Help with a solar project.

[th3w01f]

I'm looking for someone with experience in solar to help me get started.

We use a crap load of electricity (2500 kWh last month) so I'm not trying to go off grid but I have a freezer in the garage that I'd like to power, as well as creating a charging station for tools and things like that.

I have a Kill-A-Watt on the freezer now so I should have a reasonable idea of 24 hour kWh usage tomorrow afternoon.

I'm happy to pay for your time in bullets, silver or $$. :) I just need help designing and installing the system in the garage. This will be completly stand alone and not tied into our electrical in any way so I'm hoping it's not too difficult.

[DFBrews]

Ohh sounds fun. Grant h and grinheas are the PV guys if I remember correctly. The freezers usage will go up quite a bit in the hot part of the summer. You will want to have a buffer of availiable energy

[th3w01f]

Ohh sounds fun. Grant h and grinheas are the PV guys if I remember correctly. The freezers usage will go up quite a bit in the hot part of the summer. You will want to have a buffer of availiable energy

Cool, good to know, my hope is that it will prove useful and be a good learning experience. My plan is to design the system for a 3-day buffer and no more than 50% discharge.

The freezer took exactly 1.5kWh over the last 24 hours so this is probably a decent place to start. I'll let it run for another week and get the average.

From that I come up with this for the battery bank, if anyone sees any errors please let me know.

1500 (watts) * 3 (buffer) * 2 (50% discharge) = 9000 watts. I plan on using 6v golf cart batteries from Costco or Sams so I get 9000/6 = 1500 Ah that I need. With the batteries being just over 200Ah I come up with 8 batteries to be on the safe side.

I'm planning on a 12v system but using the 6v for the calculation, I don't think that will change the number of batteries I need.

For panels I think a pair of 200w or 250w should work well.

2 * 200 * 5 (peak sun hours) = 2000w. That should provide a good buffer for loss as well.

Anyone have any advice, feedback, thoughts that might help?

[vectorsc]

Rocky Mountain battery service has a lot of industrial batteries cheap.

Panel yield is always a big question. I like to plan like a panel has 2/3 of it's rated output.

Don't forget inverter loss. And finally I like victron solar stuff the best.

[th3w01f]

Now I have to learn about charge controllers and inverters. Any advice on sizing with the plan that I may double this in the future to also support a refrigerator?

Any feedback on Renogy panels? I've been using one to charge my Goal Zero Yeti and I have to say that their customer service is awesome. I had a 2 year old panel that I paid $200 for fail last week and they shipped me the new version for free and even refunded the difference from what I paid in 2015 since the price has come down. No hasltes at all and I was very surprised about the refund.

[gnihcraes]

Grant H. is the one to help. All I mess with are small single battery setups. (ham radio, camper stuff)

[Not_A_Llama]

From the cold-hearted perspective of an energy commodities guy... this is costing you about $0.15/day. If energy use were the same year-round as it was in your last 24 hours, you'll be spending $55 a year on electricity.

I like my projects ("investments") to return 10% or better, to match stock market performance. That means an initial cash investment of not more than $550, if it completely took your fridge offline, and the system cost nothing to run per year.

Another thought - do you actually need a battery? On an industrial scale, cold storage is considered one of the few *real* ways to store energy, in the sense that you can run the compressor balls-out during times of peak generation (lowest cost, in my world), and the "excess cold" carries forward to the times when the compressor isn't running. I don't know about the cooling ranges achievable with home systems, or the quality of insulation, but you might be able to tweak your thermostat to make the whole rig battery-free.

[th3w01f]

On an industrial scale, cold storage is considered one of the few *real* ways to store energy, in the sense that you can run the compressor balls-out during times of peak generation (lowest cost, in my world), and the "excess cold" carries forward to the times when the compressor isn't running. I don't know about the cooling ranges achievable with home systems, or the quality of insulation, but you might be able to tweak your thermostat to make the whole rig battery-free.

I'm going to have to sober up before completely digesting this one. :)

[th3w01f]

As I dig into this more I think 24v is the way to go. I don't think it changes any of my calculations but please let me know. My goal is to move my experience over to an off grid system for our well pump by next spring.

[Not_A_Llama]

I'm going to have to sober up before completely digesting this one. :)

When you have power (daytime), run the compressor past its usual cutoff point, which is usually around 0F. R134a boils at -15F, so maybe somewhere around there. The extra 15 degrees is a thermal buffer that acts like a battery. Maybe enough to make the system run battery-less. If you keep the freezer mostly full (water/ice bottles?), your opening losses will be minimal and you'll have crazy good heat capacity.

Aw hell, let's get nerdy:
Specific Heat of Water Ice in the range of -15 to -25C is ~= 1.94 kJ/kgK

Let's say you have a 15 cubic foot chest freezer that's packed 70% full of frozen items that I'll model as ice. In the extra 15F you get by running the compressor past the usual 0F cutoff to -15F, you have effectively stored...
specific heat * capacity of freezer * density of water * pack density of fridge
1.94 kJ/kgK * 15 cubic feet * (1 g/cm^3) * 70% * 9 kelvin = 1.4 kWh
(and the fun google query that calculates it, if you wanna do it with specific numbers (https://www.google.com/search?q=%281.94+kJ%2F%28kg*Kelvin%29%29+*+%2815+c ubic+feet%29+*+%281+g%2Fcm%5E3%29+*+%2870%25%29+*+ %289+Kelvin%29+in+kilowatts*hours&oq=%281.94+kJ%2F%28kg*Kelvin%29%29+*+%2815+cubic+f eet%29+*+%281+g%2Fcm%5E3%29+*+%2870%25%29+*+%289+K elvin%29+in+kilowatts*hours))

So effectively, just running it down to -15F in a mostly-packed fridge, you get a free day of energy storage (well; so long as the freezer is efficient enough to keep the cold in, during the heat, and as you're opening and closing). Realistically, you have about double that before you hit 32F, and then even more as the 32F stuff starts melting.

So that's an idea.

[DFBrews]

When you have power (daytime), run the compressor past its usual cutoff point, which is usually around 0F. R134a boils at -15F, so maybe somewhere around there. The extra 15 degrees is a thermal buffer that acts like a battery. Maybe enough to make the system run battery-less. If you keep the freezer mostly full (water/ice bottles?), your opening losses will be minimal and you'll have crazy good heat capacity.

My chest freezer cuts out at -10 I did a PID controller to bypass the factory thermostat and program it to avoid short cycling. I run my lagering chamber for home brewing this way I have a tub of glycol a pump and then a heat exhxanger in a separate box where i keep the beer

[Not_A_Llama]

My chest freezer cuts out at -10 I did a PID controller to bypass the factory thermostat and program it to avoid short cycling. I run my lagering chamber for home brewing this way I have a tub of glycol a pump and then a heat exhxanger in a separate box where i keep the beer

Cool, let's rejigger my calculations, then..
1.94 kJ/kgK * 15 cubic feet * (1 g/cm^3) * 70% * 5 kelvin = 0.8 kWh

So it's less rosy here. A lot depends now on real-life performance - can your freezer keep a load of -10F goods below 0F in a 24 hour span? If so, you're probably good battery-less. If not, you're still discounting your battery installation.

Assuming your 6V figure from before, that's 800 Watt*hours / 6 volts = 133 Amp Hours of battery. Half and a bit of battery.

Edit: Mother of god. I have created the ultimate unit mixing disaster. Begone, google calculator! Look on my works, ye mighty, and despair! (https://www.wolframalpha.com/input/?i=(1.94+kiloJoules%2F(kilogram*Kelvin))+*+(15+cub ic+feet)+*+(1+g%2Fcubic+centimeter)+*+(70%25)+*+(1 0+degrees+rankine)+in+kilowatt+hours&rawformassumption=%22UnitClash%22+-%3E+%7B%22%25%22,+%7B%22Percent%22%7D%7D&rawformassumption=%22UnitClash%22+-%3E+%7B%22degrees+rankine%22,+%7B%22DegreesRankine %22%7D%7D&rawformassumption=%22UnitClash%22+-%3E+%7B%22kiloJoules%2F(kilogram*Kelvin)%22,+%7B%2 2KilojoulesPerKilogramKelvin%22%7D%7D)

[th3w01f]

I'm still a bit confused.... and I have to admit I haven't' done anything to sober up, but are we talking about the equivalent of 'overclocking' freezers.? So I bought my freezer at Best Buy and it only goes down to 0f but if i make some chages i can get it down to -30 during periouds of cheap electiricitly? That would be awesome but I'm not sure I bought the right one.

Really I just want to keep a freezer running while charging some basic household devices during a major outage.

[Not_A_Llama]

Yeah, basically. Except that with the common variety of refrigerant on the market, DFBrews reports the most he can get down to is -10F. My spitballed earlier number was -15F, based on the boiling point of R134a.

[DFBrews]

I might be able to go lower. but my glycol mix is only a -20 and want to keep some fluidity so the pump doesn't work too hard. I just checked my other chest freezer where I keep my bulk meat and it is at -5 with no modifications

[th3w01f]

Does anyone have a recommendation on where to find batteries in Denver, or preferable south Denver - Co Springs?

I'm going with 8 x 6v. I've read decent things about the ones from Sams and Costco. Our local Sams only has the more expensive ones for $117 + core charge. At that price, I think going with Trojan T105 would be better for just a little bit more.

I'm going to check Costco today, I've seen recent posts from other stats with Sams and Costco having the lower end 6v (~210ah) for under $90.

[Not_A_Llama]

Says these are in stock at the Castle Rock Club (#4853) 5940 Promenade Pkwy.

https://www.samsclub.com/sams/duracell-golf-car-battery-group-size-gc2/prod3590228.ip?xid=plp3990117-auto:product:1:1

[th3w01f]

Says these are in stock at the Castle Rock Club (#4853) 5940 Promenade Pkwy.

https://www.samsclub.com/sams/duracell-golf-car-battery-group-size-gc2/prod3590228.ip?xid=plp3990117-auto:product:1:1

Thanks, I looked when I was there but didn't see those and there was no one to help. I'll go back today and take a closer look.