Solar PV & Tesla Powerwall.

[Dodgy]

Some unnecessary maths:

I’ve saved £3.08 in the last couple of days

38% from using solar instead of grid
45% from shifting daytime to nighttime rate
17% from generation and export tariffs

Does the BYD battery allow charging at night? If it does, it would have saved me £1.77 at a better ROI than my Powerwall. If not, it would have saved me £1.28, at a lower ROI.

 

[Dodgy]

One more question about the BYD: what’s it’s maximum output? I’ve just discovered the Powerwall has a maximum of 5kW, which sound like loads, but our baseline demand from fridges and freezers is 100-400W, the underfloor is 4kW and the dishwasher that I forgot to set off last night is 1kW when it’s heating the water.

As an aside, our Microwave on a 600W setting seems to use 1.4kW. WTF?

 

[Deleted member 126969]

Actually, I should apologise for using the phrase “no axe to grind” as it kind of implies others do, and that wasn’t what I meant. I should have chosen my words more carefully. My intent is just “we’re having a conversation”.

 

[Deleted member 126969]

Found an image grab of when the PW was doing that low-discharge oscillation thing back in January.

 

[Dodgy]

That’s messy. I will definitely be raising a support call if I see anything similar.

Today was my best so far for solar production - a massive 6.1kWh. Looking forward to the longer days...

I’ve noticed that I’m seeing different numbers for energy going into and out of the Powerwall. Today was 18.2 in and 16.1 out. Given that it’s filled every night and emptied every day, I’m a bit puzzled about the meaning of the difference. Any ideas?

Quick update on the financials: 15% of the benefit is from the FIT, 52% from using economy 7 during the day and 33% from using solar power instead of grid. I can imagine that it will be a totally different split in the summer.

 

[Deleted member 126969]

It was a good day wasn’t it. 8.3 here.

I’ve also noticed the poor round trip efficiency at times. It’s worse when it’s cold I think, it seems to use a fair amount for warming the battery. I’ve seen the odd day where it’ll take a chunk from the grid to top up and warm up and give nowt back at all.

It’s a shame they decided to drop the DC version, I’ve no doubt that would have given somewhat better efficiency overall by removing two conversion stages, but mostly, it’s the cold weather I reckon.

 

[Dodgy]

Solar envy...

If I hadn’t just spent silly money on the panels and battery, I would be looking for a house with a big, south-facing roof in a place where the sun shines a bit more!

I wondered whether it could be as simple as efficiency, but 10% seemed quite a large loss.

Only three days to the solstice and less than two weeks to the latest sunrise. Looking forward to seeing the numbers go in the right direction.

 

[Deleted member 126969]

We are lucky with this roof. It even has a better pitch for catching the rays than a more typical one.

It’s funny you mention the costs. I agree, it feels like a lot of money.....but then when I compare it to what I’ve lost in depreciation on the C350e in less than two years.....not so much! And in terms of house prices, it’s nothing is it, just wriggle room on the price.

They claim efficiency in the high 90s, but I think that’s only the inverter/charger path and doesn’t include “maintenance” overheads.

As you say, it’s pretty good for almost being at the winter solstice isn’t it.

 

[Deleted member 126969]

Just thought, here’s the output from the SolarEdge app. You should soon be climbing the hill

 

[Deleted member 126969]

Had 11 hours yesterday with no grid draw. Average day, both of us home, me in the shed during the afternoon with lights on and a bit of welding too.

 

[Dodgy]

Had 11 hours yesterday with no grid draw. Average day, both of us home, me in the shed during the afternoon with lights on and a bit of welding too.

Similar here, although only because I filled the battery overnight. The sooner I get rid of this underfloor heating, the better. Just need to rip the back off the house... [emoji51]

 

[Deleted member 126969]

I really must get myself on an E7 tarrif as soon as I can.

 

[Dodgy]

My first solar car charging currently in progress! 1.3kW coming from the panels, 0.9kW from the battery, which already has over 5kWh of solar generated power in it from earlier today. This evening’s errands will be 100% fuelled by today’s sunshine.

 

[Dodgy]

Spoke to my Dad today. He lives in Auckland, New Zealand. He also has solar panels. Quite a lot less than me. Average daily generation is 10kWh. Payback in 6 years.

 

[Deleted member 126969]

Our system produced 5.66MWh last year, so 15.5kWh per day on average. Going to take a bit longer than 6 years to break even.....

Presumably electricity prices are higher and/or FIT more generous??

Nearer the equator than we are so better sun anyway of course. Not jealous or anything

 

[Dodgy]

Our system produced 5.66MWh last year, so 15.5kWh per day on average. Going to take a bit longer than 6 years to break even.....

Presumably electricity prices are higher and/or FIT more generous??

Nearer the equator than we are so better sun anyway of course. Not jealous or anything

I will get the details. I think fewer panels and no battery means a cheap system, but the rest is a mystery.

 

[Deleted member 37751]

Iirc in New Zealand you can pay a fixed daily cost for your electric like you can here with water, different prices for different users obviously.

 

[Dodgy]

Update on my Dad’s setup in NZ:

1. Electricity is approximately the same price as here (20-30c per kWh - about 11-17p per kWh)
2. Solar panels are slightly more expensive than here (NZD3000 per kWh - about £1700 per kWh)
3. Electricity distributors buy exported power for roughly 1/3 of the price you pay them
4. His panels are much more effective than mine because he’s closer to the equator and his panels are aligned slightly closer to north than mine are to south (1300kWh/kWp compared to my 900kWh/kWp)
5. He has a pool, so he uses a high proportion of summer generation without needing a battery

I should have realised that a pool would be a better option than a battery!

 

[Dodgy]

I know it’s January and I really shouldn’t be getting excited, especially with a week of cloud and possibly snow being forecast, but today was a personal best.

Even after using 41% of the overnight top-up on underfloor heating plus toasters, kettles, coffee machines, lights, extractor fans, etc, the solar nearly topped up the battery. It got back up to 93% charged and would have been 100% if clouds hadn’t arrived at about 11am. It makes me wonder how much I’ll be doing the economy 7 charging. I guess that when we back off the underfloor heating, it’ll be overkill to completely fill the battery.

On average, over 55% of my savings have come from overnight charging. But if I just look at the top 5 days for solar production, it’s less than 40%. And it’s January - the top five days are only generating just over 6kWh per day! The economy 7 thing might not turn out to be as important as I expected...

 

[Deleted member 126969]

30% charge by about 9 pm is enough to see us through to the sun coming back out normally. I suspect you won’t be making much use of E7 charging buy the time we reach April.