diy panel help please

[simple man]

Hello, i am new to the solar powered world and i enjoy reading about it , but i need some help trying to figure my math out, basically i need 36 volts and 150 watts. this is for a well pump ( it can use from 12.6- 40 volts ) made to wire directly to panels. I am wanting to make the panels myself, i figure this will be a good diy project for my son and I... if i get 36 modules times .5 = 18 volts per panel then i believe i can wire the 2 panels in series for 36 volts correct ?? but then what about the amps that would leave me with 126 watts i will be 24 watts short...

Then i was thinking of making 3 12v panels wired in series for 36 volts...i need 150 watts so
150 (watts) / 1.75 (amp of each module) = 85.71 modules

85.7 (modules) / 3 (panels) = 28.57 modules per panel ???

29 modules X .5 volts = 14.5 volts that would give me enough watts but too many volts (43.5 volts )

Any help is GREATLY appreciated

 

[moggy1968]

You would need to have a voltage regulator
I would strongly recommend The Solar Electricity Handbook by Boxwell (it's on Amazon)
ideal for projects like this.
Also have a look at these guys who have a lot of the bits you may need for this type of installation.
Solar Panels, 12v Solar Battery Charger | Sunstore.co.uk | SunStore online shop

 

[simple man]

i have 2 books already solar power for dummies, and solar power for your home, i understand the basics but i am wanting some project specific advise, i just want to be 100 percent sure before i mess up a $700 pump

 

[moggy1968]

I would over egg the voltage and then use a voltage regulator. If you calculate it exactly you will never actually achieve that result because of losses within the system. Your output will also be highly variable due to angle of sun, shade from clouds, temperature etc. Solar output is very far from being a precise science. There are simply too many variables involved. The quoted output of the panels is under test condition (certain sunlight output, temperature etc) which you will never achieve in reality.

I guarantee you you won't consistently achieve an output of 126 Watts and without a consistent output your pump speed will be all over the place.

What you need is some sort of storage device (namely a battery). It doesn't have to be huge because you are basically using what your producing (ish!) so storage capacity isn't the issue, but you need the consistent output a battery can provide.

 

[simple man]

if i went to batteries for a constant flow, what would i need for the pump run 15-20 hours a day everyday ?? the pump draws 2.8 amps which if i figure right is about 70 watts ?? it doesn't sound right but it is amps times voltage right ?? how many amp hours in a battery would i need and i would be wiring two in series for 24 volts. would it be 1400 amp hours needed 70 amps times 20 hrs ?? then how would i figure how many watts of solar panel to run the pump and charge the batteries ?? i have a headache now...lol

 

[wstevew]

I think you are a bit muddled up.

3A x 20h = 60ah

 

[simple man]

so i would need at least 2 60ah batteries wired in series to run the pump for 15-20 hours a day ? then how many watts of solar panel would it take to charge what the pump pulls out of the batteries ? turns out the pump pulls 3.4amps from a 24v battery bank. here are the pump spec from their site.

"Uses 25 to 100 watts Made for 24 volt; at 12 volts runs half speed with 50% water delivery but still full lifting depth. At 120 ft. of lift, current measures 3.4 amps from 24 volt battery; or 2.9 amps with 12 volt battery. Runs directly from one or two 75 watt solar modules. Add a Linear Current Booster to increase hours of solar direct operation."

 

[wstevew]

You wouldn't want to discharge the batteries completely. So probably best to have 130ah of leisure battery.

 

[simple man]

so i need 2 130ah batteries for my 24v system ? how many watts of solar panel would i need ? thank you very much for helping

 

[wstevew]

I guess it would depend on your location, the charge controller etc. If I were you I would use the "contact us" option on the site in the first reply you had. It looks as if the specialise in what you need and will be able to give you some options.