Direct solar power

Introduction

Common solar power setups include four elements: solar panels, charge controller, inverter, and a battery pack. Out of these, the batteries are the ones that will need replacing sooner than the other components. Additionally, the more frequent replacement of the batteries also relies on fossil fuel to produce the equipment needed for the solar power setup. The batteries end up being the most costly component of the setup, and also the component with the largest fossil fuel footprint.

We can move away from using batteries though a combination of optimizing the energy consumers in our house to only consume energy during the daytime (or when the sun shines on the panels) and a shift in our mentality away from "infinitely available" energy.

LOW←TECH MAGAZINE describes how the author has moved to using direct solar power for their home . Their article serves as the basis for this article.

Rationale

Adapt energy consumption to the weather (as was done before the Industrial Revolution ).

Direct solar energy is much cheaper and more sustainable.

Some appliances are only used during the day.

Many appliances already have batteries.

Non-electric energy storage

Two essential energy consumers raise problems in the case of direct solar power: the fridge and the cooker. These need to keep working even after the sun has set.

The fridge

Refrigerators with the most energy-efficient labels have limited insulation, usually 2.5 cm (0.984252 inch). A thickness of about 12.5 cm (4.92126 inch), results in a reduced energy consumption drops by a factor of four.

The LOW←TECH MAGAZINE article on direct solar power explains: "Research shows that doubling the insulation thickness from 2.5 cm (standard insulation) to 5 cm reduces the annual electricity consumption of a refrigerator (50 litre capacity) from 250 to 125 kilowatt hours. 13 With an insulation thickness of 10 to 12.5 cm, electricity consumption halves again to around 60 kilowatt hours per year. Even thicker insulation brings a smaller reduction in electricity consumption and is no longer attractive because thicker insulation also increases the cost and size of the refrigerator. The study concerns a solar-powered AC fridge that operates thanks to an inverter and a battery, which is less energy-efficient than a direct solar-powered fridge."

A water tank inside the fridge can further increase its cooling capabilities. The water is converted to ice during the day, and this helps keep the fridge cool at night.

Such a fridge would open at the top, instead of at the front. The cool air is heavier and this way of opening the fridge reduces energy consumption.

The LOW←TECH MAGAZINE article mentions: "A study of direct solar refrigerators in very sunny regions (Texas and New Mexico, USA) showed that they maintained their cooling capacity for 6 or 7 days without power supply. The units operated year-round with solar panels of only 80W to 120W."

The cooker

A single hot plate on a conventional cooker needs 1,000 watts of electrical power. A LOW←TECH MAGAZINE article describes the inefficiencies of the process of cooking using heat: "The cooking process is similar to heating an uninsulated building with all the doors and windows open".

A cooker using direct solar power packs the cooktop with thermal insulation.

The LOW←TECH MAGAZINE article notes: "Researchers at US California Polytechnic State University (Cal Poly) built the first solar electric cooker in 2015. Their 12-volt device, which has since been further developed, needs only a 100W solar panel to work. It boils a litre of water in an hour. With a full day of sunlight, it can cook almost 5 kg of beans, rice, stew or potatoes."

"Cooking after sunset is possible by using a cooking pot with a much thicker bottom (5-10 kg). Cal Poly’s research team managed to bring the temperature of that solid heat storage to 250°C in five hours with a 100W solar panel. They were then able to boil a litre of water in three seconds after sunset. In another test, they stir-fried 1 kg of vegetables in two minutes. The ideal configuration consists of two cooking pots: one with and one without heat storage. Thus, an electric solar cooker can cook both slowly and quickly, depending on the time of day and the dish."

Heating

Coming soon