help with solar panel

Re: help with solar panel

Is that 6 batteries or one 6 vdc 225 ah battery?

What are (and how) are you going to power with this system?

Tony

Re: help with solar panel

First,

Your 345 watts of PV will be lucky to give you ~ 700 watt hours of power on a perfect day, enough to power a 200 watt tv for 3.5 hours.

Second, that 345 watts of PV will be lucky to give you 15-20 amps of charge current under perfect conditions. If you are relying on PV to charge 675 amp/hour (12vdc) you will be seriously under charging your batteries. The suggested charge current for flooded lead acid batteries is between 5-15% of ah capacity. This would suggest a minimum charge current of ~33 amps, or a max somewhere near 100 amps.

Two quick rules of thumb, If you take the name plate rating of your PV, cut it in 1/2 to account for all system loses, multiply that number by the number hour of good sun (seldom more than 4) and that gives you the total number of watt hours you can expect under ideal conditions. So 345/2*4= 690 watt hours

The second rule, is people over estimate the amount of solar power they get, and they under estimate the power they use, usually resulting in damaged batteries.

I suggest that you get a very good handle on your daily loads, using a KIll-A-Watt meter. By knowing your REAL loading, you can begin to get a feel for how much you will be able to power with PV.

Tony

Re: help with solar panel

I'm not familiar with the calculator you link, but here is some things that I think you should know.

In order to figure how big a PV system needs to be you need to figure out your loads.

Using the calculator you link, or just pen and paper, add up all the loads that you are likely to use, how big they are and how long you are likely to use them. For example lets say you burn 3 15 watt CFL bulbs for 4 hours a day. 15*4=45. That is 45 watt hours. (wh)
TV, 150 watts for 4 hours= 600 wh

Do that for all your loads, estimating worst case. After you have all your loads calculated you can begin to figure out how to power them. Remember, most if not all your loads will be powered by the batteries, through the inverter. All these systems have efficiency losses. Starting at the PV, you have PV efficiency, wiring loses, charge controller losses, and basic battery charging efficiency, more wiring loses, inverter efficiency. Add all these loses up and in simple terms, they add up to about 50% net net. So any loads have to include the system loses as a load as well.

So using my own small off grid system as an example. We have 300 watts of PV. On a perfect day, our system will put ~20 amps into the batteries for about four hours, or 80 ah, or in simple numbers ~960 whs. (V*A=W) 12v *20*4=960ah

On the same good day, we might use ~600 wh of power, leaving us with a surplus of ~400 wh, so nearly everyday our batteries get fully charged.

A battery bank needs to be sized to power the loads with out excessively drawing down the batteries. Some folks consider a 50% draw down to be OK, I personally think it only good to draw the batteries down 20% to ensure long lived batteries. (Battery life is directly related to how many times they are drawn down and by how much. Lower draws equal longer life,, it really is that simple. So batteries need to be sized for the expected loads PLUS some reserve to allow for days with no sun. Most folks like to design in a three day reserve before needing to charge the battery from a generator.

So in my case, I only draw my batteries 450ah 20%, or about 90 ah or ~1 kwh. So if I am using ~.6 kwh/day, I can easily go 2 full days with total darkness and still only draw my battery down to ~80%. In fact I get some solar charge nearly every day, so in fact I get 3-4 grey days before I need to charge from the generator. It is also important that batteries are not left partially charged for more than a few days, or they will suphate and be quickly destroyed.

So, in short, you need to figure out your loads FIRST, then design the PV/batteries.
So until you can really give us an pretty accurate load calculation we will be hard pressed to give you useful information.

I suggest before you go much further you read and understand the following:http://www.batteryfaq.org/
http://www.windsun.com/Batteries/Battery_FAQ.htm#Lifespan%20of%20Batteries

Good luck, and keep in touch,

Tony

Re: help with solar panel

One of the forum members here has a web site with a lot of good info, and he started out pretty much the same as you.

http://www.2manytoyz.com/

Re: help with solar panel

I think a 2/71 is a Detroit diesel, 2 cycle, 2 cyld with 71 cu.in" per cyld.

What I don't get is why are you running such a big generator, if all you are powering is the small loads that you have listed?

My 5 kw lister diesel burns ~1/4 gallon per hour at full load, so I would suggest that you are running the generator at a very inefficient load range. Get a smaller generator as bill suggests. A Honda Eu 1-2000 will put out a lot of power for a long time on little fuel.

To suggest that you are "going to get free power" from the sun, suggest a fundamental misunderstanding of the real costs of battery based solar electrcity.

Tony

PS Does Ready, fire aim come to mind?

Re: help with solar panel

Consider using Propane or Natural gas for space and water heat.

Also, it is at least 3 times more efficient to heat water directly with solar, than it is to convert sun to electricity and then back to heat. Same with space heat. Solar hot water is pretty easy and simple compared to Pv.

Why 2000 watts of outdoor light?

Tony

Re: help with solar panel

We are 150 miles from the nearest power line on an Island and we have no outside lights! Not quite true, we have a few, but rarely turn them on.

I have always found that specific task lighting, (inside or out) is way more effective and more efficient that huge general lighting.

It seems to me that you are sort of ready, fire, aiming this system,

Tony