Air 40 wind generator

Re: Air 40 wind generator

For winter, you could install a smaller panel/array on your wall (or tilt your panels vertically as Tony says) and be quite happy with the results.

Batteries when fully charged (when you button up the cabin) will not freeze even at -40C/F. And they have much lower self discharge.

You could get away with a 1% rated panel and small controller (or use your existing controller):

• 29 volts charging * 740 AH * 0.01 rate of charge = 215 watt panel/array

Your existing array is on the "small side", but if you are using it weekends during the summer, it probably serves you well (not too much generator usage).

Normally we recommend between 5% and 13% rate of charge for your solar array:

• 740 AH * 29 Volts charging * 1/0.77 panel+controller derating * 0.05 rate of charge = 1,394 watts (minimum 5% rate of charge)
• 740 AH * 29 Volts charging * 1/0.77 panel+controller derating * 0.10 rate of charge = 2,282 watts (large array at 10%)
• 740 AH * 29 Volts charging * 1/0.77 panel+controller derating * 0.13 rate of charge = 3,623 watts (maximum cost effective array)

The above is just some starting point rules of thumb. Many people used to recommend that off grid power systems install a huge battery bank for best performance.

Around here, we have pretty much convinced ourselves that you should design your battery bank to match your load requirements (typically 1-3 days of "no sun" and 50% maximum discharge) and install a good sized solar array to quickly and fully recharge the battery bank. Then size the solar array to your bank size (5-13% rate of charge) and your daily loads (I aim for generator usage only during the "dark" ~3 months of winter).

If you have a "too large" battery bank, it forces you to install even a larger array (to meet minimum charging current requirements and to keep up with self discharge as the banks age)--And when the batteries eventually fail (every ~6-10 years or so), you have to pay a bunch of $$$ to replace the existing bank.

A suggestion for the long term, take a look at a Battery Monitor (or Victron Energy)... It makes managing your (expensive) battery bank much easier--plus it is easy to teach spouse/kids/guests some basic usage... I.e., stop using power/start the genset if less than 50% state of charge; if approaching 20% state of charge, turn off all loads and ask for help (why genset is not charging, etc.). If you have flooded cell batteries, a hydrometer is still a good investment to check the health of the battery bank. And I suggest getting a DC Current Clamp Meter (like this inexpensive $60 one) so you can monitor current sharing between your two parallel battery strings.

-Bill

Re: Air 40 wind generator

I really don't know what the size of your solar array and battery bank should be... But, using some basic rules of thumb as a starting point, a large battery bank should have a larger array for proper battery charging (which usually increases battery life).

But, back to your current battery bank... More or less we use 1-3 days of "no sun" and 50% maximum discharge in "normal use". Lets take 2 days and 50% max discharge, or basically the battery is 4x your daily average load (or you discharge the battery by 25% per day):

• 740 AH * 24 volts * 25% = 4,440 Watt*Hours per day average load
• 740 AH * 25% = 185 AH @ 24 volts per day (if you prefer working in Amp*hours)

Using PV Watts for Toronto Canada (guess), more or less your hours of sun per day are:

Month Solar Radiation (kWh/m2/day)
1 2.69
2 3.51
3 3.98
4 4.68
5 5.29
6 5.48
7 5.51
8 5.23
9 4.96
10 3.61
11 1.95
12 1.97
Year 4.07

Using February as your worst of 9 months of the year, you have 3.51 hours of sun (fixed array mounted at latitude), and you would need a solar array of:

• 4,440 WH per day * 1/0.52 PV system derating * 1/3.51 hours of sun = 2,433 Watts of solar array

So, a 2,433 watt solar array would just about break even based on using 1/4 of your battery bank capacity per day (4,440 WH or 185 AH @ 24 volts per day).

Your current panels are 6x 130 watts or:

• 6 * 130 watts = 780 Watt array
• 2,433 Watt array recommended for your battery bank / 780 watt existing array = 3.1

Your battery bank, from our normal rules of thumb is about 3x larger that we would have recommended for a "balanced system"...

But, again I do not know your needs... Are you using 4,400 WH per day or much less? Is this a weekend cabin with summer only use? (yes, I understand you are planning on Spring through fall usage--just giving some rough guidelines I like to start with) Do you use the genset to keep the battery bank well charged when needed? Is generator fuel easy to obtain and cost efficient for your needs? Is there seasonal power variations (irrigation, fans, visitors, etc.).

I am not trying to say that everything was done wrong--But I do not understand yet your power needs (WH/AH per day, Seasonal usage, trade-off between generator usage vs more solar panels, etc.).

So, I have now calculated the the "optimum array", both based on battery charge capacity (1,400 to 3,600 watts) and on estimated power usage assuming you use 1/4 of the battery capacity per day (no sun) (~2,400 watts based on worst of 9 months--February).

In the end, power usage is very personal. And I (we) are just trying to give you the tools to design/build a system that will, cost effectively, meet your needs.

-Bill

Re: Air 40 wind generator

Are you asking about a 12x 130 Watt array? Typically they are Vmp~17.5 volts (need exact Voc/Vmp/Imp ratings):

• 12 x 130 watts * 1/17.5 volts = 89 amps

So, you would need 3x C40 controllers to stay within their ratings.

Otherwise, there are 60 amp / 80 amp / 80+ amp MPPT controllers which would allow you to use only two, or even possibly one controller (one ~$700 mppt).

Take a look at this one and read the specs and the manual: Midnite Solar Classic

May, or may not meet your needs (I am certainly not the expert in this controllers). But a good start to learn about the higher end solar charge controllers.

Something else to think about too... If you have not purchased your panels yet, you may wish to look at larger/higher voltage panels... They tend to be less expensive per watt and have fewer electrical connections (i.e., fewer 200 watt panels vs a bunch of 130 watt panels). Also, with MPPT charge controllers, you can run a higher voltage Vmp-array (~100 VDC max for typical 150 VDC limit controller and weather conditions). You can use smaller gauge wire and/or a longer run from the solar array to the battery shed/installation.

You may have to do several designs with different controller/panel combinations to see which is the best fit for your place.

-Bill