{"id":611,"date":"2017-03-22T15:59:53","date_gmt":"2017-03-22T15:59:53","guid":{"rendered":"https:\/\/jimkerkhoff.com\/test-roycreekranch\/?p=611"},"modified":"2017-07-14T17:12:26","modified_gmt":"2017-07-14T17:12:26","slug":"solar-powered-rainwater-project-to-grid-tie-or-not-to-grid-tie-that-is-the-question","status":"publish","type":"post","link":"https:\/\/jimkerkhoff.com\/test-roycreekranch\/2017\/03\/22\/solar-powered-rainwater-project-to-grid-tie-or-not-to-grid-tie-that-is-the-question\/","title":{"rendered":"Solar Powered Rainwater Project – to Grid-Tie, or not to Grid-Tie. (that is the question)"},"content":{"rendered":"

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Previously, we discussed<\/a> the amount of power needed, and how that determines\u00a0the size of the solar array. We also mentioned Days of Autonomy and how that informs\u00a0battery storage. Now for\u00a0Charge Controllers<\/strong> and Inverters<\/strong> — the brains that tie everything together.<\/p>\n

There are two categories of charge controller<\/strong>, Pulse Width Modulation (PWM)<\/strong> and Maximum Power Point Transfer (MPPT)<\/strong>. Both have advantages. PWM charge controllers are generally less costly, and are best for smaller (under 200 watt) systems. They work by turning the direct current (DC) from the solar panels into a stream of pulses that vary in width and thereby control the amount of power transferred. This is great for small systems, but there is a cost — some of the power from the panel is wasted as the controller interrupts power to safely charge\u00a0batteries.<\/p>\n

MPPT charge controllers<\/strong> on the other hand, are more efficient. By transforming the power from the solar panels into the optimum voltage and current for the\u00a0load, they allow the panels to work\u00a0at their most efficient voltage\u00a0— usually several volts higher than the load needs. There is\u00a0a closer match between power supply and load. Unfortunately\u00a0they cost more. For larger systems though, the added cost is more than compensated by the increased efficiency. I decided on\u00a0an MPPT model.<\/p>\n

Now to\u00a0convert power from the solar panels and batteries into Alternating Current (AC). Inverters<\/strong> do this but\u00a0there are some special considerations. Normally, one would simply match the load, in this case less than\u00a01000 watts, and get an inverter with at least that capacity or perhaps a little more. Pumps use capacitor-start motors however, and although my 3\/4\u00a0horse pump\u00a0may have a running load of only 900 watts, it’s\u00a0starting current can be 5 to 7 times that while the motor spins up. Also, they run best on true sine wave power. Cheaper modified sine wave inverters may work, but the motors operate less efficiently and generate extra heat. In time, I want to run the well pump also. It has\u00a0a 1 1\/2 horse motor. With a run-time load of over 2000 watts, it might briefly need as much as 10,000 watts to start up.<\/p>\n

There are quite a few inverters on the market that will supply the required power, but I was put off by their expense. Then I spotted a model from Sun Gold Power. It came in several power capacities, and\u00a0combined a 40-Amp\u00a0MPPT controller and a charger in the same unit. Why a charger? The price was attractive though, so I gave it a serious look.<\/p>\n

It turns out the charger made the Sungold unit capable of\u00a0Grid-assist<\/strong>. I wanted the rainwater system completely separate from the grid, because grid-tie systems are disabled during a power failure. This seems counterintuitive, but it prevents feeding power back into the grid and endangering electrical workers who aren’t expecting live power in the dead system. It’s an important safely feature, but it defeats my purpose: to have water no matter what.<\/p>\n

Grid-assist systems<\/strong> work differently. Instead of feeding excess power back to\u00a0the grid, that power is used to charge batteries. With a Grid-assist system, if the panels can’t produce enough power or there’s\u00a0no sunshine, the grid can be used to run the system. The inverter\u00a0can be set to prefer solar\/battery power, so use of the grid is limited. It also acts like an uninterruptible power supply — loads are always powered. It can even start an outboard generator should both the solar and grid power fail at the same time. Also, unlike grid-tie systems, no approval is needed from the power company for\u00a0installation.<\/p>\n

So here’s what I bought:<\/p>\n