# Can you connect different renewable energy power sources with equivalent power ratings in series and/or parallel?

You should be able to connect multiple solar panels of the same voltage and watt rating in series and/or parallel.

What about connecting two different power sources with equivalent (or similar) voltage/current/watt ratings?

Example: Connecting a solar panel rated at 12V/10W in series or parallel with a wind turbine's permanent magnet generator output that is also rated at 12V/10W.

For the sake of this question, please assume the generator output has been DC rectified and limited to the specified voltage but please account for the fact that both those sources might vary from their maximum power output to near zero throughout normal use.

Beyond a simple yes, no, maybe I'd appreciate some insight into why this is or isn't, might or mightn't be possible or advisable.

For series connection, your devices need to agree on a common current. A wind turbine and a solar panel won’t. If both would produce a somewhat similar voltage and current, you’d might get away with a bypass diode across each. As both a wind turbine and a solar panel will happily produce zero voltage and current, this isn’t an option to you.

For connection in parallel, if your wind mill is already rectified and not producing more voltage than your PV can handle, you’d might get by by just connecting them in parallel. A much safer bet would be a Schottky diode in series with each to make sure there are no shenanigans.

simulate this circuit – Schematic created using CircuitLab

But the elephant in the room is energy efficiency as the I-V-characteristic for both PV and wind is very unfavorable for your use. What you really want is an MPPT for each one, capable of both peak voltage and current for each. If you have a 24 V battery system, there are boost MPPTs which can take your 12 V input and output 24 V.

simulate this circuit

• the short version seems to be: connecting sources in parallel forces the voltage to be the same and connecting in series forces the current to be the same. While diodes can prevent sources getting back-driven they can't force both sources to be in the optimal part of their I/V curve at the same time. Commented May 19, 2023 at 15:45
• @user253751 That’s exactly right. KVL and KCL in practice. Commented May 19, 2023 at 16:21
• @winny clear and helpful - thanks, much appreciated. Commented May 19, 2023 at 18:57
• hm maybe I should write an answer about I/V curves Commented May 19, 2023 at 19:07
• @user253751 Please do! Commented May 19, 2023 at 20:53

When you wire two things in parallel you force their voltage to be the same; when you wire two things in series you force their current to be the same.

Each power source outputs a different amount of current depending on the voltage, or a different voltage depending on the current, depending which way you choose to look at it.

For each power source you can draw an I/V curve that shows the relationship between current (I) and voltage (V). The current and voltage will be somewhere on this line. Here's an I/V curve for some random solar panel (source):

Depending how you hook it up you could get 2.7 amps and 0 volts (short circuit), or 2.7 amps and 10 volts, or 2.5 amps and 17 volts, or 0.5 amps and 20.5 volts, or 0 amps and 21.2 volts (open circuit), or so on.

The marked point is the point where you get the most power. Looks like about 2.5 amps, 17 volts in this particular case. Since getting power is the whole purpose of having a solar panel, you'd rather keep it at this point as much as possible. You could use a 6.8 ohm resistor (if your goal was to heat up a resistor). Realistically you either use an MPPT converter which automatically finds and holds the maximum power point (hence the name, Maximum Power Point Tracking), or the other usual thing to do is you attach it to, say, a 12 volt battery and you just accept that you won't get the maximum possible efficiency, but you also don't need to pay for an MPPT converter.

This chart is just the electrical properties. I didn't even talk about the amount of sunlight. You get a completely different line depending on the amount of sunlight:

If you connect two solar panels directly together in parallel, you force the same voltage. That's not a bad bet, for solar panels of the same type. You can see that the maximum power point is about the same voltage, no matter the amount of sunlight. If you connect them in series you force the same current, and this is bad because the weakest panel limits the current. It's still something that people do - in fact it's necessary, since a single solar cell only makes 0.6 volts - they wire a bunch in series to make a panel. You just have to be aware that if something is blocking the sunlight onto one panel or cell, it hamstrings the entire series chain. The point is, when connecting together several of the same type of solar panel, you don't lose much power because the max power points are close together.

Now I don't know about wind turbines, but I imagine they have something similar. And I imagine that wind turbine I/V curves are completely different from solar panel I/V curves. I found a set here (not legally copyable). Unlike the solar panel, the MPP voltage changes a lot depending on the turbine speed and so does the MPP current.

That means if you force the same current or the same voltage, one or the other or both are going to be quite far away from their maximum power point. Maybe you can design a system where both are at their MPP in good sun and wind, but what when the wind slows down or it gets cloudy? They won't stay balanced. Not like two solar panels that stay balanced because they get cloudy or sunny at the same time because it's the same sky.

Therefore it's a good idea to give each power source its own MPPT converter which can keep that one producing its maximum power. Sometimes you even see solar power designs with separate converters for different groups of solar panels.