Power failure? - Generator!

Reading time 6 minutes

Power cut - now what? If you have a generator, you're in the clear. But, as is so often the case, there are a number of things to bear in mind if you don't want to risk fireworks on the one hand and operate a reliable power source on the other.

Very easy ....

There are ideas like „then I'll just plug my Jockel into a socket in the house“. Fortunately, the generator has a plug-in socket and no plug as an output. But that doesn't stop such imaginative minds from quickly making a suitable plug-plug cable - it works!
Then you are happy that at least this one phase is „running“, lean back and enjoy the TV movie - until you are suddenly torn out of your TV world by a loud bang with a flash fire and find yourself in the dark. The generator can only be recognized as such in the light of the flashlight that was quickly grabbed.
The power company simply rectified the fault without asking and switched the power back on.

The colleague next door rubs his eyes in amazement, shakes his head and says „How can you do that!“. But on closer inspection, the supposed smart guy turns out to be just a little more thoughtful: he has at least switched off the (all-pole isolating) RCD.
Now that his neighbor is sitting in the dark, he switches off his generator, pulls the plug of his hobby cable out of the generator and then out of his house socket. He had cleverly mounted it on the outside of the house wall.
Finally, he switches the RCD back on - and everything is as it always was.

... or not?!

Now that you can guess how NOT to do it, let's take a closer look at the facts, especially in accordance with the applicable regulations, which were not conceived here for the sake of regulations, but were actually developed to protect our belongings - and not least our lives.

Electricity from the socket may seem harmless, but it has plenty of deceit and trickery in store, which has catapulted many an unsuspecting person into the afterlife. Some mistakes you only make once.

Emergency power supply

If the grid fails, not just for a short time but possibly for days, reliable power generation is needed. But what kind and at what cost - including financial cost - is shown here.

Based on a normal detached house with an air-to-water heat pump and standard household appliances with a 3 x 20A domestic connection, the aim is to find the most economical solution.

Profitability comparison of all options

Let's start with an overview of the four main options available for this application. Each of these solutions has its own characteristics and, most importantly, different price points that can range from a manageable investment to a veritable small fortune.

Option A - Mobile diesel unit

Let's start with the supposedly simplest solution: the mobile diesel generator. At first glance, this option looks attractive: a compact device that can be parked in the cellar or garage and simply started in an emergency.

• Acquisition costsA genset with sufficient power (14-20 kVA), such as the SDMO J17 or the FG Wilson P17.5, already beats with 6,500 to 11,000 euros significantly more than the often quoted 2,000-5,000 euros, which only apply to weaker 8 kVA devices.

• Incidental costs: In order to integrate the unit properly, a Automatic transfer switch (ATS) required, which is 1,500 euros. In addition, the electrical installation costs a further 1,500 euros.
  Total approx. 3,000 euros.

• Operating costs: Such an appliance consumes around 3.5 to 5 liters of diesel per hour during operation, which is 250 operating hours round 1,400 to 2,000 euros makes the difference.
• Maintenance costs: With a service life of 250 hours / year, the following can be expected 300 to 500 Euro can be expected.

What speaks for this?
- The device investment itself is comparatively low.
- The unit is mobile
- Simple repairs can often be carried out on site.

What speaks against it?
- There are no automatic start (AMF), This means that the generator has to be set up and connected every time there is a power failure, as there is no stationary approval for permanent operation in accordance with DIN VDE 0100-551.
- Without an additional housing, the device is neither weatherproof nor soundproofed.
- An ATS retrofit is complex and not permitted due to a lack of corresponding approval.

Option B - Stationary diesel genset

The stationary diesel genset with fully automatic control. For example, consisting of the DPX-19800.1 with Perkins 403A-15G2 motor (17 kVA continuous output), the ATS DPX-27500 Logic (four-phase switching with 45 A / 25 kVA), a DSE 6120 controller and ABB ESB20-20N-14 N-PE bond contactor.

• Acquisition costs: The generator costs 7,150 euros, the ATS DPX-27500 1,580 euros and the ABB ESB20-20N-14 N-PE bond contactor costs around 30 euros. Total 8,760 Euro.
• Incidental costs800 to 2,000 euros can be budgeted for the foundation plate or sound enclosure. Electrical installation by a specialist company costs between 2,000 and 4,000 euros. Total averaged 2,800 to 6,000 euros.
• Operating costs are manageable: the diesel consumption is 3.1 liters per hour at 75% load, i.e. approx. 1,255 Euro for 250 operating hours.
• Maintenance costsAnnual maintenance at 500-hour intervals costs approx. 500 Euro. The monthly trial run (1-2 hours) costs around 5 to 10 euros per month.

What speaks for this?
- Fully automatic AMF start by the DSE 6120 controller.
- 17 kVA continuous power at only 1,500 rpm is more than sufficient, even the high starting current of a heat pump (briefly over 200% possible) is no particular challenge.
- The four-phase ATS changeover (incl. neutral conductor) complies with DIN VDE 0100-551.
- Thanks to the N-PE bond via a KG auxiliary switch, the RCDs remain functional even in emergency power mode.
- The device has an IP55 protection rating, making it weatherproof.
- The Perkins engine is an industry standard with worldwide spare parts availability and a service life of over 20 years.

What speaks against it?
- The sound pressure level is around 68 dB(A) at a distance of 7 meters.
- Fuel must be kept available (maximum 1,500 liters without a special permit).
- A monthly test run is necessary to keep the unit ready for operation.
- Depending on the location, exhaust gas and noise requirements (TA Lärm) must be checked.
- The grid operator must be informed of the installation if necessary.

Option C - PV system with battery storage

The combination of photovoltaic system and battery home storage with 3-phase island operation is the most technologically elegant solution. The system is based on three Victron MultiPlus-II 48/5000/70-50 inverters, configured as a three-phase system, a Cerbo GX as the system controller, a 20-30 kWh LFP storage system (e.g. BYD HVM+ or Pylontech) and a PV system with a capacity of at least 10 kWp.

• Acquisition costs : Let's take a closer look at the cost structure: The three MultiPlus-II cost 575 to 650 euros each, so a total of 1,725 to 1,950 euros.
  The Cerbo GX costs around 350 euros.
  The storage tank is the largest single item: for 20 kWh, you need to calculate 6,000 to 10,000 euros, for 30 kWh 9,000 to 15,000 euros.
  The PV system with 10 kWp costs 8,000 to 13,000 euros.
  Total 28,000 to 48,000 euros net.
• Incidental costsInstallation including commissioning requires again 3,000 to 6,000 euros.
• Operating costs: Practically zero.
• Maintenance costsfor the inverters of approx. 100 euros per year.
• PV yieldA 10 kWp system delivers around 9,000 kWh in central Europe, up to 11,000 kWh in southern Sweden, around 8,000 kWh in central Sweden and 6,000 kWh in northern Sweden.

What speaks for this?
- Silent and emission-free.
- The switching time in the event of a power failure is less than 20 milliseconds
- The PowerAssist function buffers starting currents from the battery
- The system is economical even without a grid failure, as it continuously reduces the amount of electricity drawn from the grid.
- The memory is scalable.

What speaks against it?
- The high total investment.
- PV system is absolutely essential. In winter, when there is little sun and longer outages, the storage is limited: 20 kWh is sufficient for around 5-6 hours with a 3.5 kW heat pump, 30 kWh for 8-9 hours.
- Check the starting current of your heat pump: With older direct-start compressors, the starting current can briefly reach 70-100 A. Check the data sheet before making a purchase decision (keyword: Ilr = starting current, LRA = Locked Rotor Ampere).
- Installation and commissioning are more complex than with a simple diesel genset.

Option D - The hybrid solution

The combination of option B and option C. Diesel unit and PV battery system, whereby the genset only starts up if the storage tank is empty or there is a risk of an outage lasting several days.

Acquisition costsThe addition of option B and C, whereby small synergies can arise through joint installation work. Total 35,000 to 55,000 euros.

Operating costsSince the genset only goes into operation when the storage tank is empty, which is perhaps 5-20 hours per year, this corresponds to a diesel consumption of approx. 25 to 100 euros diesel per year.

What speaks for this?
- Maximum reliability. The diesel genset is available as a backup for power outages lasting several days.
- Maximum self-sufficiency.

What speaks against it?
- Highest investment of all options.
- System integration is complex.
- This solution only makes sense for very high security requirements or in areas with frequent and long power outages.

Conclusion

Option B (DPX-19800.1 + ATS DPX-27500 Logic + DSE 6120 + ABB ESB20-20N-14) is the only fully automatic, standard-compliant and economically viable solution without an existing PV system. Investment realistically €12,000-15,000 net incl. installation. A system that works reliably for decades, starts fully automatically in the event of a power failure and meets all normative requirements.

Option C (3× Victron MultiPlus-II 3-phase + LFP storage) is the superior choice if a PV system is available or planned. The significantly higher investment will pay for itself over an estimated 8-14 years through the ongoing electricity savings. It is noiseless, emission-free and offers a switching time of less than 20 milliseconds.

Option A is generally not recommended for the present application - fully automatic emergency power supply for a heat pump with 14 kVA. It is neither economical (prices are significantly higher than previously stated) nor technically suitable for automatic operation. Anyone buying a mobile genset should be aware that manual intervention is necessary whenever there is a power failure, whether in the middle of the night or in any weather.

Option D (hybrid) offers maximum reliability. At 35,000-50,000 euros, however, this is only justified in exceptional cases, for example in areas with very frequent and long power cuts or where the highest safety requirements apply.

All options require installation, testing and acceptance by a licensed electrician in accordance with DIN VDE 0100-551 and DIN VDE 0100-600. Inform the grid operator before commissioning.