A sceptic’s guide to Voltage Optimisation

Senior Solar Design Engineer -Andy Barton
By Andy Barton
Senior Solar Design Engineer at Custom Solar

Voltage optimisation is often treated by many as the “crystal healing” of renewable technologies because there appears to be no difference to the consumer. However, it is the more subtle effects of over-voltage of the electrical grid in the UK where real savings emerge. The only people who know about the real benefits are the ones who stop and think a few years after installation. Purveyors of voltage reduction often focus on projects like a car park with high pressure sodium lighting where dramatic and immediate effects are seen; the power consumption is reduced on a primarily resistive device or the incandescent light bulb user – if you can still find one.

 

The effect of voltage reduction on other devices is more subtle. If a car park has LED lighting, the voltage reduction will probably not reduce the power as the LED driver will not change its output. In fact, the LED converter may run more efficiently at a higher voltage, but it will not run as long. This longer life has serious cost implications for replacement, but these are virtually impossible to predict.  The capacitor on the mains input will be toast far quicker than a unit run on a nominal 230V phase. The reason this is especially vital is that the electrochemistry and physics of the capacitor mean there is a rapid increase in cost per unit energy at the 350VDC (rectified 250 VDC) point, so LED units will rarely stand high voltages for long, but will cope with brown out quite readily.  The same applies to domestic LEDs, CFLs and any power supply that has the same technology: phone chargers, computer power supplies and industrial drives (notice many of these are expensive!).

 

A friend in the computer industry said he’d been in a brown out and witnessed his computer turn on at 75V AC (36% of grid minimum). Even a moderate 275 VAC (108% grid max) will kill most supplies in a few mains cycles. At 75VAC his incandescent bulbs did not glow, but his CFL bulbs did.  Then there is the vacuum cleaner. Working in solar PV I have a large array on the roof, and an inverter as large as the DNO will allow. This means that we tend to use the vacuum on a nice sunny day to maximise own usage (vacuuming is not a frequent event though).  Frequently the ring main is at 253-254 VAC. Our vacuum overheats and stops. The first two times I took it to bits, but it checked out fine, I reassembled it and it ran OK. Then I realised I just needed to leave it to cool and it’s fine. You have to ask, is it good for the vacuum to hit the thermal limiter? And should I have had to buy three vacuum cleaners in 10 years, even though I don’t clean that often? The same physics applies to any mains connected motor and the same problems.

 

Electrical heaters, such as kettles, electric showers and washing machines always tend to use the same energy no matter what the voltage, but they also suffer. They calcify quicker if they heat quicker; heating elements running at max power tend to develop imbalance hot spots quicker. This happens in air heating equipment too, such as fan heaters and incandescent heaters.
Do you have to speak up to make yourself heard over the kettle? It may need a good defuzzing, but the defuzzing will last longer with a voltage optimiser, and so will the kettle.

 

This article originally appeared in Solar Business Focus UK – Issue 11