Tesla to unveil home storage batteries

Martyn1981 · 10 May 2015 at 3:19PM

zeupater wrote: »

Hi Mart

In the case of the larger system - well, that seems to be a different animal altogether, not designed for daily deep cycling, but as a backup designed for occasional/weekly cycling. As such I see this being suitable for very remote rural areas where weather has a greater than average effect or areas of the world which suffer regular power generation failures. Although 10kWp storage at the Tesla levels is good if the expected battery life is believable,

HTH
Z

Hiya Z, I was actually referring to the Powerpack 100kWh (not the larger10kWh Powerwall), when I mentioned their larger battery.

I'm actually inclined to agree with you about domestic storage needing a foot up, but I was thinking, pondering, (ok guessing) that if the Powerpack shares technology, then those sales may be enough to help maximise the investment in the new 'Gigafactory' and help to bring down Tesla battery costs in general, including the Powerwall.

Of course, they may be totally different beasts and my guess is complete nonsense.

The pluses for the Aussie market look good, great solar generation, massive uptake of domestic PV, and high leccy prices. But the down side seems to be relatively high prices for batts and ancillary equipment when compared to US/EU. If batts become economic in Aus (for on-grid) then the market would get big, very very fast.

It will be interesting to see where the bigger batts go. In most of the articles I read concerning shipping container sized batts, they often seem to be deployed for use at PV and wind farms to smooth out the leccy supply.

Fancy taking any guesses at how long it will be before the storage market explodes (so to speak)? I really don't have a clue now as the Tesla offering seems to have shaken things up more than I expected.

Mart.

zeupater · 10 May 2015 at 3:28PM

Martyn1981 wrote: »

I should probably clarify that statement. The cheapest way to integrate PV and storage would probably be a hybrid inverter that monitors export and diverts excess into batteries. It then releases stored energy when needed. So PV inverter, battery inverter, charge controller and demand/export monitoring all rolled into one.

But .... this would place the batteries before the TGM. So for older, and higher FiT rates, the battery conversion loss of perhaps 5 to 10% would have a significant impact on FiT income. In my case, if I could use 1,000kWh of stored leccy, I'd need to put approx 1,100kWh into the batteries. Resulting in FiT losses on that 100kWh.

Not so important for my WNW system at 20p, or new installs at 13.39p (soon to be 12.92p). In 10 years time, if the current degression programme doesn't change, then FiT rates will be 8.5p at most, and have little relevance to an integrated PV + storage rollout.

So for older systems, it may be better to install the batts (and charge controller, and two way inverter) after the TGM with a 'simple' diversion switch approach monitoring export. But this system would be slightly less efficient overall.

Mart.

Hi

Our SB inverter has an inbuilt feature to switch an external load at a pre-set threshold, this could be direct to battery before the TGM, or just open/close a relay to utilise household power ... not pretty, but doable ... However, the most likely setup would be equivalent to a proportional control DHW, just using charge control & inverter ....

Still being on-grid, a maximum draw from the batteries of 500W would probably suit most users ..... that level would cover base-load, so import would just start when a high-draw appliance is being used, so we're not really talking about a particularly large or expensive unit ....

Regarding storage efficiency losses ... I'd look at something above 5% to 10% ... Tesla specs say "92% round-trip DC efficiency", so there's inverter/charger losses to account for too, so probably a range of 85% to 87.5% 'system' efficiency would be closer to the mark ....

HTH
Z

Martyn1981 · 11 May 2015 at 8:07AM

zeupater wrote: »

Hi

Still being on-grid, a maximum draw from the batteries of 500W would probably suit most users ..... that level would cover base-load, so import would just start when a high-draw appliance is being used, so we're not really talking about a particularly large or expensive unit ....

HTH
Z

Not fair Z, that set me off on a long ponder!

So a relatively cheap and small inverter to supply 500W would provide for baseload, and evening demand. It would also cope quite well with leveling out demand and supply when PV generation (on average) exceeds washing machine, or dishwasher demand (on average) but can't meet water heating spikes. Interesting.

Assuming reduced draw from the batts also means a reduced charging rate too, then that would solve a problem I've been wondering about. Picture Germany, with their enormous demand side PV generation. During week days, when household demand is low, but industry/commercial demand is high, the batts would be charging all morning, supplying little leccy, then around mid-day when the batts are full, leccy supply would rocket. But a smaller battery draw all day would maintain a more steady export rate too.

I guess what we're talking about here isn't a system to store as much as possible, and meet as much need as possible, but rather one that just levels things out a bit, at a smaller more reasonable cost?

Presumably, there must be some economic papers investigating all the options, and trying to work out the most cost-effective method of matching demand peaks with intermittent generation.

Mart.

zeupater · 11 May 2015 at 11:26AM

Martyn1981 wrote: »

Not fair Z, that set me off on a long ponder!

So a relatively cheap and small inverter to supply 500W would provide for baseload, and evening demand. It would also cope quite well with leveling out demand and supply when PV generation (on average) exceeds washing machine, or dishwasher demand (on average) but can't meet water heating spikes. Interesting.

Assuming reduced draw from the batts also means a reduced charging rate too, then that would solve a problem I've been wondering about. Picture Germany, with their enormous demand side PV generation. During week days, when household demand is low, but industry/commercial demand is high, the batts would be charging all morning, supplying little leccy, then around mid-day when the batts are full, leccy supply would rocket. But a smaller battery draw all day would maintain a more steady export rate too.

I guess what we're talking about here isn't a system to store as much as possible, and meet as much need as possible, but rather one that just levels things out a bit, at a smaller more reasonable cost?

Presumably, there must be some economic papers investigating all the options, and trying to work out the most cost-effective method of matching demand peaks with intermittent generation.

Mart.

Hi

Yes - think about it in terms of a hybrid vehicle .... the battery soaks up energy when excess power is available and releases it when required, either to assist in times of power deficit (acceleration/kettle) or cover total demand when power/energy requirements are relatively low (low speed maintenance/short journeys/domestic base-load) ....

Because the engine is there the battery doesn't need to be able to cope with maximum power demand, just help out - this is comparable with being able to release (say) 500W from a domestic reserve when you're generating 700W and switch a 2.5kW kettle on with the grid playing the part of the engine - when the water's hot then the battery recharges ....

HTH
Z

pinnks · 11 May 2015 at 5:31PM

I have been thinking on similar lines for a while.

My immersion diverter knows how much is being generated and then works to divert the excess to whatever is attached. So why not use that sort of technology to turn a battery charger on and off (not proportionally of course) when there is sufficient excess. This charger could feed some batteries.

Then, using the diverter principle in reverse, when generation drops below a threshold, turn on a small 200W or 500W inverter to push the battery power back into the house to cover base load, or up to the 500W or whatever. It should presumably be possible to match load up to the max to avoid exporting.

Not perhaps the most efficient way to do things but is something like this possible and would it cost an arm and a leg?

lstar337 · 12 May 2015 at 9:55AM

pinnks wrote: »

So why not use that sort of technology to turn a battery charger on and off (not proportionally of course) when there is sufficient excess. This charger could feed some batteries.

Then, using the diverter principle in reverse, when generation drops below a threshold, turn on a small 200W or 500W inverter to push the battery power back into the house to cover base load, or up to the 500W or whatever. It should presumably be possible to match load up to the max to avoid exporting.

There are inverters that already do this internally. Wouldn't that be more financially viable?

pinnks · 12 May 2015 at 8:25PM

I don't know as this has just been idea buzzing round my head as a potential add-on. Do you mean the 200/500W inverter or the main PV one? wouldn't seem to make sense to change the main one.

Martyn1981 · 13 May 2015 at 8:04AM

zeupater wrote: »

Hi Mart

Regarding the subsidy for daily storage, I don't really see the demand anywhere growing to a level which would seriously drive prices down without an initial subsidy ... that's effectively what Musk will be looking for, a change which will switch focus from generation to a form of integrated micro-generation+storage ...

Hi Z. Read this today and thought of your post:

Germany: KfW subsidizes over 10,000 solar battery systems

Demand for solar power storage systems in Germany is continuing to rise, with reports that over 10,000 storage batteries for PV systems have been subsidized since 2013. Q1 2015, meanwhile, has seen a 40% YOY increase in the subsidization of such systems.

I'd be very interested to know how the subsidy costs work out. Does the shifting of generation to higher priced daily periods mean it's cost effective now (unlikely?), or just a test programme to kickstart the market, ready to displace high cost (carbon and health) of Lignite burning.

As mentioned earlier, I'm not convinced that the UK should consider a support scheme, since our PV generation is no where near disruptive (yet), and there are plenty of cash rich countries already moving into the storage arena.

[Edit: Actually, I'll contradict myself, perhaps give it two years for costs and tech to develop, then organise (with a leccy company or DNO (or both)) a supported test rollout on new builds with PV and a small amount of storage! M.]

I'm still finding all this fascinating, but must admit, I can't work out if things are actually snowballing yet, or just teetering on the edge, with impressions being muddied by the recent media coverage.

Mart.

zeupater · 13 May 2015 at 11:32AM

Martyn1981 wrote: »

Hi Z. Read this today and thought of your post:

Germany: KfW subsidizes over 10,000 solar battery systems

I'd be very interested to know how the subsidy costs work out. Does the shifting of generation to higher priced daily periods mean it's cost effective now (unlikely?), or just a test programme to kickstart the market, ready to displace high cost (carbon and health) of Lignite burning.

As mentioned earlier, I'm not convinced that the UK should consider a support scheme, since our PV generation is no where near disruptive (yet), and there are plenty of cash rich countries already moving into the storage arena.

[Edit: Actually, I'll contradict myself, perhaps give it two years for costs and tech to develop, then organise (with a leccy company or DNO (or both)) a supported test rollout on new builds with PV and a small amount of storage! M.]

I'm still finding all this fascinating, but must admit, I can't work out if things are actually snowballing yet, or just teetering on the edge, with impressions being muddied by the recent media coverage.

Mart.

Hi

At around 25p/kWh Germany would show a storage B/E well before here, they also have an issue with the high penetration level of pv having a potentional effect on grid stability ... currently this is handled by inverter functionality which reduces inverter output (eg - http://www.sma.de/en/partners/knowledgebase/sma-inverters-as-grid-managers.html ) thereby wasting energy generation potential, something which managed diversion to a storage system (local battery or grid scale) would go a long way towards solving ....

This is why the Tesla offering is so interesting - yes, storage needs support at the moment, probably on a global scale, but this could simply be in the form of subsidy reallocation from large-scale generators to storage solutions, therefore no additional public funding ...

In addition to the above, as technology economies of scale and competition kick in causing prices to fall (similar to pv), subsidy levels can actually be reduced, something which never seems to happen to grid-scale generation subsidies, they only ever increase ...

HTH
Z

JimLad · 19 May 2015 at 11:20AM

Not sure if this is new, but some tech specs here and you can now reserve them in the USA.

http://www.teslamotors.com/powerwall

Tesla to unveil home storage batteries

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