Off-grid solar just 10 years payback - what have I done wrong?

[IMHO]

I've been spec'ing up a few isolated solar systems for my somewhat spread out house. One of them is a system to run my pool, which just so happens to be the easiest to calculate & plan as it's a nice steady load.

Loads:

Main pump & chlorinator: 700 watts, 11 hours/day runtime

Jacuzzi pump: 1000 watts, <= 1 hour/day

Waterfall pump: 1000 watts, <= 1 hour/day

Garden lights: 84 watts, 12 hours/day

Other lights: 28 watts, <= 4 hours/day

Daily nominal load: 10,820 Wh

The system:

16x 250Wp PV @ 5400 Baht ea = 86,400 Baht

12x 12V/200Ah batteries @ 8200 Baht ea = 98,400 Baht

2x 4kW hybrid inverters with parallel kit @ 60,000 Baht the set

Accessories (rails, clamps, breakers, wiring, etc) and a few days labor from my electrician: 25,000 Baht

Total price: 269,800 Baht (give or take a little on the accessories & labor).

Losses used in calculations:

Inverter loss: 10%

Battery charging loss: 20%

General system losses: 14%

Working on a rate of 4.8 Baht/unit inc tax (sometimes it's lower than this, but presumably it will get even higher over the payback period), the nominal bill offset would be 2,225 Baht/month, making the payback period just 10 years.

Of course, the batteries won't last that long, but if they live up to manufacturer claims they should get pretty darn close to making it. if all loads ran on battery, DOD after all losses are factored in would be 40% - but the inverters I'm using are able to support "PV first" priority, so actual DOD should not get that low, seeing as on clear days the pumps will have 4-5 hours of runtime during PV harvest. Note that the inverter also supports grid charging, so minimum 40% DOD can be maintained.

What am I missing? surely you can't get off-grid to provide ROI this fast?

[IMHO]

Argh, never mind, I found it...

My spreadsheet was referencing daily avg PV harvest, rather than daily avg load. Corrected ROI is closer to 14.5 years, assuming current rates remain idle.

[IMHO]

Even with the corrected numbers, and factoring in replacing the battery bank after 8-10 years, it still bucks popular opinion that off-grid can never pay for itself though..

I suppose the big question is: will batteries actually achieve manufacturer cyclic claims in TH?

The place my battery rack would go in never gets sunlight, and ambient temps vary between 15c and 40c year-round (avg would be around 30c), which from what I've read is still pretty lead acid friendly.

[Naam]

What am I missing?

from what i gather you missed to consider any potential yield generated by 269,800 Baht capital. even a mini-yield of 3% p.a. would result in an additional compound yield of 150,000 Baht over a period of 15 years.

assuming steady electricity prices (as guidance only) you would have to harvest additional 33.300 kWh to break even.

p.s. not considering blocked capital yield loss is quite common in reports of photovoltaic aficionados.

[jvs]

Maybe a dumb question but do you really need batteries?Could you not just run the pump while the sun is shining?

[peterrabbit]

Batteries are the biggest problem. They are designed with redundancy so that they will eventually fail. If the manufacturer doesn't cover your your time period then forget them lasting that long especially in this heat. Its no surprise that Tusk is building the world's biggest factory to manufacture more efficient batteries for his cars and also home solar storage. I would look at just powering things you can use while the sun shines as a totally separate system. (You could power your lighting circuits off batteries as they use little power, esp LEDs).

[ksamuiguy]

You are 10 years to early, the technology is not there for home use yet.

[IMHO]

Maybe a dumb question but do you really need batteries?Could you not just run the pump while the sun is shining?

Sure - If the sun shined a useful amount 11 hours/day

[IMHO]

What am I missing?

from what i gather you missed to consider any potential yield generated by 269,800 Baht capital. even a mini-yield of 3% p.a. would result in an additional compound yield of 150,000 Baht over a period of 15 years.

assuming steady electricity prices (as guidance only) you would have to harvest additional 33.300 kWh to break even.

p.s. not considering blocked capital yield loss is quite common in reports of photovoltaic aficionados.

It was a lot more exciting when my spreadsheet calculated monthly bill offset based on harvested power, rather than what you actually get after losses

[IMHO]

For those still with their calculators out..

Domestic tariff for households using > 400kWh/month

2005: 2.84 Baht/unit inc ft = 3.04 Baht/unit inc VAT

2015: 4.42 Baht/unit inc ft = 4.73 Baht/unit inc VAT

Change in 10 years: 55.6%

Based on that alone, I'd like to ask the MEA/PEA if I can pre-pay for the next 20 years supply

[AlphaSoiDog]

Off grid in Oz works now, no need to wait 10yrs. My neighbour will have his paid for in 6yrs (at current prices... ), and he paid top dollar for his gear. Since then batteries and cells have both come down in price. (BTW, his lead acid batteries are expected to last 20yrs if he keeps within the discharge limits given).

I haven't done the research for Thailand though and given the difficulties and costs of importing anything combined with the (current) comparatively lower cost of power it's not going to be as good as Oz.

If you are a bit technical have a look at the "used" Nissan Leaf batteries that can be bought from the US. They are cheap storage if you can get them and understand the differences in charging them (quite a few inverter/chargers now have a Li ion option which may be fine for the nissan batteries). Li-ion is becoming very popular in this usage for a number of good reasons (plus lower shipping costs ).

And anyone that is now tempted to talk about hand grenades and fires please think first about that knee jerk reaction. There are many factors, e.g. Li Ion cobalt batteries are unstable and need very good care (the ones Boeing used in the 777...). But you can hammer a nail into Li Ion Phosphate batteries and just get a small fizz and wisp of smoke (see youtube).

Note that solar cells will continue to get cheaper, and there have been a number of interesting breakthroughs that will shake the market when finally commercialised. Tesla's gigafactory will also affect prices. I read a couple of years ago that Tesla was soaking up something like 50% of the Li-ion battery market, so it's a dramatic increase in production when that comes online. There have also been a large number of breakthroughs that will make Li-ion continue to get cheaper as well as increase capacity and life. Some of these have already been commercialised but are being slowly fed to the market to increase profits.

eg: one tech already in most mobiles can increase capacity by about 55% but they are introducing that at about 10% per yr and have done for about 2 years.

The point is that if it isn't financially attractive yet, keep checking as it will get better every year. Many pundits think that the whole commercial electricity production business will radically change within about 5yrs because of this.

[Paul944]

At the moment the best ROI you get will be with a grid tied system without a battery backup. You have to check with your electricity supplier which inverters they allow to use and if they allow the meter to spin back during the day. Then you can size your installation so that the current you deliver to the grid during sun hours match your power usage during the night.

The disadvantage of an off grid installation is it inflexibility to deliver more current as the inverter is designed for. Meaning if you always have to keep in mind you can not run power hungry appliances in parallel. it is a nuisance to have to switch of the air conditioning before doing the laundry.

[IMHO]

At the moment the best ROI you get will be with a grid tied system without a battery backup. You have to check with your electricity supplier which inverters they allow to use and if they allow the meter to spin back during the day. Then you can size your installation so that the current you deliver to the grid during sun hours match your power usage during the night.

The disadvantage of an off grid installation is it inflexibility to deliver more current as the inverter is designed for. Meaning if you always have to keep in mind you can not run power hungry appliances in parallel. it is a nuisance to have to switch of the air conditioning before doing the laundry.

With commercial installed prices ranging from 50 - 70 Baht per Wp for grid tied systems in Thailand, an off-grid system with a 500 Baht/day local sparky doing the work is competitively priced..

The system I proposed in my OP would work out to about 67.5 Baht/Wp - but that also increases with additional system losses and battery replacement of course.

It's the 50K++ everyone wants for the install, red tape and paperwork that makes grid-tie nowhere near as good value as it should be. An off grid sysem doesn't need approvals/red tape, and is well within the capabilities of my sparky.