Please help design this system

samitrix

Hi all,

Been away from this forum for sometime but it's good to be back and see how much progress has been made through this forum!

Anyway, I'm just a beginner on solar and in dire need of your expert opinion on the solar power system I'm hoping to purchase. I'm thinking to buy all my components from the online store here. OK attached is my AC and DC loads with details Attachment not found.. Could you please help me design everything for this system?

Well I'm actually hoping that 1kW will be sufficient for my purposes but once I see the full design then I might make few adjustments here and there to keep the system at 1kW.

Thank you so much in advance and looking forward to your views. Oh by the way, I'm currently based in Solomon Islands (Honiara city) where Peak Sun Hour is 5.5 hours.

Sam

Cariboocoot

Re: Please help design this system

Hi Sam!

Boy I hope you have a lot of money. Did you measure any of these loads with a Kill-A-Watt or are they just calculated? That freezer, whereas not unrealistic, is a killer at nearly 3kW hours per day. I'd investigate that one very carefully if I were you, and even consider replacing it with a more efficient unit.

Otherwise you're looking at about 3.2 kW hours AC per day which is around 3.5 to 3.6 DC (depending on inverter efficiency) plus 198 Watt hours DC for lights plus whatever the inverter will need (let's say 480). Grand total: 4216 Watt hours DC. No small amount.

I have to ask: why are the lights DC? Keep in mind that makes them Voltage specific to the system. If they are 12 Volt lights you've chosen you'll need something to power them because the other needs are definitely in "48 Volt territory". There usually is no point at all in having DC equipment when you've got to run an inverter anyway.

So on 48 Volts you'd be using close to 100 Amp hours daily: 4.8 kW hours. As such you'd want around 400 Amp hours of battery for 25% DOD limit. You might be looking at two parallel strings of eight GC2's (cheap Watt hours) for 440 Amp hours @ 48 Volts.

Then you'll need a 60 Amp MPPT type controller and around 2742 Watts of array.

Ironically your inverter itself doesn't have to be very large as the total running Watts is quite small. The biggest demand will be getting the freezer compressor started. What is the power standard there? I believe it is the same as North America so that's a help. It looks like the smallest good 48 Volt inverter is Outback's FX3048.

So, what do we have to adjust now?

zoneblue

Re: Please help design this system

No i think you need to measure the freezer. There isnt a (domestic) freezer anywhere that uses that sort of amount of energy. It might say 115W on the sticker, but thats usually kind of an outside limit. And it only runs for part of every hour.

Either get a killawatt or look it up on a consumer website which will list it in kWh/year. Take that figure and divide by 365.

Ditto the "mobile chargers". 30W is enough to power (and charge) a laptop.

The sewing machine looks about right considering its on and off ratio. Lights look ok.

Dont forget to allow a buffer for the little things you forget but add up.

As Coot said the beginning is no place to get your numbers wrong.

vtmaps

Re: Please help design this system

Cariboocoot wrote: »

Did you measure any of these loads with a Kill-A-Watt or are they just calculated? That freezer, whereas not unrealistic, is a killer at nearly 3kW hours per day.

Yes, the freezer is much too high. I suspect that Sam did not correct for duty cycle. --vtMaps

Cariboocoot

Re: Please help design this system

Oddly enough I've got a chest freezer here that would burn that much power in a day. During Summer, before I put the thermofan on the room to ventilate it in the heat. That helped a lot; well worth the electric the fan draws for the drop in the amount the freezer uses.

samitrix

Re: Please help design this system

Cariboocoot wrote: »

Boy I hope you have a lot of money.

No I don'tttttt which is exactly why I need your expert opinions.

Cariboocoot wrote: »

Did you measure any of these loads with a Kill-A-Watt or are they just calculated? That freezer, whereas not unrealistic, is a killer at nearly 3kW hours per day. I'd investigate that one very carefully if I were you, and even consider replacing it with a more efficient unit.

Nope, they are all written on the spec sheet. I think I definitely need to purchase Kill-A-Watt meter. It surely will help me in various ways.
OK ya'll have to know that in this part of the world, our options are quite limited. There are bunch of Chinese junks here with no proper information or spec sheet or support. Things are just dumped here and without many options we just have to go with the flow as they say. I call it 'electronic slavery.' lol. But on a serious note, I'm thinking to buy a good freezer outside of Solomon Islands and have it imported here. It would be costly for now but a good investment in long run. So what would you guys recommend, DC or AC freezer?

Just a little background on electricity situation in Solomon Islands. We go by 240VAC 50Hz. Electricity cost here is THE most expensive in the world as per the data last year around June. Maybe it has changed little bit but I'm sure its in the top 10 range! 1 unit of electricity here is US$0.88/kwh!!! And the irony is this country is listed as an LDC or Least Developed Country. How do you expect people or even business to survive?? And by the way the electrification rate here is around 15% which means 85% of the population doesnt even have access to mdern electricity. Out of this 85% roughly 40% live in outer islands where some haven't seen electricity yet.

Cariboocoot wrote: »

I have to ask: why are the lights DC? .

Because that's what's available to us mortal beings here. lol.

Cariboocoot wrote: »

So, what do we have to adjust now?

I guess I was quite wrong about the system size. OK in that case, please advise me if I can keep solar at 1kW and still be able to use some freezer that you guys can recommend?

Thanks a lot!
sam

Cariboocoot

Re: Please help design this system

Wow. You are in a bad place electricity-wise. $0.88 per kW hour almost makes off-grid solar viable.

Your standard is probably 230 VAC 50 Hz, which is "European". I know it says 240 VAC but that's not something you're going to find an exact match for. So in this case matching the 50 Hz European standard would possibly be best.

Although in some ways it sounds as though you could just ignore the 'standard' and bring in all of whatever you need because the local market is not very accommodating. It also sounds like electric service is a rare thing in general.

So let's see what we can sort out.
Voltage of the DC lights: is it 12? That can pose some problems both for making up a good system to power the AC devices and for overcoming Voltage drop on the DC wiring.

Freezer: what can you afford to get? They make DC freezers which will run on 12-24 Volts, but they are pricey and may not even be available to you. A standard AC freezer should draw in the neighborhood of 120 Watts running and cycle about 1/3 of the time meaning you end up with at least 1kW hour usage right there. Now if the system has to stay at 12 Volts due to the DC Lights this presents some issues. Not insurmountable, but not the best choice. Or else you can add another piece of equipment to the list to lower the 24 VDC to 12 VDC just for lights. Not attractive either way.

Now about this "1kW" figure. What do you base that on? The array size? Because off-grid systems should be sized according to the Watt hours they can supply. The good news there is that a 1kW array at your location should be good for 2.5 kW hours AC (assuming favourable insolation and 5 hours of good sun). You can run quite a bit with that. Including some refrigeration.

BB.

Re: Please help design this system

Looking up in:

http://solarelectricityhandbook.com/solar-irradiance.html

for Salomon Islands, fixed array facing to the equator:
Honiara
Average Solar Insolation figures

Measured in kWh/m²/day onto a solar panel set at a 81° angle from vertical:
(For best year-round performance)

Jan
Feb
Mar
Apr
May
Jun


5.15
4.75
4.81
5.03
4.80
4.74


Jul
Aug
Sep
Oct
Nov
Dec


4.56
4.92
5.11
5.33
5.51
5.30


So, a 1 kWatt array (1,000 watts) would generate on a 4.0 hour minimum sun day:

• 1,000 watts * 0.52 average system eff * 4.0 hours of sun per day = 2,080 WH per day

A 2 day average storage battery discharged to a maximum of 50% would be around:

• 2,080 Watt*Hours per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volts = 408 AH @ 24 volt battery bank

2x 6 volt @ ~220 AH * 2 parallel strings (4 batteries total) would be a nice bank to make with deep cycle golf cart batteries (if they are available/cost effective in your region).

A ~1,200 to ~1,500 Watt AC inverter is usually required to power an "average" fridge/freezer compressor

Your average highs and lows run from upper 80's (day time) to mid-lower 70's at night. High average room temperatures really push up refrigeration costs.

It appears that a 1,000 Watt array may just be enough to run a single energy efficient refrigerator or freezer. But you would have to keep a close eye on the system (and find the right appliance for your needs).

You probably are between a rock and a hard place... Costs a lot of money to import a high efficiency refrigerator/freezer, and costs you a lot of money to get the supplies needed for a solar power system.

Which will be better--In general, it is more cost effective to do agressive conservation vs building out a larger solar power system... But you may have to simple do several designs with different options and price them out to get the optimum solution for your home.

-Bill

wooffi

Re: Please help design this system

Hi there,

I'd like to chime in, I gave up on the 12 volt light all together. I had some separate lines wired for that purpose, but with the modern LED lights I now have my place totally converted to LED and I might say we have a crazy light show going on in our nursery in Spring. The draw is incredible low.

As to the freezer, yes, my fridge freezer has always been the largest draw for me as well. I have a real old vest frost from Denmark.

Sam may want to look at a propane freezer to keep the load off his system all together. But since energy seems to be very expensive on his island, propane might be outrages as well.

Wolfgang

vtmaps

Re: Please help design this system

Try to rethink the 12 volt lighting. If you are going to have an inverter for the fridge, you might as well run the lights of the inverter. Since there is 240 volt grid, there must be available 240 volt light bulbs (or put some bulbs in that freezer you intend to import).

A 12 volt system will vary quite a bit in voltage, dipping below 11 volts when the freezer starts, and exceeding 15 volts while charging. This is not good for some 12 volt lights. Your inverter output voltage will be much more stable. Also, if you give up the 12 volt lighting you can run a 24 volt system.

Your inverter should be a pure sine wave inverter, and look for one with an adjustable low-voltage-disconnect. This will turn off the inverter before you can damage the batteries by over discharging them.

--vtMaps

samitrix

Re: Please help design this system

Cariboocoot wrote: »

Wow. You are in a bad place electricity-wise. $0.88 per kW hour almost makes off-grid solar viable.

Indeed, and precisely why we need renewable energy solutions here. being so close to the equator, solar energy seems to be the best renewable energy solution.

Cariboocoot wrote: »

Your standard is probably 230 VAC 50 Hz, which is "European". I know it says 240 VAC but that's not something you're going to find an exact match for. So in this case matching the 50 Hz European standard would possibly be best.

Yup European/Australian standard is correct.

Cariboocoot wrote: »

So let's see what we can sort out. Voltage of the DC lights: is it 12? That can pose some problems both for making up a good system to power the AC devices and for overcoming Voltage drop on the DC wiring.

Through the various comments I've received here, seems like it's not a good idea to use DC lights just coz its available. AC lights are available too..not many selection to choose from but I guess I can go with that. As you guys suggested that if you are using DC-AC Inverter anyway, then better off not to mix AC and DC. If that's the case then I will be looking at AC refrigerators. There are few choices but with absurd prices when i checked last year...hopefully things have changed.

Cariboocoot wrote: »

Now about this "1kW" figure. What do you base that on? The array size? Because off-grid systems should be sized according to the Watt hours they can supply. The good news there is that a 1kW array at your location should be good for 2.5 kW hours AC (assuming favourable insolation and 5 hours of good sun). You can run quite a bit with that. Including some refrigeration.

Well it's rare here but I found a really cheap deal on some solar panels so I just bought it which is why this strange figure of 1kW-I should have made it clear in the beginning. Anyway, one question, normally 1kW system at my location should produce about 5kWh but you mentioned a figure of 2.5kwh, are the losses really that bad? its 50% off right away.

Thanks,
sam

samitrix

Re: Please help design this system

BB. wrote: »

So, a 1 kWatt array (1,000 watts) would generate on a 4.0 hour minimum sun day:

• 1,000 watts * 0.52 average system eff * 4.0 hours of sun per day = 2,080 WH per day

A 2 day average storage battery discharged to a maximum of 50% would be around:

• 2,080 Watt*Hours per day * 1/0.85 inverter eff * 2 days storage * 1/0.50 max discharge * 1/24 volts = 408 AH @ 24 volt battery bank

4x 6 volt @ ~220 AH * 2 parallel strings (8 batteries total) would be a nice bank to make with deep cycle golf cart batteries (if they are available/cost effective in your region).

A ~1,200 to ~1,500 Watt AC inverter is usually required to power an "average" fridge/freezer compressor

Your average highs and lows run from upper 80's (day time) to mid-lower 70's at night. High average room temperatures really push up refrigeration costs.

It appears that a 1,000 Watt array may just be enough to run a single energy efficient refrigerator or freezer. But you would have to keep a close eye on the system (and find the right appliance for your needs).

You probably are between a rock and a hard place... Costs a lot of money to import a high efficiency refrigerator/freezer, and costs you a lot of money to get the supplies needed for a solar power system.

Which will be better--In general, it is more cost effective to do agressive conservation vs building out a larger solar power system... But you may have to simple do several designs with different options and price them out to get the optimum solution for your home.

-Bill

Thanks Bill for the detailed analysis. So the trick really is to find good energy efficient appliances especially refrigerator. will have a look this weekend at some of the shops we have here and report the spec and prices later.

samitrix

Re: Please help design this system

vtmaps wrote: »

Try to rethink the 12 volt lighting. If you are going to have an inverter for the fridge, you might as well run the lights of the inverter. Since there is 240 volt grid, there must be available 240 volt light bulbs (or put some bulbs in that freezer you intend to import).

A 12 volt system will vary quite a bit in voltage, dipping below 11 volts when the freezer starts, and exceeding 15 volts while charging. This is not good for some 12 volt lights. Your inverter output voltage will be much more stable. Also, if you give up the 12 volt lighting you can run a 24 volt system.

Your inverter should be a pure sine wave inverter, and look for one with an adjustable low-voltage-disconnect. This will turn off the inverter before you can damage the batteries by over discharging them.

--vtMaps

Thank you for the advice and I'm convinced to get rid of the 12V DC lights. I will have a look at the AC ones available here.

samitrix

Re: Please help design this system

wooffi wrote: »

Hi there,

I'd like to chime in, I gave up on the 12 volt light all together. I had some separate lines wired for that purpose, but with the modern LED lights I now have my place totally converted to LED and I might say we have a crazy light show going on in our nursery in Spring. The draw is incredible low.

As to the freezer, yes, my fridge freezer has always been the largest draw for me as well. I have a real old vest frost from Denmark.

Sam may want to look at a propane freezer to keep the load off his system all together. But since energy seems to be very expensive on his island, propane might be outrages as well.

Wolfgang

Thanks Wolfgang, as a matter of fact, I'm giving up on DC lighting. And as for propane freezer, I haven't even heard of such a solution here! so i guess we are still quite far back. anyway i'll do some price check on AC refrigerators here this weekend.

BB.

Re: Please help design this system

Samitrex,

I had to fix my post (and the copy you made)... I first started out the design as a 12 volt battery bank, but once a quick calculation showed that it would be ~800 AH @ 12 volts, I changed it to a 24 volt battery bank, but forgot to update the 2x 6 volt strings (12 volt) into 4x 6 volt strings (24 volt).

That, of course, doubles the number of "Golf Cart" sized batteries.

By the way, there is nothing magic about GC batteries--They just are usually cheap and available in many locations--And "good enough" for a smaller off grid system.

Sorry,
-Bill

BB.

Re: Please help design this system

There are other possibilities too... For example get a "simple" refrigerator or freezer (not frost free), and see if you can have the pump changed to a Danze 12-24 VDC pump.

Of course, that means you have to find a source for the pump, refrigerator/freezer, and somebody very knowledgeable (or take a crash course in refrigeration). If you have good ship's chandler nearby, perhaps they can help you with refrigeration or know a knowledgeable person. There are many marine refrigeration systems (you buy the pump/cold plate and build a well insulated box for the food):

http://www.seafrost.com/BD.html

-Bill

vtmaps

Re: Please help design this system

samitrix wrote: »

anyway i'll do some price check on AC refrigerators here this weekend.

We usually recommend AC fridges over DC fridges for two reasons:
1) around here the DC fridges are MUCH more expensive. With the money you save on an AC fridge, you can buy an extra solar panel or two.
2) if you have to have a big inverter for other reasons (pump, blender, microwave, etc) you might as well use it for the fridge

These reasons may not apply to you. There are some advantages to DC fridges. For one thing, you do not need a big inverter. An AC fridge that draws 120 watts may need a 1000 watt pure sine inverter to start it. The bigger the inverter, the more power the inverter uses by just being turned on. So in a small system DC refrigeration may make sense. btw, my Outback inverter consumes as much power every day as my refrigerator.

Many of the DC fridges use Danfoss compressors. These fridges self configure to either 12 or 24 volts DC. If you get a DC fridge, you can then use a very small & efficient inverter for the lights, radio, etc. Does your sewing machine really draw only 15 watts?

--vtMaps