New solar / wind system ... pulling it all together

Re: New solar / wind system ... pulling it all together

Welcome to the forum Paul.

First regarding the panels...

piejukes wrote: »

I'm putting together a stand alone 24V solar and wind system -:
- 2.5KW solar (10 x REC250PE-BLK 250 W , polycrystalline cell http://www.apolloenergy.com.au/products/rec/REC245PE-BLK_7)
- 1KW horizontal wind turbine (still waiting to here if the one I'm looking at has the controller integrated ... they quote 24VDC figures so I assume it does)
- Batteries (Raylite 24V 1380Ah - 6 x MTE21S, 24V 1380Ah Battery Bank)

Now I am not sure what can and cant be done ... but ...
I'm looking to split the panels into 2 arrays. One with 6 in parallel and the other with 4 in parallel. So both at nominal 24V. Both feeding a seperate controller such as a 60A 24V MPPT Solar Charge Controller (http://www.dhgate.com/product/productdisplay.do?pid=ff8080813e9e1285013ebd0654714b65).

Nominal 24 volt panels have Vmp around 35-38 VDC to account for Vmp drop as the panels operate hot (heating from sun) and wiring/controller drops. Your panels with Vmp of 30 volts are too low to optimally charge a 24 volt battery bank (which needs near 30 VDC + voltage drops).

So, that leaves placing two panels (or more, depending on controller and distance from array to controller/battery shed) in series, then paralleling those. With 10 panels, that would be 5 strings of 2 panels each.

And then us a MPPT type solar charge controller (which can efficiently take high voltage/low current from the array and down convert it to low voltage/high current for charging the battery bank).

Also in the future I will be adding a micro hydro to the property "grid" ... and that could be quite large as I've got good water flow but not all year every year and a big elevation drop. (Needless to say I've got a few questions about that as well if anyone has expertise ) not the least of which is how to get the power back up the 1000m from the bottom of the creek ... high voltage?!)

That will be a whole project/discussion in itself. Sending the power longer distances is possible--But will need a lot of thinking and penciling out of designs to figure out what is optimal for your needs.

So my questions are -:
1. How is my matching of batteries to power generation?
2. Is it possible or desirable to connect multiple controllers such as this to the one battery bank?
3. If so what are the limitations ... eg should they be all MPPT or can you mix with PWM or the wind controller which may be integral?
4. If I put the wind turbine way up a big tree and the cable run is say 50m+ (whatever that is in yards ) would I be better to bring the presumably 3 phase power down before turning it into 24VDC?
5. What do I do with all the extra power especially when I get the hydro going? .... boil water, make ice, pump water, split water into hydrogen and oxygen ... any other ideas hahaha?

1. There are several ways of approaching the question... My suggestion is to "know your loads" (peak watts, average watts, average Watts*Hours per day, etc.). Then take that WH number * 4 (2 days of storage, 50% maximum battery discharge) * 1/24 volts for battery AH capacity. You can certainly pick the array and size the bank to the array, or choose the battery bank and sizing the charging/inverter to match... But if you can predict/measure your loads first will have a better chance of the system meeting your needs.

2. Yes, you can connect multiple charge controllers to a battery bank. The charger with the "highest" voltage setting will win. You want to wire them properly (I suggest all controllers have their own wire run to the battery bus). And if you use hydro/wind power, generally those units connect directly to the battery bank and you use a "shunt" or "dump" controller that, when the battery is full, turns on and dumps the excess power to a resistor bank (air or water heating).

3. The type/mix of charge controllers (PWM, MPPT, series or shunt) does not matter in the end... However, each controller is picked for your needs. There are MPPT charge controllers that can work with wind/hydro too--And the proper MPPT controller can double or more the output of the turbines vs direct connect to battery bank ("matching" the output characteristics of the turbine to that of your battery bank) and using a shunt controller. However, this requires lots of money as MPPT controllers (and some have integrated dump loads) are not cheap. Limitations include--Generally, a battery bank has around a 13% maximum rate of charge unless you use thermal management (such as a remote battery temperature sensor). Hot batteries need lower charging voltage set points. Otherwise you can get thermal run-away where the battery gets hotter, its charging voltage drops, and the charge controller supplies more current because it thinks the battery needs it. Around 25-30-35% (of the battery banks 20 Hour capacity) would be the maximum charging current recommended for flooded cell banks. Some batteries may have lower charging current limitations (many GEL batteries have a 5% or C/20 maximum rate of charge and are not usually recommended for off grid power systems).

4. Wind turbines are tough... There are not many will built/reliable "store bought" turbines out there. Many will not perform anywhere near their specifications. And, the reality is, that the tower, concrete, wiring, electronics, battery bank are the major costs for a wind installation. The tower should be ~18 to 30+ meters tall (and higher than any local obstructions, trees, houses, etc.). They have to be mounted high to get out of the turbulence of the wind near the ground (turbulence usually kills the energy available in the wind and causes tracking problems for turbines with the rolling air flow). Turbines (if done right) are going to be heavy and have significant side loads. There is no way (that I can see) that you would be able to put a turbine in a tree and have any useful amount of energy.

5. Extra energy--That is your choice. I would suggest conventional loads (resistor banks, water pumping, etc.). Hydrogen is a tricky gas and can end up blowing up you and your family pretty easily.

So:

a) measure your loads
b) design battery bank
c) design solar charging system
d) design gasoline/diesel backup generator system
e) install above
f) look at hydro and wind. Hydro done right is a sweet system. Wind--That is more difficult and why many successful installations are DYI type systems. Wind is usually only practical if you go outside and say "boy, this is a miserably windy place". Placing the turbine on high towers (over 25 meter) is a big help (fly a kite and see how high the kite gets before it gets into non turbulent air flow). Installing turbines below ~18 meters--Not usually worth the time and money to do it (unless you live on a dead flat windy prairie--and even then, off the shelf wind turbines need a lot of maintenance to keep working--if you can).

Note, I am not a fan of small wind. There is not much out there for sale that will last or output near rated power. And turbines need maintenance--So you need equipment to access the turbine/tilt the tower, etc. or to hire a lift truck every year to service the unit at the top of the tower.

-Bill