---
layout: wiki
title: AutonomousSolarSystem
updated: 2011-07-21 23:01
author: rick
default: false
---

## Target

Power a 12V/2A (24W) system for 24h/24h, using an autonomous solar system in the Netherlands (read: not very sunny).

## Initial thought

` 24W * 24h =~  0.6kW and 2A * 24h =  48.0Ah }}}, so given ourself a {{{100 Ah` battery (AGM, deep-cycle), should last us to roughly 2 days of operation.

After first measurements my 20W Solar panel is preforming `50%` less if I put it a bit into the shadow (balcony fences). Putting it into fully into the sun makes it generate roughly 1.2A/12V which is indeed [as advertised](http://humietrading.nl/index.php?option=com_content&task=blogsection&id=5&Itemid=34). The input should run at `17.5V` to make it take the full `20W`.

The change controller [Steca Solsum 6.6F](http://www.stecasolar.com/index.php?Steca_Solsum_F_en) seems to regulate the input to `12V`, leaving me wondering if the panel will be fully utilized. Cause `20W/14W * 100% = 70%` e.g. loosing `30%` seems a bit to much.

Taking this numbers into account we need at bare minimum at least {{{ 48Ah \* (100% / 70%) =\~ 69Ah }}}. Giving the fact that effectively we have 4 hours of sun in the Netherlands will this make {{{ 69Ah / 4 = 13Ah }}} which correspond to a 160W panel.

Estimated cost for bare minimum will be:

```
Panel 150W             : 600 EUR
Accu 100Ah             : 200 EUR
Charge Controller 10A  :  50 EUR
Connectors and cables  :  50 EUR
Measurement Electronics: 100 EUR
--------------------------------
Total                   1000 EUR
```

This setup is geared towards most optional numbers. Now take more realistic numbers into a account:

- The sun in the Netherlands will do roughly [1800 hour](http://www.zonnepanelen-info.nl/zonnepanelen/zon-nederland/), but [75(!) days](http://www.vwkweb.nl/cms/index.php?id=1334&option=com_content&task=view) of the year I will not see any sun at all. If this period last for more than 2 days my battery will be depleted, so I properly need to add extra battery-pack to my system (+200 EUR).
- The panels are not always running at 100%, I expect average case to be 50% and worst case 25% (if sun is shying during the winter). Consequences will be that I need between 1 to 4 panels of 120W (which gives me +2400 EUR).
- Looking at [Wind Energy](http://humietrading.nl/index.php?option=com_content&task=blogsection&id=4&Itemid=33) might be a more suitable  

## Experiments

- Using a dummy load (20W, I like to see if the panel is able to generate the full 20W).
- The Current Controller needs to be build/bought to be able to generate statistics on long running experiments.

## Idea/Brainstorm

- Use [mirrors](http://www.geo-dome.co.uk/article.asp?uname=solar_mirror) to increase efficiency.
- Measure DC current with an [LT1495 and Arduino](http://openenergymonitor.org/emon/node/31).
- The [Solar calculator](http://www.batterystuff.com/solar-calculator.html) suggests Power `25W/24h` using `2 * 120W` and `100Ah` accu. (giving 5h of direct sunlight). 

## Verbs

```
Vpmx  : Voltage at rated power.
Voc   : Open Circuit Voltage. 
Lpmax : Current at rated power.
Isc   : Short Circuit Current.
```

## Misc

500mA - 50W - 17Ah = werked