DC Microgrid/Solar

Most DC grid installations we've talked about so far use solar power as their main energy source. So even though it's not directly part of the microgrid, here's a small collection of information on solar energy

Getting cheap solar panels

Used solar panels are ideal for us. There are a few places to get them

• Used-Solar has an ebay shop. They ship panels, or you can pick them up in Leipzig. We got our panels for CCCamp19 from them
• SecondSol is an online market place for used and new solar gear
• eBay & eBay Kleinanzeigen

NOT getting cheap solar panels

• AWM Wertstoffhof Plus
• eds-r (that place where the Wertstoffhof brings their panels to)

Charge Controllers

Charge controllers connect the solar panels to the battery (and sometimes also to the load). There are cheap ones from China that work decent enough, and proper expensive ones. Also, there are OpenSource projects.

• Cheap charge controller from China, works well enough for its price, great for getting started
• LibreSolar, open source MPPT with 10A or 20A, and a 20A PWM controller (also on OSE wiki: BMS
  • All connected together in a Goal Zero Yeti like box: SolarBox (GitHub)
• SMBS4080 older opensource project, for lithium batteries. Newer versions apparently availble but not sure if they are opensource [1]
• Open Solar Project Controller (via HackADay)
• Open Green Energy has a few DIY charge controllers on instructables. Some of his stuff seems to be on GitHub as well
  • Latest PWM controller
  • Much smaller PWM controller
  • MPPT controller - might not work according to notes in the instructable
    • There's some derivative work on GitHub: JoshSilver8/MPPT-Charge-Controller and aplavins/Arduino-MPPT
• NinjaSCC
• Freifunk MPPT
  • Forum post, GitHub Repo

Some of our own DIY approaches are in the midst of happening over here: Solar Charge Controller

Power Usage

• My fridge needs 0,7 kW/h per day in normal family use.

Guerilla-PV in General

This shop has compiled some good information. There seems to be a lot of things to adhere to when plugging panels into The GridTM. I might guess it could all be ignored (hence the name Guerilla?), but if something happens, there will probably be a lot of questions. Also keep insurances in mind. If something starts a fire you don't want to pay repainting a whole house out of your own pocket.

More info in German from some official looking people: PVplug eine Arbeitsgruppe der DGS (Deutsche Gesellschaft für Sonnenenergie e.V.).

Project ideas

• Integrated box with solar SunCrafter

Guerilla-PV cum Zombie-Mode

• Be simple, reliable, idiot-proof
• have enough stored energy to run for 1 week in cloudy weather
• Guerilla-PV sets at GreenAkku

On no-Zombie:

• Have Grid-Tie-Inverter to offset all the things wasting power in standby.
• charge battery for Zombie
• not discharge battery over night (unless battery + PV has enough power that we don't care)

On Zombie

• Run in island-mode (inverter with no grid tie) from battery to run smartphone, laptop, radio and fridge.
• continue to charge battery from PV when there is enough power

Needs

• PV panel (used?)
• something to charge battery from PV
• maybe something to charge battery from grid?
• battery (run down lead-acid car-battery?)
• Inverter being able to tie into grid
• Inverter being able to run stuff stand-alone
• ???
• Profit!

Questions

Can I put more PV on a controller than it needs without blowing it up?

Guerilla PV is limited to 600W per German law, but if I put panels with 600Wpeak in bad lighting on it, I will never reach that. So can I attach maybe 1200Wpeak to the controller without destroying it in the rare case of sunshine?

The current understanding of Chris (i.e. might be wrong/there is certainly more to it): If the panels are not properly loaded, the voltage will go up to "open-circuit". If that is higher than the controller can handle, it might break it. Also, coldness raises Voc, which means that a cold, sunny winter-day is most likely to roast the controller.