Living offgrid with small solar system(s)

[IMHO]

I am using a hybrid system for precisely the reasons Crossy lists. I got mine direct from MPP Inc. Taiwan http://www.mppsolar.com/v3/

I have three PIP-MS 4Kw units paralleled up (stacked) which came to a total of US$2275 and that included the parallel kit and UPS carriage.

After sales service is excellent. Best location for the inverters is outside the house because with three units the fan noise can be a bit distracting (I think that would apply to all inverter/chargers). I did have one problem with a unit which turned out to be caused by a lizard getting into the thing, but the support I got from MPP was very good and fast.

I have been looking at the MPP inverters for some time now.. good to hear some actual feedback from an owner.

[IMHO]

You could probably use the hybrid inverter I linked to earlier with a minimal battery to provide the extra oomph to start the A/C.

Can the inverter be programmed in such a way that it won't run down the batteries when PV harvesting drops though?

[Crossy]

You could probably use the hybrid inverter I linked to earlier with a minimal battery to provide the extra oomph to start the A/C.

Can the inverter be programmed in such a way that it won't run down the batteries when PV harvesting drops though?

Probably, the manuals are online, it's incredibly adjustable.

[George Harmony]

Don't start electric motors directly off PV only - work out a system using supplementary mains or batteries to assist with startup.

ok...understand.

With a timer wont work also when its cloudy and the panels dont give enough voltage/watts/amps It will drain the battery. Is there a tool which works like a switch depending on the amps? Like a thermoswitch depending on the temperature but then depending on the amps.

[IMHO]

Don't start electric motors directly off PV only - work out a system using supplementary mains or batteries to assist with startup.

ok...understand.

With a timer wont work also when its cloudy and the panels dont give enough voltage/watts/amps It will drain the battery. Is there a tool which works like a switch depending on the amps? Like a thermoswitch depending on the temperature but then depending on the amps.

That's the burning question

I hybrid inverter/charger that's programmable enough could possibly do the job, but it's going to have to be clever enough that you can program it to:

1. Only turn on the 220V output when there's enough PV harvested to support the load (outside of that, use PV to charge the batteries).

2. Only use the batteries to assist with initial startup, then put them back into 'float charge' mode.

3. Turn off the 220V output when there's no longer enough PV to support the load (and not pull from batteries otherwise there's no startup capacity tomorrow).

I've read a lot of inverter manuals (but not them all) and I've not yet seen one that can be that programmable....

Also note that I have a keen interest in this, because the thing I really want to run off PV and off-grid is my pool - which has 3 motors to start, plus a chlorinator, and has runtime hours that can be supported directly by PV, and runtime hours that need to be battery supplied. I've taken my research all the way to the PV azimuth level, and determined that an array split East/West facing will mean I need less battery than the same PV panels facing South, for example

i.e. in my location, an East/West facing array results in a minimum average harvesting time of about 5.5 hours/day, vs a minimum average of 4 hours/day for a South facing array. That extra 1.5 hours of daily harvesting time makes a big difference on battery capacity required, but comes at the expense of sacrificing about 9.4% annual overall PV output.

Edited March 1, 2016 by IMHO

[Muhendis]

You could probably use the hybrid inverter I linked to earlier with a minimal battery to provide the extra oomph to start the A/C.

Can the inverter be programmed in such a way that it won't run down the batteries when PV harvesting drops though?

Probably, the manuals are online, it's incredibly adjustable.

The hybrid inverter/charges I'm using are fully programmable so that the user can choose which power source takes priority. In other words the order of preference can be arranged to suit. I have mine set up so that priorities are PV - Batteries - Utility. Also the units are programmed so that the utility supply will never be called upon to charge the batteries. In other words, if there is no PV power and the batteries are low the the house gets the utility supply and the batteries have to wait till the sun shines. That is, for me, the preferred choice because charging the batteries takes more power than the house first thing in the morning which is the most vulnerable time for my power supply.

My inverters will run off the batteries quite happily in the absence of utility power (mains failure) and, obviously, without solar power (night time) but batteries are an essential element in the circuit and if they become disconnected the inverter will alarm and stop working 'til the problem is sorted leaving you on utility supply.

Also the charging characteristics are fully programmable for all battery chemistries.

Edited March 2, 2016 by Muhendis

[Crossy]

@IMHO

That InfiniSolar inverter is smart, but I don't think it's that smart

However all is not lost. A Hall-effect current sensor (these can detect DC) on the battery leads with some electronics could be used to control the AC load, probably possible with hard-wired electronics but using a PLC would give some intelligence.

Simplified:-

Batteries charging = load on.

Batteries discharging = load off.

Add in some delays to manage the start pulse and you're in business.

Rest assured, it's not nearly as simple as it sounds

[IMHO]

All isn't lost, if using a hybrid inverter/charger that all allows you to choose priority like the MPP Solar ones.

In the case of the 260W AC unit, what George needs to do is decide how many hours/day he wants AC to operate.

From there, work out the minimum average PV harvest, and how much AC runtime needs to be supplemented by battery.

Then it's just a case of working out how much total PV is needed to keep the batteries charged, and run the load itself.

This is exactly what I'm doing, but I have the benefit of a very stable, very known, load and runtime. AC usage will be more dynamic than my pool pumps. Even so, if you work on some 'worst case' numbers, it's not that hard.

e.g.

Let's say George wants to run the 260W AC for 6 hours/day

Let's say that at least 4 of those hours are in peak PV harvesting time, so won't draw on battery other than at startup. That means the other 2 hours need to be supported by batteries.

Based on this:

Battery load is 2x260W = 520Wh. Add 15% for inverter loss = 598Wh. From there, just decide on what DOD you're happy with to size the bank...

A good solar battery will give you over 4500 cycles at 20% DOD - for that you'll need 2990Wh. At 40% DOD you'll get at least 3000 cycles, which would need 1995Wh, as examples.

To calculate PV load, we work two numbers:

Battery charge requirements: 598W/day + 20% to cover charging loss = 718W/day

Direct PV supported load = 4x260w = 1040 + 15% to cover inverter loss = 1196W/day

So total PV harvesting needed = 1196W + 718W = 1914W, adding 15% for system losses (wiring losses, dirty panels etc) = 2200w you need PV to harvest.

Assuming South facing panels at a reasonable angle (15 degrees +/-10 degrees) the worst harvesting month will be August, where you get about 4 hours harvesting/day on average. So therefore, 2200W / 4 hours = 550Wh of PV needed.

Of course, that's all based on averages though, and not every day is average. In order to give yourself some headroom for cloudy days, and cover cell degradation, you will want to increase your PV. You'll also want to include some general headroom everywhere as well too. This post is complex enough already though

In short, as a minimum spec for this system you'd probably use 2x 300W panels (~2400Wh/day avg min). a 200Ah 12V battery (2400Wh = ~40% DOD), and a 1000w nominal inverter that supports a 2000W peak to handle motor startup.

Edited March 2, 2016 by IMHO

[IMHO]

Just a an aside, this site is the *best* PV calculator I've been able to find:

http://pvwatts.nrel.gov/

This not only takes into account your geographical location and PV angle - it also marries that up with actual weather data, and allows you to specify the array azimuth precisely (not many roofs are exactly due South, for example). It also gives you separate numbers for DC harvest, and AC output (the latter based on grid-tie inverter efficiencies though).

Make sure you read and understand all the inputs fully, and also make sure you download the monthly/hourly CSV files, which contain much more insights that what's displayed on page.

Super tool!

[Crossy]

Nice find IMHO

[George Harmony]

In short, as a minimum spec for this system you'd probably use 2x 300W panels (~2400Wh/day avg min). a 200Ah 12V battery (2400Wh = ~40% DOD), and a 1000w nominal inverter that supports a 2000W peak to handle motor startup.

Thank you very much. Im orientating now on buying batteries. According to one supplier here a tubular deep cycle is one of the best for such purposes but rather expensive. He quoted a price of about 11.000 baht for 150ah. Anyone use tubular?? Other deep cycles are just a little bit more expensive than amorn in thailand.

Im planning to maintain my current system for lighting and fans. For the planned wok cooking and perhaps thay aircon i soon will buy more panels, battery and ofcourse a controller with enough amps for the future. I posted two examples videos above and if can achieve that + wok cooking i am satisfied

[IMHO]

In short, as a minimum spec for this system you'd probably use 2x 300W panels (~2400Wh/day avg min). a 200Ah 12V battery (2400Wh = ~40% DOD), and a 1000w nominal inverter that supports a 2000W peak to handle motor startup.

Thank you very much. Im orientating now on buying batteries. According to one supplier here a tubular deep cycle is one of the best for such purposes but rather expensive. He quoted a price of about 11.000 baht for 150ah. Anyone use tubular?? Other deep cycles are just a little bit more expensive than amorn in thailand.

Im planning to maintain my current system for lighting and fans. For the planned wok cooking and perhaps thay aircon i soon will buy more panels, battery and ofcourse a controller with enough amps for the future. I posted two examples videos above and if can achieve that + wok cooking i am satisfied

Got a cyclic life (DOD vs Cycles vs degradation) chart? Only that can tell you if they are expensive for a reason or not.

i.e. like this:

Which is for the Globatt Inva batteries, that are widely available/cheap in Thailand.

[George Harmony]

Cause I did not plan well there is a small problem if I buy other (bigger) panels.

Only solar panels of exact or similar current should be wired together in series. When you connect a 3A panel to a 3.5A panel, the overall current will be dragged down to 3A. Such a reduction in current will by all means lead to a reduction in power output and therefore loss in system performance.

http://solarpanelsvenue.com/mixing-solar-panels/

It means that I must have seperate independent systems.....or does someone know a solution to make it one (bigger) system??

[George Harmony]

We have been talking about the possibility to measure voltage. if the PV panel give a certain voltage activate or cut.

Im not an electrician but is this perhaps a solution???

[IMHO]

Cause I did not plan well there is a small problem if I buy other (bigger) panels.

Only solar panels of exact or similar current should be wired together in series. When you connect a 3A panel to a 3.5A panel, the overall current will be dragged down to 3A. Such a reduction in current will by all means lead to a reduction in power output and therefore loss in system performance.

http://solarpanelsvenue.com/mixing-solar-panels/

It means that I must have seperate independent systems.....or does someone know a solution to make it one (bigger) system??

You will just need separate solar chargers for each PV array, or buy an inverter+charger with dual/triple MPPT PV inputs. Don't mix different panels in an array, even following that link's guidance. The current panel variance of -0/+5% is already enough to contribute an average loss of 10%+ in a multi panel array - if you start mixing panels the losses will be great - even of they're not that far away in spec.

Consider this: an MPPT charger will extract up to 30% more power out of an array than a PWM charger. Start mixing panels and the losses will be great, because MPPT simply cannot get the optimum out of mixed cells. Anyone that thinks the losses are minimal when mixing panels must be using PWM, in which case they don't know how much power they're missing, mixed panels or not

Edited March 2, 2016 by IMHO

[IMHO]

We have been talking about the possibility to measure voltage. if the PV panel give a certain voltage activate or cut.

Im not an electrician but is this perhaps a solution???

PV Panels output a wide range of voltage and current depending on how much solar radiation they're exposed to - the solution to getting the maximum out of them under all conditions are MPPT chargers/inverters. The solution to your startup problems are supplementary power. The solution to when to start/stop the load (i.e. when there's enough power being harvested) is going to be a highly programmable combination charger+inverter (good ones show you exactly how much PV energy is being harvested in real-time... so they know).... or just some simple math based on desired runtime and load, as already presented.

Edited March 2, 2016 by IMHO

[Jing Joe]

Don't start electric motors directly off PV only - work out a system using supplementary mains or batteries to assist with startup.

ok...understand.

With a timer wont work also when its cloudy and the panels dont give enough voltage/watts/amps It will drain the battery. Is there a tool which works like a switch depending on the amps? Like a thermoswitch depending on the temperature but then depending on the amps.

George mentioned Supercaps when he first raised thoughts on his solar project. With all the great knowledge that's been forthcoming lately about; inverter, panels and battery discussions how about this suggestion;-

If there was a decent power diode feeding but isolating George's inverter from the panels, (isolating for whatever external reasons) and (considering your "no-battery discussions) and there was a suitable sized Supercap straight across the inverter input, could this be designed to handle the x 6 times momentary start currents of his 240v motors he is concerned about? Yes I realise there are many considerations especially under/over charging the Supercap.

Even a Supercap with diode connected as above in a minimum sized battery system could alleviate possible momentary sagging of inverter input voltage. Yes I realise there would be at least 0.6v volts drop always present from that battery to the inverter but could be a good trade off for any motor-start challenge.

Previously when I discovered the charge requirement for Supercaps i sort of gave up on the idea of using them, for a while yet.

How about the excellent brains trust out there getting together to help George, and others?

I haven't followed much of your discussions about panels directly into inverters so forgive me for however much this suggestion is off track.

Just brainstorming, just thinking.

Edited March 3, 2016 by Jing Joe

[Naam]

as ar as optimal technical solutions are concerned i was and, up to a certain extent, still am acting like our esteemed friend Harmonic George. namely striving for the egg-laying sow that has piglets every now and then, can be sheared for wool, milked daily, acting as guard dog scaring away burglars / armed robbers and growing every three months two additional hind legs to be smoked.

alas, nothing ever worked in order to reach the targeted 110%; i had to make concessions and be happy with 91.75% achieved.

[George Harmony]

@jingjoe, i was thinking also about the possibility of using supercaps to start a fridge or aircon.

buy an inverter+charger with dual/triple MPPT PV inputs.

If i can find it here, this is i think the easiest solution. Thanks for the tips.

[George Harmony]

Again a question.

If i buy 2 batteries usually they are not 100% fully charged. Do i have to charge 1 by 1 before connect to paralel or can i connect then charge???

[IMHO]

Again a question.

If i buy 2 batteries usually they are not 100% fully charged. Do i have to charge 1 by 1 before connect to paralel or can i connect then charge???

Just connect them in parallel - they will equalize. In fact, they don't even need to be connected to a charger for that to happen..

[Muhendis]

Again a question.

If i buy 2 batteries usually they are not 100% fully charged. Do i have to charge 1 by 1 before connect to paralel or can i connect then charge???

New batteries are generally supplied fully charged. I say generally because it depends on how long the batteries have been in store before you buy them and whether the supplier has looked after them. Batteries will self discharge if left unattended for long enough.

If the batteries are sealed then this is very difficult so you would need to go by the terminal voltage which is not accurate. As IMHO said the batteries will self balance if you connect them in parallel. Doing this will make both (all) batteries the same charge which will not be fully charged. The higher charged battery will give up some of it's charge to the lower charged battery until they both have the same charge. There will be a few sparks when they are connected. The greater the difference the bigger the sparks.

[George Harmony]

Thanks again for the replies.

Just wanna share a funny story. As i said b4 i mooved into my unfished house and pumped water with a genset. After i used a dc pump nabors dont hear the genset anymore. One of them asked how i get water. Told him that i use a solar (panel) system and showed him. He then ask me if the panels also use fuel.....hahahahaha...really happend, a government officer at middle management level....unbeleivable.....

First i thought: Shall i laugh,did he make a joke..... I explained him how the system works and now he is also interested to use solar for some lamps only cause of the "too often" electrical outages in this area.

[Muhendis]

He then ask me if the panels also use fuel.....

Well............actually......yes they do.....they use hydrogen burnt in an open fire 93,000,000 miles away.

[Jing Joe]

He then ask me if the panels also use fuel.....

Well............actually......yes they do.....they use hydrogen burnt in an open fire 93,000,000 miles away.

Well done Muhendis. Thinking outside the square round planet again?

Share this with your neighbour? >>

And to think it takes "about 8 minutes and 19 seconds" to be delivered after manufacture, on site, free and forever * .

"Solar power" Go George.

* Near enough.

Edited March 5, 2016 by Jing Joe

[Naam]

He then ask me if the panels also use fuel.....

Well............actually......yes they do.....they use hydrogen burnt in an open fire 93,000,000 miles away.

And to think it takes "about 8 minutes and 19 seconds" to be delivered on site after manufacture.

but this is as fast as light!

[George Harmony]

Did i give him a good advice or not?

He said its irritating when there's an outage. He wants to ADD to his grid lighting solar powered leds to his toilet/bathroom, 1 bedroom and his living room.

I advised him to buy a cheap 20wp system with 7ah battery. In thailand it will cost roughly not yet 2000bht, incl battery.

Average use per day

3watt led x 2 hours bedroom = 6wh

3watt led x 1 hour bathroom = 3wh

5watt led x 6 hours liv room = 30wh

Total 39 watt hours.

20wp panel x 5 hours per day = 100watts. Loss 50% = 50wh

What the panel produces can easily be stored in a 7ah deep cycle battery enough for his average daily use.

So, for the total cost equivalent to some ladydrinks and perhaps also a barfine he can enjoy 3 lights for many years hahahahaha......

Did i advice him well??

[Muhendis]

He then ask me if the panels also use fuel.....

Well............actually......yes they do.....they use hydrogen burnt in an open fire 93,000,000 miles away.

And to think it takes "about 8 minutes and 19 seconds" to be delivered on site after manufacture.

but this is as fast as light!

Yep!

Marginally faster than a Thai mini bus driver.....

[Muhendis]

Did i give him a good advice or not?

He said its irritating when there's an outage. He wants to ADD to his grid lighting solar powered leds to his toilet/bathroom, 1 bedroom and his living room.

I advised him to buy a cheap 20wp system with 7ah battery. In thailand it will cost roughly not yet 2000bht, incl battery.

Average use per day

3watt led x 2 hours bedroom = 6wh

3watt led x 1 hour bathroom = 3wh

5watt led x 6 hours liv room = 30wh

Total 39 watt hours.

20wp panel x 5 hours per day = 100watts. Loss 50% = 50wh

What the panel produces can easily be stored in a 7ah deep cycle battery enough for his average daily use.

So, for the total cost equivalent to some ladydrinks and perhaps also a barfine he can enjoy 3 lights for many years hahahahaha......

Did i advice him well??

A 7Ahr battery at 40% discharge will be 33.6 Whr without taking any efficiency losses into account so your friend might be better off with a bigger battery or go to bed early with his bar fine. No mention of a T.V?

Edited March 5, 2016 by Muhendis

[George Harmony]

Tv? No he did not asked me about tv use. Usually when there is a power outage,also in the evening, i see some nabors going/sitting outside in our complex. Their houses are fully aircon, probably not well ventilated. So, its getting hot inside also dark ofcourse. Perhaps i should tell him about 12v fans.