Last Updated 1 year by Lukas
You may remember time when in Czech Republic started boom with Solar Power plants. It was around year 2009 – 2010 and based on connection date you were guaranteed with better or worse prices. Those people who built big solar plants and were being paid a very favourable prices for electricity their plants created. Started to be called “Solar Barons”. Until start of 2023 it was impossible for a mere mortal to build bigger solar plant than 10kWp (kilo Watt peak). Currently even ordinary person can build system up to 50kWp without need for license (forcing you to be self-employed person under Czech law). It allows you to build system up to 20 kWp as above that there are few extra requirements. In this post I’d love to share my experience and tips how to build such system.
What is the average gain of solar energy for the place I want to put solar system on?
Not all places on the Earth are made equal from the solar power gain point of view. When you are thinking about solar power plant installation you should check at least these points in order to make sure you can get the most out of your new technology.
- Check Solar map for your given country – example for Czech Republic
- Check orientation of your roof and consider if it can take extra weight of solar system
- If possible try to observe how Sun is shining during the year onto your roof and find places in shadow
You want to be sure your roof can hold extra weight of solar panels, they are not in the shadow and they are placed on the part of the roof which has the most Sun light during the year. If some of the panels would be covered by shadow you may want to think about installing optimizers onto each solar panel.
What is average consumption of my house during the year?
You will take previous year power consumption, divide it by number of months (for which the electricity bill is created). And you will have average consumption per month, now you will take expected production of solar system you have/is expected per month and compare these two. This will give you rought assumption of the needed size of the solar system.
- Example house consumed 2 700 kWh per year
- This is in average 225 kWh per month (Red line in the picture below)
- Solar system on the picture below is 7kWp + 11,5 kWh battery + 10kW RCT inverter + heating into water
This is simplification to get an idea about the size of solar system you need. During winter months system will generate minimal gain and majority of consumption goes from grid. During spring and summer there will be a lot of energy produced and exported into the grid.
What are my expectations from Solar system?
it’s important to know your expectations from your solar system ahead of installation. It will help you avoid pitfalls and make your life easier in the future. It will also make sure maintanance cost is well within reasonable boundaries. Let’s list a few questions to ask.
- Do I plan to increase size of the system in future?
- Do I want use my system to backup house in case of power grid outage?
- Is my inverter going to be in the basement and so I do not care about the noise?
- Do I want to store any energy or just export into the power grid?
If you plan to increase size of your system in the future. Make sure you prepared cables for strings during the first installation and you don’t have to dismantle your house later. Also take into account maximal voltage per string and maximal installed power of all the panels from the inverter point of view.
In case you want your inverter to backup your grid within mili seconds, you need an active inverter. These are more power hungry (100 – 200 W standby consumption) compared to pasive ones (20 – 30 W standby consumption). If you want to backup your house, you need a battery and this can be very expensive part of the system, which may never pay itself back.
Take into account noise generated by inverter under load. Some have only pasive, silent cooling. But there are models with active cooling, which can be very noisy under load. Hence in case you install your inverter into technical room close to other people, it may be very unplesant experience.
If you want to store energy you create, you have in general two options. You can use it to heat water (the most cost effective solution), you can store energy into battery (the least cost effective solution) or you can use combination of both.
How am I going to solve issues with my solar system?
Properly installed solar systems can live for long time without any maintenance, but one day you will have to do it. Be it solar panels itself (can survive 20-30 year easily), invertor (usually up to 10 years) or battery (5000 – 6000 thousands cycles for LiFePo4 – it’s around 8 years). Or any other custom part of your system like SSR relays / WATT routers that can route energy into water by heating it.
If possible avoid unknown, special or custom made solar systems. For most people the best choice is widely used, standardised system, where we have huge number of companies that can service it. And vast number of people already using it. These people serve as proof it really works and can share their experience. Keep the system as simple as possible. Approach with caution situation when you are locked into proprietary solution, which only few companies can fix.
Is there anything more to be aware of / comply with when I have solar system?
- Keep in mind in Czech Republic we bill electricity per phase and so we have to use so called hybrid inverters. These have some maximal power they can supply single phase with. For example if your inverter is in total 10kW -> It’s approximately 3,3 kW per phase. Hence if you draw more than 3,3 kW from single phase -> The rest is taken from the outside power grid.
- Since 2023 even without license for solar power plant, you can apply for so called distribution EAN. This allows you to buy and sell electricity to different companies. For example you can buy electricity for fixed price, but sell extra electricity you return into the grid for SPOT price.
- Keep in mind if you export extra energy into the outside grid. There is maximal power you can put there based on agreement with your distributor. If you exceed this limit, you can be fined for each such occurence.