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Working on reducing mains power by best use of PV (without batteries).


Marvin

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Having now had a 5.12kW system running for about 6 months, usage seems to be forming a pattern. It appears we are buying an average of about 11kW a day so 28p times 11 times 365 days means a bill of about £1,200 including vat and daily charge etc (This includes charging the EV but see below). We are trying to improve this without becoming anal about it.

 

When you consider that our PV system realistically reaches, about 5kW max (due to orientation and roof angle) and about 1kW on a good winter's day, you begin to realise that the more you can reduce high energy peaks and spread the load over the day the less you will have to buy. Most of the time we need to think of equipment that uses electricity at a low rate of power per hour over a longer period to use most of the PV power.

 

To replace our old tumble dryer we purchased one with a heat pump. We knew that it would take longer to dry clothes and that they still use less electricity to do the job, however it was hard to find info on peak wattage. We were please to see that the peak wattage was about 1000W during drying  and overall less kWh's used, so low and slow compared with our old dryer.

 

We have a 4 ring induction hob, which to be honest is a good thing and a bad thing, as far as I am concerned.   I love being able to wipe the surface clean easily which keeps it looking good, however, when it comes to power usage I don't like it.  It is very hard to test because I would need a 45amp amperage tester, but based on timed meter readings the sounds the induction hob makes and the reaction to the contents of a pan of water, I am pretty sure that it works like this:  When you turn a ring onto full power, the small ring uses about 1-1.5kW continually. When you turn the ring down to half power it still uses 1-1.5kW but for only half the time: You can hear it ring clicking on and off and observe the water boil  / not boil. so the peak power is always the 1-1.5kW. so not good. Also easy to scorch a little of something in the bottom of a pan.... 

 

Interestingly slow cookers seem to work the same way as the induction hob, but at a different level, and turn on and off for periods of time to achieve the different levels indicated on the controls (i.e. warm, low or high).  After testing 5 new ones the results seem to show they run at about 300W peak power and turn on and off on the low setting, and so more cooking has been done recently using the slow cookers.

 

If your into bread makers they also run at a low wattage and power usage and we use one.

 

My mother had a low wattage kettle which required you to decide if you want to have a cupper in about 10 minutes time. I was not designed to do this and must have been faulty, however we are not going to use it! 

 

The item that I got wrong was the Immersion heater. I thought of low and slow but this is wrong. What happens is that as other house equipment turns off and on in the gaps suddenly there is 1 - 3kW pf power.  However I changed the immersion for a low wattage one and so a lot goes to the grid during these times which could be used to heat the hot water. I kept the original 3kW one and will swap the before the end of the summer. The immersion heater temperature setting will be set higher in the winter than the summer and the 200L HWT will be used as a thermal store in the winter. I have noticed the heat leakage from the HWT to the buffer so wish to avoid this during the summer when the ASHP is cooling the bungalow.

 

The charging of the electric vehicle is achieved in 2 ways. Using a CT relay switch, during the summer, the car will be charged when the PV produces over 3kW and in winter when the PV produces over 1.5kW. The other option is to charge whatever the PV is producing. I admit that the EV is only doing about 4000 miles a year and is plugged in when at home (most of the time). As it belongs to SWMBO I'm not allowed to transport the mixer in it!

If you drive 10,000 miles a year, spending 5 days a week at work and out at weekends, PV will not help much with charging the car (unless you spend THOUSANDS (at present) on a 80kW battery system). Note the EV is not charged at home but elsewhere about 5 times a year.

 

Going forward we are looking into a possible Ridgeblade system/ type system to produce power from wind as we live near the coast. We have installed a weather station on a shed but aim to move to the top of the ridge to obtain more accurate wind direction so hopefully we can calculate if we have enough in the right direction to think of installing something.

 

Rainfuel. We are still searching into power production from the electrical charge in rain water. Search for technical information has produced very little result and I fear needing to eventually conduct large scale trials. To do this I will need to do small scale trials and before that I need to consider as many alternative set up options related to a building installation and as many alternative ways to introduce the rain water to the contacts.

 

Good luck with your project.

 

Marvin

 

 

Situation that this information relates to:  100m2 Bungalow, 2 people, 200 litre HWT, 13amp EV charger, Solic 200 immersion controller, Energy source only electricity, with AIM and APE elements. That is Airtightness, Insulation, Mechanical Ventilation with Heat Recovery, and Air Source Heat Pump, Photovoltaics and Electric Vehicle.

 

 

 

 

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No 1, the immersion heater.  Put the 3kW element back.  Fit a PV diverter,  These send excess power to the immersion heater and by pulsing the power ensure the power sent to the immersion heater exactly equals the surplus that would otherwise be exported .

 

The tumble dryer.  Good for getting a heat pump model.  Now modify your usage.  A TD does NOT need to "dry" the clothes.  We use it sparingly for "fluffing" the things like socks and towels.  A short time in the TD then finish the drying on the airer (or outside in summer) is all that is needed to ensure fluffy towels.

 

The rest of self use is shift the use of the big appliances to the middle of the day, on a timer if you are not in.

 

The other thing I do is have the timer for the ASHP set to start DHW heating at 11AM.  By then there should be reasonable PV generation so some or possibly all it is using will be from the PV.

 

Fit an export meter (if you don't have a smart meter) so you can see how much you are exporting to see how well you are doing.  I am only exporting typically 100kWh per year.

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I've never seen a "proper" slowcooker  with any kind of simmerstat or thermostat, they generally switch the elements between series and parallel to get different ratings? Multicookers a different kettle of kippers tho...

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25 minutes ago, ProDave said:

short time in the TD then finish the drying on the airer (or outside in summer) is all that is needed to ensure fluffy towels.

Says the man with water that is softer than a babies bum to start with. So really it's move to the Scottish highlands, build a house, install some PV, design and build a diverter - then fluff any amount of towels for a short time - but only when the sun shines... Sorry I guess you already did😁.

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Hi @ProDave

 

Thanks for all the info! All good stuff:

 

Yes we have the Solic 200 PV diverter as noted at the bottom of my post. Yes like and use all the options with the tumble dryer which again reduce the kWH's.  Yes middle of the day dishwasher and washing etc. We also charge anything we can when the sun is up and the car is not charging: Phones, Computers, mobile phones, rechargeable batteries for all sorts including power tools, mobility scooter, rechargeable lights and so on. 

 

Hot water is mostly heated by the PV diverter. We have 5.12kW PV and on the Isle of Wight we have about 1900 hours sunlight a year, Scotland about 1200 hours! I am considering how to deal with the  ASHP back up timing. Maybe set for 2pm. This is a complicated calculation. But I will not bother until I have replaced immersion heater to a 3kW one.

 

At the moment we're not too worried about how much we're exporting, more how much we're buying. I know which will be worth more to us! But will get to it eventually.

 

M

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I'm wondering why you don't seem to be interested in battery storage? I can't think of many 5kW loads that would be present for hours on end when you're in peak generation season.

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2 minutes ago, Radian said:

I'm wondering why you don't seem to be interested in battery storage? I can't think of many 5kW loads that would be present for hours on end when you're in peak generation season.

Yes I am a firm believer that batteries don't yet make sense for a typical 3.68kW system where it is relatively easy to self use it all, but at 5kW that would surely make battery storage viable to power stuff after the sun has gone down.

 

I set the ASHP to heat the DHW to 48 degrees late morning so if the sun still shines and nothing else is using the PV, the immersion can heat the water hotter (probably meaning no ASHP input required next day)

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1 hour ago, ProDave said:

Yes I am a firm believer that batteries don't yet make sense for a typical 3.68kW system where it is relatively easy to self use it all, but at 5kW that would surely make battery storage viable to power stuff after the sun has gone down.

What sort of system were you thinking of?

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1 hour ago, MikeSharp01 said:

So really it's move to the Scottish highlands, build a house, install some PV, design and build a diverter - then fluff any amount of towels for a short time - but only when the sun shines

Soft water and more sunshine down here.

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We use a dc inverter motor dehumidifier to dry clothes. Runs on about 220w and can extract 25l a day in ideal conditions.

Very efficient, when coupled with a pulley ceiling clothes maiden, it’s almost as good as the tumble drier but without the preferred fluffiness.

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22 minutes ago, Johnnyt said:

We use a dc inverter motor dehumidifier to dry clothes. Runs on about 220w and can extract 25l a day in ideal conditions.

Very efficient, when coupled with a pulley ceiling clothes maiden, it’s almost as good as the tumble drier but without the preferred fluffiness.

Nice!

 

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Is a nighttime tarrif an option for you? Consider that and do most of your car charging and hot water heating overnight. That should cut your bills. Then your PV will cover your daily appliances and dump excess to your hotwater. It's what we're doing. We're down to about £1.50 a day now.

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SteamyTea

Posted (edited)

11 minutes ago, Conor said:

Is a nighttime tarrif an option for you

Works for me.

You can safely and easily draw 50 or 60 amps at night if you want to, though I really draw more than 40 (two storage heaters and the DHW).

During the day, when I am about (work evenings) I used about 2 kWh (cooker/oven and just about nothing else).

It would be good to have that amount of storage as there is now a 20p/kWh price difference, shifting that would save £73 a year.

And that is the problem, I don't use enough to invest in alternatives, even at todays elevated prices, which may well drop in the next year or two.

image.thumb.png.da5995054a733ba0319de05c4c73c460.png

Edited by SteamyTea
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3 hours ago, Conor said:

Is a nighttime tarrif an option for you? Consider that and do most of your car charging and hot water heating overnight. That should cut your bills. Then your PV will cover your daily appliances and dump excess to your hotwater. It's what we're doing. We're down to about £1.50 a day now.

Show off! 😂

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@Marvin. Nope, still not got a base made for it yet. Not needed heating for a few weeks now. The 3kW immersion is doing all our hot water. Have it time for during the day so largely covered by the PV.

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