Solar with or without a battery

Forums › Home Workshop DIY › Solar with or without a battery

Paul1977

5171 posts

Uber Geek
+1 received by user: 2192

#251226 14-Jun-2019 09:41

We are doing a new build and I was wondering about the economic viability of solar from anyone who has gone down this route.

I'm all for it in principal, but principals won't pay the mortgage. It has to make financial sense.

We use most of our power in the evening, so would presumably need a decent battery. Given the cost and life expectancy of the batteries, does it make any financial sense to look at this?

What if, instead of a battery, you sold surplus power back to the grid during the day, and then drew power from the grid at night? How much do they pay for the power you supply the grid compared to what they charge for the power you take from it?

1 | 2

29098 posts

Uber Geek
+1 received by user: 10208

Trusted

Lifetime subscriber

#2257944 14-Jun-2019 09:45

Not worth it unless you can use it when you generate it when I have done the sums every time.

If you are on a 16c-18c/kwh or similar rate then even having solar is borderline viable. All the massive savings you see blabbed about are people who're on the low user rates with stupidly high kwh prices to offset their low daily price.

Even with the new 8c export rate, and buying back at 18c thats costing me 10c/kwh to "store" it in the grid.

Richard rich.ms

wellygary

8810 posts

Uber Geek
+1 received by user: 5287

#2257950 14-Jun-2019 09:54

"What if, instead of a battery, you sold surplus power back to the grid during the day, and then drew power from the grid at night? How much do they pay for the power you supply the grid compared to what they charge for the power you take from it?"

You get paid ~8c/unit for any excess, you will pay at 2 or 3 times that to buy from the grid, so as a time shifting option its simply not worth it..

Unless you are a remote site, a grid connected system will be cheaper

(and to be honest, with a 85%+ renewable grid, you are spending a lot of money to take your power from 85% to 100% renewable)

Aredwood

3885 posts

Uber Geek
+1 received by user: 1749

#2257951 14-Jun-2019 09:55

If you do want to store your excess solar generated power. Get a large hot water cylinder and a PV diverter. Far cheaper than using batteries.

A large hot water cylinder is still a good idea even if you dont get solar. As you can use off peak or night rate power to heat it.

tdgeek

30048 posts

Uber Geek
+1 received by user: 9455

Trusted

Lifetime subscriber

#2257958 14-Jun-2019 10:02

Its not worth it. I can justify it by saying after the payback period, say 12 years, its then worth it as there is no "cost" just savings. But you really want to be in that home for a long time

Id like it, we are in a largish house, but cant get solar PV. So, I'm avoiding "oh, that's a big cheque, was it wise?"

Talkiet

4819 posts

Uber Geek
+1 received by user: 3934

Trusted

#2257963 14-Jun-2019 10:05

A couple of years ago I tried to make it even close to cost neutral for my new build in Chch as I love the idea. I never got it close. I have a 2.2kW generator in case of emergencies.

Even from an environmental viewpoint it's not justifiable if you're in the South Island.

Cheers - N

Please note all comments are from my own brain and don't necessarily represent the position or opinions of my employer, previous employers, colleagues, friends or pets.

rp1790

751 posts

Ultimate Geek
+1 received by user: 177

Lifetime subscriber

#2258006 14-Jun-2019 10:12

The only reason for doing solar if to be greener or off grid/independent, it does not and cannot financially pay for itself.

I went through the exercise recently and got quotes from 7-8 companies (for my house) ranging from the top end to the down and dirty handymen. Even looking at paying for the panels myself (sourcing them at $200 ea vs $300-$550 from those companies) and it still doesn't work out. And as a tried and true geek I really really REALLY wanted to do it but it's just too much.

If you used most of your power during the day and very little at night solar might be an option. When you start adding batteries of any sort the cost and financial payback period becomes even more prohibitive.

Dyson

Shop now for Dyson appliances (affiliate link).

Senecio

2851 posts

Uber Geek
+1 received by user: 3159

ID Verified

Lifetime subscriber

#2258016 14-Jun-2019 10:23

My In-laws have recently installed solar but they are <6 months away from retirement. Once they retire they will be home a lot more during the peak of the day to use the power while its being generated. I think that's the only way it works in this country.

The only other use case I can think of is in remote locations where the upfront cost of being connected to the grid could be comparable to the up front costs of installing solar + batteries.

Technofreak

6656 posts

Uber Geek
+1 received by user: 3474

Trusted

#2258021 14-Jun-2019 10:27

Senecio:

The only other use case I can think of is in remote locations where the upfront cost of being connected to the grid could be comparable to the up front costs of installing solar + batteries.

This ^^^^^^^

Sony Xperia XA2 running Sailfish OS. https://sailfishos.org The true independent open source mobile OS
Samsung Galaxy Tab S6
Dell Inspiron 14z i5

tdgeek

30048 posts

Uber Geek
+1 received by user: 9455

Trusted

Lifetime subscriber

#2258032 14-Jun-2019 10:44

Its a pity, as EV is too costly, and Solar is too costly.

kotuku4

485 posts

Ultimate Geek
+1 received by user: 137

ID Verified

Lifetime subscriber

#2258037 14-Jun-2019 10:51

We have PV solar, and PV diverter to a larger hot water cylinder, it works well at our site. Great roof orientation and slope, no shading, excellent annual sunshine hours.

Would rather use more of the surplus power than export it. Have investigated adding battery storage several times, but it does not work out for me at all.

With the current buy back rates Solar is hard to justify. Think of it as pre paying your power for the next 8-10 years. As a long term solution yes we are better off.
Looking at the power accounts there are lots of supply charges.

Paul1977

5171 posts

Uber Geek
+1 received by user: 2192

#2258041 14-Jun-2019 10:57

Thanks guys.

I figured this would likely be the case, and I knew there'd be many here who had already done the numbers who could confirm it for me.

It's a real shame that the numbers don't stack up.

My other thread about ducted heat pumps has evolved to talk about passive housing. But, like solar, I get the the feeling that in NZ it just can't be done in a cost neutral way either.

It just feels like there are all these great ideas and technologies, but in little old NZ the costs are too high to employ any of them.

New World

Shop on-line at New World now for your groceries (affiliate link).

KrazyKid

1247 posts

Uber Geek
+1 received by user: 616

#2258042 14-Jun-2019 11:02

When I last looked here in Dunedin the payback was optimistically 12-15 years. I passed on the option.
My house is not idea in its location and neither is Dunedin really.

If you can be confident of getting a 10yr or so payback why not - you probably won't notice the extra cost on overall build.
The trick will be using all power and not sending it back to the grid. Batteries kill the economics very quickly.

But saying all of that maybe the money would be better spent providing higher quality insulation at the time of building.
The South Island power supply is pretty green already.

Have you considered Structurally Insulated Panels, Extra insulation on the slab, triple glazing, more roof insulation, even a passive house?

If you want to go greener another option might be to spend the money on a second hand Nissan Leaf. As a second car for around town driving it's a very cash positive.
Can even make sense as a first car - however electric cars do not suit everybody or every budget.

Edit - just read your last reply - seems you have considered your build options a lot already, good on you.

Paul1977

5171 posts

Uber Geek
+1 received by user: 2192

#2258064 14-Jun-2019 11:25

KrazyKid:

Have you considered Structurally Insulated Panels, Extra insulation on the slab, triple glazing, more roof insulation, even a passive house?

Just started a thread specifically about passive housing technologies here. Interested in any and all thoughts.

rogercruse

644 posts

Ultimate Geek
+1 received by user: 211

ID Verified

Lifetime subscriber

#2258091 14-Jun-2019 12:34

We've had solar panels for the past five years and a Tesla Powerwall battery (version 1) for the last three years in our existing home, but won't be installing either in our new home.

The good stuff about solar panels and batteries:

Unlimited hot water
Most of the power generated is best converted into hot water. And even on cold grey days like today, there's enough power to top-up the 300 litre hot water cylinder.
Use the build-in timers on your power hungry appliances
check your dish washer and washing machine and get used to setting these to run during the day

The not so good stuff:

Get a bigger hot water cylinder
This will help you store more hot water for cold grey days like today!
Get an intelligent controller redirect and generated power to keep the hot water cylinder topped-up
These aren't cheap, the solar panel supplier will know what models are available and which will suit you best.
The return on investment is still too long, I reckon its more than ten years at current prices

However, while the installation costs for the panels gets a little cheaper each year, you don't get much money for any electricity that you sell to the power company and battery technology is still too expensive to store anything other than enough power to keep the lights running for a couple of hours.

Also, there are simpler and more effective ways to reduce your power bills,

Use a Heat pump to heat water
Switch to a power company that provides a free 'hour of power' each day.

Hope the above helps.

tdgeek

30048 posts

Uber Geek
+1 received by user: 9455

Trusted

Lifetime subscriber

#2258096 14-Jun-2019 12:42

rogercruse:

We've had solar panels for the past five years and a Tesla Powerwall battery (version 1) for the last three years in our existing home, but won't be installing either in our new home.

The good stuff about solar panels and batteries:

Unlimited hot water
Most of the power generated is best converted into hot water. And even on cold grey days like today, there's enough power to top-up the 300 litre hot water cylinder.
Use the build-in timers on your power hungry appliances
check your dish washer and washing machine and get used to setting these to run during the day
The not so good stuff:

Get a bigger hot water cylinder
This will help you store more hot water for cold grey days like today!
Get an intelligent controller redirect and generated power to keep the hot water cylinder topped-up
These aren't cheap, the solar panel supplier will know what models are available and which will suit you best.
The return on investment is still too long, I reckon its more than ten years at current prices
However, while the installation costs for the panels gets a little cheaper each year, you don't get much money for any electricity that you sell to the power company and battery technology is still too expensive to store anything other than enough power to keep the lights running for a couple of hours.

Also, there are simpler and more effective ways to reduce your power bills,

Use a Heat pump to heat water
Switch to a power company that provides a free 'hour of power' each day.

Hope the above helps.

Good post I have solar HW and I still cant justify PV, although I'd just like it! But I cant get it due to our roof design

Solar HW is worth it. Its great

I use EK, so that 30 free hours per month is good

Its annoying that we all want to be green, but its often not viable.

1 | 2