Solar system - does it really payback and saving you money?

[CLW]

Short description of the current situation: Planning to build a two-storey house in Bangkok with flat roof, two adults plus one children live in the house. Me and my partner are out for work on daytime five days a week, the son at school until afternoon, we have an EV as only car.

 

Initially, I was thinking to install on-grid-hybrid solar system with feed-in and battery storage. Since I can (and probably will) apply for a TOU meter, at current electricity prices I am questioning the investment of a solar system.

 

Where can I do calculations for this or can anyone speak from their personal experience? As much as I am for renewable energies I don't see a point for the huge investment.

[Crossy]

If you give us a clue as your expected usage (with day/night split) and how much space you have for panels. We can give you a guesstimate.

 

Can you go all week on one charge of your EV (top up from solar at the weekend)?

 

Solar here does pay back, having a hybrid inverter with storage can extend the ROI significantly, using a contractor rather than DIY can make it even more expensive.

 

If you can get on the Thai feed-in-tariff that could enable you to balance your TOU costs without using storage!

 

How long do you expect to stay in your home? Once you have covered your costs the energy truly is free! Expect to break-even in 4-10 years.

 

[KhunLA]

I'm not seeing the ROI anytime soon.  Everyone basically out during the daytime, so the system would be simply charging up the ESS for nighttime use.

 

ESS being the expensive part of the system.   We don't use much over night, 6-7kWh at the most, and that's 1700-0830 hrs, 2/3rd of the day, and not when producing.  

 

That's 2 frigs, one 13BTU AC till midnight or later, laptop & 65" TV.  Just the 2 frigs and maybe a fan or AC on low, midnight till waking, about 6hr, and sunrise.  

 

You'll be out of the house before it starts producing much.

 

You won't be charging the car on the ESS, and since using TOU overnight for that, you'll be keeping the costs low.

 

Decent system, ~ ฿200k (5kWh Hybrid, Panels, 10kWh ESS)

10kWh / day on grid, 300 / month = ฿1500 bill

฿200k ÷ ฿1500 = 10+ yrs ROI +/-

 

Doesn't take into consideration of the EV charging, as it won't be on the solar.  Just weekends, so we call that a wash ???? 

 

If you were able to top up EV on weekends, and last all week, without needing to charge, then you'd probably need another inverter & string of panels.

Edited March 3, 2023 by KhunLA

[Bandersnatch]

Having an EV really helps with payback if you can charge it from your solar system. 

I agree with previous comments about batteries  - they do extend the payback period.

 

I did these calculations for my system over a year ago, so will be a bit out of date with current prices:

 

Payback:
Main Components
20,000 Watts of PV @ ฿9/W = ฿180,000
9kWh LiFePO4 Batteries ฿68,000 x 3 = ฿204,000
Inverters ฿36,000 x 3 = ฿108,000
= ฿492,000
 
Savings: 
Gasohol saving ฿5,000/month
PEA saving ฿3,500/month
= ฿8,500/month 

฿102,000/Year saving 
Payback = 5 Years

 

 

[khunPer]

19 hours ago, Bandersnatch said:

Savings: 
Gasohol saving ฿5,000/month

Where do gasohol savings come from in an electricity usage calculation..?

[Bandersnatch]

5 minutes ago, khunPer said:

Where do gasohol savings come from in an electricity usage calculation..?

 

19 hours ago, Bandersnatch said:

Having an EV really helps with payback if you can charge it from your solar system

Prior to to installing solar I was paying PEA ฿3,500/month, now I am paying ฿26/month. I also changed my gasohol powered car which was costing me ฿5,000/month for an EV which as it is powered by excess solar in the middle of the day so saves me ฿5,000/month.

[KhunLA]

3 minutes ago, Bandersnatch said:

 

Prior to to installing solar I was paying PEA ฿3,500/month, now I am paying ฿26/month. I also changed my gasohol powered car which was costing me ฿5,000/month for an EV which as it is powered by excess solar in the middle of the day so saves me ฿5,000/month.

Ditto ... PEA ฿3k-3.5k  ... now ฿26

PTT ... ฿3K  ... now -0-

[CLW]

On 3/3/2023 at 6:11 PM, Crossy said:

If you give us a clue as your expected usage (with day/night split) and how much space you have for panels. We can give you a guesstimate.

 

Can you go all week on one charge of your EV (top up from solar at the weekend)?

 

Solar here does pay back, having a hybrid inverter with storage can extend the ROI significantly, using a contractor rather than DIY can make it even more expensive.

 

If you can get on the Thai feed-in-tariff that could enable you to balance your TOU costs without using storage!

 

How long do you expect to stay in your home? Once you have covered your costs the energy truly is free! Expect to break-even in 4-10 years.

 

Thanks crossy for your prompt and informative reply. Appreciate it.

 

Trying to answer your questions below:

 

expected usage: as said, the house will be empty during daytime on weekdays. We plan to have five ac units in total installed. 2 bedroom, 1 office, 1 living room, 1 dining room. I'm quite conservative with ac use and except hot season normally running fans. The house space will be approximately 90 sqm on two floors = 180 sqm. The available roof space for panels I would estimate between 50 and 70 spm.

 

ev charging: I expect to have my EV charged every second day (quite far to commute to work and relatively small battery in the MG 4 with 51 kWh.

 

feed in: Is this possible? I've heard so many conflicting information about this. For example with digital or TOU meter it is not possible anymore to spin the meter backwards etc.... 

 

house occupancy: definitely expecting to stay more than ten years in this house and not hoping to have the need to relocate and/or build a second house.

[CLW]

On 3/3/2023 at 7:14 PM, Bandersnatch said:

Having an EV really helps with payback if you can charge it from your solar system. 

I agree with previous comments about batteries  - they do extend the payback period.

 

I did these calculations for my system over a year ago, so will be a bit out of date with current prices:

 

Payback:
Main Components
20,000 Watts of PV @ ฿9/W = ฿180,000
9kWh LiFePO4 Batteries ฿68,000 x 3 = ฿204,000
Inverters ฿36,000 x 3 = ฿108,000
= ฿492,000
 
Savings: 
Gasohol saving ฿5,000/month
PEA saving ฿3,500/month
= ฿8,500/month 

฿102,000/Year saving 
Payback = 5 Years

 

 

Your solar panels cost more than the estimated building costs of my house ????

[CLW]

On 3/3/2023 at 6:41 PM, KhunLA said:

I'm not seeing the ROI anytime soon.  Everyone basically out during the daytime, so the system would be simply charging up the ESS for nighttime use.

 

ESS being the expensive part of the system.   We don't use much over night, 6-7kWh at the most, and that's 1700-0830 hrs, 2/3rd of the day, and not when producing.  

 

That's 2 frigs, one 13BTU AC till midnight or later, laptop & 65" TV.  Just the 2 frigs and maybe a fan or AC on low, midnight till waking, about 6hr, and sunrise.  

 

You'll be out of the house before it starts producing much.

 

You won't be charging the car on the ESS, and since using TOU overnight for that, you'll be keeping the costs low.

 

Decent system, ~ ฿200k (5kWh Hybrid, Panels, 10kWh ESS)

10kWh / day on grid, 300 / month = ฿1500 bill

฿200k ÷ ฿1500 = 10+ yrs ROI +/-

 

Doesn't take into consideration of the EV charging, as it won't be on the solar.  Just weekends, so we call that a wash ???? 

 

If you were able to top up EV on weekends, and last all week, without needing to charge, then you'd probably need another inverter & string of panels.

That's right. Battery or ESS very expensive at current electricity costs. 

Therefore the tendency to install just small panel to setoff electricity costs during weekends.

Waiting for crossy reply, too

[Bandersnatch]

3 minutes ago, CLW said:

Your solar panels cost more than the estimated building costs of my house ????

Smaller house  - you probably need less solar ????

[nglodnig]

The solar system will NEVER payback. Mars, Venus, the Moon, Mercury - then the steroid belt and the outer frozen gas giants - will all be money pits and no return will ever be seen. Oh, sorry, wrong Solar System?

[007 RED]

@CLW my system is considerably smaller that those run by @Crossy, @Bandersnatch and @KhunLA.

 

My small scale system comprises:  4 x 415W mono half cut panels connected in series to a 2200W Sofar grid tied inverter.  No ESS involved.  Old type meter spins backwards (naughty).  The build was DIY, so no labour costs other than my time and effort.  Total cost of hardware was 28,000 THB.  I originally estimated a ROI of 2.5 years.

 

As at the date of commissioning, the local PEA was charging us 4.2 THB per unit, and I've continued to use this figure to calculate my ROI, even though the cost per unit has recently increase.  The system has now been running for just over 17 months and has generated approximately 4030 units, which at 4.2 per unit equates to a saving of 16,926 THB.  Obviously if I took the recent price increase into account the ROI period would be reduced.

 

So, yes even a small scale solar system can be a worthwhile investment.