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United KingdomDoes the job (7 months on and counting)
Had this kit installed (2 batteries, BMS and 5kW AC inverter) to maximise the usage of Economy 7 tariff (effectively moving grid consumption from daytime rate to nighttime, so saving ~30-40p / kWh each day: EDF have a very weighted day/night rate at the moment in Eastern England where I am). So a saving of £1.50 a day / £500 a year based on current rates (September '23). Kit works well, simple to install and app allows you to keep an eye on it. Setting the window for charging was a little bit of trial and error - have to estimate when to start the charging so it is 'just' full by the time the rate changes, as it doesn't seem possible to have it do all of the following: charge then notice its full, stop charging but not discharge (to preserve battery life), wait for the rate change timepoint and then start to discharge in preference to drawing from the grid. Instead, it was a case of calculating the charge rate, dividing the capacity by that then add a bit as the charge rate tails off as it gets full. One other important thing to consider: my real-world usage using 90% of the stated capacity has 4.6kWh of charging for 3.8-4.0kWh of discharge, so the round-trip effective efficiency is only 80-85%. I think part of the problem is that the invertor is not near its 5kW limit (it is typically discharging during the day at around 0.5kW) which impacts the inverter efficiency. I have observed that if it discharges quickly (e.g. I run the dishwasher in the morning, and do some cooking) then I can get 4 or even 4.1kWh back out. I'm not an electrician, but suspect I've over-specced the inverter - a 3kW or even 2kW may have been sufficient, and would be more efficient in the round-trip. Debated whether to drop a star for this, but chances are, every other system has similar issues, but it does change the economics. Having had 2x2.6kWh units (giving me 4kWh of daytime savings each day) since February, it has worked well enough that I am going to buy 2 more batteries and take it to 8kWh which should be 95% of my daytime usage over the year. Would have been great to have an Economy 10 tariff with two charging windows, as this would have avoided me needing to buy the second pair of batteries - and an annual saving of £1,000 a year from just this kit - but sadly no one seems to offer these tariffs anymore...
United Kingdomfox products from ITS
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