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billt

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  1. Yes it's true. The output drops with high temperatures. There's a characteristic in the panel spec called NOCT, typically about -05% per degree C increase. If the module is at 55C (quite likely in these conditions, the output will be reduced by about 15%. However it's not particularly important as a midsummer day with near constant sun is going to generate more energy than a cool cloudy day.
  2. Probably not, but it depends where you are, what your electrical consumption is and how good the site is. If you are thinking of replacing a gas boiler with a heat pump you definitely won't be able to do it. I have a sort of off-grid system which is well over sized and it won't cover our winter usage. This shows our monthly generation which varies from 115kWhr in December (3.7 kWhr per day) to 1352 kWhr in May (44kWhr per day). That's a 12:1 variation through the year; in fact it would be more than that but quite a lot of potential generation in the summer is lost as it can't be used. This site isn't ideal and you could get more winter power with a site on the south coast with ideal orientation and no shading. The other issue is how long you need autonomy for, IOW how much battery storage you will need. You tend to get several days together with no usable solar in the winter. You will need enough storage to cope with this and hope that you get a good sunny day at the end! For instance, our big array averaged 2.2kWhr per day in late December and didn't get to a reasonable 11.2kWhr until the 9th of January. If you are very frugal and only use 8kWhr per day you would need at least 10 days of storage or 80kWhr and it would probably still not be enough. People who seriously go off grid have a generator to cover winter/dull day shortfall.
  3. 63kWh here. It could have been over 80 but the batteries were full at 10:30 and the inverters throttled back. However, only got 9.9kWhr on the 5th of June.
  4. I'm sure that you can, although it's not something that I've done. I think that it uses a modified version of the Open Energy Monitor CMS so the data is there. I upload to a local EmonCMS instance and that does all the processing that I need. If you want any more information https://docs.iotawatt.com/en/master/ should tell you all that you want.
  5. Yes, it's a US company and they only sell direct, but they do respond promptly. They were out of stock of the 240V reference transformer when I ordered the latest one. Any 9V AC transformer should work, you can calibrate it in the Iotawatt setup. I had a couple of these left over https://shop.openenergymonitor.com/ac-ac-power-supply-adapter-ac-voltage-sensor-uk-plug/ and they work fine. The power supply is a standard 5V usb supply. Incidentally, if you're installing many CTs in the consumer unit, it's better to use small toroidal ones rather than split core as they're much more compact. They seem to be a bit difficult to get hold of here. I had some of these https://www.brultech.com/store/index.php?id_product=45&controller=product from another project.
  6. It's worth looking at the Iotawatt. https://iotawatt.com/ They don't advertise, so you won't have heard of it, but having tried the Emon devices, the Brultech GEM and Brultech ECM, the Iotawatt is the best of these. (I wouldn't consider the emporia - don't like cloud dependency.) It's a development of the Emon monitors, but it's a neat solution, logs locally (but can upload to other databases). I've just bought my 4th, arrived from the US in just over a week. It will do everything that you list, it uses a voltage transformer for a voltage reference, so measures power correctly. 3, you just put a CT on the feed from the PV inverter. 4. The Iotawatt can record either the actual power on a circuit, including direction, or it can just log positive or negative power. 6. Presumably you can get access to the individual feeds for each device so you should be able to monitor them separately.
  7. Yes to the first question less any losses, which could amount to 15-20%. Yes to the second question. The peak power available depends on the peak discharge current capability of the batteries, but increasing the voltage reduces the current demand. My system uses 400Ah LiFePO4 batteries which can be discharged at 3C or 1200A, theoretically that's 57kW, but the inverter is limited to 6kW continuous, 8kW for 30 minutes or 9kW for 5 minutes. However the inverters (SMA Sunny Island 8.0H) can be paralleled to increase output or 3 of them can be used in a 3 phase system.
  8. Standard solar diverters are incompatible with heat pumps. The principle of the diverter is to switch the immersion on when generation exceeds local consumption and switch it off when consumption exceeds generation. Because local consumption changes from second to second, as does PV production, the immersion is switched on and of very frequently. An immersion heater can cope with this but it won't do a heat pump any good at all. If you want to feed excess solar production to a heat pump you are going to need a more sophisticated solution, possibly battery storage, which will be expensive and inefficient or a delay system to make sure the heat pump runs for some time after it has been started, but that is likely to use mainly grid supplied power rather than locally generated power.
  9. It's because you want as low a temperature drop across the emitters as possible to keep the mean emitter temperature up, unlike a condensing boiler system where you want to control the flow so there's 20C or so drop across the emitters to keep the boiler return temperature in the condensing range. With a high flow temperature the emitters will still have a reasonably high output. John Cantor's web site has a very useful simulator which lets you fiddle with flow rates and radiator sizings etc to get an idea of optimum radiator sizes and flow rates. https://heatpumps.co.uk/heating-simulator-for-radiators/ It seems sensible to me; that's all disruptive work so it makes sense to do it when you're doing other disruptive work. installing the heat pump itself should be fairly straightforward and can be done at a later stage.
  10. In the video he seems to be saying that you can throw a heat pump into any old house with no calculation and it will work as if by magic. I see no evidence that he actually designed a system and his claims for performance are dodgy at best. Claims like that need supporting evidence and I don't see any in the video.
  11. Yes, he's being economical with the information. If you look at the OEM graph that he shows, he claims that the outside temperature was low and he was still getting a COP of 2.85. When you actually look at the graph, although the temperature did drop for a few days at the end of the period, the average was about 8-9, so not impossible that the COP was reasonable. I seriously doubt that that system could actually heat the space over several days of sub zero temperatures. On the other hand, the Open Energy monitor video is very good and that and the John Cantor web site convinced me that it is possible to run a heat pump system effectively in high energy demand housing. You don't do it by waving your hands in the air, though. You calculate the heat losses, flow rates etc and design the system to suit. IOW you need BIG radiators in a leaky house. John Cantor https://heatpumps.co.uk/ is something of a heat pump expert, and Trystan Lea knows his monitoring. https://www.youtube.com/watch?v=m2-_x0XZUSM
  12. Yes, I' definitely a good idea if the grid connection costs are high. No, it doesn't feed into the grid. It's a DIY non MCS install and the SI 8.0 isn't approved for grid connection. Battery life - how long is a piece of string? The makers claim 7000 cycles at 70% DOD. That works out at 19 years at a cycle a day, however they tend not to do a full discharge every day so the batteries aren't being driven very hard and who knows how credible the makers life expectancy is. I thought of another cost, loss of interest. At a pessimistic 2.5% that adds 16p per unit.
  13. I think that you've misinterpreted the cost per kWh. The 9p per kWh seems to be based on the generator running costs; the generator can be run at full load and hence maximum efficiency if charging a battery bank intermittently, with assistance from PV. They are not accounting for the capital cost, which will push the cost per kWhr up nearer 75p. Because I'm stupid and like playing with toys, I have an (in effect) off grid system. It has 14.7kW of panels, 13kW of inverters feeding a Sunny Island 8.0 inverter/charger with about 19kWh worth of LiFEPO4 batteries. It cost about £32,000, including 20% VAT (would be quite a lot cheaper now, as costs have dropped a lot since I started buying bits) and generated about 5,000 kWh over the last 12 months. It should generate a bit more now it is completely commissioned and I've got some extra load in the summer. If you assume a 10 year life, that gives a unit cost of £0.65. If you were lucky and got 20 years out of it the cost drops to £0.33, however that doesn't include fuel for the generator in the 3 months when PV is inadequate.
  14. I have several SunnyBoy inverters and all use bluetooth communication to Raspberry Pi Zeros running SBFspot to upload PV data to PVoutput. Once setup there are no issues. But I actually use a couple of Iotawatts (https://iotawatt.com/) to measure output for local logging. Stick one current transformer on the Inverter output and one on the Sunamp input and Bob's your uncle. (And there are 12 other inputs for logging other feeds.)
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