Taking the plunge

System · December 2007

Hi Everyone. This is my first post.

My wife and I bought some land with a small house in much need of repairs. We've built a tiny cabin to live in while we work on the house. Its time to power the cabin and we want to be as self sufficient as possible. Our electrical load consists of a few lights, a radio, and a fridge. We've ordered a chest freezer (10 cf) with the intent of converting it to a fridge. I've read the posts here and elsewhere on that subject. So far I've bought one 64w panel. I've ordered a Vector 2500/5000 watt inverter. I know I need more panels, a charge controller and batteries but I really dislike the idea of batteries and would like to keep the number to a minimum. If the inverter has a low voltage shut off, can I run the fridge without batteries, if I have enough panels? I know it would only run when the sun shines but I'm in Houston and we have lots of sunshine. I think I would rather use a small generator for cloudy days than batteries. Possible or not? Thanks for the feedback.

Chuck46 · December 2007

Re: Taking the plunge

Hey Dean welcome,
While I am fairly new to this forum I have lived off grid for 15 plus years and counting. So I like everyone have an opinion.

I dont understand your dislike for batteries. While they seem to be a hassle they provide a service. Namely less gennny time and a place to store extra energy. My first home was generator powered and boy did it get expensive and iritating, it came to the point where solar and batteries were a blessing and the investment was less painful then the fuel bill.

if most of your loads were DC and only a few AC loads you might get by with an inverter, pannels and a genny but I would not like to see fast moving clouds. This could really create wildly varing power output and disconect problems. As I recall your area does have cloud issues.Now understand I am not saying it cant be done just there seems to be potential for lots of problems. Living off grid should not be a trial by fire but some what comfortable and pleasent.

My experiance says go the extra mile and use batteries also. If maint is an issue, remember fuel costs are going up and that can pay a person to do the maint on the batteries. Remember this is JMHO.

Have fun Chuck

icarus · December 2007

Re: Taking the plunge

I ditto most of what Chuck says, (with a few additions)

The first thing you need to do is calculate your loads. The advantage of having a battery system is that it is very difficult to design a system that perfectly matches your loads. For example, the duty cycle of a fridge causes it to turn on and off. The panel needs to be big enough for the starting load(s) and then all the excess power that the panel will generate will be burned off as waste.

Another suggestion is to avoid what I call "ready, fire aim". For example you have ordered an inverter that may or may not suit the needs of a system that is yet to be designed.

There is a wealth of information on this site to help you with the process.
I too have lived off grid for ~20 years, and what we have found is that as the solar has become better over the years, we rely on it more. We used to be 100% generator, now we are 99% solar. The beauty is that it is always on and quiet. (Not really cheaper however in the short term.)

A final caution. Use the solar for that which it good for, ie lighting, electronics etc. Try not to use it for motor loads, and especially not for heating loads. (That is unless you want to build a really big system) Having said that, consider a Propane fridge and freezer. I think you will find that the added cost of the solar to run the fridge is far outweighs the added cost of the fridge and the fuel for it. Since you will have a generator anyway, you can use it for your shop/power tool loads.

As for batteries, yes they are a big expense, but with simple maintenence they will last many years. Make sure that you consider the size of the battery bank, relative to the expected loads, and the expected charge (solar)capacity.

Good luck with your project and consider spending some time with some proper planning and I think you will love the outcome.

Icarus

System2 · December 2007

Re: Taking the plunge

So far I've bought one 64w panel. I've ordered a Vector 2500/5000 watt inverter. I know I need more panels, a charge controller and batteries but I really dislike the idea of batteries and would like to keep the number to a minimum.

I don't know if this http://www.donrowe.com/inverters/vector_2500.html is your inverter, but if so, it is modified sine wave and may kill the fridge/freezer motor. Although I don't use modsine, many folks here advise that they have burned out refrigerator motors and other devices. Also, a 2500 watt inverter relative to your modest load may operate at a quite low efficiency. Documentation of some sine wave inverters suggests that a load of 1/3 to 1/2 of the inverters' nominal capacity is the efficiency "sweet spot". A few lights (CFL presumably), a radio and your freezer shouldn't be a running load of >300 watts so a ~600 to 1000 watt inverter may be a better choice. Modified sine wave inverters' efficiency may be different though, I don't know.

I know I need more panels, a charge controller and batteries but I really dislike the idea of batteries and would like to keep the number to a minimum. If the inverter has a low voltage shut off, can I run the fridge without batteries, if I have enough panels?

I would guess that it would be possible to run your 'fridge on panels, but when the motor starts, the panels would have to be able to supply the entire surge power requirements. As others have stated, clouds could be a problem. When a cloud passes over your panel, the motor stops. When the sun comes back out a minute later, if the high and low pressure sides of the system haven't equalized the motor may not be able to start. It could overheat and trip the internal breaker (if installed).

Spring for the batteries. Sam's used to sell US2200 golfcar batteries, almost identical to Trojan T-105's for about $55. I don't know if they still do but a pair of them in series would be a great set to start with, lots of power and low cost.

To design a system that meets your requirements would require more details from you though - daily refrigerator, radio and lighting kwh requirements. I made an Excel solar calculator that's attached to one one of my earlier posts, you can use that to more accurately define your requirements.

Cheers

System2 · December 2007

Re: Taking the plunge

Thanks for the responses. That is the inverter I bought.

This is Vector's claims.

"The MAXX 2500 runs most AC powered electronic equipment, including ... Refrigerators ....."

"Featuring SST™ Soft Start Technology
Ensures Smooth Start-Up of Tools and Appliances"

I bought the 2500 because that is about the smallest any of the manufacturers recommend for a refrigerator.

If the modified sine wave is going to wreck my new fridge, I guess I need another inverter.

We considered a propane fridge but decided against it for reasons I won't go in to now.

I priced batteries and thought I would be spending $1000s every couple of years. But at $55 each, I would not complain.

To size my system do I have to the meter to measure the electrical consumption of the fridge, or can I use the manufacturers numbers.

Chuck46 · December 2007

Re: Taking the plunge

Dean,
You can start with theeir numbers but it is better to measure using a Kil-a-watt meter, this gives you a solid idea of 24 hour power usage of a component

Chuck

icarus · December 2007

Re: Taking the plunge

Chuck,

First, Read and begin to understand : http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Batteries are perhaps the most misunderstood part of any RE system. Poor knowlege kills expensive batteries quickly. Good, simple care makes them last for years or decades. Chronic over or undercharging will kill them. I have been running off grid for ten years on 4 l-16 batteries (explained in the above link) that cost be $400 used. (More now though)

Also look into your inverter question. Vector is a mass produced, mass marketed modified sine wave inverter, designed primarily to be used on a vehicle. Be very cautious of claims made as to what they will run.

I go back to my previous suggestion. Spend a lot of time on this forum, and other places learning what it is you need, and then act accordingly. Too often people make haphazard choices based on guesses and hype and then become disapointed. While the temptation is to go for the cheap alternative at the start, in the long run it becomes way more expensive to buy 1 cheap piece of hardware, only to replace it with a more expensive one that will really do the job. (I speak from lotsa real live experiance with this)!

Please avoid the ready, fire aim, and K.I.S.S.

Icarus

PS. Another note on fridges and PV. Look carefully at the 'Real world" power consumption. I know that there have been complaints that some of the so-called "solar compatable" fridges (sunfrost??) have used way more energy than claimed. By contrast, Sundanzer has a good Rep.

Chuck46 · December 2007

Re: Taking the plunge

Icraus,
I think you got me confuse with Dean, he is the OP and asked about not using batteries

Have fun Chuck

mike95490 · December 2007

Re: Taking the plunge

ready, Fire, oops .. Aim,

icarus · December 2007

Re: Taking the plunge

Chuck,

I may not be smart, but I am thick!

Sorry 'bout that. "Fire, ready, oops aim!"

Tony

Chuck46 · December 2007

Re: Taking the plunge

Hey Icarus
I am never guilty of anything like that. Nope and the sun dont shine in AZ.
chuck

westbranch · December 2007

Re: Taking the plunge

Dean, further to Tony's ...read, read, read, there are a couple,of stirings just on fridges and consumption.. very informative.

Eric

System2 · December 2007

Re: Taking the plunge

dean wrote: »

I priced batteries and thought I would be spending $1000s every couple of years. But at $55 each, I would not complain.

My curiosity got the best of me, I went to Sam's to check out their current golf car battery offerings. They now have Powerfast by Interstate, group GC2, 6v, 225ah; the same basic specs as the Trojan T-105. $61.48 plus whatever fees, maybe another $10 if you don't have an old battery for a core.

Cheers,

Bad Apple

System2 · December 2007

Re: Taking the plunge

I'll have to find someone with a Sams card.

icarus · December 2007

Re: Taking the plunge

There seems to be something wrong with the price from Sam's. The prices I see on the web are closer to $150 for T-105's. Are we sure they are the same specs. The amp hour rating sounds the same, but is the basic construction of the battery similar?

Icarus

System2 · December 2007

Re: Taking the plunge

icarus wrote: »

There seems to be something wrong with the price from Sam's. The prices I see on the web are closer to $150 for T-105's. Are we sure they are the same specs. The amp hour rating sounds the same, but is the basic construction of the battery similar?

Icarus

I went to a sticks and bricks Sams, not the website. I went back today and took a picture with my dingleberry phone (attached to this post), sorry for poor image quality. Specs are as I stated in the earlier post - the same as the T-105, picture shows the price tag.

Cheers,

Bad Apple

System2 · December 2007

Re: Taking the plunge

Dean baby, What about using all 12 volt stuff and a gas refrig.? You can buy a used or wrecked camper and strip everything out of it, including its gas fridge, and you are all set with a few $55 batteries....no inverter no nothing. Don't worry, be happy.

Taking the plunge

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