The Digital Agency for International Development

The Solar Diaries - Day 4

By Alan Jackson on 16 September 2010

Image of PV panel in gardenIt's the beginning of day four of my solar experiment and off to a good start. The sun is out this morning, bright blue skies, although the forecast is for the weather to worsen over the day. So getting up early and getting the panel in place is important today.

I am using the equipment we used for the "Small Is..." festival to see if I can go "off-grid" for my work electricity requirements. This is a pilot to investigate the possibility of the whole of Aptivate being powered by renewable energy.

Because my house faces East-West, to get the morning sun means either dragging the panel through the house and putting it outside the front door or dragging it down the far end of the garden. Trying the garden this morning - it will be interesting to see how the sector of sun moves across this part of the garden.

Right now I've only got about 4 metres of cable to run to the PV panel which means I have to drag the 33kg battery down the garden too - made all the more difficult today because I broke my toe yesterday running into my baby's high-chair!

Really I need to get the panel up higher... which means drilling more gridbeam.

Today was going to be a particular challenge to stay "off-grid" as I'm supposed to be pair-working out of "The Skiff" with Nate. I've had a last minute reprieve as Nate's not going to be there until the afternoon - but how do I stay off grid there? The battery is too big to carry.

For pair-working we want to use a decent sized screen. We use an one of the Iiyama 12 volt 24" monitors, which in Eco mode takes about 20 Watts. Interestingly the Samsung N220 netbook we have can drive the big screen quite happily. It would be useful to get a bigger battery for the netbook anyway, so I could conceivably run a whole working day off the netbook's battery. That only leaves powering the monitor.

There are small lead acid batteries that I could carry to the Skiff. For an 8 hour day I would need a battery with about 20 Ah. That's 20 Watts / 12 Volts  x 8 hours x 1.5. The 1.5 is to make sure the battery never gets below 1/3rd capacity as this would shorten its life.

A shadow has shifted and is covering one of the cells on the PV panel, and if the voltage from one cell drops it tends to pull the others down with it apparently, so be back in a minute...

...ow! Never try and cut back brambles without gloves. I didn't realise this solar experiment would be so dangerous.

A 20 Ah lead acid battery would weigh about 6kgs - which could just be carried but is on the heavy side. The screen takes about the same power as a netbook, so I'm wondering if a lithium-ion battery would be more appropriate - they are about a third of the weight. I imagine I would need some kind of charge controller for it - the solar charge controller is specifically for sealed lead acid batteries.

...Nate and I didn't use the large screen for pairing today so I've got through day 4 without mains electricity using the battery in my laptop and netbook for the afternoon.

battery voltage at the end of day 4:  12.11V

Sept. 17, 2010, 7:47 a.m. - Mark

What does Eco mode mean for the monitor? Is it less bright than some other mode?

Sept. 18, 2010, 11:24 a.m. - alan

The monitor is very bright normally and uses something like 25 - 30Watts which is fairly good anyway. In Eco mode it's apparently supposed to take as low as 13 Watts according to Iiyama's website but when I measured it at the plug it was more like 19Watts which is still very good for a 24" monitor. Eco mode is dimmer than normal and disables the brightness controls. Indoors it's perfectly bright enough for me. I don't know if Eco mode does anything more interesting than just setting the brightness down. Aleutia are supplying 12Watt 12V 15" monitors and Inveneo apparently have a 7Watt monitor, both of which sound interesting!