Home made PV system

Re: Home made PV system

Martin,

First, it is very difficult to build reliable/"fire safe" solar panels. Before you invest a bunch of time and money in DIY, try these few panels in the sun for a few months and see how they work. Personally, I don't believe they will last 1 year before they start to fail. And depending on how they are built and what fails--they can fail by catching stuff on fire.

Next, the 6kW inverter--Solar PV systems are very expensive to build and maintain--And most people over estimate how much power they can get generate and underestimate their loads. A 6kW is pretty large and would require a large battery bank and solar array to be useful for most people

Which gets back to the basics... I would recommend that you work on conservation first--It is almost always cheaper to conserve (new energy efficient refrigerator, florescent/LED lights, the most efficient A/C system you can use, and use fuel for cooking/heating/hot water.

Next, measure your loads--Peak Watts (starting surge), average Watts, and how many hours per day you run the load.

For example, a microwave running 1,500 watts for 30 minutes a day may actually use less energy on a solar power system than a 250 watt desktop computer system running 12 hours per day:

• 1,500 watts * 1/2 hour = 750 Watt*Hours per day
• 250 watts * 12 hours = 3,000 Watt*Hours per day

Using a smaller laptop computer (around 30 watts) is one example were lots of power can be saved.

Regarding your questions about solar panels... You have several choices to make...

First the charge controller. The less expensive charge controller is a PWM (Pulse Width Modulation) type. Basically an "on/off" switch between the solar panels and the battery bank. For best efficiency, the Vmp (voltage maximum power) of the solar panels should be just a bit above the battery charging voltage... Typically around 17.5-18 volts or so for charging a 12 volt battery (35-36 volts for a 24 volt bank, etc.).

A MPPT (Maximum Power Point Tracking) solar charge controller is much more expensive, but allows you to run Vmp of your solar array from ~17.5 volts to 100 volts Vmp for a 12 volt battery bank. The high voltage allows you to use much thinner copper wire from the solar array to the charge controller...

Remember that Power=Voltage*Current. 2x the voltage then 1/2 the current for the same amount of power. If your solar array is more than a few meters away from your charge controller (which should be close to the battery bank), a MPPT solar charge controller can make things much easier and keep the wire size smaller and less expensive.

When deciding on series / parallel arrangement for your solar array... Decide on your array's Vmp... If Vmp=17.5 volts and you have 17.5 volt panels, then you just put them in parallel. The output current Imp will simply add.

If you need Vmp=35 volts (24 volt battery bank and/or MPPT charge controller), then you would put two panels in series and put the rest of your panels 2 up in series, then parallel them together. Series, the Vmp will add, while the current remains the same.

If you have a mix of solar panels, Ideally the Vmp for parallel should all match to ~10% or better. For adding in series, the Imp of the panels should match to ~10% or better... The farther away you get from 10% match, the more power you will loose.

You have taken a pretty big bite of a complex issue... My recommendation--Don't buy anymore hardware until:

1. measure your loads
2. look at conservation to reduce your power needs as much as possible
3. plan your power needs in Watt*Hours per day by season
4. plan the battery bank
5. plan the solar array to recharge your battery bank
6. plan the solar array to supply the power to support your loads (yes, you need to plan your array in two different ways)
7. review loads and decide 12 volt / 24 volt or 48 volt battery bank
8. Backup power (grid, generator). Size battery charger and power source to support battery bank in bad weather
9. pick solar charge controller PWM/MPPT/Size/Options
10. Now buy parts and install.

In the US, solar PV power costs about 10x (or more) per kWH vs utility power. You need to plan your loads to most efficiently use the solar power. It is too expensive to "waste" if other options are available.

If you have hot water/heating needs, Solar Thermal panels (hot air, hot water) are actually a pretty nice DIY (do it yourself) type project... And much better place to invest your time and money for heating needs. Solar PV is just too expensive to run most heating loads.

-Bill