Solar Electric Project

[hayden]

Hi Everyone,

Thanks for the replies.

FLHayman - your system sounds very much like my 1st generation system. I suspect over time you'll expand yours, if nothing elses for the fun of it. What amazes me is how much you can do on a few hundred watts. At this point our place has all the features of a "normal" house and we are typically consuming about 250W. If it goes over 500W, I wonder what's going on.

Just think how much electricity (and fuel that creates it) we'd save as a nation if any measurable portion of the homes in the US really focused on their electric usage like you are forced to when you are off-grid.

The Prosine looks to me like a real nice unit. I don't recall - does it include a charger too or is it just an inverter? I also heard a rumor that Xantrex was discontinuing it.

Tommu56 - thanks for the report on the MX and FX. I was refering to audible noise, but you've caused me to wonder whether I interpreted the original questions correctly. How many watts of panels do you have on your MX? I've got just under 700 on mine and the fan doesn't run. I've read a lot of reports of fan replacements on systems where it does run a lot.

 

[hayden]

But I do have one question that I'm suprised that no one else has asked. What about fire danger? I can't see where a wooden battery box will meet NEC or NFPA code for containing a fire.

I checked out the 2005 NEC on this subject. There are no stipulations for battery banks under 50V, which is pretty much all small power systems since 48V is the highest they go with readily available equipment.

However, for systems over 50V NEC requires that the battery enclosure be made of insulated material. So, they came down on the side of preventing the fire over containing the fire. I imagine there was lots of debate over the pro's and con's, but this is where they landed. I suspect the logic is similar to plastic outlet boxes and conduit in home wiring.

I sure do like the idea of an automatic fire supressions system, though....

 

[woodlandfarms]

Hayden

Could you address servicing of your system (old and new?) What do you do and how often do you do it? From the batteries to the panels to all that is inbetween (filters?)

Thanks

Carl

 

[hayden]

Hayden

Could you address servicing of your system (old and new?) What do you do and how often do you do it? From the batteries to the panels to all that is inbetween (filters?)

Thanks

Carl

Sure.

90% of the maintenance is around the batteries. That's why grid-tied system (which don't have batteries) are so attractive. In an off-grid system like mine is almost all about the batteries.

There are two parts to battery maintenance; watering and proper charging.

Watering involves checking the electrolyte level in each cell in each battery adn topping them off with distilled water. If you've been around a while, it's the same maintenance you used to do (but probably never did) on your car battery before maintenance free batteries came along. There is a cell for every 2V in a battery system, so a 48V string has 24 cells to water. For more battery capacity there are often multiple parallel strings of batteries which double, triple, etc the number of cells.

These are big cells too. Each one is about 2.5 Gal of electrolyte, so watering can consume several gallons of water across all the cells. To minimize the amount of water loss, there are special cell caps that you can get that recombine the hydrogen released during charging with oxygen from the air to create water that drips back into the cell. My chemistry is too antiquated to remember the exact reactions, but they significantly reduce the water loss.

Battery charging is a much more complicated subject with whole books dedicated to it. However, there are two basic rules to follow. First is don't let the batteries get too discharged. Under normal operation they should only drop to 80% charged (that's 80% charged, so 20% has been consumed). Under extreme conditions you don't want them to go below 50%. Fortunately, modern systems will detect such a state of discharge and fire up the generator.

The other thing is to be sure the batteries return to full charge on a regular basis, say every few days. As long as you have enough charge capacity compared to your usage, this happens every sunny day. Understanding the loads and sizing the panels to be sure this happens is a major part of system design.

That's the bulk of it. The only other thing is adjusting the solar panel tilt angle as the seasons go by. If you have tracker mounts this is automatic, and if you have fixed mounts there is nothing to adjust. Otherwise you need to change the tilt 2 or 4 times a year. I've been changing mine twice a year at each equinox. In the winter they are almost vertical to catch the low sun and to shed snow. In the summer they are almost horizontal to catch the high overhead sun. There's lots of science to the seasonal tilt angles. For further refinement you can adjust the tilt 4 times a year to gain a more optimized angle for spring and summer. I might try this with my new system.

Other than that, just sit back and enjoy.

 

[hayden]

After a few weeks doing other things I'm finally getting back to this project. Part of the system revamp includes a new generator. My old one is 120V (no 240V), only 4000 watts, and has racked up about 2500 hrs. My new system is 240V and will load the generator to about 6000 watts just charging. To power loads at the same time requires even more. The inverter can pass a max of 60A, so that sets the upper limit of usable power. I figure something in the 10-12KW range is about right.

I'm currently running off propane, but decided to switch to diesel with the new system. Ultimately I'd like it to be biodiesel. I didn't stick with propane for two reasons.

First is overall efficiency, especially at partial load. For comparison, a diesel generator at 1/4 load is about 20% effecient and at full load it goes up to over 30%. A propane (or gas) engine is only about 13% efficient at 1/4 load and 23% at full load. The efficiency numbers are simply the BTU value of the electric output divided by the BTU value of the fuel consumed.

Second is that nobody seems to make an 1800 RPM propane generator that's less than 20KW. The smaller ones are all 3600 RPM which is a non-starter from a noise and longevity perspective.

I looked at Kohler and Cumins/Onan. I liked the Cumins product, but they apparently have no interest in doing business with me. I couldn't get call backs, and when I finally did the rep kept promising a quote an not delivering it. I heard every salesman line of BS in the book. I finally called the sales manager and asked if my needs were a match for them since nobody seems to want to sell me a generator. He appologized and 24hrs later I got a quote for $25,000 for a 10KW generator . I got the sales engineer on the phone and got the quote down to $10k by getting rid of all the stuff I didn't need or ask for. I followed up a week later with a couple of questions and again for no reply. After several unanswered phone calls and emails, I decided Cumins was not the company for me. With that kind of support/service when I'm trying to buy something, just imagin what it would be like when something doesn't work!

Then, I came across Kubota's line of commercial generators. They are very effecient and VERY quite. One call and I got my questions answered, another call and it was ordered, two days later it was at the local dealer ready for me to pick it up. That's how I like to do business.

I hate it when an American company drives customers to foreign alternatives. Oh well, I tried.

Anyway, here are some pictures of the generator being unloaded and then it's temporary home in the shop. I've got a temp hookup rigged to manually charge the batteries. I'm now switched over to the new inverter and batteries and with about 2hrs of gen time each evening things are working great. Tomorrow my son and I are going to start setting up the solar panels so I can stop running the generator every day.

 

[charlz]

Then, I came across Kubota's line of commercial generators. They are very efficient and VERY quite. One call and I got my questions answered, another call and it was ordered, two days later it was at the local dealer ready for me to pick it up. That's how I like to do business.

Sweet! Mind if I ask how big it is and what it cost?

 

[hayden]

Sweet! Mind if I ask how big it is and what it cost?

The generator is an SQ1140 which is 14KW. It's on the big side of what I need, but is the smallest they make in the SQ series. The SQ stands for Super Quiet. It's completely stand-alone with a built in fuel tank, meters, etc, and the engine is the same as in the L3240 tractor.

I'll be doing a permanent installation with the exhaust and hot air piped/ducted outside. I also expect to connect it directly to my bulk diesel tank. If you look at KUBOTA GENERATORS you can see spec sheets etc. For some reason they list it as the SQ14, but it's same thing. I paid $12,500. A 10kw Cumins is about $10k and a 12kw is about $11k, so the pricing is right in range.

 

[hayden]

Today was VERY productive, and special thanks go to my son for his help. Our first project was to fill the support poles with concrete. I made the poles a few feet longer than the manufacturer suggests to be sure the panels would clear the snow. I still expect to have to plow around them, but at least I won't have to do it every snow fall. With the longer length I have about 4 1/2 feet of ground clearance.

The extra pole height made me wonder about the structural stressed and TBN's Philbuilt was kind enough to run the numbers on some engineering software that he uses for work. Sure enough, in a good wind the software predicted that the poles would buckle when they enter the concrete base. Filling them with concrete solves the problem since it prevents the compression side of the pole wall from caving in which is the normal failure mode. When concrete filled, the tension side of the pole has to tear in order to break.

So, we mixed up 8 bags of ready mix and filled the poles one bucket at a time.

 

[hayden]

After lunch we assembled the array mounting frames and got them up on the pole tops. It was quite the trick to reach everything but by tiping the frame forward and backward as well as rotating it we were able to get everything within reach of the 8' step ladder we were working from. We got both frames up in about 2 hours

 

[hayden]

And last, up go the first 12 panels to complete one of the two arrays. We thought getting the frame together was a pain - the panels were twice as hard. There are about 5,000 bolts, washers, and nuts, all of which need to be torqued down once everything is assembled.

Tomorrow I plan to start digging the trench for the power line.