siwhi

ProDave and Marvin, thanks so much for that input, it's useful and interesting. Yes I can see the advantages of missing out the DNO in the issue, but I'm wondering whether I would miss the flexibility. I need to think about whether I could justify the expense of a MyEddi. Marvin, my back of the envelope calculations were: 2400 W rated system, so 2000w good case scenario output for 8 hours max per day = 16KW. Just to get an attainable upper benchmark. A 300 Litre tank, with ideally temperature increasing from 5C to 65C (an increase of 60C), would require this much power: Pt = (4.2 × L × T ) ÷ 3600 L = litres = 300 T = temperature = 60 Pt = (4.2 X 300 liters x 60) ÷ 3600 = 21KWH If we only wanted to heat it to say 45C, and only needed 200L, then it's: Pt = (4.2 x 200 x 40) ÷ 3600 Pt = 9 KWH So, basically the same number you got, which is reassuring! So this system would, on a good day produce enough to sort us out for hot water. Obviously, as with any scenario with PV, when there's less sun, less output, but even so, it would be a helpful addition for us at what might be quite low cost. Hopefully I can get an old inverter (of either type) for say £300 and 6x 400w panels for say £115 each, so about a grand. I have a roll of 6mm cable. No idea what the ROI would be, but probably around 10 years (10% ROI), plus reduced CO2 emissions. But still not sure what the best set up would be and how to automatically prioritize (or not) where power gets used if it's via the domestic AC system, or else how to set up a direct system.

Hi All, We have a 3.3KW PV system on our south facing roof. We are moderate - low electricity users and the system works well for us. However, we use most of the electricity and have little left over for other uses such as water heating which is be a big draw. I am considering getting another 2.2KW of panels and installing them against the south facing back garden fence using a basic frame, with the sole intention of using it to heat water. We have a 300L immersion tank with 3KW element to it which feeds water at up to 65C into our gas combi boiler which tops up the domestic water temperature if required, and separately also heats the radiators. I assume this is a resistive dump load compatible hot water tank element (meaning it takes any level of power input), I think they all are, but if not I can swap it for one. My question is, what is the best way to connect the PV panels to the 300L hot water tank? Can I do something simple myself. The options seem to me to be: 1) Buy from eBay a used DC/AC inverter and connect it to the main fusebox as normal. Then connect (plug in) the immersion tank element to the house (as it is currently set up). But I would then need to de- prioritize the boiler element somehow, getting it to cut out when the power output is low, otherwise it will draw from the grid. Currently I have to manually switch it on and off, which is a hassle and I could easily forget about it causing a big electricity bill. Using a My Eddi or similar would be very expensive. Are there any other products or options to identify when we have excess solar and divert part of it to the water tank? 2) Buy a more basic resistive load inverter which I wire straight into the tank element, (bypassing the main house fuse box altogether). Questions then are - is this DC>AC or is it all DC? If all DC would the element work OK? Would the element which has a high / low knob on it, cut out power automatically when the water got sufficiently hot, or would I need another temperature sensor switch? I would of course have fuses in the wiring as well. 3) Any other suggestions for a cheap-ish solution to hook up PV to an immersion heater? Overall option 1 is more flexible, meaning when the water was hot enough we could use the power for other things, whereas option 2 would be cheaper to set up. Thanks for your thoughts!