Makes more sense to export unused solar than use to heat water/charge car

[conor_mc]

How much does a battery cost, how long does it perform at it's max, and how long until it realistically needs replacing..?

The answer seems to be it depends. To remove a 5kWh battery from my quote was -€1250…. great, I’ll add a second, I said… that’ll be +€2,250 then. Wholesaler discount passed on, yadda, yadda.

I see the same unit advertised at €1400+ VAT.

But, I ordered a GobelPower 15kWh battery from China (good rep, see OffGridGarage on YouTube) delivered duty paid for €2300, albeit shipment takes 2-3 months.

Batteries are generally warrantied to retain min 80% capacity for 6000-10000 cycles, so 15+ years at average of 1 cycle per day.

The real value is they protect your Solar PV investment by giving you options - either buy-low-sell-high when gap between night/EV-rate and export rate is favourable (as it generally is currently) or maximise self-consumption if/when it’s not.

 

[Itchy]

About to put in a bigger battery so I can justify 7c/32c on an EV tariff

What are the economics of that? The 7c rate is only available for 4 hours a day? Whats the maximum draw from the grid during that time 9kW/hr? 9*4*(.32-.07) = €9 per day, maximum savings if you store and use everything drawn from the grid, less if you export the unused. If the battery capacity is 15kW then 15*(.32-.07) = €3.75 per day if you consume it all.

 

[Buddyboy]

What size system have you installed, if you don't mind me asking, please?

System is 22x 440w panels, 12 facing East, 10 facing west. Inverter is a Solus 5kWh. Have Eddie and Zappi installed, but very little driving and hotwater use (I charged the car last Saturday and still have more than 1/2 charge left). Eddie is turned off at the moment.
Heat pump installed

Looking at the stats for the last few days, most of our electricity is used during the night (night rate 12c) by the heat pump including DHW. For example, right now @ 15:17, house is using .3kWh, panels producing 1.7kW, 1.4 kW exported. Today so far, since midnight, imported 20kWh, Generated 19kWh, of which 5kWh consumed. 14kWh exported.

 

[conor_mc]

What are the economics of that? The 7c rate is only available for 4 hours a day? Whats the maximum draw from the grid during that time 9kW/hr? 9*4*(.32-.07) = €9 per day, maximum savings if you store and use everything drawn from the grid, less if you export the unused. If the battery capacity is 15kW then 15*(.32-.07) = €3.75 per day if you consume it all.

Max draw from grid in 4 hours is 63A(main fuse) x 230V x 4 hours = 58kWh. I wouldn’t aim to max it out, but even our EV charging is only about 10-15kWh a night.

So with say a 90% round-trip efficiency and exporting 90% of battery capacity at 20c, you could “earn” (.20 - 0.07) x (15x90%x90%) x 365 = €576 per annum.

That’s a theoretical floor as in reality I’ll use a portion to offset consumption at 28c instead of exporting at 20c. I’d personally ignore 32c as that’s not what I would pay if I hadn’t changed to an EV tariff, so it would exaggerate the benefit.

My own battery payback calc’s are about 4-5 years, being conservative.