Solar options for home in 2022.

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1769 posts

Uber Geek

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Subscriber

#3339342 4-Feb-2025 20:57

LightbulbNeil:

On a really good day for Dec Jan , our 10kW east west will get to 10kW output. Our roof is shallow at 15deg. Nov 2024 to now has been alot more productive than Nov 2023 to end of January 2024. Its looking like about 8 to 10% more production. So it seems there are quite significant changes in the years for solar production. We based our system for the highest winter production. On average the 10kW east west is about 8 kW of peak production and about 6kW from 10 to 3 pm or so in Dec Jan. This season our peak daily production has been up to 112kWh a day or more are in the 107 a day range. A lot higher than last year.

How do you heat the house in winter at night?, does the Battery have enough saved energy to run the heating over night?. I can see the benefits for me in summer and the spa in winter days just struggling working out the pros and payback of batteries over winter. In lower North Island gets pretty cold where we are

LightbulbNeil

57 posts

Master Geek

#3339354 4-Feb-2025 21:49

Hi Stu1,

We don't have any batteries. We just sell the excess to the grid.

As we have a 3pase system, currently with our inverter would require 3 batteries. Based on last winter, we would have needed about 50kWh of battery to get us through without charging the batteries from the grid. Based on a 15 year battery life, would be a cost each year of about $3500 to pay off the batteries. We get about $1200 cash after a years selling of solar and no bills at all, including running a spa pool year round.

Our house is heated or cooled by 3 heat pumps. One in the bedroom 2.5 kW, one in the lounge/kitchen area 4.8kW, and a 3.kW in the rest of house unit. Our hot water is by bottled gas instant hot water, which effectively is paid for by the solar currently. We use from the grid in winter an average of 26kWh a day. If there is a lot of sunny days, then we use less. If cold, rainy days, then we use more. The most we use in winter, from the grid, has been 34kWh. We do not do anything to be saving energy specifically, but do use the heat pumps in the day to use what we can from the solar.

This coming winter, we are going to try and heat the house quite warm in the day and see what happens if we turn off the heatpumps at night.

If you only have single phase supply, then the sell back is mostly limited to 5 kW.

The pro of a battery is you have power if there is a problem with the grid. Some take the view of with batteries, are not wasting the excess generated power , and can then use it at night etc. All true. For us in Hamilton, currently the grid is our battery. But when it goes down, we just don't open the fridge etc. So far we have not had any long time power cuts in the last 10 years. Most have been less than 3 hours.

Stu1:

LightbulbNeil:

On a really good day for Dec Jan , our 10kW east west will get to 10kW output. Our roof is shallow at 15deg. Nov 2024 to now has been alot more productive than Nov 2023 to end of January 2024. Its looking like about 8 to 10% more production. So it seems there are quite significant changes in the years for solar production. We based our system for the highest winter production. On average the 10kW east west is about 8 kW of peak production and about 6kW from 10 to 3 pm or so in Dec Jan. This season our peak daily production has been up to 112kWh a day or more are in the 107 a day range. A lot higher than last year.

How do you heat the house in winter at night?, does the Battery have enough saved energy to run the heating over night?. I can see the benefits for me in summer and the spa in winter days just struggling working out the pros and payback of batteries over winter. In lower North Island gets pretty cold where we are

EgorNZ

50 posts

Geek

#3339477 5-Feb-2025 10:05

For comparison... I have a 10kW solar system with 13.5kW Powerwall 2 battery. There's one large ducted heat pump servicing the whole house, this unit can consume up to 8-9kW at full power. Hot water is from two electric cylinders (no gas at all). I work from home so the house is occupied all day.

Here's my usage on a relatively bad day last winter. You can see that solar production was low, there must have been thick cloud (probably raining). The heat pump was programmed to turn on at 6:30am and warm up the house in the morning. It was able to run for 2 hours off the battery, before beginning to import from the grid at around 8:30am, while solar production wasn't significant until after 9:00am. The house is already up to a comfortable temperature at this point, and the heat pump only has to maintain it there. From 10:00am consumption is low enough and solar production, though meagre, is sufficient to allow the battery to be charged. By 2:00pm the battery is back to about 50% full, but temperatures are falling and more heating is required. The combination of battery and solar allows for another 2 hours of heating without importing from the grid, but by 4:00pm solar has ebbed away and the battery is depleted. From 5:00pm the heating (probably some cooking and hot water in here too) must draw from the grid only. But at 9:00pm my free power tariff (Contact Good Nights plan) kicks in, the heat pump is cranked up to full and the battery is fully recharged by midnight. Then the heating is turned off during the night.

In total on this wet, winter day: a whopping 61.1kWh consumed, of which only 12.8kWh came from solar, 15.2kWh from the battery. But by time shifting to take advantage of the night tariff and the battery, I only paid for 23kWh of grid energy (~$5.50) with another 33kWh imported for free.

On the other hand, a sunny summer day looks more like this: lower consumption with no heating required, and high solar production over the whole day resulting in a surplus of energy exported to the grid. Nothing is imported from the grid outside of the free period - when it's used to top up the battery and run the heat pump in air conditioning mode, cooling down the house before bed.

(note the import cost figure in this screenshot is incorrect as it's unaware of the different timed tariffs)

Stu1

1769 posts

Uber Geek

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#3339763 5-Feb-2025 20:13

@egorNZ and @lightbulbNeil. Thank you really appreciate the detailed response, something to ponder on. I’m on gas central heating but could apply same approach. The heating comes in 630 AM to about 8 then on again 5 to 10pm . A battery would help during the early morning and early evening to heat the house. Once it’s heated it’s pretty good

sibel

9 posts

Wannabe Geek

#3340017 6-Feb-2025 21:32

@egorNZ , we were with Contact - on the same Good Nights Plan.

However, we have recently changed to Meridian. Meridian were offering a daily fixed charge of 69c/day vs $2.78/day; a kWh rate of 25.84c/imported kWh vs 29c/kwh; and a buy back rate / feed-in-tariff of 17c/kwh (inc GST) vs 9.2c/kwh (inc GST)... Fixed for 5-years.

Further, Contact up'd our prices - from $1.30/day and 19c/kwh. The change to Meridian was easy to make.

I would be interested to see what your charges will be - I do appreciated that different parts of the country are charged differently.

We also have a 10kw inverter system (with 9.6kw bifacial panels), but with 12.6kw Sungrow battery.

I further understand that Contact no longer offer solar installed customers the Good Nights plan.

fastbike

212 posts

Master Geek

#3340025 6-Feb-2025 21:57

sibel:

@egorNZ , we were with Contact - on the same Good Nights Plan.

However, we have recently changed to Meridian. Meridian were offering a daily fixed charge of 69c/day vs $2.78/day; a kWh rate of 25.84c/imported kWh vs 29c/kwh; and a buy back rate / feed-in-tariff of 17c/kwh (inc GST) vs 9.2c/kwh (inc GST)... Fixed for 5-years.

Further, Contact up'd our prices - from $1.30/day and 19c/kwh. The change to Meridian was easy to make.

I would be interested to see what your charges will be - I do appreciated that different parts of the country are charged differently.

We also have a 10kw inverter system (with 9.6kw bifacial panels), but with 12.6kw Sungrow battery.

I further understand that Contact no longer offer solar installed customers the Good Nights plan.

What part of the country ? We have $1.029 per day for the line charge, import is 30.3c for 7am to 9pm and 18 cents from 9pm to 7am and 17c for feed in. This is Christchurch.

Otautahi Christchurch

EgorNZ

50 posts

Geek

#3340026 6-Feb-2025 21:58

sibel:

@egorNZ , we were with Contact - on the same Good Nights Plan.

However, we have recently changed to Meridian. Meridian were offering a daily fixed charge of 69c/day vs $2.78/day; a kWh rate of 25.84c/imported kWh vs 29c/kwh; and a buy back rate / feed-in-tariff of 17c/kwh (inc GST) vs 9.2c/kwh (inc GST)... Fixed for 5-years.

Further, Contact up'd our prices - from $1.30/day and 19c/kwh. The change to Meridian was easy to make.

I would be interested to see what your charges will be - I do appreciated that different parts of the country are charged differently.

We also have a 10kw inverter system (with 9.6kw bifacial panels), but with 12.6kw Sungrow battery.

I further understand that Contact no longer offer solar installed customers the Good Nights plan.

@sibel yes, I just noticed that Contact is not accepting customers with solar on this plan any more. 😞 I hope they don't kick me off!

Our prices increased in December too. Daily charge went from $2.65 to $3.11, and import from 27.72c to 32.55c per kWh. Export remains unchanged at 9.20c. (inc GST)

If I look at Meridian, in my location they're offering a daily charge of $2.32 (25% less), import of 23.32c (28% less), and export of 17c (84% higher).

It's quite clear the fees on the Good Nights plan are high and the export rate is uncompetitive. But when I consider that 55-75% of my energy is free on this plan, I calculate that I'm still better off (especially in winter months).

sibel

9 posts

Wannabe Geek

#3340088 7-Feb-2025 10:18

fastbike:

What part of the country ? We have $1.029 per day for the line charge, import is 30.3c for 7am to 9pm and 18 cents from 9pm to 7am and 17c for feed in. This is Christchurch.

Correction - our import rate is 28.54c/kwh.

We are in Christchurch also.

@egorNZ, ouch - those day rates are a killer! I changed our plan to lower the day rate. At $2.78 say, we would have to export approx. 30kwh of power to break even. What we found pretty quickly was that the export credit didn't cover the day charge - even with the battery making us essentially 'off-grid' (thanks largely to the wonderful Canterbury overcast summer!).

Now with Meridian, the same export (30kwh) gives us a gross credit of $5.10, or net of $4.41; which, at 28.54c/kwh purchase, is around 17kwh -- more than we would ever use during the 9pm-midnight free power period.

For January, we exported 850kwh, which would have been $78.20 with Contact, or $144.50 with Meridian. Taking into account the daily fixed charges, we have to pay $86.18 with Contact, or $21.39 with Meridian. Clear to see, we are building credit with Meridian of some $123.11, or 431kwh to purchase at a later date.

My modelling of average production during the winter period is around 18kwh, so we won't be exporting anything (rather a net importer) - making the day rate an important driver for the change. The January export will top up of 3 weeks in the middle of winter, assuming a top up import of 20kwh/day.

fastbike

212 posts

Master Geek

#3340090 7-Feb-2025 10:32

sibel:

We are in Christchurch also.

We're lucky in Otautahi Christchurch to have relatively low daily charges. Friends north of the Waimakariri in the MainPower area are paying double, probably reflecting the lower density ans smaller connection base.

sibel:

My modelling of average production during the winter period is around 18kwh, so we won't be exporting anything (rather a net importer) - making the day rate an important driver for the change. The January export will top up of 3 weeks in the middle of winter, assuming a top up import of 20kwh/day.

My system has only been fully live since early Jan but is out performing the modelling (compared to a nearby reference site).

With current sunlight hour's we're only importing a small amount at day rates (export and night import are very close so no real need for a battery for night running), but this will change as the days shorten. We currently only use the oven when the sun is shining etc. Our heat pumps come on late May and we run them through to mid Aug, so that will be the test as the generation will only be 25% of current output.

Otautahi Christchurch

dantheperson

174 posts

Master Geek

#3340093 7-Feb-2025 11:05

At close to $3/day I would think the payback on an off grid sized off the shelf 48v battery setup would look attractive. I'm paying outrageously high daytime unit charges on octopus, but lucky enough to be on the no daily charges tariff they briefly offered on launch.

LightbulbNeil

57 posts

Master Geek

#3340094 7-Feb-2025 11:06

I think this year is an exceptional year for solar generation compared to last year.

EgorNZ

50 posts

Geek

#3340097 7-Feb-2025 11:15

dantheperson:

At close to $3/day I would think the payback on an off grid sized off the shelf 48v battery setup would look attractive. I'm paying outrageously high daytime unit charges on octopus, but lucky enough to be on the no daily charges tariff they briefly offered on launch.

Indeed the daily charges accounted for more than 70% of my January bill.

But going off grid would require much larger batteries, and probably more solar panels. Even at ~$1100 per year for the grid connection, I'm not sure that this is financially justifiable.

fastbike

212 posts

Master Geek

#3340192 7-Feb-2025 15:32

LightbulbNeil:

I think this year is an exceptional year for solar generation compared to last year.

I haven't had my system in long enough to do a year on year comparison. However the reference site I used for the basis of the production side of my modelling shows Jan was down a bit on previous years (purple on left is Jan '21, green is Jan '25)

According to my model, my site should be producing 2.24 times the power produced by the reference site (this is corrected for orientation, tilt and array size)

Real world data shows reference site producing 958 kWh, with my site producing (869 + 2018 ) 2887. That is just over 3 times the output, so hopefully my payback period is a bit shorter than modelled. Winter performance will be interesting.

Otautahi Christchurch

HarmLessSolutions

969 posts

Ultimate Geek

Subscriber

#3340195 7-Feb-2025 15:51

LightbulbNeil:

I think this year is an exceptional year for solar generation compared to last year.

For us in the Naki generation December 23 vs 24 is 1,105 vs 1,207. January 24 vs 25 is 1,309 vs 1,267.

I suspect much of the reduction for last month is due to excess voltage issues we're experiencing presently which seems to be compromising both total generation and export by ~10% so overall this year is looking about average allowing for that.

https://www.harmlesssolutions.co.nz/

fastbike

212 posts

Master Geek

#3342219 13-Feb-2025 06:40

fastbike:

Power bill from 11 Dec to 10 Jan was $172.05 CR. This comprised $110 for imported energy, $32 for line charges and an export credit of $282.

We had the house (10kw) installed at the end of Nov so this covered the whole month, but the stand alone garage (5kW) only came online on 3 Jan so the bill does not fully reflect our setup yet.

We have an Iammeter 3 phase meter at the grid connection, this showed we consumed 382 kWh from the grid (Night 312, Day 72) and exported 1655kWh. These figures are close to the figures on the bill so the meter is within 1% accuracy.

It's a little hard at the moment to figure out self consumption as most of the load is in the house, except when we charge the car which is plugged into the garage so the consumption figures are not included on the house inverter meter. Although we don't use the car much so maybe 50kWh of charge over the month.

The house consumed 704 and it looks like 377 of that was self generated. I have not made any effort to move any of the night time loads yet as our export rate and night time rate are very close (17c vs 18.4c).

I am working on some automation for hot water heating and car charging during the day to keep our exports and imports lower.

Just updating this with our most recent power bill covering 11 Jan to 10 Feb. This is the first bill where we have had the system fully commissioned. It shows a net credit of $324.93. Our power bill at the same time last year was $200, so we are $524 ahead for this month. Although we use most of our power in winter so this will diminish as the days close in.

Night units (9pm-7am) 232kWh $42.08

Day units 53kWh $16.06

Daily charge $31.90

Solar credits 4441kWh $414.97

Otautahi Christchurch

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