help needed for off grid PV/Wind powered system

System

Hi I hope someone can help me

We want to run an off grid system to provide between upto 5 amps per hour for about 8 hours per day 5 days a week. Currently there is a 24 V system with 2 x 12V 130Hr batteries in series to provide 24V which I think would also be rated at 130 AHrs, these are being charged by a 120W solar panel & a 200W Wind turbine, given that in winter we get only 1 hr direct sunlight per day in this area and average wind speed is 4.9M/sec, is this enough to keep the batteries topped up or do we need to addd extra solar panels &/or a larger wind turbine?

Thanks n advance for any advice

Jon

System2

Re: help needed for off grid PV/Wind powered system

Hmmmm I thought this looked like a helpful forum.... guess I was wrong :oops: :?

James

Re: help needed for off grid PV/Wind powered system

come on now, be nice. not all the members here are on the site 24 hrs a day.
there are a couple of the regular boys that will catch up to your posting and add some additional advice.

At first glance, it would appear that you can get by with your system as is, based on your load requirements.
but what we don't know is how cold the batteries get, wire loss and other factors.

i personally feel another 120 watt panel is in order due to the close margins you are at. your present system dosent leave much room for variables or unforseen load variations

mike95490

Re: help needed for off grid PV/Wind powered system

Jon RG wrote:

average wind speed is 4.9M/sec

What is the Turbines rated output at that speed ??
Who is Mfg, & model # ??

niel

Re: help needed for off grid PV/Wind powered system

the 120w pv is probably 12v and i'll bet the 200w wind genny is too. i do trust these aren't in series with one another to come up with 24v as it just won't work. each solar or wind generation must be able to stand alone at the particular operating voltage prescribed by the batteries. if this is the case parallel the wind and solar outputs to the batteries which will now be in a parallel 12v configuration. another pv would be able to be placed in series to bring the pvs into 24v service, but it would not be a good idea to do that with wind gennys unless the wind genny is already a 24v model and if so then go ahead and add another pv in series to the 12v pv you have to upgrade the pvs to 24v service. if i've misread what it is you have then please clarify.

BB.

Re: help needed for off grid PV/Wind powered system

It would be helpful to know, approximately, where you are located, what type of charge controller(s), temperature range, etc... I believe you have an existing system--are you logging information so that you know how much is already being generated by solar and wind? Collecting real data will probably be more accurate than anything we can predict over the Internet.

Is the 1 hour per day because you are near the "poles", or is it because of shading (trees, mountains, buildings, etc.). Generally, for good wind power you have to mount the turbine well clear and above local obstructions... And if you can do that for the turbine, can you move the solar panels to a better area? Solar (and wind) is already very expensive--giving them optimum exposure to sun (and wind) is very important. Can the solar be moved to a better location?

Do you need power for sure? I.e., do you need a generator too?

Is the load already designed to be as low power as possible? Generally it is less expensive to conserve power with solar than to just through panels at the problem.

-Bill

System2

Re: help needed for off grid PV/Wind powered system

All Thanks for the reponses & apologies if I seemed a bit grumpy.

I will need to find out the answers to some of the questions raised which may take me a couple of days as I was not involved in the original set up of the system. The system is being used by a "green" charity & if possible want to be able to run without a petrol/diesel back up generator except in exceptional conditions.

In the meantime what I can say is that the system is in the UK, temperature range in this area is not really extreme, the normal range (not average temp which would be even less extreme) would be up to 30 deg C in summer & down to -5 deg C in winter (maximum range is 38deg C in summer & -15 deg C in winter but both of these are V. rare). The latitude is about 51 deg N, the site is not shaded & the PV panel is in direct sunlight and angled to maximise the sun available in winter when the sun is shining!! The Wind turbine is an Aerogen at a height of about 6 meters & well clear of obstructions but I don't know what the technical info is .... yet!

So the info. I think I need to get so you can help is :-

1. PV Panel voltage
2. Wind turbine Voltage
3. Wind Turbine model & performance data at the average wind speed
4. Charge comtroller rating
5. Confirm that charging rom PV is seperate to charging from Wind turbine
6. Make sure PV & Wind turbine are charging at the same voltage

Please let me know if I have missed anything

Thanks for all the help

Jon

BB.

Re: help needed for off grid PV/Wind powered system

Jon,

Also, try to find out more about the load... is it 5 amps x 12 vdc or 5 amps x 24 vdc (60 watts vs 120 watts) over 8 hours, 5 days per week.

Sounds like it may be a piece of office equipment (like a computer?). In any case, if it is 120 watts x 8 hours x 5 days * 4 weeks/month = 19.2 kWhrs per month... That is not an insignificant amount of energy (100 kWhrs per month is a well designed low energy / off-grid home).

One hour of "full sun" on a 120 watt panel would, realistically, give you about 60 watts/hour available at the battery (panel derating, charger controller derating, losses in a lead acid battery charging, etc.), with about would only supply your load for an 1/2 an hour to one hour per day--not the 8 hours you are looking for...

I don't have any real wind turbine experience--but if this is windy bluff and the system is sort of working now--it may be supplying much more energy that we expect.

Getting actual numbers generated would be a big help--if available.

-Bill

PS: A few things to add for discussion...

1. For general purpose storage batteries, it is recommended to only discharge them to 50% capacity to insure long life. So, your 130 AH bank would be ~65 AH available for use--at 5 amp*hours, that would be 65/5 = 13 hours or a day and a half of use (if no wind or sun)... Usually, one would try for about 3 day of storage as a good compromise.

2. Generally, a conventional wind generators start around 6-8 mph (9.6-12.8 kph or 2.6-3.5 meters/sec--if I did the conversions correctly). And they will make nameplate rating around 25 mph (40 kph or 11 mps)... And the power goes with the cube of the wind speed--so wind speeds would have to be pretty close to 25 mph to generate anywhere near name plate rating.

3. If this system is to be operated by relatively un-knowledgeable users (or even for somebody who wants to track every aspect of system performance), a battery monitor should be installed (draining batteries flat and/or not properly recharging can kill batteries in a matter of months).

http://store.solar-electric.com/metersmonitors.html

4. If new/more batteries are needed--it may not make sense to mix the new batteries with the existing battery bank (if the batteries are more than a year old or if they have been badly maintained)... It would be better to replace the entire bank at once.

5. If new batteries are being looked at--consider AGM type. They are sealed batteries and, if not over charged, will last as long as flooded cell batteries and there will be no water to add and very little cleaning required. Also, AGM's are also more efficient (AGM:~90% vs flooded-cell:~80% power out / power in).

6. Check the controller and see if a battery temperature monitor option is available and installed on the batteries... As you increase available power for charging (wind+solar), thermal runaway is very possible (as batteries get hot, the voltage requirements to charge drop--causing the battery to "try" and accept more charge--causing them to get even hotter)...

7. Site security--if more panels/batteries/controllers/copper wire are added, the risks of theft/vandals increase.

8. Check installation for "phantom loads". For example, an inverter is left on but no loads are present/needed on nights/weekends.

-Bill