May 30, 2017

Solar alone vs. Solar plus Back-Up

Some Solar companies advertise installing Solar as disaster-proving your home.

Any grid-tie Solar system, single or Micro Inverter, will lose output in less than one tenth of a second when the power grid fails. No grid, no output.

To have reliable power when the grid fails you need a battery bank and a Back-Up Inverter. Critical circuits in your house are connected now to the BU Inverter. When the grid fails the BU Inverter switches to battery power in about one twentieth of a second, like the smaller computer UPS units do. During daytime Solar can feed into the battery for charging. How long you can sustain depends on the amount of batteries, size of Solar feed in and the load you draw.

SMA offers a new line of single Inverters with an emergency power output of 1500 Watt AC. Buel Solar argued with SMA that that feature is not thoroughly enough explained and is misleading. The 1500 Watt are only available with an array of 3000 Watt or more during core daytime hours with no shading or clouds. Also the 1500 Watt offer no surge power like larger refrigerators have during starting the compressor. So, this power is good to charge cell phones, power a small refrigerator or lights. Of course sometime in the afternoon all power will turn off. Some companies offer 3 or 4 kilo Watt hours BU systems which are too small to provide reliable power for 12 hours in most cases. Should you think that this is enough power for you, a larger UPS unit can help you for less cost.

Buel Solar installs complete BU units with a minimum of 10 kilo Watt hours capacity tied together with the Solar system. Starting price at about $10,000. For example, if you are an entertainer or entrepreneur and a power failure means a $50,000 loss in one day, then a $45,000 BU system is reasonable. But for the normal household $ 10k are not justifiable, since the power grids in California are fairly reliable.