*3.2. Standard Method 2*

This other standard method is used mainly in Spain, so that four hours of sunshine are ensured around midday on the winter solstice. In this way, in place of estimating the positions for a particular sun height, the latitude of the place is the necessary data for the use of this other standard method. It is obtained that the measured distance across the rows (d) of the PTCs of height W' is shown at Equation (5) (Figure 5) [27].

$$\mathbf{d} \le \mathbf{W'} \cdot \mathbf{k} \tag{5}$$

where k is the zero-dimensional factor, which varies according to the latitude of the place

$$\mathbf{k} = \frac{1}{\text{tg}\left(\left(\mathbf{61}^\circ - \Phi\right)\right)}\tag{6}$$

and Φ as latitude in (◦).

**Figure 5.** Minimum PTC row alignment as solar altitude function (standard method 2).

The spacing achieved (d) should be added to the horizontal length collector spacing at an inclination angle (α), W·sin α, as reported on Equation (7) [28].

$$\mathbf{D} = \mathbf{d} + \mathbf{d}' = \frac{W'}{\text{tg}\left(61^\circ - \Phi\right)} + W\sin\alpha = W\left(\frac{\cos\alpha}{\text{tg}\left(61^\circ - \Phi\right)} + \sin\alpha\right) \tag{7}$$
