ANSWER

Static electric fields

Since solar panels generate direct current, a static electric field is created between the positive and negative cables of the solar generator when light hits the solar panels during the day (usually not at night). These two cables should run relatively close to each other, also for lightning protection reasons. Due to their close proximity, the static electric field can only be measured very close to the solar panels and cables. Static electric fields are only considered harmful at high levels. According to the Standard of Building Biology Testing Methods (SBM), a static electric field of up to 500 V/m is considered a slight anomaly. (V/m is the electric field strength in volts per meter.)

Static magnetic fields

The static magnetic field generated by a photovoltaic system fluctuates with the amount of sunlight. The same installation recommendations apply as for static electric fields. According to the Standard of Building Biology Testing Methods (SBM), a static magnetic field of up to 2 µT is considered a slight anomaly. (µT is the magnetic flux density in microtesla.) Therefore, the static magnetic fields of a photovoltaic system are not usually problematic.

Power frequency fields

In a photovoltaic system, power frequency fields are mainly present on the line from the electricity meter to the inverter and on the inverter itself. Power frequency electric fields are considered significantly more harmful to human health than static fields. Consequently, the SBM threshold level for a slight anomaly in sleeping areas is 5 V/m for power frequency electric fields, measured with reference to ground. Although direct current normally flows in the cables to the solar panels, power frequency electric fields are often also measured on these cables. The following are possible causes:

1. If direct current (DC) cables are run close to alternating current (AC) cables, the DC cables will couple into the existing power frequency electric field of the AC cables. For example, a power frequency electric field can still be measured at the solar panel during the day and at night from a standard AC cable connected to an outlet or attic light.
2. From a building biology perspective, inverters with transformers are preferable because they physically separate the alternating current (AC) and direct current (DC) sides. Unfortunately, such devices are rarely available on the market anymore.
3. Some transformerless inverters do not cleanly separate the AC and DC sides. This creates a power frequency electric field on the solar panel and the string cables between the panels and the inverter. According to the VDE (the German Association for Electrical, Electronic & Information Technologies), solar panel frames in systems with transformerless inverters must therefore be grounded. However, grounding alone is insufficient to reduce electromagnetic pollution.
4. The electromagnetic interference (EMI) that the inverters generate and feed back into the power grid can also be problematic. Converting direct current into alternating current creates higher frequency harmonics. Transformerless inverters have lower power frequency magnetic fields, but they usually have higher frequency electric fields. Electric fields, even in the higher frequency ranges, can be shielded relatively easily.

Power frequency magnetic fields

Power frequency magnetic fields are considered more biologically harmful than power frequency electric fields. The SBM threshold level is therefore only 0.1 μT for slight anomalies. Inverters generate significant power frequency magnetic fields, but only during the day. The strength of these fields depends on the amount of sunlight. Therefore, inverters should be installed farther from areas used for sleeping, resting, or working during the day. There are several ways to reduce the harmful effects of a photovoltaic system. A good start is selecting appropriate inverters and other materials. However, the following strategies have the greatest impact on reducing electromagnetic pollution: the correct installation of all wiring, proper grounding, and proper inverter location. If elevated levels of electromagnetic interference are detected on the AC side during a building biology assessment, a mains filter may need to be installed.

Summary

Contrary to popular belief, photovoltaic systems add only low levels of electromagnetic pollution when installed correctly. For instance, the power frequency magnetic field of a clock radio next to a bed is often higher than the levels measured coming from a photovoltaic system.

Always implement the following strategies:

• Keep the components of the photovoltaic system as far away as possible from rooms used during the day.
• Ground the solar panels.
• Keep induction loops between the positive and negative DC cables small.
• Use shielded, grounded string cables, or run them in grounded metal conduit.
• Position the inverter as far away as possible from areas where people spend a lot of time, such as beds or office workstations.

Werner Bopp, a Baubiologe IBN and master electrician from Mainfranken (www.baubiologie-mainfranken.de) answered this question.