May 15, 2016 17:03:11
Over the last few months I have contributed to various threads on this forum and shared that I had decided on a battery storage solution and placed an order. I had hoped that the system would be installed during April but demand has been so high that it did not happen until 9 May. Even then, the actual batteries were held up in Customs and they were fitted last Friday. I opted for the SolaX X-Hybrid EPS system with 2 x Lithium batteries (5Kwh).
It’s very early days but I now know that my concept of battery storage was way off the mark. As I have watched the subject discussed I got the general impression that you generate during the day and store power in the battery for use at night. To some extent that is correct but due to the less than ideal weather conditions of the last couple of days my batteries have only reached 50%. This has meant that by 2200 hours the batteries have reached the standard configured cut off point of 20% reserve to be used in a power cut.
You might think that I would be disappointed but that could not be further from the truth. On average, day in and day out, we use about 15kWh of imported peak rate electricity and 3kWh night rate (Economy 7). There is a constant background demand of 600w from the fridge, freezers, network, aquarium and so on. All the heavy intermittent demand like washing machine, tumble drier, dishwasher, cooker, kettle accounts for the rest. Since the SolaX system started up we have still used the 3kWh overnight (battery exhausted) but our day time import has been less than 1 kWh. On our EDF peak rate tariff that represents a saving of approximately £2.10 a day. Quite frankly I am not too concerned about the battery running out before night time at the moment because it only represents about 18p on the daily bill.
Others may be fully aware of this but as I say, I just did not appreciate how a battery storage system could achieve such an immediate and significant reduction in my bill. What I now realise is that for much of the time the power generated by my PV is only “stored” for a matter of seconds before being used. Basically, the system is constantly juggling with generation, storage and demand to ensure that it only ever imports from the grid to top-up any momentary shortfall. There is a nice app that allows you to connect an iPad/iPhone/Android device directly to the system via WIFI so I have included 2 screenshots from today to try to illustrate what is going on. Each screenshot represents just a brief moment in time, one when demand was high (washing and ironing) and another when demand was lower. I will try to explain what I understand is going on in each.
1 = a moment of high demand 5817w as shown in the middle. The PV was generating 3094w, the battery was providing 732w so the system imported 2189w from the grid (note the number is negative). Of course a split second later the thermostat on the iron or washing machine probably stopped demanding power, while a cloud may have reduced PV generation and more was drawn from the battery so everything changed and so on, again and again.
2 = a moment of low demand 578w as shown in the middle. The PV was generating 2815w which was more than sufficient to satisfy demand so the system can be seen sending (yellow dots) 1973w to charge the battery and 1w back (note the number is positive) to the grid.
It’s important to remember that our FIT is paid on what we generate, not what we export (unless you have an export meter) and I know that my generation meter has clocked up exactly what it would have done before the battery storage system was installed. When I got up this morning I took a meter reading (peak rate) and it was 91322.9 just after 0700 hours. As I conclude this post at 1747 hours the meter shows 91323.3. Things may pan out a bit different during the winter months but it looks like this system could slash my annual electricity bill.
Looks like I have to add each screenshot and one of the system separately.
May 15, 2016 17:06:47
Screenshot 2 low demand
May 15, 2016 17:07:38
System installed in loft space
May 16, 2016 07:07:16
Excellent post dwilliams! Have you enough experience of the system yet to calculate likely pay back time?
May 16, 2016 16:24:33
Excellent post dwilliams! Have you enough experience of the system yet to calculate likely pay back time?
Thank you Capetown. The system cost £5300 but regarding pay back time I think it would be too early really to make any valid calculations. As I have mentioned before, pay back is not my prime consideration. The EPS mode could prove invaluable to me and it's ironic that we should have a 2 hour power cut in the area on the Friday before installation!
Previously I made reference to the app that connects locally to the inverter via wifi. There is also a web portal which I may be able to share with others in due course if it would be useful. For now I have attached another screen shot from today so far which I will try to interpret.
With no generation and no demand for power the graph would be flat along the 0W line. From midnight to just after 0600 you see a blue line running below zero and this is what I describe as the background demand from the fridge, freezer, aquarium etc. much of which is on the cheaper Eco7 rate. Shortly after 0600 you see a sharp spike in demand as the kettle, toaster and TV come on. Around 0630 our PV starts to generate and you can see a green and brown line slowly rising up above the 0W line. Note that the blue demand line follows a similar reducing trend as the PV provides more power. Shortly before 0900 the blue line starts to peak above the 0W showing that we are no longer importing any power from the grid. Shortly after 0900 we get back from the school run, make coffee and use the cooker for a while but the demand is too much for both the PV and battery combined to sustain. Once the cooker is off the blue demand line jogs along a little above and a little below the 0W line. I believe when the blue line goes above the 0W line we are actually feeding power to the grid. Just before 1200 the dishwasher goes on as the sun is shining brightly (green line) but soon after the cloud comes over and the solar generation drops to 557W. Note that to compensate the battery (brown line) compensates by outputting 1377W. If it hadn't done that the demand for import which shows at 1553 would have been that much higher (clearly the oldish dishwasher is not A rated). We jog along the 0W line for an hour or so then the clouds clear and solar generation (green) shoots up. You can see the export blue line shoots up soon after as does the the output (brown) from the battery. You might ask why … I haven't a clue yet. From about 1500 the clouds clear again and solar generation heads upwards.
May 17, 2016 15:06:18
I'm surprised they installed the batteries in the loft space. I have recently been thinking about the efficiancy losses of having my inverter in the loft and found an app which connects to the bluetooth of my SMA inverter and tells me the temperature of the inverter, its not pretty on these warm sunny days. I would have thought that batteries like the heat even less.
Good luck and please keep us updated with what you learn and think about living with the batteries.
May 17, 2016 17:42:23
Hi Kevin, I did have this discussion with the company. Apparently the shorter the cable runs the better, especially the DC run from the panels to the inverter. Our SMA SunnyBoy inverter has been in loft for nearly 5 years and survived so it made sense to locate the new one there too.
The data sheet shows the inverter operating range to be -10C to +50C. It does have a fan that kicks in every now again but I have only realised that when I was in the loft and standing next to it. The battery units show the operating range to be -25C to +60C.
The company who supplied and installed our system is Rural & Country Energy Solutions aka Generation Renewables. Although based in Cheshire they work all over the country. The chaps who installed our system on the Monday were staying down south for the rest of the week installing another 5 systems (Reading was mentioned as their next job).
I have learned that Rural & Country (as their name suggests) are specialists in agricultural energy solutions like Biomass, heat pumps, off-grid systems and battery technology and have extended more into the domestic arena as interest in storage takes off. Many of the companies offering the same SolaX product are domestic PV companies branching into battery storage since the FIT reductions have caused demand to reduce significantly.
Anyone interested in definitive answers to questions like this would probably do better to contact their Surveyor & Design Consultant Mike Lowes who I found to be very knowledgeable and rather passionate about the subject!
Today our battery got to 100% so looking forward to seeing how long it lasts into the night. The graph is looking interesting so I might post it tomorrow.
May 17, 2016 17:50:04
The android app I found called oxley solar, reads the temp on the sma inverters, mine has been above 50 degrees for the last few days, i don't know if that's ambient but even so, it must have an impact. I read something recently that it's not really the case about short cable runs as long as it's less than 15 or 20m.
I've got quite a lot of background usage but am not using as much as 600w/h. You might want to look into how that's split up.
May 19, 2016 11:47:26
This is a very interesting post and I bet many users of this site are considering battery storage and will be keen to hear of your long term experience.
Picking up on what Kevin has said, I am also surprised by your high background usage, although I must admit I haven’t a clue on how much an aquarium uses. My own background usage is 110w/h (measured this morning with the fridge/freezer buzzing away and all the usual suspects on standby), this increases to about 250w/h when the central heating pump kicks in and a few lights are switched on.
I recommend you investigate your background usage as this could result in the battery storage being much less effective during the winter months as it may rarely get chance to charge.
May 19, 2016 15:05:46
Hi all, been a bit busy and would rather add a few comprehensive experiences with analysis of graphs rather than drip, drip what's happening each day which could become rather boring. Tuesday was a fantastic generating day here and the batteries went to 100% while we were out. Our demand was met right past bedtime until about 2300 hours. Meanwhile Wednesday was what a long miserable winter day would be like but still, with just snatches of sunshine, the batteries got a reasonable charge but were exhausted soon after 1800 hours.
So far as my background usage is concerned, it's no mystery to me. I expect the aquarium uses about 150w with pumps, heater, UV filtration, daylight/darkness lights even though everything is low energy like LED. Add to that several PC based servers and 3 nest box surveillance cameras (each have micro PC) and you can see where it goes. Now we are into Spring/early Summer there's 8 hydroponic water micro circulation pumps and air pumps for the tomatoes, cucumbers etc. etc. Having listed it out like that I am quite pleased at 600w really!
It's nearly been a week now since the batteries were fitted and obviously I ask myself if I regret having taken the plunge? I can honestly say … absolutely not and still delighted. The SolaX portal provides a public link to the system so here it is http://www.solax-portal.com/dz/home/overview/36875