THE ADVANTAGES OF BUYING A PHOTOVOLTAIC WATER HEATING INSTEAD OF A PHOTOVOLTAIC POWER PLANT

The sun is unreliable. The sun is an excellent source of energy, inexhaustible in our foreseeable future, but it requires specific conditions. It’s not really the sun itself, but it’s our Earth that causes the unreliability of solar energy (due to weather, day/night, seasons), so overproduction of solar power needs to be stored. Fortunately, most of our homes are still connected to the electrical grid, so not relying entirely on storing power is quite easy.

 

First, you need to consider which appliances can be sensibly powered by solar energy. These are the appliances we’d like to power when there is enough solar energy.

This eliminates heating, which is statistically still the biggest source of household energy consumption (about 60% in Central Europe). Of course, by insulating homes and building low-energy and passive houses, the energy consumption for heating is continually decreasing.

In any case, you need heating the most when the sun shines the least. In winter, there is less daylight, and the sun is at an unfavourable angle. Clearly, using solar energy for heating is not practical.

What about appliances such as washing machines, fridges, stoves, irons, TVs, computers, and lighting? Indeed, we use these appliances almost daily, and when you add up their consumption, they account for roughly 20% of the household consumption (based on the same statistics as for heating).

But it’s not that simple. On a working day, most of the consumption takes place in the evening when everyone returns from work and school when the sun is setting and generates little energy. In the summer, the days are longer, and the sun sets later, but people spend much more time outdoors, so they turn on appliances later.

Therefore, if we want to power appliances by photovoltaic energy, we can not do so without batteries. A photovoltaic power plant charges the batteries during the day when the household consumes a minimum amount of energy. You can use this energy in the evening when the consumption is big, and the production is small or zero. Unfortunately, batteries still have some disadvantages. The biggest disadvantages are probably price and limited lifespan. The limited lifespan is due to the way the batteries are used. It’s not possible to discharge the battery to zero, and then recharge it up to 100% while the sun is shining. Fortunately, this problem can be partially solved by electronics, but you can’t depend on using all the capacity that the accumulator shows.

What is the advisable battery format? This is not an easy question, and the correct answer is based on what we know about typical household energy consumption. Household energy consumption patterns can fluctuate significantly. They are strongly affected by appliances with a high consumption that are used irregularly, such as washing machines, dishwashers, dryers, irons, etc. If you have large battery capacity for the days when you use the most power, the batteries will be costly and will be mostly unused on days when you do not wash, iron or cook. Using cheaper batteries means that you’ll have less capacity, so if the batteries run out, you’ll be dependant on the grid.

With photovoltaic water heating, the situation is different. It’s possible to predict the domestic hot water consumption precisely. Even if people don’t realize it, they behave quite regularly, and this is reflected in the consumption of hot water. Depending on the number of people in the household, the performance and accumulation capacity of the system can be precisely calculated. The accumulation element, in this case, is a common boiler. The price difference between a one-hundred-litre and a two-hundred-litre boiler is about a hundred euros. About ten kWh of energy can be stored in a two-hundred-litre boiler. A battery with the same capacity would cost thousands of euros.

How much percent of the domestic consumption is required for heating water? The same 20% as all other appliances! Of course, you could say "now our TV is playing for free," but it isn’t free. It actually costs quite a bit more more than a shower or bath full of hot water.

In conclusion, warm water is one of the most effective ways of using the energy produced by the sun.