SteamyTea

They are pretty relaxed about it. They eventually take you to court for theft. They don't often lose. So how would you feel about it?

Not sure what that really is. watts (W) is power day (24 hour) is time So do you mean 2100 [W] x 24 [h] = 50.4 kWh/day

Does depend what you mean by an immersion. Assuming that you mean a traditional hot water cylinder, then you can think of it as just a large kettle. You put cold water in, heat it up with a 3 kW element at the bottom (or midpoint/top depending on design), once the water is hot enough, you use it. Then it gets refilled with cold water (does this without you knowing as it is just replacing the hot water that you need) and either automatically turns the heating element on, or waits until the timer says it is time to switch on and heats the water if it needs it (think Economy 7 after midnight). There are generally two ways to 'manage' domestic hot water (DHW) in a cylinder. One it to use the water that is actually in the cylinder, the other is to have a heat exchanger that separates the cold mains water that you want to heat up from a volume of static stored water in the cylinder. The heat exchanger does not have to be very fancy, often just a coil of pipe within the cylinder. The Sunamp is basically a box of 'heat' that cold water is passed though to get warmed up via a heat exchanger. The difference between a normal cylinder is that the substance holding the heat (heat is the old word for energy) is not water but a phase change material (PCM). PCMs are sometimes a little hard to understand, but the easy one is water changing from solid ice to liquid water at 0°C. So imaging that you have some ice at exactly 0°C, as it changes into liquid water, the temperature stays at exactly 0°C. As it changes state (called phase in grown up science) it releases energy. We call this melting (or latent heat of fusion for lab coat wearing grown ups). The energy released can be transferred, via a heat exchanger, to 'something else', usually the air around the ice. The really odd thing is that a disproportionate amount of energy is released as materials change state. So imaging that solid ice can store 2.1 kJ/kg.K (J, joule, is the unit of energy) and liquid water can store 4.2 kJ/kg.K of energy you may think that as it fuses it would be somewhere between the 2, well it isn't. It is 334 kJ/kg, or about 100 times the difference (note that there is no K (kelvin) as the temperature stays the same at 0) The Sunamp does a similar trick but at a higher temperature, about the temperature you want your hot water at (that was lucky or it would be useless). So, when you want some hot water, though some sciency magic and trickery, the material in the Sunamp changes state and releases energy though the heat exchanger, warming up the water. If you want to know exact details, ask Sunamp or a Physicist, or at a push a Chemist (not Boots or Lloyds). This allows the Sunamp to store a relatively high amount of energy is a small box. There are some other odd things that happen with PCMs, one is the ability to store a lot of energy at a low temperature i.e. room temperature, but still release the energy at a higher temperature when needed. This reduces the need to have lots of insulation around the store. To give you an idea of how high thermal losses can be with a traditional hot water cylinder, I was loosing more energy from mine than I actually needed to bathe every day (reduced it with extra insulation, so not insurmountable). Some things just need lots of insulation, a DHW cylinder is one of them. A Sunamp is not much good in an airing cupboard as it looses little thermal energy to the air around it. So pros and cons. A normal water cylinder is well understood by most people, is simple (if electrically heated) and relatively cheap to install. The downside is that they are large, can be noisy (if you have a bad installation), heavy when full of water and can have very high thermal losses. A Sunamp is much smaller and lighter and has much lower losses. It is more complicated as there is a pump and control systems, and can seem, in isolation, more expensive, but that is down to installation and location to a certain extent. I do not have any connection with Sunamp, but have seen @JSHarris installation and was quite impressed with the unit (apart from the old bleed valve position which I think is now improved). There is probably a lot more to discus about the two different technologies, and I may not have got everything correct, or may have got muddles. But basically they are both ways to make cold water into hot water, which is very basic technology and engineering, so don't fret too much when comparing systems/installations.

JFGI, all the info is there, but will take some time. You may find that your main router has something to show data usage, my old TalkTalk one did. Try logging in with 192.168.0.1 and the supplied password

You can check what your PC is using easily enough. Settings-->Network & Internet-->Data Usage

It is kWp really

I might be wrong as I do not know the finer details, so that was just generic advice really. The main thing to always remember are the laws of thermodynamics, no one ha managed to break them yet.

I used Resintite, it is pretty cheap and can be made just about as thick or thin as you like. https://www.amazon.co.uk/Resintite-Powdered-Wood-Glue-1-5/dp/9792100415 It is waterproof as well. No idea of the EPS density, was just something I had kicking about.

I think that @AndyT is saying that you use the immersion heater when the PV is only producing a small amount of excess energy, when the PV produces more it disconnects the immersion and helps run the heat pump. But you can only use either the immersion or the heat pump, not both. This is because there is a secondary electrical element in the heat pump and it may overload the eddy box of tricks, or kill the CoP as the stored energy is at a too higher temperature to get a decent CoP from the heat pump, which would cause the heat pumps internal immersion to kick in. Ideally you never want to use the heat pumps internal immersion heater. If you are using a thermal store then the water that you use (what comes out the tap) and the stored energy (which may be a brick, PCM or a fluid) can be separated with a heat exchanger. This gets rid of the Legionella problem (not that it is a real problem anyway, but that is another debate).

Glad you mentioned the export rate and the index linking, people seem to forget that bit. It is odd how people still think that the FiT rate should be the old high rate of 41p, that was 6 years ago and only lasted just over a year. As you have an ASHP, having PV could work to your advantage as any power generated can be absorbed by the ASHP and/or an immersion heater, so the 50% deemed export could work to your advantage, rather than an export meter. All you have to do is make sure that your domestic hot water (DHW) is heated up either side of Noon Universal Time. That is when, on average, you will get most power. Then you fit your lifestyle around that. You could get a more complicated system with a power diverted and use anything over a fixed amount to help heat your DHW. Storage for DHW is your cheapest option to reduce exports. Also make sure you size your heat pump correctly to run at no more than 40°C. You get a much better coefficient of performance (CoP) then.

Biggest wheels possible.

Or comic sans

How easy, and costly, is it to use a PIC to send the data wirelessly. I fancy having a go with them sometime, but the learning curve may be a bit too steep for me.

I have just ordered a new RPi3 with wireless as I thought it may be down to using the original RPi1b. I am using the code written my Matt Hawkins, bme280.py. I have similar issues with the GPS module. It 'sees' it but can't get any data from it, just says it has 'no fix', which may or may no the the case. Shall give it a day or two break until I get the new 3.

??? The TV is probably churning out 400W, each person watching it 80W.

Yeah right, I can use a bedpan to save to ever getting up as well.

I could easily live with that restriction, but it is nice to be able to get up in the middle of the night and make some tea and not have to worry about whether the water is heating or not. A m2 of biomass will yield around 2 kWh/year, a m2 of PV will give about 130 kWh/year. To put that into perspective, in December, that same m2 of PV will yield over 10 kWh. Not much I grant you, but a lot better than the 'sustainable' biomass option. Eigg has a total surface area of 30.5 million m2, at 0.25% efficiency (about what plants produce) and at an annual irradiation level of 90 kWh/m2, the island could produce about 7 MWh/year of biomass energy. There is no 'sustainable' biomass plan for the island.

Dug out my BME280 sensors and fixed them up to my RPi Trouble is I am not getting a humidity reading. It would also be nice if it was easy to use the SPI bus rather than the i2c one. I have the RTC on that and one BME280. If I plug in another BME280, it gives gibberish readings for the air pressure. How easy is it to make something that can cycle though the sensors, maybe just by switching the Vcc in and out.

I slept in the rain last night (wind changed direction and had window open). So had a little think about this 'semi' off grid problem. Could you not wire the house a bit differently so that you have light, fridge, freezer, central heating pump/controls and maybe a couple of spare sockets on the island grid. It may still be possible to use more than 5 kWp, but mush harder to. I have no idea what actually happens if you do go over the 5 kWp limit. Does it blow a fuse and need someone from the DNO to fix it, or trip out and just need a reset? Or do they do the decent thing and charge £2 a unit. The rest of the house could then be on a secondary circuit, one that is only connected to your own generation and storage. That way you can use more power if it is being generated or has been stored. As the island increases its renewable generation/storage, they may give you another, higher limit, then it is just a case of transferring a few circuits to the island grid. I also think that it is worth moving away from all combustion technologies. Shame that the island is going RE electric, then some islanders fill the local area up with smoke and fumes. Rather defeats the object.

Does it do that with the TV turned off too?

Welcome First thing you need to know when going just about off grid is what your energy and power requirements are. So you need to break them down into categories i.e. Space Heating, Hot Water, Cooking, Lighting, Clothes Washing, Vacuuming, etc. Then look at the maximum power needed i.e. 100W for lighting, 3kW for water heating, 4 kW for cooking. Then the total energy required for each over a 24 hour period. Add in some contingency and you should be able to work out the storage needed. It is harder to reliably calculate the generation from wind and solar, but that is what the storage contingency is for. Or just get a generator and a relatively small battery storage system.

All I am going to say on this subject

What a good idea. I would be quite interested in making a couple of them too. One for home and one for the car. Maybe the home one should be an inside and outside one.

Welcome I like charts