Variable Solar Storage with Batteries

[SteamyTea]

Lots of talk about what can be generated by PV, not much information about time of demand (TOD).

That is the important thing here, the rest is just hardware (either what you have or can afford).

TOD is behaviour.

Here is mine for the last 90 days.

 

[MikeGrahamT21]

Surely the time of demand would be changed, depending on the hardware though? For example your TOD at 2-3am, wouldn't happen surely if you didn't have battery storage?

 

For example, i wouldn't put the dryer on in the middle of the night, because I have no storage, i'd wait til daylight at least to use the PV

Edited May 15, 2018 by MikeGrahamT21

[MikeGrahamT21]

Just doing a bit more research, looks like the Pylon Tech batteries are Lithium Iron Phosphate: http://www.renugen.co.uk/pylontech-lithium-iron-phosphate-us2000b-2-4-kwh-battery/

 

This is for the previous model (4000 cycles) http://www.renugen.co.uk/content/Renewable Energy Batteries/Pylontech Lithium Iron Phosphate_Battery/Pylontech-Lithium-Iron-Phosphate-2.4kWh-Battery-Brochure.pdf

 

This is also quite impressive, many different batteries all linked up on a live chart https://batterytestcentre.com.au/results/pylontech-us2000b/

Edited May 15, 2018 by MikeGrahamT21

[Jeremy Harris]

AFAIK, @SteamyTea just has Economy 7, with no other energy supply (no PV, no batteries).  The high night time use will be at the E7 rate heating up the hot water tank.

 

For those with PV, then the sensible thing to do is use an excess energy diverter to heater the water (or other heat storage system) during the day, when the PV is generating.

 

There's merit in looking at E7 before battery storage as a way of reducing energy cost, as that significantly reduces the night time rate, albeit at the cost of a higher standing charge.  For us E7 is just slightly more expensive overall, as we don't save enough on the lower night time rate to cover the increase in standing charge.

[MikeGrahamT21]

1 minute ago, JSHarris said:

AFAIK, @SteamyTea just has Economy 7, with no other energy supply (no PV, no batteries).  The high night time use will be at the E7 rate heating up the hot water tank.

 

For those with PV, then the sensible thing to do is use an excess energy diverter to heater the water (or other heat storage system) during the day, when the PV is generating.

 

There's merit in looking at E7 before battery storage as a way of reducing energy cost, as that significantly reduces the night time rate, albeit at the cost of a higher standing charge.  For us E7 is just slightly more expensive overall, as we don't save enough on the lower night time rate to cover the increase in standing charge.

Ahh OK, but the demand profile still suits the situation, rather than the other way round.

 

I dont think E7 would work for us if I'm honest, pretty sure it would end up being more expensive.

[Jeremy Harris]

2 minutes ago, MikeGrahamT21 said:

Just doing a bit more research, looks like the Pylon Tech batteries are Lithium Iron Phosphate: http://www.renugen.co.uk/pylontech-lithium-iron-phosphate-us2000b-2-4-kwh-battery/

 

This is for the previous model (4000 cycles) http://www.renugen.co.uk/content/Renewable Energy Batteries/Pylontech Lithium Iron Phosphate_Battery/Pylontech-Lithium-Iron-Phosphate-2.4kWh-Battery-Brochure.pdf

 

This is also quite impressive, many different batteries all linked up on a live chart https://batterytestcentre.com.au/results/pylontech-us2000b/

 

 

Yes, they are LiFePO₄, a decision made largely because of the slightly better safety margin LiFePO₄ cells used to have.  The downside is that the energy density of LiFePO₄ is lower than other chemistries, because of the lower cell voltage.  My experience with early LiFePO₄ cells wasn't positive, either, I bought a lot of 10 Ah cells for my first electric motorcycle battery pack and the failure rate was high and the capacity dropped with age pretty rapidly.  It's notable that LiFePO₄ cells are not the chemistry of choice for companies that have invested heavily in lithium chemistry cells - they are almost uniquely a China-only product, it seems.

[MikeGrahamT21]

13 minutes ago, JSHarris said:

 

 

Yes, they are LiFePO₄, a decision made largely because of the slightly better safety margin LiFePO₄ cells used to have.  The downside is that the energy density of LiFePO₄ is lower than other chemistries, because of the lower cell voltage.  My experience with early LiFePO₄ cells wasn't positive, either, I bought a lot of 10 Ah cells for my first electric motorcycle battery pack and the failure rate was high and the capacity dropped with age pretty rapidly.  It's notable that LiFePO₄ cells are not the chemistry of choice for companies that have invested heavily in lithium chemistry cells - they are almost uniquely a China-only product, it seems.

Right, so maybe not the best. Looking at an in depth review, it seems the US2000B comes with either LiFePO4, or LFP, how does LFP fare?

 

I'm not going to purchase this yet, as its still too expensive at the moment, so I'll certainly keep an eye on developments over the next couple of years.

[SteamyTea]

Yes I am on E7 only.

If I take the total cost i.e. standing charge and VAT into account then my kWh price is, on average 15p/kWh over the last 50 days.

This goes down in the winter as my day time usage is pretty constant, but my night time goes up (all to cock this year as my E7 element broke, but other years show a consistent pattern 15% day usage, 85% night usage).

Quite simply, if you want to store energy, do it as DHW first (200 lt cylinder with elements about £300 and will last 30 years), this can be either for direct usage or as pre-heating.  A Sunamp will do the same, but at several times the cost.

Then, if you have any spare electricity, stick it in a storage heater that is placed centrally in the house i.e. hallway, or somewhere that is permanently cold i.e. dark north side.

 

Whenever I look at batteries they just don't make technical (you have to inform your DNO you got them if grid connected) or financial sense.

Good fun to play with though.

 

Realistically rather than looking at price, CO₂ emissions should be the metric.

[Jeremy Harris]

4 minutes ago, MikeGrahamT21 said:

Right, so maybe not the best. Looking at an in depth review, it seems the US2000B comes with either LiFePO4, or LFP, how does LFP fare?

 

I'm not going to purchase this yet, as its still too expensive at the moment, so I'll certainly keep an eye on developments over the next couple of years.

 

LFP = LiFePO₄ normally, or can refer to LiFeMnPO₄ cells, which are broadly very similar.

[MikeGrahamT21]

Thanks for all the information, its been very helpful.

 

Sure there will be a lot of development on this, led by electric cars, and if the tesla model 3 ever makes it to the UK, and tesla remain a viable company, it may be worth going down that route instead, at least the model 3 is within reach second hand.

[SteamyTea]

The main point I would like to make is 'know your usage pattern'.

[MikeGrahamT21]

I still think on the whole that can be modified to what equipment you have, but the more information you know about your usage, the better.

 

Thanks for alerting me about DNO requirement for storage, i didn't realise that, i found a form which would need filling out should I ever go down this route.

[SteamyTea]

As far as I know the rules about storage are the same as PV.  It is to stop linesman's being shocked.  And they like to know where all the isolators are.

I would not be surprised that in the not too distant future the fire brigade would need to know as well.  Lithium and fire do not mix well.

Edited May 15, 2018 by SteamyTea

[Jeremy Harris]

FWIW, my money is on Tesla when it comes to the "best" battery technology.  Their battery packs are proving to be very reliable, and outperform those made by just about anyone else.  Other companies, like Renault, and even Nissan, are struggling to come up with reliable battery packs that are durable.  Both Nissan and Renault accept that their packs will lose more capacity with time that it seems that Tesla packs do, and I strongly suspect that a large part of that has to do with the way Tesla have integrated cell production into their business, rather than just buy cells in from someone like LG.  Nothing at all wrong with LG cells, but Tesla just seem to have the edge over everyone else, and their latest 2170 cells seem likely to be cheaper, have a higher capacity and longer life than any cell they've produced before.  AFAIK, these new 2170 cells have just refined the chemistry of the LiNiMnCoO₂ cells (also referred to as NMC) that they were using in their previous 18650 form factor cells, but have been aimed specifically at reducing cost for the Tesla Model 3.  I'll lay money that the next generation Powerwall will have these 2170 cells, and there seems a good chance that it may well be cheaper than the current versions which use the older 18650 cells.

[pdf27]

10 hours ago, jack said:

I'd love it if someone would cobble together a system that let you use a proportion of your car's storage to provide time-shifted power to the house in the evenings. I know there are long-term smart grid ideas that take this concept further, but as a country we can't even manage a roll-out of basic smart meters, so I'm not holding my breath for smart grid functionality arriving in the next decade.

See http://www.autoexpress.co.uk/car-news/103256/ovo-launches-vehicle-to-grid-charger-for-nissan-leaf - even without smart meters it's possible to make a profit selling electricity from cars back to the grid.

[jack]

Interesting, thanks. I remember hearing about this a while ago but didn't realise it had launched. Shame it's Leaf (+ that commercial vehicle) only - that's too big and expensive for what I want/need from an electric car right now.

[ragg987]

Just occurred to me that my DHW cylinder is behaving like a battery, except it stores the energy as heat and not electricity.

 

DHW has 300l capacity, so potentially the equivalent of approx 15kWh battery. 1,225 kWh of solar PV was diverted to the cylinder in the last 12 months. Approx £150 saving per year at 12p per kWh.

[ProDave]

12 minutes ago, ragg987 said:

Just occurred to me that my DHW cylinder is behaving like a battery, except it stores the energy as heat and not electricity.

 

A battery that won't wear out, won't get bothered if over charged or over discharged. What is not to like.

[SteamyTea]

22 minutes ago, ragg987 said:

except it stores the energy as heat and not electricity.

"That's entropy man"

[NSS]

13 hours ago, ProDave said:

Another thing people tend to do with FIT solar PV is optimise the panel orientation for maximum yield.  That is fine if your objective is to maximise payment.

 

But for a non FIT self use scheme, you don't just want a passive peak in the middle of the day that you are unlikely to be able to fully self use.  Instead my plan is some panels facing east, to get a much earlier start to useful generations levels and less facing south so the mid day peak will not be as large.  Also if I can manage some facing west would be good to extend generation into the evening, but that is harder to arrange here.  The total yield would be lower, but my feeling is you would generate more self usable power throughout the day.  One option I am looking at is making my east facing bank on a simple flip over mount so they would in effect be on a very basic tracker and those same panels could do the evening burst as well.

This is precisely how ours is configured (7 x 285w panels facing east, 3 south and 4 west) and whilst we are generating less in total, the spread is far more usable. For example, today we were generating 1kW+ from 0715 until 1745 this evening but our peak was only 2.4 and total for the day 22kWh.

Edited May 15, 2018 by NSS

[Jeremy Harris]

I agree, and wish we were able to have some facing East, in particular.  The combination of the cooler temperature early in the morning, the tendency for the air to be clearer and the fact that the sun rises a fair bit North of East in summer, means that East facing panels here would start generating well early in the morning and continue through for several hours.  West wouldn't be so useful for us, as the air seems to always be less clear in the late afternoon and evenings here, probably a consequence of a hot day and the stream and ponds to the West. 

 

I'd did some playing around with a small solar panel when I fitted our solar powered outdoor lights, and was surprised at just how well an East facing panel did.  It slightly out performed the same panel mounted facing South, which I suspect is mainly due to the temperature difference between the two, due to the different times of day that they were working.

 

One long term plan I have is to add some panels to the East facing side of the garage roof, as I'm convinced that a bit of early morning boost would be useful pretty much all year around.  I doubt I'd bother with an MCS install, as we already have consent from the DNO for up to 10 kWp, and currently only have 6.25 kWp. and I doubt that I could get more than a couple of kWp on the garage roof anyway.  The most useful thing would be to have a bit more early morning generation to top up the Sunamp first thing.

[MikeGrahamT21]

I quite like our split system too, although perhaps doesn't generate as much as a south system could, we can at times have generated 2kwh before i even get out of bed. The split wasn't intended, but it does work well. If we ever have a dormer put on, it'll go on the west side, and those 8 panels will get moved to the utility roof, which is south facing.

[SteamyTea]

If you can't fit East or West, but have spare room on the South, then a few extra panels could generate just as much in the mornings.

It is easy to be amazed by generation figures on a very sunny spring or autumn day, there are a number of reasons these can look impressive i.e sun angles, temperature.

But the truth is we usually have cloudy weather, and when we do, angles become less important.  Part load inverter efficiency can dominate then (though they are all pretty good these days).

[Jeremy Harris]

On the topic of batteries, this article about how disruptive battery technology can be when used in specific cases is interesting: https://cleantechnica.com/2018/05/15/elon-musk-harpooned-baseload-power/

 

In essence, Elon Musk took a gamble by making South Australia an offer they couldn't refuse, following major power outages and fluctuating demand that was making wholesale spot market prices vary by thousands of %.  He offered to build a large battery storage facility to enhance grid stability for $50M by a set date, if he failed to meet the date the plant would be free.  In the first four months of operation it saved $35M, a massive return on a $50M investment. 

 

It's an extreme example, created in large part by the chaotic way the power generation system was working (or rather failing) in South Australia, but we're getting to the stage here in the UK where we have enough excess renewable generation to make the wholesale spot market prices go negative very occasionally now.  In a couple of years I suspect we'll see negative pricing on a more regular basis, which then makes big battery installations like this look increasingly attractive.

 

I will admit to admiring the way Elon Musk does things; pretty much all he has done has created significant change, from Paypal, through Tesla to SpaceX.

[jack]

56 minutes ago, JSHarris said:

I will admit to admiring the way Elon Musk does things; pretty much all he has done has created significant change, from Paypal, through Tesla to SpaceX.

 

You can't criticise the scale of the man's vision(s).