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An increasing number of people who already have mains power nevertheless choose to run their homes partially or totally from solar. If/when required they draw current from the mains (using the supply in effect as a ‘battery’), and they sell excess current to the electricity supplier. These systems are known as ‘grid interactive’.
The solar modules used may be exactly the same as those used in RV systems, but there is a growing trend to using specialised modules that double as the roofing material. Some of these specialised modules have the same electrical characteristics as those that we are more familiar with. But some are specifically intended (electrically as well as mechanically) only for this application.
Systems large enough to wholly or partially drive home appliances tend have their solar modules controlled by a Multiple Power Point Tracker (MPPT). This converts the incoming voltage and current to optimise watts. That incoming voltage is not critical. It is typically anywhere from 48-120 volts, but can be as low as 15 volts.
Unless an RV system has an MPPT unit installed (and very few currently yet have) using a solar module intended for grid interactive usage may have inadequate voltage output for a conventional RV solar system – or in many instances may produce close to 40 volts – with a very real risk of damaging the solar regulator. In the former category (too low voltage) Uni-Solar’s ES-62t (62 watt) module produces 4.1 amps at 15.0 volts. As with most grid-interactive modules the ES- 62t appeals to motorhome builders as it is readily flush-mounted (i.e. there is no protruding connector box). But that 15.0 volts output is far too low for battery charging (most conventional solar modules produce up to 21 volts).
Kyocera’s KC 200 GT (200 watts) produces optimum power at 26.3 volts – and produces up to 32.0 volts. BP’s 175 B (175 watts) produces close to 40 volts. All of these modules may be used (with an MPPT) at their single unit voltage – but are more likely to be series-connected for higher voltages. If you have installed the ES-62t 15 volt modules all is not lost. The fix is a bit costly but simply involves replacing the existing solar regulator with an MPPT unit.
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