Plus the big number painted on front of the generator indicates it's start up load capacity, not its continuous running mode.

Another consideration would be a propane oven, if propane is available in your area.
 
Troy Rhodes
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What they said.


To bring some order to the chaos of an off grid electrical system, here are a couple super handy guidelines to help you sort through the various issues and restrictions that come with an off grid pv set up.

Watts are watts. If you are getting confumbled by the various volts and amps and ac and dc, just convert to watts.

volts x amps = watts, easy

100 watts in dc are equivalent (for many purposes) to 100 watts of ac.

100 watts at 24 volts are equivalent (for many purposes) to 100 watts at 120 volts.

example, am I better off with (1) a 12 volt RV fan that uses 15 amps (in terms of total energy use) or (2) an AC 120 f an that uses 1.2 amps??

looks like an apples to oranges comparison right? But convert it all to watts and the mystery just evaporates:

1. 12 volts x 15 amps = 180 watts

2. 120 volts x 1.2 amps = 144 watts

AHA, the 120 volt appliance uses less electricity. Boom, end of mystery.

Sure you could go all fancy and consider that the 12V fan uses energy right from the battery and doesn't need an inverter, which has efficiency losses. Figure 15 or 20% total losses if you have to run the appliance off the inverter rather than straight from the battery. But still we have killed the mystery of the different voltages and amperages.



OK, second big rule that helps a lot:

watts are a rate. Like miles per hour.


watt-hours, that's an amount, like how far can you go on a gas tank.

example: 100 watts is what a light bulb is using right now (a rate)

100 watt-hours is the total amount of energy (gas tank analogy) the light bulb uses in one hour (watts x hours)



So, in your stove question, if the stove needs 3 kilowatts (the amount it uses RIGHT NOW) your 2.4 kilowatt inverter just can't supply it that fast, even with everything else turned off. This is like the speed of the car. The inverter just can't go that fast.


If you run it for an hour, it needs (the rate) 3 kilowatts x (the time) 1 hour = 3 kilowatt-hours. That's the size "gas tank" your battery bank would have to be to supply that much, not forgetting that you can't or shouldn't draw it down past 70 or 80% depth of discharge. If you tell us the voltage and amp-hour rating of your battery pack, we could that simple calculation too.


Hope that helps!


 
allen lumley
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Troy Rhodes : That is the Best, Clear, and Concise Explanation I have ever seen, For some reason I could never use the stream of flowing water analogy to ever explain

the idea to a 2nd or 3rd person, it always seemed to breakdown somewhere between my ears and my mouth ! High Speed ! Low Drag!

Even as you read this I am filing off the serial numbers and claiming it for my own !!!

Thanks and an Apple ! For the Crafts Big AL
 
Rob Bouchard
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Location: BC, Canada
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That is the best, simplest explanation I've seen. I live totally off grid and still have to think about that sometimes. Lol

For the record, I find propane oven/ranges vastly superior to electric. And they use none of my precious battery power.
 
Raye Beasley
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I have a wind and solar system, batteries and a 5000W inverter. You cannot run, electric stoves, water heaters or dryers. They are just too big of a drain. Smaller appliances like microwaves, toasters, toaster ovens may be used one at time, sometimes two, if your system/inverter is large enough. Even though your inverter says its good for 2400 watts it is just like running a generator. You must take into account the start up load as well as the running load. Just as important, large appliances drain batteries very quickly and in almost all home systems, faster than the batteries can be recharged. On a strictly solar system, there is the added problem of no recharging at all during the dark hours. As mentioned before, a propane stove is far superior to electric and not just because they don't use electricity.
 
Robert Sigvaldason
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Thank you all so much for your advice I have a better understanding now.
By 2400 watt system I meant I have eight 300-watt panels. My inverter is a 3524 VHX Outback and I have six Rolls Surrette S-550 batteries. It's six months old.
 
Troy Rhodes
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Your battery bank has about 16 kilowatt-hours of storage. If you use them conservatively down to 70% depth of discharge, that gives you roughly 11 kilowatt hours.

The internet says a typical oven uses 2,500 watts, or 2.5 kilowatts. That's the rate. 2.5 kilowatts x 1 hour = 2.5 kilowatt-hours, about 1/4th of your battery capacity to run the oven for an hour.

It is possible you have a meter that tracks how many watt-hours go into the battery bank on a sunny day. That would affect the discussion.

Your inverter can do something over 3,000 watts, so theoretically it could do it maaaaybe. If you were careful to not run anything else. Keeping in mind it will put a lot of wear and tear on the batteries if done regularly.


The other problem is most ovens need 220 volts, and (I believe) your inverter only does 120 volts.


Not recommended. I prefer propane or natural gas over electric any day.

 
Sherri Lynn
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I, too, have been debating the cooking issue as we would like to get fully off-grid. I have the added complication of having a reaction to petroleum products. In food (dyes and preservatives) as well as fumes, it makes me sick. So what if we traded in the range and got an induction cook top and a small convection oven that is 120 watt? I have looked at the following extra large toaster oven, as it can hold a casserole, pizza or cookie sheet, but is 120 volt, 1500 watt. http://www.oster.com/deals/labor-day-sale/oster-extra-large-digital-toaster-oven-with-convection-bake/TSSTTVXLDG.html
I was wondering if I used it during peak solar hours if it would work.

As I also have had some asthma related problems, I was trying to stay away from wood, except for occasional winter heat (we have a well insulated passive solar home.)

We have a 4400 Magnum pure sine inverter, three banks of batteries 48V, and 17 banks of 12v solar panels (4 each to make 48 volts, a total of 68 in use). BTW, we bought them used for $10 each.
 
Sherri Lynn
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I meant 120 volt, not 120 watt.
 
Troy Rhodes
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Hi Sherrie,

It looks like your inverter could easily do occasional loads of 1,500 watts, or 1.5 kilowatts if you prefer. Especially if you make sure you don't have other big loads on at the same time, or a bunch of small loads that add up to 4 kilowatts.

Does your system have a state of charge meter, or a meter that shows watt-hours used and/or watt-hours produced? How many hours do you anticipate using an electric stove top and/or toaster oven?

I'm fishing for if your system is running right on the edge, using every little bit of energy that the panels produce, or if you run a generous surplus, and the batteries rarely ever get below 40 or 50% depth of discharge.


In general, it is better to run big loads on a bright sunny day so you use it (sort of ) directly, rather than making it, storing it in the batteries, and then using it at night. It's a little easier on the batteries if you can arrange it that way. It is not a hard and fast rule though, just a nice little optimization.


 
Sherri Lynn
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Thanks for the answer. My husband is the one with the electrical knowledge in our household, but the photovoltaic system is new to him as well. We have been adding items cautiously. He put the new box next to the electric grid box and has been moving wires over bit by bit. So far, the well pump, the freezer, lights and electrical outlets are over and the state of charge has not gone below 79, and that was after many cloudy days. Next to move over is the refrigerator. I have more information on our system with pictures and cost here: http://www.powellacres.com/p/blog-page_1.html

The state of charge has gone to a hundred these last three days in a row.

The toaster oven would be used in the afternoons prior to 6:00 usually. We know with the new system, we will have to develop good solar habits.

Sherri
 
Troy Rhodes
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Then it sounds doable.

Keep us posted.


Hey, how about a solar oven

Perhaps as a supplement to the electric, or vice versa?

It is not a hard do-it-yourself project and there are tons of plans on the web.
 
Sherri Lynn
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It works! We are running our oven off grid! I did a thorough review of our new extra large toaster oven on my blog, http://www.powellacres.com February 17, 2016 post. To see our system, click on the photovoltaics tab.
 
Troy Rhodes
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Yay! it works!


Better living though math and physics.
 
Larisa Walk
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Our off-grid PV system is 2.3KW, located in Minnesota. We run a 900W hot plate on sunny days. We have a 12V homemade oven that runs at 300-660W. We can run it year round, even on lightly cloudy days. During canning season, we have a commercial 1500W hot plate for the steam canner. In the winter we cook on our masonry stove. We have an LP cooktop as a backup but most of the time it is covered up and only used a few times each year. You can see photos of some of what I'm talking about at http://www.geopathfinder.com/Energy-Wise-Cooking-Canning.html.
 
Sherri Lynn
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By the way, I do intend to have a solar oven eventually. It has always been on my mind to have a solar kitchen on our deck so during the summer we can keep the heat out of the house. It's on the list, so I hope we will get to it one day. . .

(So many things on that list!)
 
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