Home Photovoltaic System Payback

Trying to found a workable non violent free trade zone nation of airports is my hobby.

Political Science and History now force me to study and really really think about economics.

As a hobby creating a nation is right demanding.

So far I've succeeded in making a fool of myself a few times.

Still I did alright to not get put in prison for sedition, and have even been guarded a few times.

Speakers permit in NYC was only 15 bucks for Dag Hammerskold Plaza, and they sent a cop to watch.

The economics of power are now to be figured, along with on book and off book realities.

The modern era is demarcated by wind power that allowed for long voyages in wind powered ships. Now we are getting around to at least thinking of motive power for grid utilization for a grid.

Hydro power has long run much of the NorthEast, and tide power is available to be utilized.

Finally did determine that insurance policies for all citizens of my particular set of working class heroes was the key to an economy in conflict with traditional capital.

Whole Life for everybody gives some equity to borrow against, though of course risk is risk and somebody will lose no matter how perfect the system.

Even the banks end up with overpriced capital they can't sell, and write offs are required.

Real Globalization across all borders and you need some law enforcement.

Difference between the EU and US is supposedly that the US enforced economic conformity out of the prosecution of the Civil War. I posit WWI and WWII are the equivalent.

Looks like mirror based and black paint for solar are cheap and available to the working classes.

Read a wonderful story by Edignan, (Emmett) about playing Golf on Midway, and hitting a Gooney Bird in the head with a golf ball.

I trail off wondering how to make not just bows, but arrows...

Hi,

you will find this very interesting:

http://cr4.globalspec.com/thread/49021/Self-assembling-solar-arrays-as-easy-as-mixing-oil-and-water

I am really amazed at these very attractive payback periods...The last time I calculated this (for a location with good year-round solar insolation), we were looking at a payback on the order of 40 years...But, then, we were also considering the ENTIRE system, not just the panels. When you factor in the cost of batteries (and replacement of batteries on a four to five year cycle), inverters, etc., and then figure how much energy you are not buying from the utility, I do not see how you can expect a payback of less than 20 years, unless you live somewhere like California where they seriously overcharge for grid service...The panels are the cheap part. Look at what else is required, in sizes to support the load you are going to put on the system.

The cost per watt ratio has experienced significant change...and electronics are much more efficient than 10-15 years ago, battery recycling avails deep discounts too.

Although the tendency is to need to replace batteries fairly often, as you mentioned, this is mostly a function of the charging circuit, as to just how long they last.

If the capacity is not fully used, (full capacity implies some overcharging and gassing), but only say around 70% of the capacity, then as long as water is replaced when needed (seldom when only using 70%), then the batteries should last far far longer.

I have a leisure battery in my caravan that is already over 6 years old and still going strong!! The charger was designed and built by myself......

I am just a lowly consumer, who decided many years ago to do solar landscape lighting , as a way to reduce wires ,transformers, etc.---I have found that the cost of replacing the batteries has more than NOT COMPENSATED for the energy savings--Am I doing something wrong? The battery cost (2 batteries or more per light), times 40 lights, is astronomical. The batteries fail at a high rate--the recharging systems in these unit fail at a high rate also----I am going back to low voltage--Tired of finding cheap Chinese solar stuff, being marketed at high U.S. prices. Have a neighbor who just installed a full house system--Cost $ 15- 18000, after rebates (Here in California)--The power company will only buy back so much electricity from you ($2000/ year), so don't not over energize your system if it doesn't reimburse your upfront costs. It will take him 8 years to recoup the cost. Now--go to Whole Earth or Real Goods, and you will find out at they are reselling commercial panels, that have "degraded" and no longer viable for commercial service--Check to see how much it will take to "upgrade" your panels after 10-15 years (remember, your investment is based upon a 10 or 15 year return)--What if your panel doesn't put out enough voltage to input your energy into the grid, and needs to be replaced? Does your contractor, or Kyocera dealer, give you a 15 year panel warranty? How much to replace the solar panels? Throw in labor and recycling costs-- Now are you back at square one?--I need some help with this, and I know that I have throwing off a lot of negatives--Just need some good tech info-- Best, C-MAC

I think you have it right.

I don't think it all pencils out without a big infusion of subsidies...

Would you buy a prius with the expectation of saving money?

I don't think that the $7k difference in price between it & a comparable yaris, will ever get paid back..

A good check for many (not all types can be so checked, my own design cannot be so checked!) 12 volt battery chargers is to measure the open circuit voltage without a battery connected.

Anything over 13.5 volts will overcharge the battery in terms of gassing and plate damage.

There is quite a good article in .pdf form with a great graphic at:-

http://www.scubaengineer.com/documents/lead_acid_battery_charging_graphs.pdf

If long life is the aim, set your charger's maximum output voltage to 13.25 volts. Set the trickle so that the battery voltage either remains constant over a long period or even drops every so slightly (with no load!). This means that the battery will never achieve full capacity, so buy batteries that are at least 30% larger than you need (which will live a REALLY long time).

Leisure batteries are always best as normal LA batteries (Auto for example) start to get damaged once the battery goes below 12.6 volts if not immediately recharged....!

You will probably find that there is not a battery charger available over the counter that will follow those rules or is adjustable........which is why I have built my own for more than 10 years....

There are plenty of circuits available on the web that are adjustable for output voltage, or with the addition of a Pot are then adjustable, just look around.

If you are not charging from the mains, make sure that a diode is included in the output to stop the charger circuit draining the battery when no input voltage is available. This will also prevent shorts if you connect a battery the wrong way round.....but will mean that the output voltage adjustment pot will need to be re-adjusted higher due to the voltage drop over the diode.

Sorry to be such a late entry into this thread.

Payback depends on the price of the whole system and the cost of the alternative. In my case it is diesel and I have just recently come to the conclusion that I need to double or triple my solar installation to become independent of the oil.

Currently I have 760W of panels producing about 400Ah/day (12V) in summer. I still need to top that up with during the periods that a washing machine is running, say one hour a day. This is to support 4 people. Winter months needs about 3 hours.

I pay about €0.66/litre for diesel and my generator consumes about 1.5l/h thus about 1€/h. If on this rough calc I estimate 2h/day average that costs me €730/year. That equates to about 2 panels at today's prices. So to double the system I need 6 more panes, = 3 years amortization. If I have to go to 12 more then clearly I get a 6 year break-even.

I dispute some of the figures given regarding batteries. Tubular positive plate batteries, typically 2V cells should last upward of 10 years, a 15year life time is not unusual. They are more expensive to buy than 12V blocs but well worth while in the end. 2V gel or AGM batteries are even better, but are probably not worth the extra in a stationary bank.

Probably the best option is NiFe cells which have very long lifetime of 25years or more. Not so easy to get hold of and they have a poor Ah/volume ratio, but that is not usually important with stationary banks. SAFT is the best known supplier.

Andy's advice re charging may work for his caravan on weekend trips but it is not a good charge for daily cycling. 13.5V is a float, or trickle charge. It will take a very long time to fully charge the batteries, OK if you have all week with the system on charge in idle but not for extended trips or, more pertinently, if you are living in a house and cycling the battery every day. All major charger manufacturers now use a three (or more) stage charge cycle of 14.3V, reducing to 13.25V once the batteries are full. These figures are at 25ºC (77ºF) and vary a little, (+/- 0.1V)between manufacturers. At temperatures above 25º the charge voltages are reduced by 5mV/ cell/ ºC

Northern Arizona Wind and Sun have a very informative FAQ page

http://www.solar-electric.com/deep_cycle_batteries/deep_cycle_battery_faq.htm

I hope this sets things a little straighter

Regards, Chas

My method is simply aimed at the longest life of the battery, together with around a 70% charge capacity........that is enough to supply all our needs for up to 3 days....and extends the battery life many times!

The charge methods of the battery companies (the diagrams you posted for example) are designed to both give a 100% (or close!) charge AND to NOT extend battery life appreciably, at the end of the day they want to sell you more batteries!!! Please don't forget that!!!

One should always be most careful with following the advice of a manufacturer..... they design to give a reasonable life only, so that you come back as a customer!!!

I design to give the maximum life - period!!! Thats two quite separate methods. You have to choose which one you want, its as simple as that!!

By the way, my method simply does not required temperature compensation (which is a further design plus point for me) as temperature compensation is ONLY required when going on the knife edge of full 100% charging.......which I never do! I simply buy a battery that is larger (at least 30% or so) than I need and keep the charging current to less than C/10, often nearer C/20......!