Swallow me all the electricity

Use photovoltaic electricity yourself - optimize your own consumption with 3 tips

Using photovoltaic electricity in the home yourself is more attractive today than ever before. Coffee maker, refrigerator, dishwasher: it feels good when we can generate the electricity for our beloved everyday helpers in an environmentally friendly way - with a photovoltaic system on the roof. In the long term, this is also easy on the wallet. But what if you generate more electricity than you use? Excess solar power can be fed into the public grid for a fee. But it's financially less and less worthwhile. That's why I advise you to optimize your own consumption! This is very easy with the following tips. They mark the beginning of our blog series "The 3 × 3 for an energy self-sufficient house", in which you will find out how you can use regenerative energies optimally.

Article series Part 1: The 3 × 3 for an energy self-sufficient house

Self-consumption - how does it work?

Sustainable and independent: Free electricity is simply obtained on your roof, from a source that never runs out. Because as soon as the sun shines, the photovoltaic system produces electricity. However, this is direct current. However, alternating current is made available through the public power grid. That is why all electrical devices work with alternating current.

The so-called inverter provides a remedy here. This converts your photovoltaic electricity into alternating current and thus makes it usable. Whenever your photovoltaic system generates electricity, you can operate your household helpers directly with your own electricity and do not need any electricity from the public grid. It all works very easily via your normal socket. So you always benefit when the sun is shining. If it doesn't do that, you don't have to do without a dishwasher and light - then the electricity simply comes back from the energy supplier.

So much for the ideal case. Often, however, exactly the opposite occurs: You generate a lot of electricity, especially on sunny days, especially around noon. Usually, however, this is also the time when you need little electricity: It's bright - you don't need any light. You are not at home - the television, radio and computer are not on. What happens to the excess electricity?

The interaction of solar system, electricity storage and the x-change heat pump from Kermi.

Save costs, increase returns

You can feed the electricity into the public grid. According to the Renewable Energy Sources Act (EEG), you receive a so-called feed-in remuneration from the network operator for every kilowatt hour of solar power fed into the grid. However, this is becoming less and less worthwhile because the remuneration rates are falling. In addition, the high subsidies currently still in place for existing systems will gradually cease to exist from 2020 onwards. So is a solar system no longer profitable? On the contrary! Because electricity is more expensive than ever. In the first few months of this year alone, according to comparison portals, many German basic suppliers raised their prices by an average of five percent. With your own photovoltaic system, you make yourself independent of such developments. So my tip: Increase your own consumption! Because today it is not the falling feed-in tariff that decides the return on your photovoltaic system, but the amount of your own consumption and the saved electricity costs.

How to increase your own consumption - 3 practical tips

1. Use the time programs of the devices

Washing machines, dishwashers and the like: When they do their job, it usually doesn't matter. That's why it's best to let it run during the day, when the photovoltaic system produces the most electricity and at the same time little is needed for other consumers such as lighting. My extra tip for everyone who, like me, is not at home at lunchtime to turn on the washing machine: You can set many devices to the desired starting point with time programs or even via the app

2. Save electricity

In the long term, installing an electricity storage system is worthwhile. As the name suggests, it stores your solar power that you cannot use right away. So you can use it even when the sun isn't shining - for example in the evening for lights and television. You can find out more about this in our next blog posts.
You can find a clear video here: https://www.youtube.com/watch?v=F8S9s5Hc3UI

3. Use electricity for heating

Do you heat with gas or oil? As the owner of a photovoltaic system, you should think about using electricity for heating. We will introduce you to various options in detail in the second article on the blog series. For example, you can easily heat up your bathroom at short notice for the morning shower with electric radiators. A particularly sustainable heating solution is created when you combine your photovoltaic system with a resource-saving heat pump. Here the solar power can be used sensibly for the operation of the heat pump. You not only save the continuously increasing costs of fossil fuels, but you also help the environment. But more on that in the third part of the series of articles.

In the next two blog posts I will show you how stylish and comfortable heating with electricity can be and how you can even live almost completely self-sufficient with a clever concept. Take a look again.

Part 2: Clever heating with electricity - 3 options for different requirements

Part 3: Living energy self-sufficient - in three steps independent of electricity suppliers and fossil fuels

This is how you use electricity from renewable energies sustainably

That's how much electricity costs for your heat pump

This one Contribution share!

    About Sandra Beutlhauser

    I am the online marketing manager at Kermi and make sure that the latest news also reaches our readership.

    17 reply

    1. Christopher Scheuring
      February 16, 2021 at 13:08


      I use a PV system with 14kWp and operate a Kermi air / water HP x.change dynamic 8 AW E for heating and hot water and another e-Therme with currently limited to 9kW. First of all: Despite buffer temperatures (compact storage tank with 1000l) of 50 ° C, we still have a COP of 2.5 at -8 ° C outside temperature and only need the e-Therme as an additional heater from below -8 ° C. Therefore we are currently very satisfied with the special stage.

      What bothers me, however, is that the control options to store the PV surplus in heat via the HP or the e-Therme as WEZ2 are more than rudimentary. The whole thing is only possible via perceived workarounds over the scenes - an automatic use of the surplus via the S0 interface does not work at all. And you have to build hacks to bypass EVU blocks.

      In addition, the example described in https://www.kermi.de/raumklima/produkte/waermepumpe-und-speicher/waermepumpe-und-photovoltaik/ has not really been thought through. If, for example, I have 3 kWh of PV excess, and then the heat pump runs with 3 kWh of electrical energy, for example, I have 0 kWh at the SO interface - and thus a chicken-and-egg problem.

      To control the whole thing e.g. via an external load management (Raspery PI and Co) is not possible, because I cannot read out any external inputs in the scenes besides the EVU and Smartgrid. How does Kermi imagine that? It would also be practical if I could read out the real-time data from the heat pump for my existing home automation, e.g. via Mobbus or MQTT. Because the use of the cloud part is completely net - but not usable for automation.

      Currently I solve this over a crutch with follow-up time and a separate hysteresis in the S0 performance, etc. But Optionmal is different.

      It would be great if Kerni would provide the customer with detailed information on this - because the heating engineers are overwhelmed with it and they simply lack the appropriate training, especially now during the Corona period.

      1. Sandra Beutlhauserauthor
        February 17th, 2021 at 11:20 am

        Hello Christopher, thank you very much for your feedback and description of your experience regarding the use of excess PV electricity via the S0 interface provided. We will check the feedback internally as to whether and which improved solution we can offer the system operator and skilled tradesman in this case.
        If we have worked out an improved solution for this, we will provide you with details. Kind regards, Sandra

    2. Hardt Ralf
      February 7th, 2021 at 8:09 pm

      Please give your opinion. !
      We would like to modernize our 25 year old house (not well insulated) and have a concept in mind that I would like to give free to express my opinion. We spend around 360 euros a month on electricity and heating oil, so a total of 4 people. 7500 KW / H and approx. 4000, - liters of oil per year. We want to get away from that completely and are considering becoming more self-sufficient in the future.
      Our idea:
      - Hybrid photovoltaic power generation with solar water combi on the south side of the roof, approx. 100 2m
      - geothermal drilling
      - Water-guided wood-burning stove
      All of these 2 supplying components go into the heat exchanger and the generated electricity is fed into the circuit with battery for 3 days of bridging electricity.
      Is that efficient?
      I doubt the efficient temperatures for the house in winter for heating and hot water.
      As you can see from the old consumption, we live very warm and have a high energy requirement.
      How much do you value the investment and do you even achieve the values ​​that an oil heating system brings in order not to have to change our habits?

      1. Sandra Beutlhauserauthor
        February 8, 2021 at 10:59 am

        Hello Ralf, thank you for your message.
        In principle, your idea of ​​replacing the old oil heating system with a combination of a brine / water HP + photovoltaic system with battery storage and a water-bearing wood-burning stove is the right one.
        The basic requirement for this is an exact calculation and planning of the new WP hybrid system in advance, which should include the following points:
        • Calculation of the building heating load. The oil consumption of the last 5 years can be used as a guide
        • Determination of the extraction rate for the borehole, taking into account the hot water heat demand and the number of people
        • Determination of the maximum flow temperature for the heating system. A flow temperature of> 45 ° C should be avoided with the use of a HP
        A cost estimate for the investment based on the information available cannot be quantified on our part. For this purpose, a specialist company / specialist companies must first look at the local conditions and determine the environmental measures to be taken. We therefore recommend that you first get in touch with a specialist company you trust and discuss the options for implementing a HP hybrid system and then submit a binding offer.
        Kind regards, Sandra

    3. Knop Reinhart
      23 August 2020 at 12:24


      On a slightly cooler Sunday I have a question about the heat pump and storage tank.
      The two of us live in a two-storey house with an area of ​​approximately 12 x 12 m. We have a PV system with over 15 kWp
      -The heat is supplied directly via district heating, i.e. no heat exchanger at the transfer point
      Space for a heat pump is not a problem
      The hot water storage tank with a capacity of 400 l could be supplemented with a heating water storage tank
      The district heating connection could be retained for "cold days"
      A quite large fireplace is also available
      I think with the right design of the heat storage system it should be possible to reduce the use of district heating as much as possible.
      Question: is my approach OK? And where can I get support with dimensioning the components?
      Thank you in advance and I'm curious!

      1. Sandra Beutlhauserauthor
        August 24th, 2020 at 12:07 pm

        Hello Reinhart, thank you for your message. The approach you described goes in the right direction. Above all against the background of reducing the use of district heating.
        The first step here is to find out what heat demand has been covered by district heating for your house in the last 3-5 years. This information provides an initial reference point that is relevant for dimensioning the heat pump output and the storage tank size for heating and drinking water. Our recommendation is to make an on-site appointment with the heating company you trust so that a clean and coordinated system concept can be planned in advance. Kind regards, Sandra

      2. Christoph Michel
        January 15, 2021 at 23:23

        Unfortunately, heat pumps and photovoltaic systems do not go together at all, although this can be read over and over again in the network and is also claimed here. Then when the heat pump needs a lot of electricity - namely in winter, the PV system provides particularly little electricity. I have a brine heat pump myself and would like to install a PV system on my roof. A provider I spoke to advised me not to operate the heat pump with it for the reasons mentioned. With the PV system (80 m2 roof area) I can only save part of the household electricity, but that only makes up a third of my total electricity requirement. I find the practical quantities quite sobering.

        1. Christopher Scheuring
          February 16, 2021 at 13:11


          We use this with a 14 kWp system - with crutches over these scenes - usefully. Currently we can store a good 10-30 kWh in warm water in the 1000l buffer on nice days even in winter.

          However, I find the implementation via the x-center very stumbling.

        2. Dag brown
          March 10, 2021 at 12:39

          Hello Christoph,

          Basically, there is little PV power coming from the roof in winter, but there is also a transition period when it is heated
          and hot water is needed all year round. It is important to take a close look at the consumption and consumption behavior.
          The blanket announcement 1/3 house electricity, 2/3 heating electricity is not meaningful.
          We have been 100% electric for years (air-water heat pump for heating and domestic water as a separate system, of course also household electricity and 2 electric cars, as well as PV) and drive everything via the normal tariff (i.e. no HP tariff) and are with it
          very inexpensive on the way. Your approach to installing PV is the right one, everything else is just a calculation.
          Tell me your electricity consumption in detail and then we will investigate.

          Sunny greetings

    4. Heiko Hane
      11. July 2020 at 18:00

      We would like to have a PV system installed with maximum utilization and, for effective use, also a heat pump that is operated by solar power! My question is, can the heat pumps store the water and thus use it for a shower in the evening? A memory is out of the question for us because it is too expensive and secondly, it is not necessary due to home office, and all technical devices can otherwise be programmed for the day!
      Kind regards

      1. Sandra Beutlhauserauthor
        July 13th, 2020 11:33 am Answer
    5. Schmidt, Hartmut
      16. August 2019 at 18:32

      I would like to use solar power to heat water. To do this, the oil heating has to be running in the mornings and evenings in summer.
      Who builds something like that?

      1. Sandra Beutlhauserauthor
        19. August 2019 at 14:53

        Hello Hartmut, thank you for your comment. a general statement is difficult. The best thing to do here is to involve your heating engineer and electrician. Depending on the size of the system, storage volume, feed-in tariff, etc., many factors must be taken into account so that the use of solar power makes sense. The most efficient and simplest solution here is to combine oil heating with a drinking water heat pump. As a result, the oil heating is usually not required for DHW heating from spring to autumn. If there is no solar power available, the drinking water heat pump generates drinking water with a very high level of efficiency. If there is enough solar power available, the drinking water heat pump can increase the temperature in the integrated drinking water storage tank and thus store the solar electricity in the drinking water storage tank for later consumption. In addition, the efficiency is increased because the heat pump converts the solar power into heat with a very good efficiency (COP).
        I hope the information helps you. Kind regards, Sandra

    6. Alexander Dickbauer
      June 27, 2019 11:12 am

      I quote from the text: "You can, for example, easily heat up your bathroom at short notice for the morning shower with electric radiators."

      That will hardly be possible because in the morning before the shower there is no solar yield from the roof. So I would have to save it at least overnight. However, stored electricity is very valuable and expensive and should never be used up for heat.

      A kWh of heat from natural gas or oil comes to around 6-10 cents. 1 kWh of stored electricity is more expensive. The purchase of the electric heater and its service life, including an additional electric heater, is quite a nonsense.

      1. Sandra Beutlhauserauthor
        June 28th, 2019 at 8:35 am

        Hello Alexander, thank you for your message. I understand your concerns. However, sustainability and independence from fossil fuels are also in the foreground with this topic. You can also increase your own consumption. On sunny days you can optimize the self-consumption of your solar power and don't have to feed it into the grid. Kind regards, Sandra

      2. Malte Maier
        August 12, 2020 at 19:37

        I am currently planning the house, currently a PV system with inverter and an air-water heat pump is planned. I would like to use electricity from the PV for the household and LWWP myself, but I would also like to be able to feed in excess electricity. Can this be done with a single electricity meter?

        1. Sandra Beutlhauserauthor
          August 13th, 2020 at 8:24 am

          Hello Malte, thank you for your comment. As a rule, an electricity meter, a so-called bidirectional meter, should be sufficient for your project. However, I would coordinate this with your energy supplier. We wish you the best of luck with your building project. Kind regards, Sandra