If you operate a solar power system, you produce the electricity for your household yourself. However, the yield of PV energy naturally fluctuates depending on the weather, time of day, etc. Power generation is usually most effective at midday. This is when the sun shines particularly strongly on the solar modules. However, most people are at work at this time, the children are at school etc., so household consumption is correspondingly low. This means that household consumption is correspondingly low. As a result, more electricity is produced than can be used - creating a PV surplus. We explain how you can best utilise the surplus solar energy and increase your own consumption.
If you have invested in a solar system, you naturally want the costs to pay off as quickly as possible and the investment to be amortised. Utilising the PV surplus as sensibly as possible plays a decisive role in this. After all, you could of course send the surplus to the public grid and receive a feed-in tariff for it - but this is very low. Soit's not worth it. What's more, you probably haven't invested in your own electricity generation in order to buy electricity from the grid. But there are even more reasons to make sensible use of surplus PV.
The calculation is actually quite simple: the more PV electricity you use yourself, the less electricity you have to buy from the grid. That pays off, because: The energy from your own power generation is free (apart from the cost of purchasing the system), while electricity from the grid costs around 36 cents per kilowatt hour. So if you use the surplus in your home as much as possible, you can maximise your savings on electricity costs. The aim is therefore to maximise self-consumption - i.e. the amount of self-generated PV electricity that is used in your own household.
If you make your PV surplus available to the electricity grid, you become a so-called partial feeder. This means that you receive 7.94 cents (as of March 2025) for every kilowatt hour of PV electricity that you make available to the public. This does not cover the acquisition costs for a solar system. Especially not if we consider that you have to buy the missing electricity again for 36 cents. It's clear that the calculation doesn't work out, even without a calculator. We realise that we should use the surplus from our electricity generation ourselves, as the feed-in tariff does not cover the costs.
Saving on electricity costs is usually the main reason for PV. The other is independence from public energy providers. If you make the best possible use of your PV surplus in your own household, you will of course also be much less affected by rising electricity prices. A high level of self-consumption can also help you to avoid price fluctuations and grid charges. The surplus from your own electricity generation not only saves you money on electricity costs, but also gives you more independence.
There are many different ways in which you can put your surplus solar power to good use. All of them are more economical than feeding it into the grid for a low feed-in tariff. Today we are focussing on the three most efficient options: using a battery storage system, heating water with solar power and charging an electric car with excess PV power. We will also show you how to use Shelly, a clever energy manager, to utilise the surplus in the best possible wayand, above all, completely automatically.
The best way to store the amount of electricity that you cannot use in your household is to use storage systems. They work like large batteries that ensure that you can use your surplus solar power flexibly when you need it - regardless of whether the sun is shining or electricity is being generated. You can programme your energy management system so that it only fills your storage systems when you produce a certain amount of electricity and the base load in the house is covered.
You can use a Pro 3EM for the scenario (depending on the system and required amperage), for example. Simply have it installed in your distribution box by a professional and combine it with the smart socket Plug S Gen3 . As a WLAN-operated 3-phase power consumption meter, the Pro 3EM records how much energy is produced, consumed and fed into the grid. You then define the desired values in the Shelly Smart Control app - in our example it is 500 watts. As soon as the energy manager recognises that the value has been reached, the socket automatically starts the charging process for the storage systems. In the evening and at night, you then use this to cover the base load in the house
The PV surplus offers great potential for saving energy costs, not only in terms of electricity consumption, but also when it comes to heating. For example, the preparation of hot water can be optimised via the energy manager. If the system recognises that there is a surplus, it starts the operation of a heating element in the hot water tank in order to convert the surplus PV energy into usable heat. This makes the preparation of hot water particularly efficient and cost-saving. If in doubt, a electrical professional will know which device is best suited to your electronics - for example, you could combine the Pro 3EM and the Pro EM 50
You can use the same procedure to programme your wallbox so that it always charges your electric car when there is a PV surplus. However, instead of the smart socket, you use a WLAN switch, such as the Shelly Pro 1PM, which controls the operation of your wallbox. If the Pro 3EM then recognises that there is a PV surplus, the system communicates with the Pro 1PM (thanks to the scene you have previously created) and releases the charging process for the electric car. In this way, you drive with the power from the surplus and have optimally utilised the energy from your own power generation.
Now that we know how easy it is to automate the use of PV surplus with Shelly, we naturally want to find out how much we can save by doing so - so we'll do a sample calculation. To do this, we compare how much it costs us to heat water with mains electricity and how much it costs us to use the surplus. In the example, we assume that the heating element for our hot water cylinder consumes 1,250 kWh per year.
If we feed the surplus into the public grid, we receive the feed-in tariff, but have to buy additional grid electricity to heat the water. The calculation would therefore be as follows:
Costs for grid electricity: 1,250 kWh x 36 cents per kWh = 450 euros per year
PV surplus fed into the grid: 1,250 kWh x 7.94 cents per kWh = 99.25 euros feed-in tariff.
Effective costs: 450 euros - 99.25 euros = 350.75 euros per year
Now let's compare this with what the calculation looks like if we use the surplus for hot water. Here we assume that the entire PV surplus is sufficient to cover 80 per cent (i.e. 1,000 kWh) of the electricity requirements of the heating element.
Costs for PV surplus: 1,000 kWh x 0 cent per kWh = 0 euro per year
Costs for mains electricity: 250 kWh x 36 cents per kWh = 90 euros per year
Effective costs: 90 euros per year
In our example, using the PV surplus for hot water saves around 260 euros per year - and this can be achieved automatically with a clever energy management system like Shelly's.
If we feed the surplus into the public grid, we receive the feed-in tariff, but have to buy additional grid electricity to heat the water. The calculation would therefore be as follows:
Costs for grid electricity: 1,250 kWh x 36 cents per kWh = 450 euros per year
PV surplus fed into the grid: 1,250 kWh x 7.94 cents per kWh = 99.25 euros feed-in tariff.
Effective costs: 450 euros - 99.25 euros = 350.75 euros per year
Now let's compare this with what the calculation looks like if we use the surplus for hot water. Here we assume that the entire PV surplus is sufficient to cover 80 per cent (i.e. 1,000 kWh) of the electricity requirements of the heating element.
Costs for PV surplus: 1,000 kWh x 0 cent per kWh = 0 euro per year
Costs for mains electricity: 250 kWh x 36 cents per kWh = 90 euros per year
Effective costs: 90 euros per year
In our example, using the PV surplus for hot water saves around 260 euros per year - and this can be achieved automatically with a clever energy management system like Shelly's.
Excess PV energy can be stored and used for heating, hot water or charging electric cars. Alternatively, it can be fed into the grid, whereby self-consumption is more economical.
Smart devices such as the Shelly Pro 3EM can be used for this purpose. They measure the electricity flows in the house and display them in the app, for example.
A heating rod for storing the PV surplus is worthwhile if surplus solar power is regularly available and a cost-effective way of heating water is sought.
The PV surplus can be utilised with an electric heating system, a heat pump or an electric hot water pump.
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