Planning for how to run a fridge on solar.
Nov 12, 2013 16:57:31 GMT 10
Ammo9, StepfordRenegade, and 3 more like this
Post by shinester on Nov 12, 2013 16:57:31 GMT 10
Well it's Wayne's fault I'm writing this up, I'm only at the planning stages and I would prefer to iron out any possible kinks before hand, though if I had the cash I would just buy these components I've listed.
Why solar and why fridges?
We can do without for lighting, washing, cooking, internet [not sure I can] but refrigeration is one of the best ways of preserving foods over the short term. Obviously we can preserve for longer term, dehydration, salting, smoking, canning etc, but nothing beats a fridge for throwing it in and keeping it fresh for a week or two. It's better to preserve things such as vitamins and medicines also. I have chosen solar because it is renewable and most components will last some time as they're no moving parts. I'm looking to get started as economically as possible whilst still thinking of future capabilities. My other consideration is that I want to be able to mount my solar set up on a cart or be man-portable in some way.
The fridge
Fridges usually use a great deal of electricity. We can test this with something like a watt-meter/energy meter such as THIS. Because they are made for costs, size and convenience the ones in our homes are not particularly suitable for solar as they use a lot of electricity, perhaps mostly because they don't have a great deal of insulation. To give you an idea, for a fridge with 590kWh/year [my small fridge in the shed] or an average of 1.76kWh/day you would need to get at least 1000w on the roof of your house in Melbourne [$1000 for the panels alone] as well as a similarly expensive battery bank to handle it in the winter. Some figures on that are, 1000w makes an average of 1.44kWh/day in winter and 4.14kWh/day in the middle of summer.
What we need is to get a fridge that uses much less power than a standard fridge. The answer it seems is to use a chest freezer running at fridge temperatures. Freezers are made with thicker insulation than just about any fridge and because cool air sinks, the chest freezer holds this cool air when opened, unlike upright fridges and freezers. It's less convenient sure, but THIS guy says he uses on average 0.1kW/day or 33.6kWh/year, which is a significant difference, meaning we can don't need nearly as much power.
Some other helpful links are HERE where we find that their freezer-to-fridge uses 200-300Wh/day and a fairly detailed explanation HERE including the day-to-day use with the practicalities of using chest freezer-to-fridges. Their power consumption figures are higher again, though they do have a larger one.
Some more info, first women suggests 100W/day and the second guy suggests 250W/day. It could be something as simple as the energy star rating or fridge seal that makes that kind of difference.
Insulation
Some details on adding insulation to a normal fridge HERE which I think would also be a good idea to drop consumption down further in any application. Something that I plan to do. The second video shows what can be done with insulation and ice alone. The insulation is 45cm [18"] thick! Some other information I have found suggests fridges and freezers of boats are made with 100mm and 150mm insulation. Overall looking at normal fridges we can see that there's not nearly enough insulation put on them in this application or in our normal life for that matter. Whilst you can put a lot of insulation around and it seems to make quite a difference often it's the seal is the weak point on any fridge/freezer, and I think the ultimate might be to have multiple seals.
Fridge to freezer
So how do we get the freezer to work at fridge temperatures? The easiest way is to plug in THIS temperature controller to do the work for us. It might use a little power itself of course, but would be fairly marginal, probably only 1-10Wh/day. The temperature sensor would have to go into the freezer of course and we want to make sure that doesn't spoil it being air-tight and full insulated. Being a fan of multiple uses, without the temperature controller the freezer would work on mains power as a freezer, so we could store our olive oil, freeze our meat etc. in there.
Making power
Solar
Obviously solar cells generate power, turning sun rays into electricity. Pointing the cells north will help get the most sun during the day and you can even adjust the tilt angle depending on the time of the year. It's a little tricky with times of year and so on, so HERE's a calculator to get the best performance out of your cells.
What to buy? - Basically solar cells of the same rating are going to produce similar amounts of power. Mono's are the best choice for $$ and size, so just go that way and make it easier. It seems that the price point of 120W cells gives you the best dollar/W on ebay [better to get 2x120w than 1x250w!] perhaps because of postage. HERE's one I had my eye on, probably doesn't have a charge controller on it but for my set up I want to use my own and it's the best price on ebay on the date I posted. 120W will give you 0.26kWh/day in winter up to 0.66kWh/day in summer on average, allowing for losses via the charge cycle when on Lithium Ion batteries. This is well above the stated needed output, better to allow a little extra than not enough.
Peddling
Yes, you could peddle for your power, although it does literally use your food as you will be eating more or burning more energy. A fit 'laborer' or someone who rides bikes a lot could do about 75W of mechanical energy for 8hrs which translates into about 50W of electricity, so in effect you could charge your batteries up enough for your fridge in about 3 hours. Not a lot of fun.
Batteries
AGM - Most systems use AGM batteries, which can be thought of as a better quality car battery. They work similarly though internally they are designed to be able to go deep cycle and not deteriorate. They will however only give you about 50-60% of the electricity back as usable power. So you will need to charge them for longer. So if the solar cells put in 100aH, they will only give you around 50aH of usable power. Ideally they are kept close to fully charged to keep their full life expectancy of about 10 years. They only slowly discharge at a rate of about 3%/month if being unused. Their life cycle is rated as approximately 250 cycles @ 100% DOD (depth of discharge), 500 cycles @ 50% DOD and 1250 cycles @ 30% DOD as per HERE. The ideal situation is when they are only lightly drained with most of the work being done during the day [being charged by the sun].
Lithium Ion [Li+] - Similar batteries as you will find in your phone/laptop etc. They pack a lot of punch into a small package and if you're willing to make up your own packs of smaller batteries work out cheaper than AGM batteries with a larger charge cycle. What I have in mind is to use a battery holders and make my own packs up out of them and attaching a bunch of them in parallel to boost the Amp hours [how long you can run stuff for]. 18650's come in 5.3Ah [amp hours] now, for $1.80ea, so 12 packs of 3 [63.6aH @ 11.1v] is a pretty decent amount of storage in a small package. The charge cycle 'has' to be right or else they could catch fire, so they have to use a different charge controller to a normal solar cell charger. They loose 5-10% if being unused and can be heavily discharged without major loss of life expectancy but last about 400 charges, so a lifetime of 2-3 years is expected with fully charged and fully discharged.
00% DoD 300 – 500 cycles
50% DoD 1,200 – 1,500
25% DoD 2,000 – 2,500
10% DoD 3,750 – 4,700 SOURCE
As you can see the less they discharge, the longer they live, well out performs AGM.
Since they are also about 1/2 of the price of a similar sized AGM and convert more of the solar electricity into usable power [about 90%] they are in my opinion a better option. Back up batteries can be stored and charged once every 4 months or all just hooked up and will last a VERY long time in this configuration. The technology is only about 15 years old so no one knows how long they would work as backup and the full characteristics of their degrading over time. If you loose one cell [easy to test with a multimeter] you can replace just that cell or take out that pack loosing only 5.3Ah capacity. They weight a LOT less too, making them much more portable. The 'packs' of batteries typically used with scooters are prohibitively expensive still, I guess we're waiting for cars instead of laptops to dominate the use of these batteries.
Charge controller
As mentioned earlier you need a specific controller to charge Li+ and they're around the $25 for a 20Amp controller. The extra capacity will not stress it out and give you less issues in the long run. Some losses are expected converting the variable voltage of a solar cell into the voltage that the Lithium Ions need.
Inventor
This is where you convert 12v DC into 240v AC. You loose about 10% of your stored power doing this and if we could get 12v fridges with thick insulation [they do exist] for the same sort of price as a chest freezer, then it would be the better option. However, we're going 240V for the fridge and it also allows us some scope to use our stored power for other applications. Many are around, but you're best to use a pure-sinewave inverter for the fridges compressor. They are more expensive but necessary. Whatever size the compressor motor is [the Watts or Amps it draws is on the back of the fridge] you will want to at least double your inverter to handle the start-up current. Whilst a 600W pure sine wave [$100] would probably do it, I'm playing it safe and thinking of other applications and going for a 1000W pure sine wave, and they start at around $170.
Costs?
Power
120w Panel, 63.4Ah battery, 20A charge controller, 1000W pure sine-wave inverter $390.
120w Panel, 191Ah battery, 20A charge controller, 1000W pure sine-wave inverter $572
360w Panel, 424Ah battery, 20A charge controller x 3, 2000W pure sine-wave inverter $1403
freezer
Second hand for $100, to $500 for a high efficiency new chest freezer
Temperature controller $15
Mounting hardware
Could be free or lots of dollars, depending. The smaller one could be put into a tool box [plastic] with a plug for the panel.
I'll build probably one in the next few months, I want something like this for camping anyhow.
Alternatives
I looked at LPG fridges [there's one on Gumtree right now for $200] but I didn't like the usage of 1.5kg/day if older than 30 years or 0.75kg/day if younger. If I was storing gas I would much rather be using all of that energy for cooking. Kero, I must admit I don't know enough about, I do know that it's really hard to find a second hand and working version and that the new ones are fairly expensive. [read cheap skate].
Evaporative cooler fridges, or Zeer refrigerators, a simple one with no power made with clay pots
Excellent for getting things cooler for just the cost of water. The downside is it's not going to bring things down to below 4 degrees, but it will be cooler in arid [or at least low humidity] environments.
The plan
I have not done this yet, it's still some time away for the full set up. I will start shortly with the freezer itself or insulating a standard fridge and see what I can do with it's power consumption by insulate it, get it running at fridge temperatures etc as it is the heart of the whole system. Once I get that right, building a solar system [as detailed above] that suits it, will be much more straight forward.
Why solar and why fridges?
We can do without for lighting, washing, cooking, internet [not sure I can] but refrigeration is one of the best ways of preserving foods over the short term. Obviously we can preserve for longer term, dehydration, salting, smoking, canning etc, but nothing beats a fridge for throwing it in and keeping it fresh for a week or two. It's better to preserve things such as vitamins and medicines also. I have chosen solar because it is renewable and most components will last some time as they're no moving parts. I'm looking to get started as economically as possible whilst still thinking of future capabilities. My other consideration is that I want to be able to mount my solar set up on a cart or be man-portable in some way.
The fridge
Fridges usually use a great deal of electricity. We can test this with something like a watt-meter/energy meter such as THIS. Because they are made for costs, size and convenience the ones in our homes are not particularly suitable for solar as they use a lot of electricity, perhaps mostly because they don't have a great deal of insulation. To give you an idea, for a fridge with 590kWh/year [my small fridge in the shed] or an average of 1.76kWh/day you would need to get at least 1000w on the roof of your house in Melbourne [$1000 for the panels alone] as well as a similarly expensive battery bank to handle it in the winter. Some figures on that are, 1000w makes an average of 1.44kWh/day in winter and 4.14kWh/day in the middle of summer.
What we need is to get a fridge that uses much less power than a standard fridge. The answer it seems is to use a chest freezer running at fridge temperatures. Freezers are made with thicker insulation than just about any fridge and because cool air sinks, the chest freezer holds this cool air when opened, unlike upright fridges and freezers. It's less convenient sure, but THIS guy says he uses on average 0.1kW/day or 33.6kWh/year, which is a significant difference, meaning we can don't need nearly as much power.
Some other helpful links are HERE where we find that their freezer-to-fridge uses 200-300Wh/day and a fairly detailed explanation HERE including the day-to-day use with the practicalities of using chest freezer-to-fridges. Their power consumption figures are higher again, though they do have a larger one.
Some more info, first women suggests 100W/day and the second guy suggests 250W/day. It could be something as simple as the energy star rating or fridge seal that makes that kind of difference.
Insulation
Some details on adding insulation to a normal fridge HERE which I think would also be a good idea to drop consumption down further in any application. Something that I plan to do. The second video shows what can be done with insulation and ice alone. The insulation is 45cm [18"] thick! Some other information I have found suggests fridges and freezers of boats are made with 100mm and 150mm insulation. Overall looking at normal fridges we can see that there's not nearly enough insulation put on them in this application or in our normal life for that matter. Whilst you can put a lot of insulation around and it seems to make quite a difference often it's the seal is the weak point on any fridge/freezer, and I think the ultimate might be to have multiple seals.
Fridge to freezer
So how do we get the freezer to work at fridge temperatures? The easiest way is to plug in THIS temperature controller to do the work for us. It might use a little power itself of course, but would be fairly marginal, probably only 1-10Wh/day. The temperature sensor would have to go into the freezer of course and we want to make sure that doesn't spoil it being air-tight and full insulated. Being a fan of multiple uses, without the temperature controller the freezer would work on mains power as a freezer, so we could store our olive oil, freeze our meat etc. in there.
Making power
Solar
Obviously solar cells generate power, turning sun rays into electricity. Pointing the cells north will help get the most sun during the day and you can even adjust the tilt angle depending on the time of the year. It's a little tricky with times of year and so on, so HERE's a calculator to get the best performance out of your cells.
What to buy? - Basically solar cells of the same rating are going to produce similar amounts of power. Mono's are the best choice for $$ and size, so just go that way and make it easier. It seems that the price point of 120W cells gives you the best dollar/W on ebay [better to get 2x120w than 1x250w!] perhaps because of postage. HERE's one I had my eye on, probably doesn't have a charge controller on it but for my set up I want to use my own and it's the best price on ebay on the date I posted. 120W will give you 0.26kWh/day in winter up to 0.66kWh/day in summer on average, allowing for losses via the charge cycle when on Lithium Ion batteries. This is well above the stated needed output, better to allow a little extra than not enough.
Peddling
Yes, you could peddle for your power, although it does literally use your food as you will be eating more or burning more energy. A fit 'laborer' or someone who rides bikes a lot could do about 75W of mechanical energy for 8hrs which translates into about 50W of electricity, so in effect you could charge your batteries up enough for your fridge in about 3 hours. Not a lot of fun.
Batteries
AGM - Most systems use AGM batteries, which can be thought of as a better quality car battery. They work similarly though internally they are designed to be able to go deep cycle and not deteriorate. They will however only give you about 50-60% of the electricity back as usable power. So you will need to charge them for longer. So if the solar cells put in 100aH, they will only give you around 50aH of usable power. Ideally they are kept close to fully charged to keep their full life expectancy of about 10 years. They only slowly discharge at a rate of about 3%/month if being unused. Their life cycle is rated as approximately 250 cycles @ 100% DOD (depth of discharge), 500 cycles @ 50% DOD and 1250 cycles @ 30% DOD as per HERE. The ideal situation is when they are only lightly drained with most of the work being done during the day [being charged by the sun].
Lithium Ion [Li+] - Similar batteries as you will find in your phone/laptop etc. They pack a lot of punch into a small package and if you're willing to make up your own packs of smaller batteries work out cheaper than AGM batteries with a larger charge cycle. What I have in mind is to use a battery holders and make my own packs up out of them and attaching a bunch of them in parallel to boost the Amp hours [how long you can run stuff for]. 18650's come in 5.3Ah [amp hours] now, for $1.80ea, so 12 packs of 3 [63.6aH @ 11.1v] is a pretty decent amount of storage in a small package. The charge cycle 'has' to be right or else they could catch fire, so they have to use a different charge controller to a normal solar cell charger. They loose 5-10% if being unused and can be heavily discharged without major loss of life expectancy but last about 400 charges, so a lifetime of 2-3 years is expected with fully charged and fully discharged.
00% DoD 300 – 500 cycles
50% DoD 1,200 – 1,500
25% DoD 2,000 – 2,500
10% DoD 3,750 – 4,700 SOURCE
As you can see the less they discharge, the longer they live, well out performs AGM.
Since they are also about 1/2 of the price of a similar sized AGM and convert more of the solar electricity into usable power [about 90%] they are in my opinion a better option. Back up batteries can be stored and charged once every 4 months or all just hooked up and will last a VERY long time in this configuration. The technology is only about 15 years old so no one knows how long they would work as backup and the full characteristics of their degrading over time. If you loose one cell [easy to test with a multimeter] you can replace just that cell or take out that pack loosing only 5.3Ah capacity. They weight a LOT less too, making them much more portable. The 'packs' of batteries typically used with scooters are prohibitively expensive still, I guess we're waiting for cars instead of laptops to dominate the use of these batteries.
Charge controller
As mentioned earlier you need a specific controller to charge Li+ and they're around the $25 for a 20Amp controller. The extra capacity will not stress it out and give you less issues in the long run. Some losses are expected converting the variable voltage of a solar cell into the voltage that the Lithium Ions need.
Inventor
This is where you convert 12v DC into 240v AC. You loose about 10% of your stored power doing this and if we could get 12v fridges with thick insulation [they do exist] for the same sort of price as a chest freezer, then it would be the better option. However, we're going 240V for the fridge and it also allows us some scope to use our stored power for other applications. Many are around, but you're best to use a pure-sinewave inverter for the fridges compressor. They are more expensive but necessary. Whatever size the compressor motor is [the Watts or Amps it draws is on the back of the fridge] you will want to at least double your inverter to handle the start-up current. Whilst a 600W pure sine wave [$100] would probably do it, I'm playing it safe and thinking of other applications and going for a 1000W pure sine wave, and they start at around $170.
Costs?
Power
120w Panel, 63.4Ah battery, 20A charge controller, 1000W pure sine-wave inverter $390.
120w Panel, 191Ah battery, 20A charge controller, 1000W pure sine-wave inverter $572
360w Panel, 424Ah battery, 20A charge controller x 3, 2000W pure sine-wave inverter $1403
freezer
Second hand for $100, to $500 for a high efficiency new chest freezer
Temperature controller $15
Mounting hardware
Could be free or lots of dollars, depending. The smaller one could be put into a tool box [plastic] with a plug for the panel.
I'll build probably one in the next few months, I want something like this for camping anyhow.
Alternatives
I looked at LPG fridges [there's one on Gumtree right now for $200] but I didn't like the usage of 1.5kg/day if older than 30 years or 0.75kg/day if younger. If I was storing gas I would much rather be using all of that energy for cooking. Kero, I must admit I don't know enough about, I do know that it's really hard to find a second hand and working version and that the new ones are fairly expensive. [read cheap skate].
Evaporative cooler fridges, or Zeer refrigerators, a simple one with no power made with clay pots
Excellent for getting things cooler for just the cost of water. The downside is it's not going to bring things down to below 4 degrees, but it will be cooler in arid [or at least low humidity] environments.
The plan
I have not done this yet, it's still some time away for the full set up. I will start shortly with the freezer itself or insulating a standard fridge and see what I can do with it's power consumption by insulate it, get it running at fridge temperatures etc as it is the heart of the whole system. Once I get that right, building a solar system [as detailed above] that suits it, will be much more straight forward.