Solar Energy Question

Hi all,

This is my first post here, and I'm glad to be a part of such a community. Anyway, I am intending to install a PV system that would give me 220V, AC electricity during the day. So it's really neither a grid connected system nor it is an off-grid system, so I hope you guys could help with the components that I might need.

My idea is: 1- The PV panel that I am going to use, speaking of, is a 100W panel sufficient to output 220V AC electricity? 2- Inverter, but what type? and what rating?

These are the basic components, but after some research, I found out I should also have a Solar Charge Controller + a small battery, EVEN if I'm only intending to use the system during the day, so is that correct? If so, what type of Solar Charge Controller do I need that would work with my inverter and the 100W panel? and What should be the Ahour rating on the battery?

Thanks Guys!

Hi, the panel(s) are 100W, now what DC voltage and how many?

I hope you realize you will need some storage system, as the suns output is not constant, 100W panels only put out 100W under laboratory conditions.
It will be an offgrid system, without power storage you are wasting your time and money.
What do you aim to run on 100W?

Tom… :slight_smile:

I do not understand what you mean by "neither grid connected or off grid" are there any other options?

What you need equipment-wise depend on what kind of loads you are driving. a 100W panel will give you anywhere from 100Wh/day up to maybe 1200Wh/day depending on location, if it is fixed or following the sun etc. Lets assume 1000Wh/day. that means that you battery will have store that amount of energy in order to be useful. So a 12V 80Ah will fit. I would go for a sinus inverter with good efficiency. As said before the output power depends on what loads you are driving.

Also, look over the efficiency of the whole system. It makes little sense to first step up 12V to 230V and then back to 12V again. All linear regulators should be banned from a system like this. If you want to power computers there are mobile solutions that have atx power supplies with 12v input. Lightning should be done with leds and switching constant current sources driven directly from 12V etc etc

Also note that your 100W panel may not even put out 100W under perfect conditions.

Most panels are rated as V open circuit x I short circuit.

With no load your panel may reach 18+ volts. At short circuit it may give 5.5 amps.

The problem is that at the useful voltage of about 12 - 14 volts due to the battery you get less than the rated power, in the example, around 75 W instead of the rated 100W.


Edit: this applies to the common PWM charge controllers. MPPT controllers will give more.

The simple solution is to use the solar panel to charge a 12v battery bank and then, if you really need a 230v supply use an inverter to convert the 12v DC to 230v AC. It would be much more efficient to use the 12v DC directly.

A single 100W panel will produce very little energy even if you live somewhere with near-continuous sunshine.

You should approach your design from the other end.

How much energy (watt-hrs) do you need every day? How much energy (watt-hrs) can you expect to get from your solar panel in the worst circumstances. This website can provide estimates

You can use the battery to meet short term needs that cannot be met by the solar panel. But over, say, 2 or 3 days the average solar panel output must comfortably exceed your demand and the inefficiency of the battery.

It is not wise to discharge a lead-acid deep cycle battery more than 50% because its actual capacity is a lot less than its nominal sticker capacity. Also it is essential to ensure the battery is fully recharged about once per week.

What this really amounts to is that the average energy output of your solar panel should probably be twice as much as your energy usage.