The advantage of the lean to greenhouses is that they may be placed near the house or the fence and this way they will need less space than a free-standing greenhouse. Nonetheless these types of greenhouses are less often used because their design allows them to be placed in only few locations.
They must be leaning against an existing wall and in the majority of cases there is more space in the garden or in the yard.
Since they have to be leaning against a wall, it is possible that they will be shadowed. This is why the best option is to build them next to a south facing wall.
The advantage of the greenhouses placed near a south facing wall is that it will cost a lot less to heat them during the winter months because they act as a solar greenhouse. This is possible because they are able to collect a lot of sunlight from the south through the wall of the greenhouse.
There are a lot of people who prefer the lean to greenhouses because they have direct access to it from their home. In case you decide to attach the greenhouse to your home, another advantage is that you could be using it to partially heat your home as well, because of all the heat that has been trapped in the greenhouse. Things could be working on the other way around as well: your home could be heating the greenhouse through an open window or a vent.
When choosing the location of the greenhouse, there are some aspects that you should take into consideration: as it has been mentioned before, in some parts of the day the building could shadow the greenhouse. If there isn’t enough natural sunlight you might have to provide artificial sunlight through using grow lights.
In case you need artificial light, it is good to have the greenhouse leaned against a wall, so that you will have a power source in it. Solar greenhouse has also been mentioned before, and the main point of it is that the fruits and the vegetables that you are going to grow will be healthy.
The wall that you attach the greenhouse to, will be acting as a thermal mass. It acts like a sponge that gathers the heat during the day and uses it to heat the greenhouse during the night, when the temperature is lower.
The disadvantage of having the greenhouse leaning against a wall is that the air circulation will be limited. In case you only have limited space to practice your hobby of gardening, then you should most definitely consider a lean greenhouse.
As a bottom line, the advantages of these greenhouses include the access to utilities, like water and electricity and also greater insulation and solar heating because of the wall that behaves like a thermal mass.
Naturally there are also some cons, like having limited space, limited light and also limited ventilation, but all of them could be taken care of artificially.