Battery Storage System for Solar/E7

tim_n

I have solar with enphase microinverters, therefore I have no main inverter.

Most products seem to be geared around the more efficient route of storing DC, but I obviously can't do that.

So is there any AC storage systems that can take into account energy export and store that energy into a battery system?

Similarly anything I can programme to take advantage of reduced E7 rates at night?

Andrew_Hedman

Hi, I believe the "Victron Hub 2" is capable of doing such a thing, It can be programmed to buy and store energy at off peak times from the grid and then energy stored can be used to power your home between peak times thus cutting your electric bill to virtually nothing.

I hope this helps.

EricMears

Andrew_Hedman wrote: »

Hi, I believe the "Victron Hub 2" is capable of doing such a thing, It can be programmed to buy and store energy at off peak times from the grid and then energy stored can be used to power your home between peak times thus cutting your electric bill to virtually nothing.

Andrew seems to be a new member so won't be able to post links. Here's one that describes the system he mentioned :-
http://www.homeenergystorageuk.co.uk/victron-hub-2-home-energy-storage/

It doesn't alas give any prices and the further link to the Victron site is even less helpful. But here's another link that suggests a price of Approx £4k
http://www.windandsun.co.uk/information/solutions/on-grid-solar-pv-battery-storage-solutions/victron-self-consumption-and-back-up-battery-system-(hub-2).aspx#.VmqTJf0rHRY

"cutting your electric bill to virtually nothing" is something of an exaggeration though ! If it were able to store enough so that your whole house ran on E7 power all the time, the best you could hope for is a roughly 50% cost reduction but you'd need a very large battery pack which I doubt is included in the £4k guide price above. Assuming another £10k for batteries (based on electric vehicle replacement battery estimates) and a ten year life you'd need to save well over £1000 per year even to think about buying such a system

MFW_ASAP

Solar, let alone battery storage of solar, is rarely cost effective when compared with other investments, especially if you've borrowed money to finance the investment.

If the OPs aim is to use more renewable energy, then perhaps switching to a green tariff that uses 100% clean energy would be the cheaper option than buying batteries?

Sterlingtimes

MFW_ASAP wrote: »

Solar, let alone battery storage of solar, is rarely cost effective when compared with other investments, especially if you've borrowed money to finance the investment.

I would agree that solar without battery storage, without subsidy and having regard for all of the risks of the solar investment is not cost effective compared with other investment.

I can see political advantage, however, in having the UK producing a range home produced generation types.

I would question the viability of using large scale battery storage to time shift.

Cardew

MFW_ASAP wrote: »

Solar, let alone battery storage of solar, is rarely cost effective when compared with other investments, especially if you've borrowed money to finance the investment.


Agreed

If the OPs aim is to use more renewable energy, then perhaps switching to a green tariff that uses 100% clean energy would be the cheaper option than buying batteries?

IMO the term '100% clean tariff' is questionable.


http://www.energysavingtrust.org.uk/domestic/buying-green-electricity

How green are green tariffs?

• Opting for a green tariff will not mean that the electricity you buy is all renewable. You cannot consider that your electricity supply is zero carbon or carbon neutral.
• Opting for a green tariff can provide additional incentives for new renewable generation or energy efficiency measures, and so lead to some additional carbon dioxide savings in the long term.
• If you opt for a Certified Green Energy Supply, then there will be some guaranteed additional benefit. Green tariffs are no substitute for energy efficiency and you should always do whatever you reasonably can to reduce your current use of electricity and other fuels before considering spending money on a green tariff.

The Energy Saving Trust does not recommend specific suppliers of green tariffs.

EricMears

Prices of such systems are always in the "how long is a piece of string" category My background consumption is around half a kW so 4.6kWh of storage wouldn't really be enough to last me overnight at this time of year even without any large appliances running. A hot drink at bedtime let alone cooking an evening meal is going to ramp up the size (and price !) of battery required. I based my 'guestimate' on VW's EV battery where a nominal 20kWh (but effectively more like 18kWh to avoid running at either extreme of range) Lithium battery is quoted at £11,000 (and I'll believe anyone who points to VW's current reputation and suggests a lower price would be justified)

Cardew

EricMears wrote: »

(and I'll believe anyone who points to VW's current reputation and suggests a lower price would be justified)

Current reputation? They have been at it for years!

EricMears

This is very odd ! I posted this as a reply to a new MSE member who said he was the owner of a website I'd quoted earlier ( http://www.homeenergystorageuk.co.uk/victron-hub-2-home-energy-storage/ ) but I saw later that it had been "Last edited by MSE ForumTeam3; Today at 4:43 AM.. Reason: Quoting deleted post " . The deleted post 'advised' me that a 4kWp solar installation in Derby would never exceed 12kWh/day hence I replied :-


Afraid there's an error in there somewhere.

PVGIS predicts (and 4 years local results confirm) that our 4kWp of panels (25mls N of Derby) should generate around 470kWh/month in May/June/July (and prob slightly more if our roof was steeper). That's an average of nearly 16kWh/day and of course individual 'good days' will be (indeed were) well over 20kWh/day.

But the person asking the question was actually asking if it might be possible to charge up batteries on E7 at this time of year then not buy any daytime electricity tomorrow. I'm sure that would require a huge battery !


Not only was that post deleted, but also its poster's only other contribution in which he introduced himself as the website owner has also vanished.

Martyn1981

tim_n wrote: »

I have solar with enphase microinverters, therefore I have no main inverter.

Most products seem to be geared around the more efficient route of storing DC, but I obviously can't do that.

So is there any AC storage systems that can take into account energy export and store that energy into a battery system?

Similarly anything I can programme to take advantage of reduced E7 rates at night?

Hiya Tim, what you are suggesting is relatively simple and extremely complicated at the same time.

As others have said, there are products such as the Victron (Nedap, SMA island inverters SolarEdge/Tesla etc) that can do it all, working with the PV, grid and batts.

Alternatively, something like this could be a cheaper solution, but not a recommendation. You need to watch the tech develop and also ensure it's certified for the UK.

Next you'd need to monitor import/export. Nothing new there, the diversionary switches do this, so if you are exporting more than a set amount, say 50W, you'd want to divert generation into the batts. Next, you'd need to monitor import, and if it exceeds a set amount, again say 50W, then the batts would kick in, assuming their state of charge is high enough.

You'd also need to add in some kind of timing system to coincide with E7, but this may need to be seasonal (see later).

Now comes the tricky bit, batts. For large off-grid systems I've seen figures as low as 3p to 4p/kWh. This is the cost of the batts, divided by the number and size of cycles. But these are big kits in the 40kWh to 60kWh range and typically lead acid. Do you want a huge stack of LA batts in your house?

Since you are grid connected, you wouldn't want a large battery system providing 5+ days of backup. In fact, if you intend to use E7, you might only want enough storage for the evening. As you go for smaller systems, such as the 7kWh Tesla Powerwall, the price goes up, and so does the spread cost per kwh. At the moment you'd be looking at 7p to 8p/kWh just for the batts and that probably eliminates any E7 savings.

Just to be clear, your storage needs would probably be quite low since a lot of your leccy needs would (at varying times) be met either by real time PV generation or E7. And being grid connected means you don't need to worry (economically) about longer time periods.

Back to batt sizes, I only import about 2.5kWh per day in the summer, so anything bigger (at that time) would be unnecessary, and since after providing evening/nightime coverage, I could expect the batts to be refilled the next day by excess generation, I wouldn't want to purchase any E7. Hence my earlier reference to seasonal flexibility.

So, I don't think what you are asking is too difficult, but it's not going to be financially viable at the moment, and ideally you'd probably want all of the functionality contained in a single system (inverter) but you also have the micro's duplicating costs.

On the bright side, domestic PV and storage also brings benefits to the leccy suppliers as they don't have to purchase as much leccy at evening peak prices, and it can also benefit the DNO's (local leccy distribution, as opposed to the national grid). For these reasons there's always the chance that storage costs could be subsidised, or perhaps more fairly described as spread across several interested parties. But I wouldn't hold my breath in the UK.

Here's an example of a storage experiment, but its not cheap:

Tesla Powerwall Offered To Vermont Utility Customers… $0 Down

Mart.

MFW_ASAP

Cardew wrote: »

IMO the term '100% clean tariff' is questionable.


http://www.energysavingtrust.org.uk/domestic/buying-green-electricity

Possibly, though better than nothing. If enough people move to green tariffs or totally green suppliers then 'dirty' energy companies will see the loss of market share and do something about it.

Naturally, the first step should be to reduce energy waste, then look at how you use energy and perhaps modify behaviors (i.e. half full dishwashers/washing machines, thermostats on radiators).

It'd be interesting to note whether spending solar PV money instead on fitting modern zonal/per room central heating manifolds, energy efficient appliances, lighting circuits on timers, etc. would be cheaper and give a better return. Given that most solar energy is produced in summer, when most domestic customers use less energy and very little solar power is produced in winter, when domestic customers use the most energy....