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Low Wattage Immersion Heater
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RenewableCandy



Joined: 12 Sep 2007
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Location: York

PostPosted: Fri Jan 10, 2014 7:44 pm    Post subject: Reply with quote

You want something that's time-independently useful then, like a flourmill.
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kenneal - lagger
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Location: Newbury, Berkshire

PostPosted: Sat Jan 11, 2014 3:33 pm    Post subject: Reply with quote

We've got one of those. It's manual!

I've been thinking of electrifying it though because grinding enough flour for a loaf takes about 40 minutes. I need to get a suitable second hand motor, a couple of pulleys and a belt. I need to measure the number of rotations per minute that the grinder will do without getting too hot.

We are generating 475W at the moment from 880W of panels (38A at 12.5V, roof at 40deg pitch and about 5 deg east of south) and the solar hot water is heating the tank to 38 degC from 30 degC at the bottom.

We also have a shaft of sunlight going right through the house onto the north wall which is being warmed by 1 degC over the surrounding wall.

Isn't solar power wonderful even in the middle of winter!
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Tarrel



Joined: 29 Nov 2011
Posts: 2447
Location: Ross-shire, Scotland

PostPosted: Sun Jan 12, 2014 12:36 pm    Post subject: Reply with quote

kenneal - lagger wrote:
We've got one of those. It's manual!

I've been thinking of electrifying it though because grinding enough flour for a loaf takes about 40 minutes. I need to get a suitable second hand motor, a couple of pulleys and a belt. I need to measure the number of rotations per minute that the grinder will do without getting too hot.

We are generating 475W at the moment from 880W of panels (38A at 12.5V, roof at 40deg pitch and about 5 deg east of south) and the solar hot water is heating the tank to 38 degC from 30 degC at the bottom.

We also have a shaft of sunlight going right through the house onto the north wall which is being warmed by 1 degC over the surrounding wall.

Isn't solar power wonderful even in the middle of winter!


Interested to know Ken, is your 475W the peak output (i.e. in the middle of the day), or is it averaged over the hours of daylight? Also, how does this compare with the output you get in the summer?

Cheers.
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kenneal - lagger
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PostPosted: Mon Jan 13, 2014 3:29 am    Post subject: Reply with quote

That was at about 2:00 pm so had probably been slightly higher earlier in the day. The panels were only installed a couple of months ago so I don't know about the summer output. My previous installation didn't have an energy monitor on it so I don't know what I was getting with only 440W of panels.
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mikepepler
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PostPosted: Tue Jan 14, 2014 10:05 am    Post subject: Reply with quote

Any thoughts on something useful that I could run automatically though?

For some months of the year I could just use a resistor to dump some heat - the equipment is all installed in a cool part of the house, so it wouldn't go to waste, but it's no use in the warmer months.

I think part of the answer will be when I eventually get some new batteries - I have second-hand ones at the moment (2x180Ah at 12V), but these are probably 7-8 years old. I'll probably go up to 5-600Ah when I replace them, which will give me more scope to run them down on cloudy days and absorb more power on sunny ones.

But I still think I'll have quite a bit of surplus in the summer. I suppose a low-wattage slow cooker might be a good use, though it doesn't fall into the automated category of course.
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Tarrel



Joined: 29 Nov 2011
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Location: Ross-shire, Scotland

PostPosted: Tue Jan 14, 2014 11:42 am    Post subject: Reply with quote

mikepepler wrote:
Any thoughts on something useful that I could run automatically though?

For some months of the year I could just use a resistor to dump some heat - the equipment is all installed in a cool part of the house, so it wouldn't go to waste, but it's no use in the warmer months.

I think part of the answer will be when I eventually get some new batteries - I have second-hand ones at the moment (2x180Ah at 12V), but these are probably 7-8 years old. I'll probably go up to 5-600Ah when I replace them, which will give me more scope to run them down on cloudy days and absorb more power on sunny ones.

But I still think I'll have quite a bit of surplus in the summer. I suppose a low-wattage slow cooker might be a good use, though it doesn't fall into the automated category of course.


Interesting problem, and a nice one to have! Smile Just thinking outside the box for a moment (not necessarily solid ideas, but to stimulate further thought):

- Add more batteries, so you lengthen the "feast / famine" cycle?
- Reduce your solar supply. Sell one or more panels and replace with a small scale wind turbine, so your financial investment works more consistently across the day / seasons?
- Do the above, but re-invest in additional solar thermal?
- Offer to power a neighbour's freezer?
- Take in laundry?
- Switch some of your timber processing to home and use electrically powered tools?
- Switch to li-ion chainsaw and charge at home?
- Get an electric car / quad / bike?
- Grid-tie the system (can't remember whether yours is already or not)?
- Set up a combined emergency water store and pumped storage system? (That seems such a cool idea, I might just try it myself! - 2 x IBC containers, one on top of the other, pump water from bottom to top using excess power, drain down at night, powering a small impeller-driven generator)

Of course, some of these are just fun brainstorming. The obvious immediate one, as you suggest, would be to invest in additional batteries, especially if yours are coming up for replacement anyway.
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emordnilap



Joined: 05 Sep 2007
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PostPosted: Tue Jan 14, 2014 11:58 am    Post subject: Reply with quote

If you grow food, use some of the excess power to dehydrate it. The excess power and the food might even arrive at roughly the same time.

What about growing 'herbs'? Laughing
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mikepepler
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PostPosted: Wed Jan 15, 2014 10:11 am    Post subject: Reply with quote

Thanks for the ideas guys!

I had wondered about a food dehydrator, but we don't grow enough to be worth it at present. Maybe when the fruit trees grow bigger...

Adding more batteries - this will come when we eventually upgrade them.
Swapping PV for a bit if wind power - urban location, so not ideal. Not cheap either!
doing laundry - certain a good idea in a power cut scenario!
timber processing - this may be a good one, if I get a mains electric chainsaw, as I've recently got a neat device for logging which I can use at home http://www.youtube.com/watch?v=khv_0l5o6yg
electric bike - we currently have these, but are selling them soon as we don't use them much any more (tend to be on a normal bike or else towing a lot of wood so need the 4x4...)
grid tie - the system is off-grid, and grid tying doesn't make financial sense due to buying extra DODGY and not getting the FIT.

Thanks for the help! Smile
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emordnilap



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PostPosted: Wed Jan 15, 2014 11:30 am    Post subject: Reply with quote

Excellent yoke for holding/cutting logs, Mike. Ingeniously simple.
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Tarrel



Joined: 29 Nov 2011
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PostPosted: Wed Jan 15, 2014 12:05 pm    Post subject: Reply with quote

Yes, very clever. I'm tempted to order a set of the cups, to make up a trailer version as per Mike's video. (Could make up some from plywood and hinges, but the makers deserve the business just for coming up with the design).
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mikepepler
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PostPosted: Wed Jan 22, 2014 7:13 pm    Post subject: Reply with quote

It's a very neat design, a lot of thought has gone into and they've gone through several iterations of prototype. I'll be using it for real in a couple of months, once there's space in the log store, and will report back on how it goes...
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howroyd



Joined: 15 Apr 2014
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PostPosted: Tue Apr 15, 2014 9:53 pm    Post subject: Reply with quote

Glad ive found this thread!
I have solar pv, generating loads of excess during the day, over 2kW. I have a combi boiler.
Thinking of getting a hot water tank with a couple of 1kW immersion heaters. This can hopefully feed preheated water to the combi boiler, and maybe even the dishwasher and washing machine?
I will control the immersion heaters with a small microcontroller (raspberry pi) which will know the current generation/export info and tank temperature from my Owl Intuition setup.
Ideas and comments welcome!
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emordnilap



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PostPosted: Wed Apr 16, 2014 10:08 am    Post subject: Reply with quote

Howya howroyd, welcome to PS. Adam2 should be around to give you accurate technical answers. What would we do without him?

Tell us a bit about your set-up and (rough) location.
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adam2
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PostPosted: Mon Apr 21, 2014 5:39 pm    Post subject: Reply with quote

Excess PV can be used for water heating, with a suitable controller so as to regulate the load to match the available surplus.
There are two main problems in so doing.

Firstly, immersion heaters of less than about 1KW are not readily available, therefore if you have 1,600 watts available the choice is to either energise one heater and waste 600 watts, or to energise two heaters and have to import 400 watts of expensive full price electricity simply to heat water.
More sophisticated controllers use a standard 3KW element and vary the power into it to exactly match the surplus.

The other problem is that combi boilers are intended to heat mains water on demand, there is no simple and cheap way to preheat water under mains pressure.
Heating water under very low pressure in a standard cylinder is easy but that wont be enough pressure for a combi boiler.
There are various ways around the problem involving the use of booster pumps, heat exchangers or pressure rated cylinders, but all add considerable cost, losses, or complexity.
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Pepperman



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PostPosted: Mon Apr 21, 2014 11:09 pm    Post subject: Reply with quote

I'm happy to say that on our boat we are now completely self sufficient for electricity from our 1kW of pv and should remain so until September I would have thought. We only get down to about 85% soc overnight and the batteries are floating by about 11am on a cloudy day. Without our immersion heater we'd be missing out on a lot of photons.

At the moment we're using our 1kW immersion heater when it's sunny. If the panels are knocking out 700W or more then the battery depletes quite slowly and as long as I switch off the immersion in good time the soc will get back to 100% before the end of the day. But I have a 500w immersion on order so that we can get hot water on less sunny days. Just need to make sure we get the tank up hot enough every so often to keep legionella at bay.

Would love to automate the load diversion and it's theoretically possible as our outback mppt controller has a relay, but for now manual is working OK. I'm toying with the idea of getting a gprs socket to allow remote switching of the immersion though.
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