Tesla Powerwall 2

Nice but really doesn't make any economic sense at this moment. Best value is to use it on its own to suck up night rate and use it during the day. Say you have a big house and use about 5000kWh during day time hours (charge your car at night) and you would use the Powerwall to its full capacity every day.

Than it saves you (15c - 6.7c) * 13.5kWh per day = a bit under €400 per year. That's the theoretical maximum benefit. Even if the Powerwall lasted for 20 years (7500 full cycles) with zero maintenance, you would just about break even. Or in other words - there are only 3 reasons for buying this right now:

1. you already have solar and you have a huge overproduction that you can not use. Not even feed to grid for FIT or use to heat your water
2. you want / need to be off-grid
3. you just want to do it for the craic

Oh. Watched the vid in full just now. You can't charge this with cheap night rate. Not yet anyway. I find that very peculiar. Wouldn't be very hard at all to implement and wouldn't cost much I'd have thought. Do the yanks not have cheaper night rates maybe, so they never thought of this?

unkel wrote: »

1. you already have solar and you have a huge overproduction that you can not use. Not even feed to grid for FIT or use to heat your water

There is no FiT so by definition, if you have solar, you derive no benefit from exported power. Most domestic Solar PV installations in Ireland see most of their production in the middle of the day when nobody is home, and therefore in most installations of 2kW or more (~4kW would be a reasonable domestic install in the UK or NI for example) much if not most of the power is wasted by exporting it. If you have battery... you store that excess power and use it during the evening peak. ESB has been looking at a 3-tariff system for years (peak, daytime, night) and a home battery + 4kW solar would practically eliminate most people's use of the two higher-priced tariffs.

greglo23 wrote: »

The reason it can’t use night-rate is safety. They haven’t figured out a 100% foolproof way to ensure that, in the case of a power-cut the Powerwall won’t feed
volts back into the grid with repair crews working on it. Basically an electrical non-return valve that’s guaranteed to work on any and all grids worldwide.

Doesn't a G59 relay with islanding features do that?

unkel wrote: »

Or a lot smarter than that, tariff based on actual wholesale spot price. Load your battery up when the wind is blowing in the middle of the night for 1c/kWh

ill beleive it when I see it

"Our children will enjoy in their homes electrical energy too cheap to meter." - "Lewis Strauss, then chairman of the United States Atomic Energy Commission , in 1954"

yeah , how'd that work out Lewis

Yup, nobody in the market can beat Tesla on price per kWh at the moment.

Prime Hybrid Energy requires an external inverter (replacing your existing inverter, which is an additional cost) which is limited to putting out 3kW regardless of how many batteries you connect (so you can forget about running certain appliances or charging the car during a power cut).
Each 5kWh battery block can only output between 2.32-2.85kW depending on state of charge.

The powerwall has a built-in 5kW inverter capable of supplying up to 7kW for short periods. It allows the future upgrade path of adding up to 9 powerwalls for a total sustained discharge of 45kW.

Only real competitor Tesla has is LG's RESU batteries, but they are pricier per kWh and you still need an islanding or battery capable inverter (budget €1-1.5k): https://www.mg-solar-shop.de/pv-battery-offgrid-systems/LG-Chem-Battery-strorage/

It depends on what you want to accomplish, what your current and possible future PV array looks like and what your loads are.
If you just want something cheap to reduce the amount of power exported to the grid for nothing in return Moixa are a good option: http://www.moixa.com/products/

In practically every other residential scenario Tesla rules the roost. The big issue is getting a powerwall... there's a reservation list....

unkel wrote: »

The big drawback of the powerwall is that is is fairly dumb. If only it could charge up at night rates and release during the day (so that in fact you'd only pay night rate for all your electricity needs), then it would start to make financial sense

As of now, it makes no sense. It's an expensive toy for enthusiasts or people who have to live off grid.

So the powerwall charges from the voltage from the solar panels so it's only a matter of a power supply to feed it at night. Can't be very difficult to rig up a 48V switched mode psu.

From that site wave power could be the way forward, they are producing 2Mw units which can be harnessed together, solar is also becoming very attractive after seeing what they do there. A truly smart grid is not impossible and very achievable.

Deleted User wrote: »

At 7 cent per Kwh night rate and 17 cent day it makes no sense to install solar PV

Indeed. I've just installed a 750W Solar PV system today

At a fraction of the price installers are looking for though. My payback period is about 5-6 years. The solar PV system the ESB are offering has a payback period of at least 40 years...

Got an inverter on eBay for a fraction of what they normally go for, got 3 end of line panels for a bit more than half of what they normally go for. All the stuff is click and play, 100% waterproof. Had to make one cable myself, but was pretty easy to do. Used dedicated mounting system for PV panels and spend a few hours this afternoon with a lot of help from my neighbour, putting it up on the shed. Total spend just over €500. I guess the 3 bottles of good wine I gave him will add a few months to my payback period

And I will use all of the output at full daytime rates as it is for a high electricity consuming hobby that needs about 850W 24/7, so no feeding back to the grid.

wait wut? your feeding into your home supply from a 3 pin plug?

whats your expected output per day?
what size were the panels?