Off grid solar system

[geuda]

Next year I will retire in a remote place in the Loei province and there's no utility available...

I'll need an off-grid solution. I could see lots of posts dealing with on-grid systems, but off-grid is a significantly different issue...

A first question would refer to importing goods from China. I cannot find any 250Ah batteries on the local market, can we ‘easily’ get them from China?

There are some questions I cannot answer by myself.

1.MPPT controller.

How does an MPPT controller manage the kWh produced by the solar panels?

I know how the MPPT principle works, but not how the device manages the whole power.

When the batteries are full, and when the inverter needs some current, does the current have to come from the batteries first, or does the controller feed the inverter directly?

I other words, at daytime around noon, we get the MAX power from the sun, and I do not want to bother the batteries when plenty of solar energy's available. I can see on drawings that the controller and the inverter are directly connected to the batteries.

I want to size my solar panels array in order to cover the needs at day time and provide current to charge the batteries which have been discharged overnight. Consumption overnight are a few leds, two or three small fans, a TV set+satellite receiver, CCTV cams and a fridge/deep freezer which we shouldn’t open at night...

Can we set up the maximum DOD (depth of discharge)?

I'm asking this because the battery bank is my major concern. It's a heavy investment and if we do not keep the DOD under say 20% or 30%, the batteries' life will significantly be reduced.

2. 96V versus 48V for the battery bank.

I want to use eight 250Ah batteries, if I'm in 48VDC, I'll have 500Ah available, is this better for the battery bank's lifetime than 250Ah in 96VDC? Both configurations provide the same kWh...

I'm asking this because fridges and pumps need high current during a few seconds to start running.

Is the following true?

8 batteries, 250Ah, 30% DOD, 20hours nominal capacity will give 8x12VX250Ah÷24hX20hx30%=6kWh available/day

This may sound quite oversized depending upon the answer to question 1...

3. 96V versus 48V for the whole system PV panels, controller batteries.

The panels I want to use are 60-cell panels, so 20VDC nominal voltage.

Does it mean I have to put five panels in series to feed a 96V battery bank?

5x20V = 100V, 100V > 96V... Only +4VDC, is that enough?

Does it mean I have to put three panels in series in the 48VDC configuration?

3 x 20V = 60V, 60V>48V...

I know that an MPPT controller will adjust the voltage to what's needed by the battery bank, increasing the number of Amps if necessary, that's one of the reasons why I want an MPPT and not a PWM controller. How far can we go in that voltage difference?

4. Plate sulphation.

In most cases, the primary culprit in the mechanisms of degradation of battery life is plate sulphation. Are there inverters with functionalities that enable desulphation like time limited equalization process, high frequency desulphation?

5. Water pump(s)

Is it better to use DC or AC (sewage-deep well) pumps? A small sewage pump will be used at regular intervals to oxygenate a micro wastewater treatment plant. A water pump will be used to fill a tank once a day (week) when plenty of solar energy’s available.

I’m sorry for all these questions, just hope some one went through the same process and could share some experience...

[IMHO]

A lot of your questions depend on the (hybrid) inverter you buy..

e.g. many provide the ability to control priority on what source supplies your 220V load: Solar PV, Batteries or Generator/Grid (if available). If you were to choose Solar PV priority, then at peak harvesting times your PV would be directly supporting the load, with the batteries as standby/peak-demand power.

The choice of inverter will also answer your question re: battery bank voltage. Note that 96V support is extremely uncommon - most max out at 48V.

In regards to MPPT, it's all not a difficult as I think you imagine. MPPT refers to the inverter tech, and all it means is that it gets more energy out of your PV harvest than older/cheaper PWM tech.

RE: batteries, my advice would be to only buy local, so things like warranty are supported, and replacements readily available. Before you even think about them, you need to work out exactly what your real loads are going to be, or might possibly be later on, as you don't want to go mixing new & old batteries to expand your bank if you undershoot.

12V 200Ah SLA's a readily available in Thailand. The Trojan batteries from the USA are also imported here, which give you 2V and 6V options to play with.

Most good inverters have intelligent chargers that auto-manage plate sulphation problems. Again, a question for your hybrid inverter vendor.

DC pumps will use battery power more effectively than AC ones, but OTOH are the opposite of your desire to maximise load usage of PV in peak harvesting times. Good inverters are pretty efficient, so I'd say that in a Solar-PV priority based system, AC pumps (and AC everything) probably makes the most sense, and is the easiest to calculate requirements on.

Also, you're thinking about your PV array voltages the wrong way. Read the specs on your hybrid inverter for it's MPPT range. Generally speaking they want PV arrays wired into the 100's of volts range to work - I've seen some as high as 1000V PV input. Your PV array voltage has nothing to do with the battery bank voltage or even the load AC output voltage. It's got everything to do with the MPPT voltage range the inverter has been optimised for

Bottom line:

1. Work out total maximum startup demand of all loads with motors, so you know how much inverter you'll need.

2. Go research inverter options

3. Calculate the total daily kWh the system needs to ultimately support.

4. From that, you can then work out a spec on the PV array and batteries needed.

And a note:

6kWh/day is only 6 units, which is only a bill of about 850 Baht/month. i.e. It's not a lot - most houses, especially those with AC, hot water, pumps, washing machines, fridges and ovens will use significantly more than this.

[geuda]

Thanks a lot IMHO.

I get a clearer picture now.

[IMHO]

Thanks a lot IMHO.

I get a clearer picture now.

You're welcome

Now you know why Crossy and I always talk inverters - that's where it all starts, and they are what ultimately dictate many of the decisions you end up making

[Paul944]

If you are a techinal persion I suggest to search information about solar inverters. Example http://www.sma.de/en/home-systems/solar-system-off-grid.html

First you have to get a good estimation how much power you use daily. How much of this required during sunlight hours and how much power during the night. Also the temporary maximum peak power you need. With these numbers you can calculate the amount of solar panels you need, the required capacity of the batteries and the size of the inverter.

An inverter, batteries and solar panels have different live times so the best will be a sytem that is a bit flexible in replacing components.

A worry free, comfortable system will not be cheap investment, in the 200,000 - 500,000 baht range. However, you will not have a monthly electricity bill so in the long run you pay about 30% more compared to paying monthy electricity bills.

[geuda]

Thanks Paul944, the link refers to Germany though, so I can't rely on it.

Here's another one with plenty of possibilities: http://re.jrc.ec.europa.eu/pvgis/apps4/pvest.php?lang=en&map=africa

The monthly result is wrong as for them, December is the peak month. A study made by Naresuan University (Pitsanuloke) gives December as the lowest month, which makes sense to me.

On the other hand, the average yearly irradiation fits in the picture: 5.28kWh/m2 (Average daily sum of global irradiation per square meter-year for my location: Location: 17°30'44" North, 101°38'44" East, Elevation: 337 m). Naresuan gives 5.06 for Thailand.

You wrote:"How much of this required during sunlight hours and how much power during the night. Also the temporary maximum peak power you need. With these numbers you can calculate the amount of solar panels you need, the required capacity of the batteries and the size of the inverter."

Thanks for that, this is more or less what I had in mind when I posted my thread, but I wasn't sure whether this was the right approach.

[IMHO]

When calculating your battery bank size, you should not reduce it because some loads are able to run during PV harvest time, because PV output is not a flat line - it's shaped like this: ^ and also because you are going to have cloudy days, and super hot days where PV output is minimal/limited.

Generally speaking, most off-gridders also build in 2-3 days of total battery power autonomy to get them through bad weather periods - that means whatver bank size they need for a full day with the DOD target in mind, they then double or triple it.

If you have mains power available, and a smart enough inverter, you can get away without adding these additional autonomy days of capacity to your bank, because you can rely on the grid to charge batteries/service the load when your system just can't cope. For totally off-grid, days of autonomy cannot be ignored though, otherwise you will run out of power.

Again, I need to stress that the first calculation you need to perfrom is the total startup demand of your load (which is a multiple of it's static demand). Then find an inverter solution that works, then work out your avg/max daily consumption, then work out the PV and battery requirements.

Starting with talking about batteries or PV arrays makes no sense - all you will be doing then is trying to make your load fit the system, when what you should be doing is making the system fit the load. Leave your compromises until the end, when you've picked yourself up off the floor from the sticker shock

[IMHO]

If you are a techinal persion I suggest to search information about solar inverters. Example http://www.sma.de/en/home-systems/solar-system-off-grid.html

First you have to get a good estimation how much power you use daily. How much of this required during sunlight hours and how much power during the night. Also the temporary maximum peak power you need. With these numbers you can calculate the amount of solar panels you need, the required capacity of the batteries and the size of the inverter.

An inverter, batteries and solar panels have different live times so the best will be a sytem that is a bit flexible in replacing components.

A worry free, comfortable system will not be cheap investment, in the 200,000 - 500,000 baht range. However, you will not have a monthly electricity bill so in the long run you pay about 30% more compared to paying monthy electricity bills.

I can't see any "normal" house where you could build a viable off grid system for this price range.

For a normal house that hasn't made too many compromises to run off-grid, I'd say that starting point is more like 1M Baht.

[BritManToo]

I can't see any "normal" house where you could build a viable off grid system for this price range.

For a normal house that hasn't made too many compromises to run off-grid, I'd say that starting point is more like 1M Baht.

Normal Thai houses have a few fans, fridge, tv lights, kettle and maybe a computer.

Air-con, electric cooking and water heaters are way out of normal, especially in rural areas.

Peak load in a normal Thai house would probably be under 2KW.

If you didn't use an electric kettle (easily done), 1KW would probably do the job.

1.5KW off grid system around $7,000 + batteries $2,000 = $9,000 (300,000Bht)

http://www.wholesalesolar.com/1890705/wholesale-solar/complete-systems/the-cottage-1.6-kw-6-panel-astronergy-off-grid-solar-system

It just isn't financially viable for normal people (not rich) to run a solar off grid system.

A much smaller solar and a generator for when you need the extra power would be much more affordable.

[IMHO]

I can't see any "normal" house where you could build a viable off grid system for this price range.

For a normal house that hasn't made too many compromises to run off-grid, I'd say that starting point is more like 1M Baht.

Normal Thai houses have a few fans, fridge, tv lights, kettle and maybe a computer.

Air-con, electric cooking and water heaters are way out of normal, especially in rural areas.

Peak load in a normal Thai house would probably be under 2KW.

If you didn't use an electric kettle (easily done), 1KW would probably do the job.

1.5KW off grid system around $7,000 + batteries $2,000 = $9,000 (300,000Bht)

http://www.wholesalesolar.com/1890705/wholesale-solar/complete-systems/the-cottage-1.6-kw-6-panel-astronergy-off-grid-solar-system

It just isn't financially viable for normal people (not rich) to run a solar off grid system.

A much smaller solar and a generator for when you need the extra power would be much more affordable.

Sorry, I mean normal houses that people reading this thread might live in - not their in-laws house

1kW wouldn't even be able to start up a 9,000 BTU air con.

[geuda]

I came up with questions first when I posted my thread, those questions arose after a few calculations and hypotheses.

Paul944 gave me a hint I was searching for. The problem: I don't have the data yet. Indeed, I would like to know how much will be taken from the battery bank at night, which by definition is what the PV array has to provide at day time + daytime consumption.

How did I proceed to calculate the system?

For budgetary reasons, I want to stick to eight 200Ah batteries, I can follow what IMHO suggested, buy the batteries locally is much more secure than importing them from China...

Eight batteries will give a 96VDC battery bank. I prefer high voltage low current for quite obvious reasons. Yes IMHO, there are 96VDC inverters, even 192VDC are available for small home applications.

One word about PV array voltage. I'm not talking about a grid tied system where the standard in some countries is 600VDC, the maximum according a Schutten datasheet is 1000VDC (TUV=Germany).

There are three voltages a 36-cell panel has a 12VDC nominal voltage, a 72-cell panel, 24VDC.

The grid-tied systems use 60-cell panels which are 20VDC nominal voltage panels, easier to handle than 72-cell panels. I'm going for those panels too as the MPPT charge controller enables a PV array with a higher voltage than the battery bank. A PWM controller will change that voltage difference into heat, it's a loss and we don't need heaters here in Thailand ;-))

If I consider five panels in series (or two strings of five in series), the nominal voltage will be 100VDC.

Now what about the controller. To calculate the controller one need to take Voc (open circuit voltage) into account, plus a safety buffer, people in the literature recommend 30%.

What would be my voltage: Voc=37.1V so 37.1 x 5 x 1.30=241.15VDC - I know a company I-Panda which produces the I-P-SMART1- 96V -20A or 30A with a working voltage of DC120~DC300V, so it's OK.

Shall I take one or two strings of 250W panels?

I made some calculations which gave me the following result for the shortest day in the year 21st December. I have on average 950W/m2 for five hours, from 9.30am until 2.30 pm. This is the worst case. If I take 66.7% efficiency of the whole system, I get for one 250W panel: 250 x 5 x .95 x .667=~790Wh/day/panel (worst case)

Let's go back to the batteries. I can read everywhere that the battery lifetime depends upon the DOD (depth of discharge). In the literature we can find different values, the MAX DOD being 80%, one recommend not to go deeper than 50%, some people recommend even 30%.

I don't know the Peukert's constant for the battery I'm going to use so I cannot refer to Peukert's law.

Let's consider 200Ah 20hours rate and 30% eight batteries in series: 8 x 12 x 200 x .30 x 20 ÷ 24=4800Wh. This is what I can use at night, should be OK.

I'll need 4800÷790=~6 so 6 panels. If I consider I may need another ~5kWh at daytime, I'll have another 6 panels string.

Let's do the maths 6 x 37.1VDC x 1.3=~290VDC, still below the 300VDC limit. Two strings of 6 panels, what about Amps?

Here we need to consider Isc or short circuit current = 8.92A, two strings so 8.92A x 1.3 x 2 =~23A, I can use the I-P-SMART1- 96V - 30A with a working voltage of DC120~DC300V, or equivalent.

In case of overcast weather: back-up generator.

In a nutshell:

12 poly-crystalline panels @ 250W 6500THB http://www.mechashop.com

8 12V 200Ah batteries from 8350THB I'll consider Volta double deep cycle 10 700THB

1 I-P-SMART1- 96V - 30A MPPT charge controller

1 low frequency inverter, 3000W or 4000W. (middle path 3500W?)

The whole project will obviously exceed 200 000THB

Your comments/recommendations would be highly appreciated, if you are running an off-grid system yourself.

Thanks!

Cheers,

Bernard

[IMHO]

One piece of feedback is, although the December solstice is the shortest day of the year, in most areas of Thailand the lowest harvest days are around August, during the rain season.

[geuda]

One piece of feedback is, although the December solstice is the shortest day of the year, in most areas of Thailand the lowest harvest days are around August, during the rain season.

Well, December and August are very close to each other. Do you have values from your system? I'm interested in real life figures. On this graph one can see what I'm saying: I would say that graphically December seems to be close to August but lower it's obvious when we compare the values year by year...

[Paul944]

Connecting a lot of batteries in serie or parallel has the disadvantage that a defective battery affects the whole setup. It would be nice as the inverter supports independent battery banks. For periods without enough solar power one can use a generator. If you have a fridge and a freeze you need a generator as backup anyway I think.

If you do not want to compromise with your electric power consumption, have a 150 m^2 house full of airco units you will need a 1M baht installation. In the long run still cheaper as running a 10 KW generator and also more quiet.

If you do not have airco, just the lights, tv and fridge and freezer that will be about 1 KW peak during the night, maybe 500 W average, probably less. I would look for the price of a 5 KW installation with backup generator. There will be some solar power companies it Thailand that can give you a quote, I guess.

During the day you can do the laundry and dishwasher on solar power.

Some more links:

http://www.solarpanel.co.za/solar-power-calculator.html

http://modern-off-grid.com/2013/12/30/off-grid-solar-101/

http://www.wholesalesolar.com/1890531/wholesale-solar/complete-systems/10.4-kw-grid-tied-solar-system-with-solaredge-and-40x-astronergy-260w-panels

http://www.alibaba.com/showroom/10kw-off-grid-solar-system.html

The important decision is how much power you want to have. Once you have bought the installation it will not be scalable and a 5 KW inverter will not support a 10 KW peak.

[IMHO]

One piece of feedback is, although the December solstice is the shortest day of the year, in most areas of Thailand the lowest harvest days are around August, during the rain season.

Well, December and August are very close to each other. Do you have values from your system? I'm interested in real life figures. On this graph one can see what I'm saying: I would say that graphically December seems to be close to August but lower it's obvious when we compare the values year by year...

I have access to data from two domestic grid tied systems, neither of them owned by me though. What they produce is not very relevant though, unless you live right next door to one of them, and have an array of the same age, azimuth and incline

This calculator seems to produce the most accurate predictions:

http://pvwatts.nrel.gov/

[Gary A]

What I have learned about solar power the past three years. I have four panels on the roof. It is unbelievable how dirty they get. I have too many trees to put in a larger system. My wife goes into hysterics when I suggest cutting down some of her trees. I would definitely use a ground mount for a large array of panels. They would then have the optimal orientation and most important, the tilt angle could be easily changed to suit the seasons. They could also be easily cleaned. Smaller components are cheaper than a huge set of components for the panel array. I would use three separate systems rather than one big system. If a single component fails, you wouldn't be sitting in the dark and waiting for a new component. By jockeying the power from the two working systems, you could still get by until you get the third system back up and running. Having spares wouldn't break the bank. I have been using Chinese components for the past three years and none have failed. I do have a spare charge controller and an inverter but so far have not needed them. I do advise buying MPPT charge controllers and pure sine wave inverters. The MPPT charge controller converts the extra voltage to amperage so they are definitely worth the extra money. They DO work as advertised. Mine are EP Solar Tracer brand.

I had grand plans for building a new house that would have been totally off grid. Not that I wanted to be off grid but because my ideal location IS off grid. Since that location is on ten rai, space is not a problem. The house would have had a solar hot water system on a section of roof that was reinforced. The roof hot water system would have weighed 300 kilograms. My existing water heater is 4,500 watts so that eliminates a big user. My espresso coffee maker uses 800 watts and the microwave is also 800 watts. One huge user as far as start surge is often overlooked. That is a vacuum cleaner. Start surge is 7 KW. My larges inverter is 2,500 watts and it won't start start it. The main advantage of inverter air conditioners is that there is no start up surge.

Anyways the house fell through because the boss, my wife, decided to add on and remodel our existing house. She is happy with the remodeled house and it saved a LOT of money so no complaints from me.

[geuda]

Thanks a lot Gary, eventually a life experience. We have plenty of space, so I'll go for a ground mounting. I'm not sure about the need of changing the tilt of your array. My latitude is 17°, I made some calculation taking December into account and may go for a fixed 21° tilt. Rotating the array would be more effective but far too expensive. Thanks for your hint about separate systems, it makes sense and it's worth thinking about it. Anyway, I’ll always have the generator as back-up, hopefully Murphy’s law won’t apply.

I will of course use an MPPT charge controller. And of course pure sine wave inverters. Regarding the load, if you are using lots of inductive loads, you’ll need a low frequency pure sine wave inverter, the high frequency pure sine wave inverters are lighter and cheaper but can hardly cope with the surge at the starting point of inductive loads (anything with a motor, pumps, fridges, classic aircons, etc.)

[geuda]

Thanks Paul944,

Regarding batteries, what I want to avoid is connecting them in parallel. By construction, they are always in series. A 12-volt battery is made by assembling six 2-volt batteries. The quality of your connectors, wiring is the key point. To reduce the risk, I'll compare the cost of 8 twelve-volt batteries,12 eight-volt batteries, and 16 six-volt batteries.

I've got an aircon in my house in Sriracha and it hasn't been used for more than four years now... It's not too hot at night in the Loei province and the aircon will be sold with the house.

What I have in mind is a 3kW installation with backup generator, I'll try to be smart while wiring the different circuits in my house in order to design a scalable installation with a possible second system as suggested by Gary.

[dwilko9d]

Hi,

You can find 12V 250Ah batteries at http://monosun.net/batteries. You can contact direct via the website

[geuda]

Hi,

You can find 12V 250Ah batteries at http://monosun.net/batteries. You can contact direct via the website

Thanks Danny,

I'm afraid however Pukhet might be a bit far away from Loei

[Oriental Farang]

Good evening,

 

Geuda, I was pretty interested about your post and the answers/comments as I will also relocate from Phuket to Loei next year. My wife has a 30 rais land pretty well far away from everything (especially electricity supply) so I was thinking about going solar for agricultural purposes only. I was wondering if you succeeded with your off grid solar system and also how can the panels sustain hail, as this can occur during Monsoon.

 

Thanks in advance for your reply