<div dir="ltr">Greetings, All~ Mark Frye had asked: "...with a 4000w Outback Radian, AC coupled with 2000w of PV, what is the smallest Li battery I would want for stable operation?" <div><br></div><div>Mick's reply: In the lithium arena, one often finds the ratings in kilowatt-hours rather than in amp-hours. This is an easy conversion for us energy nerds to make, so below I'm mainly using watts & watt-hours with occasional conversions to amp-hours.</div><div><br></div><div>I suggest that you start with the spec sheet (of whichever brand lithium battery is on your radar), & see what the manufacturer says about "allowable rate of recharge". You may find that C/2 is an acceptable rate with several manufacturers, Mark--much faster than what we're accustomed to with typical lead-acid batteries. Let's assume:</div><div><br></div><div>* ...that your AC coupled PV array crests around 1800 watts to the battery when there are no loads</div><div>* ...that the battery is below 100% state of charge, and</div><div>* ...that the solar conditions are optimal. </div><div><br></div><div>Let's further assume that those conditions represent your battery's highest energy rate in either direction. </div><div><br></div><div>1800w X two hours = 3,600 watt-hours dividing by 48v nominal = 75 amp-hours in the above hypothetical situation. </div><div><br></div><div>++++++++++++++++++++++++++++++</div><div><br></div><div>
The rate at which a battery can receive energy is (usually) also the rate at which it can comfortably deplete, so let's briefly look at the flip side: Assuming the battery mfr. wants the watt-hours to be no less than two times the maximum wattage, a 3600 watt-hour (C/2) battery should not be depleted faster than 1800 watts. Your 4kW Radian, Mark, could exceed that if the loads demand it--& maybe your loads don't. Motor starting surges should probably be part of the thinking & it wouldn't hurt to ask the mfr.'s opinion about short term surges which briefly deplete the battery faster than the hypothetical two hour rate.</div><div><br></div><div>By approaching this question based on the battery manufacturer do's & don'ts, one improves the chance of getting warranty coverage should it later be needed. "What the large print giveth, the fine print taketh away." </div><div><br></div><div>The Wrench List is the Bomb! </div><div><br clear="all"><div><div dir="ltr" class="gmail_signature" data-smartmail="gmail_signature"><div dir="ltr"><div>Mick Abraham, Proprietor<br><a href="http://www.abrahamsolar.com" target="_blank">www.abrahamsolar.com</a><br><br>Landline: 970-731-4675</div><div>Cell phone or for text messaging: 970-946-6584</div></div></div></div></div></div><div hspace="streak-pt-mark" style="max-height:1px"><img alt="" style="width:0px;max-height:0px;overflow:hidden" src="https://mailfoogae.appspot.com/t?sender=abWlja0BhYnJhaGFtc29sYXIuY29t&type=zerocontent&guid=74c54196-b300-4b9d-8f4a-9fa513751306"><font color="#ffffff" size="1">\u1427</font></div>